Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Jan. 31, 2017	Mar. 24, 2017	Jul. 31, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Jan. 31, 2017
Document Fiscal Year Focus	2017
Document Fiscal Period Focus	FY
Trading Symbol	AMBA
Entity Registrant Name	AMBARELLA INC
Entity Central Index Key	0001280263
Current Fiscal Year End Date	--01-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		33,524,455
Entity Public Float			$ 1.7

Consolidated Balance Sheets - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Current assets:
Cash and cash equivalents	$ 322,872	$ 268,056
Marketable securities	82,522	39,837
Accounts receivable, net	38,596	39,408
Inventories	20,145	18,167
Restricted cash	8	7
Prepaid expenses and other current assets	4,392	4,170
Total current assets	468,535	369,645
Property and equipment, net	4,988	3,448
Deferred tax assets, non-current	5,774	4,626
Intangible assets, net	4,149	4,178
Goodwill	26,601	26,601
Other non-current assets	2,224	2,117
Total assets	512,271	410,615
Current liabilities:
Accounts payable	19,955	14,175
Accrued liabilities	26,448	23,778
Income taxes payable	568	787
Deferred revenue, current	7,425	10,077
Total current liabilities	54,396	48,817
Other long-term liabilities	3,241	12,342
Total liabilities	57,637	61,159
Commitments and contingencies (Note 14)	0	0
Shareholders' equity:
Preference shares, $0.00045 par value per share, 20,000,000 shares authorized and no shares issued and outstanding at January 31, 2017 and January 31, 2016, respectively	0	0
Ordinary shares, $0.00045 par value per share, 200,000,000 shares authorized at January 31, 2017 and January 31, 2016, respectively; 33,369,032 shares issued and outstanding at January 31, 2017; 32,333,359 shares issued and outstanding at January 31, 2016	15	15
Additional paid-in capital	212,276	176,306
Accumulated other comprehensive loss	(70)	(7)
Retained earnings	242,413	173,142
Total shareholders’ equity	454,634	349,456
Total liabilities and shareholders' equity	$ 512,271	$ 410,615

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jan. 31, 2017	Jan. 31, 2016
Statement Of Financial Position [Abstract]
Preference shares, par value	$ 0.00045	$ 0.00045
Preference shares, shares authorized	20,000,000	20,000,000
Preference shares, shares issued	0	0
Preference shares, shares outstanding	0	0
Ordinary shares, par value	$ 0.00045	$ 0.00045
Ordinary shares, shares authorized	200,000,000	200,000,000
Ordinary shares, shares issued	33,369,032	32,333,359
Ordinary shares, shares outstanding	33,369,032	32,333,359

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Income Statement [Abstract]
Revenue	$ 310,297	$ 316,373	$ 218,278
Cost of revenue	105,283	111,029	79,142
Gross profit	205,014	205,344	139,136
Operating expenses:
Research and development	101,205	82,927	57,978
Selling, general and administrative	43,446	37,738	29,297
Total operating expenses	144,651	120,665	87,275
Income from operations	60,363	84,679	51,861
Other income	518	530	175
Income before income taxes	60,881	85,209	52,036
Provision for income taxes	3,071	8,701	1,465
Net income	$ 57,810	$ 76,508	$ 50,571
Net income per share attributable to ordinary shareholders:
Basic	$ 1.77	$ 2.42	$ 1.70
Diluted	$ 1.68	$ 2.27	$ 1.57
Weighted-average shares used to compute net income per share attributable to ordinary shareholders:
Basic	32,671,221	31,633,936	29,742,653
Diluted	34,327,724	33,755,709	32,278,127

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 57,810	$ 76,508	$ 50,571
Other comprehensive loss, net of tax:
Unrealized losses on investments	(63)	(6)	(1)
Other comprehensive loss, net of tax	(63)	(6)	(1)
Comprehensive income	$ 57,747	$ 76,502	$ 50,570

Consolidated Statements of Shareholders' Equity - USD ($) $ in Thousands	Total	Outstanding Ordinary Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Loss [Member]	Retained Earnings [Member]
Beginning Balance, Amount at Jan. 31, 2014	$ 156,361	$ 13	$ 110,285	$ 0	$ 46,063
Beginning Balance, Shares at Jan. 31, 2014		28,748,513
Exercise of stock options, dollar amounts net of unvested stock options exercised early, Amount	$ 8,508	$ 1	8,507	0	0
Exercise of stock options, dollar amounts net of unvested stock options exercised early, Shares		1,456,944
Exercise of stock options, Shares	1,456,944
Vesting of early exercised stock options	$ 59	$ 0	59	0	0
Vesting of restricted stock units, Amount	0	$ 0	0	0	0
Vesting of restricted stock units, Shares		484,296
Employee stock purchase plan, Amount	2,735	$ 0	2,735	0	0
Employee stock purchase plan, Shares		147,776
Stock-based compensation expense related to stock awards granted to employees and consultants	15,692	$ 0	15,692	0	0
Excess income tax benefit associated with stock-based compensation	3,286	0	3,286	0	0
Net unrealized losses on investments - net of taxes	(1)	0	0	(1)	0
Net income	50,571	0	0	0	50,571
Ending Balance, Amount at Jan. 31, 2015	237,211	$ 14	140,564	(1)	96,634
Ending Balance, Shares at Jan. 31, 2015		30,837,529
Exercise of stock options, Amount	$ 5,176	$ 1	5,175	0	0
Exercise of stock options, Shares	567,888	567,888
Restricted stock awards granted, Amount	$ 0	$ 0	0	0	0
Restricted stock awards granted, Shares		84,239
Vesting of restricted stock units, Amount	0	$ 0	0	0	0
Vesting of restricted stock units, Shares		764,517
Employee stock purchase plan, Amount	3,100	$ 0	3,100	0	0
Employee stock purchase plan, Shares		79,186
Stock-based compensation expense related to stock awards granted to employees and consultants	31,094	$ 0	31,094	0	0
Excess income tax benefit associated with stock-based compensation	(3,627)	0	(3,627)	0	0
Net unrealized losses on investments - net of taxes	(6)	0	0	(6)	0
Net income	76,508	0	0	0	76,508
Ending Balance, Amount at Jan. 31, 2016	$ 349,456	$ 15	176,306	(7)	173,142
Ending Balance, Shares at Jan. 31, 2016	32,333,359	32,333,359
Cumulative effect of change in accounting principle	$ 11,688	$ 0	227	0	11,461
Exercise of stock options, Amount	$ 3,230	$ 0	3,230	0	0
Exercise of stock options, Shares	235,923	235,923
Restricted stock awards granted, Amount	$ 0	$ 0	0	0	0
Restricted stock awards granted, Shares		184,155
Vesting of restricted stock units, Amount	0	$ 0	0	0	0
Vesting of restricted stock units, Shares		894,710
Employee stock purchase plan, Amount	4,034	$ 0	4,034	0	0
Employee stock purchase plan, Shares		125,974
Stock repurchase, Amount	$ (20,183)	$ 0	(20,183)	0	0
Stock repurchase, Shares	(405,089)	(405,089)
Stock-based compensation expense related to stock awards granted to employees and consultants	$ 48,832	$ 0	48,832	0	0
Excess income tax benefit associated with stock-based compensation	(170)	0	(170)	0	0
Net unrealized losses on investments - net of taxes	(63)	0	0	(63)	0
Net income	57,810	0	0	0	57,810
Ending Balance, Amount at Jan. 31, 2017	$ 454,634	$ 15	$ 212,276	$ (70)	$ 242,413
Ending Balance, Shares at Jan. 31, 2017	33,369,032	33,369,032

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Cash flows from operating activities:
Net income	$ 57,810	$ 76,508	$ 50,571
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	1,585	1,606	1,335
Amortization/accretion of marketable securities	246	525	675
Loss on disposal of long-lived assets	43	13	21
Stock-based compensation	48,832	31,094	15,692
Excess income tax benefits associated with stock-based compensation	0	0	(3,286)
Other non-cash items, net	40	142	26
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	812	1,262	(21,343)
Inventories	(1,978)	3,627	(11,241)
Prepaid expenses and other current assets	(216)	(572)	(563)
Deferred tax assets	853	1,291	(3,184)
Other assets	(107)	(114)	307
Accounts payable	5,780	(6,880)	12,715
Accrued liabilities	2,069	4,189	6,837
Income taxes payable	(219)	244	3,490
Deferred tax liabilities	(89)	43	83
Deferred revenue	(2,652)	4,939	274
Other long-term liabilities	505	5,644	(151)
Net cash provided by operating activities	113,314	123,561	52,258
Cash flows from investing activities:
Acquisition, net of cash acquired	0	(29,905)	0
Investment in a private company	0	0	(290)
Purchase of investments	(115,546)	(52,786)	(59,807)
Sales of investments	31,078	17,732	8,729
Maturities of investments	41,435	32,248	12,668
Purchase of property and equipment	(2,701)	(2,085)	(1,361)
Net cash used in investing activities	(45,734)	(34,796)	(40,061)
Cash flows from financing activities:
Proceeds from exercise of stock options and employee stock purchase plan	7,419	9,000	11,414
Stock repurchase	(20,183)	0	0
Excess income tax benefits associated with stock-based compensation	0	0	3,286
Net cash provided by (used in) financing activities	(12,764)	9,000	14,700
Net increase in cash and cash equivalents	54,816	97,765	26,897
Cash and cash equivalents at beginning of period	268,056	170,291	143,394
Cash and cash equivalents at end of period	322,872	268,056	170,291
Supplemental disclosure of cash flow information:
Cash paid for income taxes	2,070	1,618	1,069
Supplemental disclosure of noncash investing activities:
Increase in accrued liabilities related to non-monetary assets purchases	$ 481	$ 43	$ 75

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Jan. 31, 2017
Accounting Policies [Abstract]
Organization and Summary of Significant Accounting Policies	1. Organization and Summary of Significant Accounting Policies Organization Ambarella, Inc. (the “Company”) was incorporated in the Cayman Islands on January 15, 2004. The Company is a developer of semiconductor processing solutions for video that enable high-definition video capture, sharing, analysis and display. The Company combines its processor design capabilities with its expertise in video and image processing, algorithms and software to provide a technology platform that is designed to be easily scalable across multiple applications and enable rapid and efficient product development. The Company’s system-on-a-chip, or SoC, designs fully integrate high-definition video processing, image processing, analysis, audio processing and system functions onto a single chip, delivering exceptional video and image quality, differentiated functionality and low power consumption. The Company sells its solutions to leading original design manufacturers, or ODMs, and original equipment manufacturers, or OEMs, globally. Basis of Consolidation The Company’s fiscal year ends on January 31. The consolidated financial statements of the Company and its subsidiaries have been prepared in conformity with generally accepted accounting principles in the United States (“U.S. GAAP”). All intercompany transactions and balances have been eliminated in consolidation. Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expense during the reported periods. Actual results could differ from those estimates. On an ongoing basis, management evaluates its estimates and assumptions, including those related to (i) the collectibility of accounts receivable; (ii) write down of excess and obsolete inventories; (iii) intangible assets and goodwill; (iv) the estimated useful lives of long-lived assets; (v) impairment of long-lived assets and financial instruments; (vi) warranty obligations; (vii) the valuation of stock-based compensation awards and financial instruments; (viii) the probability of performance objectives achievement; (ix) the realization of tax assets and estimates of tax liabilities, including reserves for uncertain tax positions; and (x) the recognition and disclosure of contingent liabilities. These estimates and assumptions are based on historical experience and on various other factors which the Company believes to be reasonable under the circumstances. The Company may engage third-party valuation specialists to assist with estimates related to the valuation of financial instruments and assets associated with various contractual arrangements. Such estimates often require the selection of appropriate valuation methodologies and significant judgment. Actual results could differ from these estimates under different assumptions or circumstances and such differences could be material. Concentration of Risk The Company’s products are manufactured, assembled and tested by third-party contractors located primarily in Asia. The Company does not have long-term agreements with these contractors. A significant disruption in the operations of one or more of these contractors would impact the production of the Company’s products which could have a material adverse effect on its business, financial condition and results of operations. A substantial portion of the Company’s revenue is derived from sales through its logistics provider, Wintech Microelectronics Co., Ltd., or Wintech, which serves as its non-exclusive sales representative and logistics provider in Asia other than Japan, and through one direct OEM customer, GoPro Inc., or GoPro. Termination of the relationships with these two customers could result in a temporary or permanent loss of revenue and termination of the relationship with Wintech could result in an obligation to repurchase unsold product. Furthermore, any credit issues from these two customers could impair their abilities to make timely payment to the Company. See Note 15 for additional information regarding concentration with these two customers. Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities and accounts receivable. The Company maintains its cash primarily in checking and money market accounts with reputable financial institutions. Cash deposits held with these financial institutions may exceed the amount of insurance provided on such deposits. The Company has not experienced any material losses on deposits of its cash. The cash equivalents and marketable securities consist primarily of money market funds, demand deposits, asset-backed securities, commercial paper, U.S. government securities and debt securities of corporations which management assesses to be highly liquid, in order to limit the exposure of each investment. The Company does not hold or issue financial instruments for trading purposes. The Company performs ongoing credit evaluation of its customers and adjusts credit limits based upon payment history and customers’ credit worthiness. The Company regularly monitors collections and payments from its customers. Foreign Currency Transactions The U.S. dollar is the functional currency for the Company and its subsidiaries. Monetary assets and liabilities denominated in non-U.S. currencies are re-measured to U.S. dollars using current exchange rates in effect at the balance sheet date. Nonmonetary assets and liabilities are re-measured to U.S. dollars using historical exchange rates. Monetary and other accounts are re-measured to U.S. dollars using average exchange rates in effect during each period. Gains or losses from foreign currency re-measurement are included in other income (loss), net in the consolidated statements of operations, and, to date, have not been material. Fair Value of Financial Instruments The fair value accounting is applied to all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed in the financial statements on a recurring basis. The carrying amounts reflected in the consolidated balance sheets for cash equivalents, accounts receivable, accounts payable, accrued liabilities and other current liabilities, approximate fair value due to the short-term nature. Cash Equivalents and Marketable Securities The Company considers all highly liquid investments with original maturities of less than three months at the time of purchase to be cash equivalents. Investments that are highly liquid with original maturities at the time of purchase greater than three months are considered as marketable securities. The Company classifies these investments as “available-for-sale” securities carried at fair value, based on quoted market prices of similar assets, with the unrealized gains or losses reported, net of tax, as a separate component of shareholders’ equity and included in accumulated other comprehensive income (loss) in the consolidated balance sheets. The amortization of premiums and accretion of discounts and the realized gains and losses are both recorded in other income (loss), net in the consolidated statements of operations. The Company reviews its investments for possible other-than-temporary impairments on a regular basis. If any loss on investment is believed to be other-than-temporary, a charge will be recorded and a new cost basis in the investment will be established. In evaluating whether a loss on a security is other-than-temporary, the Company considers the following factors: 1) general market conditions, 2) the duration and extent to which the fair value is less than cost, 3) the Company’s intent and ability to hold the investment. For securities in an unrealized loss position which is deemed to be other-than-temporary, the difference between the security’s then-current amortized cost basis and fair value is separated into (i) the amount of the impairment related to the credit loss (i.e., the credit loss component) and (ii) the amount of the impairment related to all other factors (i.e., the non-credit loss component). The credit loss component is recognized in earnings. The non-credit loss component is recognized in accumulated other comprehensive income (loss). Due to the relative short term nature of the investments, there have been no other-than-temporary impairments recorded to date. Trade Accounts Receivable and Allowances for Doubtful Accounts Trade accounts receivable are recorded at the invoiced amount and do not include finance charges. The Company performs ongoing credit evaluation of its customers and generally requires no collateral. The Company assesses the need for allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments by considering factors such as historical collection experience, credit quality, aging of the accounts receivable balances and current economic conditions that may affect a customer’s ability to pay. There were no material write-offs of accounts receivable for the fiscal years ended January 31, 2017, 2016 and 2015, respectively. There were no material allowance for doubtful accounts recorded as of January 31, 2017 and 2016, respectively. Inventories The Company records inventories at the lower of cost or market. The cost includes materials and other production costs and is computed using standard cost on a first-in, first-out basis. Inventory reserves are recorded for estimated obsolescence or unmarketable inventories based on forecast of future demand and market conditions. If actual market conditions are less favorable than projected, or if future demand for the Company’s products decrease, additional inventory write-downs may be required. Once inventory is written down, a new accounting cost basis is established and, accordingly, any associated reserve is not released until the inventory is sold or scrapped. There were no material inventory losses recognized for the fiscal years ended January 31, 2017, 2016 and 2015, respectively. Property and Equipment Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful life for computer equipment, computer software, machinery, equipment and furniture and fixture. Leasehold improvements are amortized over the shorter of the lease term or their estimated useful lives. Repairs and maintenance are charged to expense as incurred. Internal-Use Software The Company capitalizes certain software that is acquired and developed solely for internal use. The capitalization costs include charges from services provided to develop software during the application development stage, costs incurred to obtain software, and certain costs from employees who are directly associated with and who directly devote time to the project. The capitalization begins when the preliminary project stage is completed and ceases no later than the point at which the project is substantially complete and ready for its intended use after all substantial testing is completed. The internal-use software is amortized over its estimated useful life. Repairs and maintenance are charged to expense as incurred. Business Combinations and Intangible Assets The Company allocates the fair value of purchase price to the assets acquired and liabilities assumed based on their estimated fair values. The excess of the fair value of purchase price over the fair values of these identifiable assets and liabilities is recorded as goodwill. When determining the fair values of assets acquired and liabilities assumed, especially with respect to intangible assets, the management makes significant estimates and assumptions. Critical estimates in valuing certain intangible assets include, but are not limited to, replacement cost. Management’s estimates of fair value are based upon assumptions believed to be reasonable, but which are inherently uncertain and unpredictable and, as a result, actual results may differ from estimates. Goodwill and In-Process Research and Development The Company does not amortize goodwill. Acquired in-process research and development, or IPR&D, is capitalized at fair value as an intangible asset and amortization commences upon completion of the underlying projects. When a project underlying reported IPR&D is completed, the corresponding amount of IPR&D is reclassified as an amortizable purchased intangible asset and is amortized over its estimated useful life. Impairment of Long-Lived Assets Including Goodwill and Other Acquired Intangible Assets The Company reviews property and equipment and intangible assets, excluding goodwill, for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset, or asset group, may not be recoverable. Determination of recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset, or asset group to estimated undiscounted future cash flows expected to be generated by the asset, or asset group. If the carrying amount of an asset or asset group exceeds its estimated undiscounted future cash flows, an impairment charge is recognized for the amount by which the carrying amount of the asset or asset group exceeds the estimated fair value of the asset or asset group. Fair value is determined based on the estimated discounted future cash flows expected to be generated by the asset or asset group. Events or changes in circumstances that may indicate that an asset is impaired include significant decreases in the market value of an asset, significant underperformance relative to expected historical or projected future results of operations, a change in the extent or manner in which an asset is utilized, significant declines in the estimated fair value of the overall Company for a sustained period, shifts in technology, loss of key management or personnel, changes in the Company’s operating model or strategy and competitive forces. There has been no occurrence of events to date that would trigger an impairment analysis. As such, no impairment charge has been recognized as of January 31, 2017. The Company tests the goodwill for impairment at least annually, or sooner whenever events or changes in circumstances indicate that the asset may be impaired. The Company has a single reporting unit for goodwill impairment test purposes based on its business and reporting structure. No goodwill impairment has been identified to date. Cost Method Investment The Company accounts for its investment in a privately held company under the cost method and reports the investment in other non-current assets in the consolidated balance sheets. The Company monitors the carrying value of the investment and records a reduction in carrying value when a decline in value is deemed to be other than temporary. To date, there have been no identified events or changes in circumstances that may have a significant adverse effect on the fair value of this investment and the Company has not recognized any impairment losses related to this investment. Revenue Recognition The Company generates revenue from the sales of its SoCs to OEMs or ODMs, either directly or through logistics providers. Revenue from sales directly to OEMs and ODMs is recognized upon shipment provided that persuasive evidence of an arrangement exists, legal title to the products and risk of ownership have transferred, the fee is fixed or determinable, and collection of the resulting receivable is reasonably assured. The Company provides its logistics providers with the rights to return excess levels of inventory and to future price adjustments. Given the inability to reasonably estimate these price changes and returns, revenue and costs related to shipments to logistics providers are deferred until the Company has received notification from its logistics providers that they have sold the Company’s products. Information reported by the Company’s logistics providers includes product resale price, quantity and end customer shipment information as well as remaining inventory on hand. At the time of shipment to a logistics provider, the Company records a trade receivable as there is a legally enforceable right to receive payment, reduces inventory for the value of goods shipped as legal title has passed to the logistics provider and defers the related margin as deferred revenue in the consolidated balance sheets. Any price adjustments are recorded as a change to deferred revenue at the time the adjustments are agreed upon. Arrangements with certain OEM customers provide for pricing that is dependent upon the end products into which the Company’s SoCs are used. These arrangements may also entitle the Company to a share of the product margin ultimately realized by the OEM. The minimum guaranteed amount of revenue related to the sale of products subject to these arrangements is recognized when all other elements of revenue recognition are met. Any amounts at the date of shipment invoiced in excess of the minimum guaranteed contract price are deferred until the additional amounts the Company is entitled to are fixed or determinable. Additional amounts earned by the Company resulting from margin sharing arrangements and determination of the end products into which the products are ultimately incorporated are recognized when end customer sales volume is reported to the Company. Revenue from margin sharing arrangements was not material for the fiscal years ended January 31, 2017, 2016 and 2015, respectively. The Company also enters into engineering service agreements with certain customers. These agreements may include multiple deliverables, such as software development services, licensing of intellectual property and post-contract customer support, or PCS. The Company does not sell separately any of these components and does not have Vendor Specific Objective Evidence, or VSOE, for the deliverables. Accordingly, revenues from these agreements are deferred for any amounts billed until delivery of all the elements. If the agreements include PCS, the revenues are recognized ratably over the estimated supporting periods. Revenues from engineering service agreements was not material for the fiscal years ended January 31, 2017, 2016 and 2015, respectively. Cost of Revenue Cost of revenue includes cost of materials, cost associated with packaging and assembly, testing and shipping, cost of personnel, stock-based compensation, logistics and quality assurance, warranty cost, royalty expense, write-downs of inventories and allocation of overhead. Warranty Costs The Company typically provides warranty on its products. The Company accrues for the estimated warranty costs at the time when revenue is recognized. The warranty accruals are regularly monitored by management based upon historical experience and any specifically identified failures. While the Company engages in extensive product quality assessment, actual product failure rates, material usage or service delivery costs could differ from estimates and revisions to the estimated warranty liability would be required. The Company’s warranty accruals were not material for the fiscal years ended January 31, 2017, 2016 and 2015, respectively. Research and Development Research and development costs are expensed as incurred and consist primarily of personnel costs, product development costs, which include engineering services, development software and hardware tools, license fees, costs of fabrication of masks for prototype products, other development materials costs, depreciation of equipment used in research and development and allocation of facility costs. Selling, General and Administrative Selling, general and administrative expenses consist of personnel costs, travel and trade show costs, legal expenses, other professional services and occupancy costs. Advertising expenses were not material for the fiscal years ended January 31, 2017, 2016 and 2015, respectively. Operating Leases The Company recognizes rent expense on a straight-line basis over the term of the lease. The difference between rent expense and rent payment is recorded as deferred rent and is included in accrued liabilities in the consolidated balance sheets. Stock-Based Compensation The Company measures stock-based compensation for equity awards granted to employees and directors based on the estimated fair value on the grant date, and recognizes that compensation as expense using the straight-line attribution method for service condition awards or using the graded-vesting attribution method for awards with performance conditions over the requisite service period, which is typically the vesting period of each award. The Company determines the fair value of restricted stock and restricted stock units based on the fair market value of its ordinary shares on the grant date. The Company uses the Black-Scholes option pricing model to determine the fair value of stock options. Determining the fair value of stock options on the grant date requires the input of various assumptions, including stock price of the underlying ordinary share, the exercise price of the stock option, expected volatility, expected term, risk-free interest rate and dividend rate. The expected term is calculated using the simplified method as prescribed in the guidance provided by the Securities and Exchange Commission, as neither relevant historical experience nor other relevant data are available to estimate future exercise behavior. The expected volatility is based on the historical volatilities of similar companies whose share prices are publicly available for a period commensurate with the expected term. The risk-free interest rate is derived from the average U.S. Treasury constant maturity rates during the respective periods commensurate with the expected term. The expected dividend yield is zero because the Company has not historically paid dividends and has no present intention to pay dividends. Upon adoption of ASU 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting in the first quarter of fiscal year 2017, the Company elects to account for forfeitures as they occur. Income Taxes The Company records income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in its financial statements or tax returns. In estimating future tax consequences, generally all expected future events other than enactments or changes in the tax law or rates are considered. Valuation allowances are provided when necessary to reduce deferred tax assets to the amount expected to be realized. The Company applies authoritative guidance for the accounting for uncertainty in income taxes. The guidance requires that tax effects of a position be recognized only if it is “more likely than not” to be sustained based solely on its technical merits as of the reporting date. Upon estimating the Company’s tax positions and tax benefits, the Company considers and evaluates numerous factors, which may require periodic adjustments and which may not reflect the final tax liabilities. The Company adjusts its financial statements to reflect only those tax positions that are more likely than not to be sustained under examination. As part of the process of preparing consolidated financial statements, the Company is required to estimate its taxes in each of the jurisdictions in which it operates. The Company estimates actual current tax exposure together with assessing temporary differences resulting from differing treatment of items, such as accruals and allowances not currently deductible for tax purposes. These differences result in deferred tax assets, which are included in the consolidated balance sheets. In general, deferred tax assets represent future tax benefits to be received when certain expenses previously recognized in the consolidated statements of operations become deductible expenses under applicable income tax laws, or loss or credit carryforwards are utilized. In assessing whether deferred tax assets may be realized, management considers whether it is more likely than not that some portion or all of deferred tax assets will be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income. The Company makes estimates and judgments about its future taxable income based on assumptions that are consistent with its plans and estimates. Should the actual amounts differ from estimates, the amount of valuation allowance could be materially impacted. Any adjustment to the deferred tax asset valuation allowance would be recorded in the consolidated income statement for the periods in which the adjustment is determined to be required. Net Income Per Ordinary Share Basic earnings per share is computed by dividing net income available to ordinary shareholders by the weighted-average number of ordinary shares outstanding during the period. Diluted earnings per share is computed by dividing net income available to ordinary shareholders by the weighted-average number of ordinary shares outstanding during the period increased to include the number of additional ordinary shares that would have been outstanding if the potentially dilutive securities had been issued. Potentially dilutive securities include outstanding stock options, shares to be purchased under the Company’s employee stock purchase plan, unvested restricted stock and restricted stock units. The dilutive effect of potentially dilutive securities is reflected in diluted earnings per share by application of the treasury stock method. Comprehensive Income (Loss) Comprehensive income (loss) includes unrealized gains or losses from available-for-sale securities that are excluded from net income. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”). The new guidance clarifies the principles and develops a common revenue recognition guidance for U.S. GAAP and International Financial Reporting Standards (the “IFRS”). Under the new guidance, an entity is required to recognize an amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. This new revenue standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. Subsequently, the FASB issued the following standards related to ASU 2014-09: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (“ASU 2016-08”); ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing (“ASU 2016-10”); ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”); and ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers (“ASU 2016-20”). Accordingly, the Company must adopt ASU 2016-08, ASU 2016-10, ASU 2016-12 and ASU 2016-20 with ASU 2014-09 (collectively, the “new revenue standards”) in its first quarter of fiscal year 2019. The new revenue guidance may be applied retrospectively to each prior period presented or retrospectively with the cumulative effect recognized as of the date of adoption. The Company is currently evaluating the impact of adoption on its financial position, results of operations and disclosures. In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. In connection with each annual and interim period, management is required to assess whether there is substantial doubt about an entity’s ability to continue as a going concern within one year after the issuance date, and to provide related footnote disclosures in certain circumstances. The new guidance is effective for annual periods ending after December 15, 2016, and interim periods within annual periods beginning after December 15, 2016. Early adoption is permitted. This ASU has no impact on the Company’s financial statements or disclosures. In July 2015, the FASB issued ASU No. 2015-11, Simplifying the Measurement of Inventory. The new guidance changes the measurement principle for inventory from the lower of cost or market to lower of cost and net realizable value. Net realizable value is the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. It applies to entities that measure inventory using a method other than last-in, first-out (“LIFO”) and the retail inventory method (“RIM”). The new guidance will be effective for fiscal years beginning after December 15, 2016, including interim periods within those fiscal years and should be applied prospectively. Early adoption is permitted as of the beginning of an interim or annual reporting period. The Company does not believe the adoption of this new guidance will have a material impact on its financial position, results of operations and disclosures. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). This standard requires entities that lease assets to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. The standard is effective for fiscal years and the interim periods within those fiscal years beginning after December 15, 2018. The guidance is required to be applied by the modified retrospective transition approach. Early adoption is permitted. The Company is currently assessing the impact of the adoption of this new guidance on its financial position, results of operations and disclosures. In March 2016, the FASB issued ASU 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, to simplify and improve the accounting for employee share-based awards. The new standard amends the accounting for employee share-based payment transactions to require recognition of the tax effects resulting from the settlement of stock-based awards as income tax benefit or expense in the income statement in the reporting period in which they occur. In addition, the tax-related cash flows resulting from share-based payments will be classified as cash flows from operating activities and cash payments made to the taxing authorities on the employees’ behalf for withheld shares will be classified as financing activities on the statement of cash flows. The new guidance also provides an accounting policy election to account for forfeitures as they occur. The Company elected to early adopt this new guidance in the first quarter of its fiscal year 2017. As a result of this adoption, the Company recorded an increase to retained earnings of $11.7 million to recognize U.S. net operating loss carryforwards attributable to tax benefits from excess stock-based compensation that had not been previously recognized and recorded a decrease to retained earnings of $0.2 million resulting from the election of accounting policy to account for forfeitures as they occur on February 1, 2016. The Company also elected to apply the presentation for cash flows related to excess tax benefits prospectively. The presentation requirements for cash flows related to employee taxes paid for withheld shares has no impact on the Company’s consolidated statements of cash flows. On February 1, 2016, the cumulative effect adjustment of these changes recognized in the beginning of retained earnings was approximately $11.5 million. In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326), to introduce a new impairment model for recognizing credit losses on financial instruments based on an estimated of current expected credit losses (ECL). Under the new model, available-for-sale (AFS) debt securities are required to estimate ECL only when the fair value is below the amortized cost of the asset and is no longer based on an impairment being “other-than-temporary”. The new model also requires the impairment calculation on an individual security level and requires an entity use present value of cash flows when estimating the ECL. The credit-related losses are required to be recognized through earnings and non-credit related losses are reported in other comprehensive income. The ASU will be effective for public entities in fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The new guidance will require modified retrospective application to all outstanding instruments, with a cumulative effect adjustment recorded to opening retained earnings as of the beginning of the first period in which the guidance becomes effective. The Company does not believe the adoption of this new guidance will have a material impact on its consolidated financial statements. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory. The new guidance requires that entities recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The new guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim reporting periods within those annual reporting periods. Early adoption is permitted but should be in the first interim period. The new guidance should also be applied on a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Company is currently assessing the impact of the adoption of this new guidance on its financial position, results of operations and disclosures. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), to require entities to show the changes in the total of cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. As a result, entities will no longer present transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. When cash, cash equivalents, restricted cash and restricted cash equivalents are presented in more than one line item on the balance sheet, the new guidance requires a reconciliation of the totals in the statement of cash flows to the related captions in the balance sheet. Entities will also have to disclose the nature of restricted cash and restricted cash equivalent balances. The new guidance will be effective for fiscal years beginning after December 15, 2017, including the interim periods within those years. Early adoption is permitted and the new guidance is applied retrospectively. The Company does not believe the adoption of this new guidance will have a material impact on its consolidated statement of cash flows and disclosures. In January 2017, the FASB issued ASU 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test of Goodwill Impairment, to eliminate the requirement to calculate the implied fair value of goodwill to measure a goodwill impairment charge. Instead, entities will record an impairment charge based on the excess of a reporting unit’s carrying amount over its fair value. This new standard will be applied prospectively and is effective for annual and interim periods beginning after December 15, 2019. Early adoption is permitted for annual and interim periods after January 1, 2017. The Company does not believe the adoption of this new guidance will have a material impact on its financial position, results of operations and disclosures.

Financial Instruments and Fair Value

12 Months Ended

Jan. 31, 2017

Investments All Other Investments [Abstract]

Financial Instruments and Fair Value

2. Financial Instruments and Fair Value

The Company has invested a portion of its cash in debt securities that are denominated in United States dollars. The investment portfolio consists of money market funds, demand deposits, asset-backed securities, commercial paper, U.S. government securities and debt securities of corporations. All of the investments are classified as available-for-sale securities and reported at fair value in the consolidated balance sheets as follows:

	As of January 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Money market funds	$	8,328	$	—	$	—		$	8,328
Demand deposits		10,000		—		—			10,000
Commercial paper		4,784		—		—			4,784
Corporate bonds		42,713		6		(41	)		42,678
Asset-backed securities		11,686		1		(12	)		11,675
U.S. government securities		23,409		6		(30	)		23,385
Total cash equivalents and marketable securities	$	100,920	$	13	$	(83	)	$	100,850

	As of January 31, 2016
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Money market funds	$	530	$	—	$	—		$	530
Commercial paper		2,598		—		—			2,598
Corporate bonds		21,342		7		(9	)		21,340
Asset-backed securities		4,586		—		(1	)		4,585
U.S. government securities		9,274		4		(6	)		9,272
Agency bonds		2,044		—		(2	)		2,042
Total cash equivalents and marketable securities	$	40,374	$	11	$	(18	)	$	40,367

	As of
	January 31, 2017		January 31, 2016
	(in thousands)
Included in cash equivalents	$	18,328	$	530
Included in marketable securities		82,522		39,837
Total cash equivalents and marketable securities	$	100,850	$	40,367

The contractual maturities of the investments at January 31, 2017 and 2016 were as follows:

	As of
	January 31, 2017		January 31, 2016
	(in thousands)
Due within one year	$	76,992	$	33,449
Due within one to two years		23,858		6,918
Total cash equivalents and marketable securities	$	100,850	$	40,367

The unrealized losses on the available-for-sale securities were caused by fluctuations in market value and interest rates as a result of the economic environment. As the decline in market value was attributable to changes in market conditions and not credit quality, and because the Company neither intended to sell nor was it more likely than not that it will be required to sell these investments prior to a recovery of par value, the Company did not consider these investments to be other-than temporarily impaired as of January 31, 2017 and 2016, respectively.

The following fair value hierarchy is applied for disclosure of the inputs used to measure fair value. This hierarchy prioritizes the inputs into three broad levels as follows:

Level 1—Inputs are unadjusted quoted prices in active markets for identical assets or liabilities.

Level 2—Inputs are quoted prices for similar assets and liabilities in active markets or inputs that are observable for the assets or liabilities, either directly or indirectly through market corroboration, for substantially the full term of the financial instruments.

Level 3—Unobservable inputs based on the Company’s own assumptions used to measure assets and liabilities at fair value. The inputs require significant management judgment or estimation.

The Company measures the fair value of money market funds and demand deposits using quoted prices in active markets for identical assets and classifies them within Level 1. The fair value of the Company’s investments in other debt securities are obtained based on quoted prices for similar assets in active markets and are classified within Level 2.

The following tables present the fair value of the financial instruments measured on a recurring basis as of January 31, 2017 and 2016, respectively:

	As of January 31, 2017
	Total		Level 1		Level 2		Level 3
	(in thousands)
Money market funds	$	8,328	$	8,328	$	—	$	—
Demand deposits		10,000		10,000		—		—
Commercial paper		4,784		—		4,784		—
Corporate bonds		42,678		—		42,678		—
Asset-backed securities		11,675		—		11,675		—
U.S. government securities		23,385		—		23,385		—
Total cash equivalents and marketable securities	$	100,850	$	18,328	$	82,522	$	—

	As of January 31, 2016
	Total		Level 1		Level 2		Level 3
	(in thousands)
Money market funds	$	530	$	530	$	—	$	—
Commercial paper		2,598		—		2,598		—
Corporate bonds		21,340		—		21,340		—
Asset-backed securities		4,585		—		4,585		—
U.S. government securities		9,272		—		9,272		—
Agency bonds		2,042		—		2,042		—
Total cash equivalents and marketable securities	$	40,367	$	530	$	39,837	$	—

Inventories

12 Months Ended

Jan. 31, 2017

Inventory Disclosure [Abstract]

Inventories

3. Inventories

Inventories at January 31, 2017 and 2016 consisted of the following:

	As of January 31,
	2017		2016
	(in thousands)
Work-in-progress	$	10,105	$	9,474
Finished goods		10,040		8,693
Total	$	20,145	$	18,167

Property and Equipment, Net

12 Months Ended

Jan. 31, 2017

Property Plant And Equipment [Abstract]

Property and Equipment, Net

4. Property and Equipment, net

Depreciation expense was approximately $1.6 million, $1.6 million and $1.3 million for the years ended January 31, 2017, 2016 and 2015, respectively. Property and equipment at January 31, 2017 and 2016 consisted of the following:

	As of January 31,
	2017			2016
	(in thousands)
Computer equipment and software	$	6,798		$	6,421
Machinery and equipment		3,405			2,706
Furniture and fixtures		797			492
Leasehold improvements		1,672			1,429
Construction in progress		755			253
		13,427			11,301
Less: accumulated depreciation and amortization		(8,439	)		(7,853	)
Total property and equipment, net	$	4,988		$	3,448

Acquisition	12 Months Ended
Acquisition	Jan. 31, 2017
Business Combinations [Abstract]
Acquisition	5. Acquisition On June 25, 2015, the Company completed the acquisition of VisLab S.r.l. (“VisLab”), a privately held Italian company that develops computer vision and intelligent control systems for automotive and other commercial applications, including advanced driver assistance systems and several generations of autonomous vehicle driving systems, for $30.0 million in cash. This acquisition will enable extensive and robust computer vision support in future solutions targeting the Company's core markets, including automotive, IP security, wearable, and UAV cameras. Of the total purchase price of $30.0 million, $4.1 million was attributed to intangible assets, $25.3 million was attributed to goodwill, and $0.6 million was attributed to net assets acquired. The goodwill represents the excess of the fair value of purchase price over the fair values of these identifiable assets and liabilities and primarily represents the intangible assets that do not qualify for separate recognition and the future development initiatives of the assembled workforces. Goodwill is not deductible for tax purposes. Pro forma results of operations for this acquisition have not been presented because they are not material to the consolidated results of operations.

- Definition

The entire disclosure for a business combination (or series of individually immaterial business combinations) completed during the period, including background, timing, and recognized assets and liabilities. The disclosure may include leverage buyout transactions (as applicable).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-Section 50
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Reference 2: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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-Paragraph 4
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Reference 3: http://www.xbrl.org/2003/role/presentationRef
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-Name Accounting Standards Codification
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Reference 4: http://www.xbrl.org/2003/role/presentationRef
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Reference 5: http://www.xbrl.org/2003/role/presentationRef
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Reference 6: http://www.xbrl.org/2003/role/presentationRef
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Reference 15: http://www.xbrl.org/2003/role/presentationRef
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+ Details

Goodwill and Intangible Assets	12 Months Ended
Goodwill and Intangible Assets	Jan. 31, 2017
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill and Intangible Assets	6. Goodwill and Intangible Assets On June 25, 2015, the Company completed the acquisition of VisLab. As a result of this transaction, there was $25.3 million of goodwill and $4.1 million of intangible assets recorded in the consolidated balance sheet. A deferred tax liability of $1.3 million related to the intangible assets was recorded to account for the difference between financial reporting and tax basis at the acquisition date, with an addition to goodwill. The Company does not amortize goodwill. The intangible assets primarily consist of IPR&D. Acquired IPR&D is capitalized at fair value as an intangible asset and amortization commences upon completion of the underlying projects. When a project underlying reported IPR&D is completed, the corresponding amount of IPR&D is reclassified as an amortizable purchased intangible asset and is amortized over its estimated useful life. As of January 31, 2017, there was no IPR&D amortized. For the fiscal years ended January 31, 2017 and 2016, there was no goodwill or intangible asset impaired.

- Definition

The entire disclosure for the aggregate amount of goodwill and a description of intangible assets, which may include (a) for amortizable intangible assets (also referred to as finite-lived intangible assets), the carrying amount, the amount of any significant residual value, and the weighted-average amortization period, (b) for intangible assets not subject to amortization (also referred to as indefinite-lived intangible assets), the carrying amount, and (c) the amount of research and development assets acquired and written off in the period, including the line item in the income statement in which the amounts written off are aggregated, if not readily apparent from the income statement. Also discloses (a) for amortizable intangibles assets in total and by major class, the gross carrying amount and accumulated amortization, the total amortization expense for the period, and the estimated aggregate amortization expense for each of the five succeeding fiscal years, (b) for intangible assets not subject to amortization the carrying amount in total and by major class, and (c) for goodwill, in total and for each reportable segment, the changes in the carrying amount of goodwill during the period (including the aggregate amount of goodwill acquired, the aggregate amount of impairment losses recognized, and the amount of goodwill included in the gain (loss) on disposal of a reporting unit). If any part of goodwill has not been allocated to a reportable segment, discloses the unallocated amount and the reasons for not allocating. For each impairment loss recognized related to an intangible asset (excluding goodwill), discloses: (a) a description of the impaired intangible asset and the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method for determining fair value, (c) the caption in the income statement or the statement of activities in which the impairment loss is aggregated, and (d) the segment in which the impaired intangible asset is reported. For each goodwill impairment loss recognized, discloses: (a) a description of the facts and circumstances leading to the impairment, (b) the amount of the impairment loss and the method of determining the fair value of the associated reporting unit, and (c) if a recognized impairment loss is an estimate not finalized and the reasons why the estimate is not final. May also disclose the nature and amount of any significant adjustments made to a previous estimate of an impairment loss.

+ References + Details

Accrued Liabilities

12 Months Ended

Jan. 31, 2017

Payables And Accruals [Abstract]

Accrued Liabilities

7. Accrued Liabilities

Accrued liabilities at January 31, 2017 and 2016 consisted of the following:

	As of January 31,
	2017		2016
	(in thousands)
Accrued employee compensation	$	14,685	$	14,512
Accrued warranty		500		234
Accrued rebates		972		824
Accrued product development costs		7,605		6,339
Other accrued liabilities		2,686		1,869
Total accrued liabilities	$	26,448	$	23,778

Deferred Revenue and Deferred Cost

12 Months Ended

Jan. 31, 2017

Deferred Revenue Disclosure [Abstract]

Deferred Revenue and Deferred Cost

8. Deferred Revenue and Deferred Cost

Deferred revenue and related cost at January 31, 2017 and 2016 consisted of the following:

	As of January 31,
	2017			2016
	(in thousands)
Deferred revenue on product shipments	$	7,725		$	12,201
Deferred revenue from licenses & services		1,748			1,653
Deferred cost of revenue on product shipments		(2,048	)		(3,777	)
Total deferred revenue, net	$	7,425		$	10,077

- Definition

The entire disclosure for deferred revenues at the end of the reporting period, and description and amounts of significant changes that occurred during the reporting period. Deferred revenue is a liability as of the balance sheet date related to a revenue producing activity for which revenue has not yet been recognized. Generally, an entity records deferred revenue when it receives consideration from a customer before achieving certain criteria that must be met for revenue to be recognized in conformity with GAAP.

+ References + Details

Other Long-Term Liabilities

12 Months Ended

Jan. 31, 2017

Other Liabilities Disclosure [Abstract]

Other Long-Term Liabilities

9. Other Long-Term Liabilities

Other long-term liabilities at January 31, 2017 and 2016 consisted of the following:

	As of January 31,
	2017		2016
	(in thousands)
Unrecognized tax benefits, including interest	$	1,905	$	10,917
Deferred tax liabilities, non-current		1,333		1,423
Other long-term liabilities		3		2
Total other long-term liabilities	$	3,241	$	12,342

On February 1, 2016, upon the adoption of ASU 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, the Company recognized approximately $11.7 million of deferred tax assets for net operating loss carryforwards from previously unrecognized excess stock-based compensation deductions. As a result of recognizing these deferred tax assets, the Company reduced the amount of unrecognized tax benefits recorded in other long-term liabilities by $9.5 million pursuant to accounting guidance which provides that an unrecognized tax benefit shall be presented as a reduction to a deferred tax asset for a net operating loss carryforward, a similar tax loss, or a tax credit carryforward, to the extent such deferred tax asset is available.

Capital Stock

12 Months Ended

Jan. 31, 2017

Equity [Abstract]

Capital Stock

10. Capital Stock

Preference shares

After completion of the Company’s initial public offering, or IPO, a total of 20,000,000 preference shares, with a $0.00045 par value per share, were authorized. There were no shares issued and outstanding as of January 31, 2017 and 2016, respectively.

Ordinary shares

200,000,000 ordinary shares were authorized at January 31, 2017 and 2016, respectively. As of January 31, 2017 and 2016, the following ordinary shares were reserved for future issuance:

	As of January 31,
	2017		2016
Shares reserved for options, restricted stock and restricted stock units		5,167,688		5,027,475
Shares reserved for employee stock purchase plan		1,252,465		974,273

Shares repurchased

On May 31, 2016, the Company’s Board of Directors authorized the repurchase of up to $75.0 million of the Company’s ordinary shares over a six-month period. On November 29, 2016, this authorization was extended until June 30, 2017. Repurchases may be made from time-to-time through open market purchases or through privately negotiated transactions subject to market conditions, applicable legal requirements and other relevant factors. The repurchase program does not obligate the Company to acquire any particular amount of ordinary shares, and it may be suspended at any time at the Company’s discretion. The repurchase program is funded using the Company’s working capital and any repurchased shares are recorded as authorized but unissued shares. As of January 31, 2017, a total of 405,089 shares had been repurchased for approximately $20.2 million in cash and recorded as a reduction to equity.

Employee Benefits and Stock-based Compensation

12 Months Ended

Jan. 31, 2017

Postemployment Benefits [Abstract]

Employee Benefits and Stock-based Compensation

11. Employee Benefits and Stock-based Compensation

401(k) Plan

The Company maintains a defined contribution 401(k) plan (the “401(k) Plan”) for all of its eligible U.S. employees. Under the 401(k) Plan, eligible employees may contribute up to the Internal Revenue Service annual contribution limitation. The Company is responsible for administrative costs of the Plan. The Company has not had any matching contributions to date.

Stock Option Plans

2004 Stock Plan. The 2004 Stock Plan provides for the grant of incentive stock options (“ISOs”) within the meaning of Section 422 of the Internal Revenue Code of 1986, as amended (the “Code”), nonstatutory stock options (“NSOs”), stock purchase rights to acquire restricted stock and restricted stock units. Upon the completion of the IPO, no additional awards will be granted under the 2004 Plan and the 2004 Plan was terminated. However, all outstanding stock options and other awards previously granted under the 2004 Plan will remain subject to the terms of the 2004 Plan.

2012 Equity Incentive Plan. The 2012 Equity Incentive Plan, or EIP, permits the grant of ISOs, within the meaning of Section 422 of the Code, to employees of the Company and any of the Company’s subsidiary corporations, and the grant of NSOs, stock appreciation rights, restricted stock, restricted stock units, performance units, performance shares, deferred stock units and dividend equivalents to employees, directors and consultants of the Company and any of the Company’s subsidiary corporations’ employees and consultants.

The exercise price of ISOs granted to a holder of more than 10% of the voting power of all classes of the Company’s shares shall be no less than 110% of fair market value on the grant date. The exercise price of ISOs granted to other employees and NSOs shall be no less than 100% of fair market value on the grant date. Options granted under the Plan have a term of up to 10 years from grant date. Options granted to new employees generally vest 25% on the first anniversary service date of the grant and remainder vest ratably over the following 36 months.

Restricted stock and restricted stock units granted to new employees generally vest as to 1/4th of the shares on the first anniversary service date of the grant and 1/16th of the shares vest every 3 months thereafter, so as to be 100% vested on the fourth anniversary of the vesting commencement date.

Vesting schedules for other service or performance condition awards vary and are subject to approval by the board of directors; provided that the performance awards shall not vest at all until the performance conditions are achieved and are subject to the award’s holders continuing to provide services to the Company through such vesting dates. The performance condition awards are automatically forfeited in their entirety, without any cost to or action by the Company, if there has been no achievement of the performance. The holders of restricted stock have voting power and other rights with respect to such shares, provided, however, that such shares are held in escrow and subject to forfeiture until the shares vested.

On February 1, 2016 and 2015, the Company added 1,455,001 and 1,387,689 ordinary shares, respectively, to the ordinary shares reserved for issuance, pursuant to an “evergreen” provision contained in the EIP. Pursuant to such provision, on February 1st of each fiscal year, the number of ordinary shares reserved for issuance under the EIP is automatically increased by a number equal to the lesser of (i) 3,500,000 ordinary shares, (ii) four and one half percent (4.5%) of the aggregate number of ordinary shares outstanding on January 31st of the preceding fiscal year, or (iii) a lesser number of shares that may be determined by the Company’s Board of Directors.

Amended and Restated 2012 Employee Stock Purchase Plan. The Amended and Restated 2012 Employee Stock Purchase Plan, or ESPP, permits eligible participants to purchase ordinary shares at a discount through contributions up to 15% of their eligible compensation, subject to any IRS limitations. The ESPP provides each offering and purchasing period of six months in duration. The purchase price is 85% of the lower of the closing price of the Company’s ordinary shares on the first trading day of each offering period or on the purchase date.

On February 1, 2016 and 2015, the Company added 404,166 and 385,469 ordinary shares, respectively, to the ordinary shares reserved for issuance, pursuant to an “evergreen” provision contained in the ESPP. Pursuant to such provision, on February 1st of each fiscal year, the number of ordinary shares reserved for issuance under the ESPP is automatically increased by a number equal to the lesser of (i) 1,500,000 ordinary shares, (ii) one and one quarter percent (1.25%) of the aggregate number of ordinary shares outstanding on such date, or (iii) an amount determined by the Company’s Board of Directors or a duly authorized committee of the Board of Directors.

Stock-based Compensation

The following table presents the classification of stock-based compensation for the periods indicated:

	Year Ended January 31,
	2017		2016		2015
	(in thousands)
Stock-based compensation:
Cost of revenue	$	1,078	$	657	$	343
Research and development		29,729		19,082		8,654
Selling, general and administrative		18,025		11,355		6,695
Total stock-based compensation	$	48,832	$	31,094	$	15,692

As of January 31, 2017, total unrecognized compensation cost related to unvested stock options was $8.1 million and is expected to be recognized over a weighted-average period of 1.94 years. Total unrecognized compensation cost related to unvested restricted stock units was $104.1 million and is expected to be recognized over a weighted-average period of 2.80 years. Total unrecognized compensation cost related to unvested restricted stock awards was $6.9 million and is expected to be recognized over a weighted-average period of 1.73 years.

The following table sets forth the weighted-average assumptions used to estimate the fair value of the stock options and employee stock purchase plan awards for the periods indicated:

	Year Ended January 31,
	2017			2016			2015
Stock Options:
Volatility		38	%		57	%		64	%
Risk-free interest rate		1.59	%		1.74	%		1.93	%
Expected term (years)		6.00		6.08			6.01
Dividend yield		0	%		0	%		0	%
Employee stock purchase plan awards:
Volatility		54	%		63	%		49	%
Risk-free interest rate		0.51	%		0.21	%		0.07	%
Expected term (years)		0.5			0.5			0.5
Dividend yield		0	%		0	%		0	%

The Company calculates expected volatility based on the historical volatilities of similar companies whose share prices are publicly available for a period commensurate with the expected term. Accordingly, the combination of the similar companies and associated stock price changes will significantly impact the volatility used in the estimate of fair value of the Company’s stock option.

The following table summarizes stock option activities for the periods indicated:

	Option Outstanding
										Weighted-
								Total Intrinsic		Average
						Weighted-		Value of		Remaining		Aggregate
				Weighted-		Average		options		Contractual		Intrinsic
				Average		Grant-date		Exercised		Term		Value
	Shares			Exercise Price		Fair Value		(in thousands)		(in years)		(in thousands)
Outstanding at January 31, 2014		3,358,706		$	6.92
Granted		428,781			36.33	$	21.37
Exercised		(1,456,944	)		5.84			$	46,427
Forfeited		(48,634	)		13.38
Outstanding at January 31, 2015		2,281,909			13.00
Granted		179,700			71.36	$	38.81
Exercised		(567,888	)		9.11			$	37,603
Forfeited		(40,331	)		35.65
Outstanding at January 31, 2016		1,853,390			19.36
Granted		110,500			47.82	$	18.76
Exercised		(235,923	)		13.69			$	10,788
Forfeited		(16,708	)		55.07
Expired		(7,735	)		14.19
Outstanding at January 31, 2017		1,703,524		$	21.66					5.16		$	51,670
Exercisable at January 31, 2017		1,367,960		$	14.94						4.42	$	49,016

The intrinsic value of options outstanding and exercisable options are calculated based on the difference between the fair market value of the Company’s ordinary shares on the reporting date and the exercise price. The closing price of the Company’s ordinary shares was $49.61 on January 31, 2017, as reported by The NASDAQ Global Market. The intrinsic value of exercised options is calculated based on the difference between the fair market value of the Company’s ordinary shares on the exercise date and the exercise price.

The following table summarizes restricted stock and restricted stock units activities for the periods indicated:

				Weighted-
				Average
				Grant-Date
	Shares			Fair Value
Unvested at January 31, 2014		1,410,089		$	14.02
Granted		1,111,204			38.60
Vested		(484,296	)		17.39
Forfeited		(56,549	)		19.93
Unvested at January 31, 2015		1,980,448			26.82
Granted		1,314,387			66.14
Vested		(769,779	)		27.82
Forfeited		(29,568	)		42.11
Unvested at January 31, 2016		2,495,488			47.04
Granted		676,598			67.68
Vested		(955,230	)		39.28
Forfeited		(41,183	)		52.49
Unvested at January 31, 2017		2,175,673		$	56.76

Total fair value as of the respective vesting dates of restricted stock and restricted stock units vested for the fiscal years ended January 31, 2017, 2016 and 2015 was approximately $51.1 million, $59.2 million, and $17.3 million, respectively. As of January 31, 2017, the aggregate intrinsic value of unvested restricted stock and restricted stock units was $107.9 million.

Net Income Per Ordinary Share

12 Months Ended

Jan. 31, 2017

Earnings Per Share [Abstract]

Net Income Per Ordinary Share

12. Net Income Per Ordinary Share

The following table sets forth the computation of basic and diluted net income per ordinary share for the periods indicated:

	Year Ended January 31,
	2017		2016			2015
	(in thousands, except share and per share data)
Numerator:
Net income	$	57,810	$	76,508		$	50,571
Less: amount allocable to unvested early exercised options		—		—			(11	)
Net income allocable to ordinary shareholders - basic	$	57,810	$	76,508		$	50,560
Undistributed earnings reallocated to ordinary shareholders		—		—			1
Net income allocable to ordinary shareholders - diluted	$	57,810	$	76,508		$	50,561
Denominator:
Weighted-average ordinary shares outstanding		32,671,221		31,633,992			29,749,354
Less: weighted-average unvested early exercised options subject to repurchase		—		(56	)		(6,701	)
Weighted-average ordinary shares - basic		32,671,221		31,633,936			29,742,653
Effect of potentially dilutive securities:
Employee stock options		1,080,864		1,245,341			1,818,401
Restricted stock and restricted stock units		565,068		865,863			704,788
Employee stock purchase plan		10,571		10,569			12,285
Weighted-average ordinary shares - diluted		34,327,724		33,755,709			32,278,127
Net income per ordinary share:
Basic	$	1.77	$	2.42		$	1.70
Diluted	$	1.68	$	2.27		$	1.57

The following weighted-average potentially dilutive securities were excluded from the computation of diluted net income per ordinary share as their effect would have been antidilutive:

	Year Ended January 31,
	2017		2016		2015
Options to purchase ordinary shares		343,936		109,958		217,514
Restricted stock and restricted stock units		891,952		163,994		167,702
Employee stock purchase plan		14,651		9,073		36,110
Early exercised options subject to repurchase		—		56		6,701
		1,250,539		283,081		428,027

Income Taxes

12 Months Ended

Jan. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

13. Income Taxes

Income before income taxes consisted of the following for the periods indicated:

	Year Ended January 31,
	2017		2016		2015
	(in thousands)
U.S. operations	$	3,092	$	3,190	$	1,978
Non-U.S. operations		57,789		82,019		50,058
Income before income taxes	$	60,881	$	85,209	$	52,036

Income tax provision consisted of the following for the periods indicated:

	Year Ended January 31,
	2017			2016			2015
	(in thousands)
Current:
U.S. federal tax	$	818		$	5,273		$	3,135
U.S. state taxes		(212	)		541			93
Non-U.S. foreign taxes		1,454			1,874			1,348
		2,060			7,688			4,576
Deferred:
U.S. federal tax		1,174			1,050			(3,208	)
U.S. state taxes		—			—			—
Non-U.S. foreign taxes		(163	)		(37	)		97
		1,011			1,013			(3,111	)
Provision for income taxes	$	3,071		$	8,701		$	1,465

The Company consists of a Cayman Islands parent company with various foreign and U.S. Subsidiaries. The primary jurisdiction where our foreign earnings are derived is the Cayman Islands, where the Company is domiciled. Under the current laws of the Cayman Islands, the Company is not subject to tax on its income. For purposes of the reconciliation between the provision (benefit) for income taxes at the statutory rate and the effective tax rate, a notional U.S. 34% rate is applied to pretax income as a result of the following for the periods indicated:

	Year Ended January 31,
	2017			2016			2015
	(in thousands)
Provision at U.S. notional statutory rate	$	20,700		$	28,971		$	17,692
U.S. state taxes		(216	)		541			90
Non-U.S. foreign tax differential		(18,357	)		(26,253	)		(15,644	)
Stock-based compensation		1,605			2,896			1,601
U.S. R&D credit		(2,226	)		(3,517	)		(2,298	)
Valuation allowance		1,901			6,090			—
Other		(336	)		(27	)		24
Provision for income taxes	$	3,071		$	8,701		$	1,465

Temporary differences that gave rise to significant portions of the Company’s deferred tax assets and liabilities at January 31, 2017 and 2016 were as follows:

	As of January 31,
	2017			2016
	(in thousands)
Deferred tax assets:
Federal and state credits	$	14,782		$	11,852
Expenses not currently deductible		2,381			2,331
Stock-based compensation		3,561			2,503
Foreign deferred		161			—
Gross deferred tax assets		20,885			16,686
Valuation allowance		(15,061	)		(12,072	)
Total deferred tax assets	$	5,824		$	4,614
Deferred tax liabilities
Property and equipment		(1,383	)		(1,378	)
Foreign deferred		—			(33	)
Net deferred tax assets	$	4,441		$	3,203

Tax valuation allowance for the periods indicated below were as follows:

							Deductions
					Additions		Charged to
	Balance at		Additional		Charged to		Expenses		Balance at
	Beginning of		Charged to		Other		or Other		End of
	Period		Expenses		Account		Accounts		Period
	(in thousands)
Tax Valuation Allowance
Year ended January 31, 2017	$	12,072		2,989		—		—	$	15,061
Year ended January 31, 2016	$	3,996		8,076		—		—	$	12,072
Year ended January 31, 2015	$	2,302		1,694		—		—	$	3,996

The Company conducts its business in several countries and regions and is subject to taxation in those jurisdictions. The Company is incorporated in the Cayman Islands with foreign subsidiaries in the U.S., China, Taiwan, Italy and other foreign countries and regions. As such, the Company’s worldwide operating income is subject to varying tax rates and its effective tax rate is highly dependent upon the geographic distribution of its earnings or losses and the tax laws and regulations in each geographical region. Consequently, the Company has experienced lower effective tax rates as a substantial amount of its operations are conducted in lower-tax jurisdictions. If the Company’s operational structure was to change in such a manner that would increase the amount of operating income subject to taxation in higher-tax jurisdictions, or if the Company was to commence operations in jurisdictions assessing relatively higher tax rates, its effective tax rate could fluctuate significantly on a quarterly basis and/or be adversely affected. Dividend distributions received from the Company’s U.S. subsidiary and certain other foreign subsidiaries may be subject to local country withholding taxes when, and if, distributed. Deferred tax liabilities have not been recorded on unremitted earnings of certain subsidiaries because management’s intent is to indefinitely reinvest any undistributed earnings in those subsidiaries. If dividend distributions from those subsidiaries were to occur, the liability as of January 31, 2017 would be $5.6 million. Cumulative undistributed earnings of foreign subsidiaries for which no deferred taxes have been provided approximated $44.0 million at January 31, 2017.

As of January 31, 2017 and 2016, the Company had deferred tax assets (net of deferred tax liabilities) before valuation allowance, of $19.5 million and $15.3 million, respectively. Realization of the deferred tax assets is dependent upon future taxable income, if any, the amount and timing of which are uncertain.

The Company also has Federal and California state research and development credit carryforwards of approximately $10.9 million and $13.8 million, respectively, at January 31, 2017. The Federal credits begin to expire in fiscal year 2033. The California credits can be carried forward indefinitely.

The Company reports its U.S. state deferred tax assets and related valuation allowance, net of the U.S federal tax rate of 35%. As of January 31, 2017, the Company has recorded a valuation allowance of $15.1 million against all of its U.S. federal research credit and all U.S. state deferred tax assets due to uncertainty regarding the future utilization of these deferred tax assets.

Utilization of the research credit carryforwards may be subject to an annual limitation due to the ownership percentage change limitations as defined by the U.S. Internal Revenue Code Section 382, as amended, and similar state provisions. The annual limitation may result in the expiration of the U.S. Federal and state research credit carryforwards before utilization. The Company does not expect any tax credit carryforwards to expire as a result of a Section 382 limitation.

The Company applies the provisions of FASB’s guidance on accounting for uncertainty in income taxes. As of January 31, 2017, the Company had approximately $38.0 million in unrecognized tax benefits, $30.1 million of which would affect the Company’s effective tax rate if recognized. The following table sets forth a reconciliation of the beginning and ending amount of unrecognized tax benefits:

	Year Ended January 31,
	2017			2016			2015
	(in thousands)
Beginning balance:	$	30,211		$	4,671		$	3,583
Additions based on tax positions related to the current year		7,830			17,169			1,284
Additions for tax positions of prior years		911			8,810			324
Reductions for tax positions in prior years		—			(37	)		—
Settlements for prior periods		—			—			(43	)
Lapse of applicable statute of limitations		(975	)		(402	)		(477	)
Ending balance:	$	37,977		$	30,211		$	4,671

The Company classified $1.8 million and $10.8 million of income tax liabilities as other long term liabilities as of January 31, 2017 and 2016, respectively, because payment of cash or settlement is not anticipated within one year from the balance sheet date.

The Company recognizes interest and penalties related to uncertain tax positions as a component of income tax expense. The Company recorded $64,000 benefit from interest accruals as a result of reserve released due to the lapse of statute of limitations for the year ended January 31, 2017 and recorded $6,000 and $7,000 of interest expense and penalties related to uncertain tax positions for the years ended January 31, 2016 and 2015, respectively. The Company recorded noncurrent liabilities of $103,000 and $166,000 related to interest and penalties for uncertain tax positions at January 31, 2017 and 2016, respectively.

The primary jurisdiction where our foreign earnings are derived is the Cayman Islands, where the Company is domiciled. Income earned in other jurisdictions was immaterial. The Company files income tax returns in the U.S. federal jurisdiction as well as many U.S. state and foreign jurisdictions. The tax years 2012 to 2016 remain open to examination by U.S. federal tax authorities. The tax years 2007 to 2016 remain open to examination by U.S. state tax authorities. The tax years 2011 to 2016 remain open to examination by foreign tax authorities. Fiscal years outside of the normal statute of limitations remain open to audit by tax authorities due to tax attributes generated in those earlier years, which have been carried forward and may be audited in subsequent years when utilized.

The Company believes that an adequate provision has been made for any adjustments that may result from tax examinations. However, the outcome of tax audits cannot be predicted with certainty. If any issues addressed in the Company’s tax audits are resolved in a manner not consistent with management’s expectations, the Company could be required to adjust its provision for income tax in the period such resolution occurs. Although timing of the resolution and/or closure of audits is highly uncertain, the Company does not believe it is reasonably possible that its unrecognized tax benefits would materially change in the next 12 months.

As of January 31, 2017, the Company’s long-term income taxes payable, including estimated interest and penalties, was approximately $1.9 million. The Company was unable to make a reasonably reliable estimate of the timing of payments in individual years due to uncertainties in the timing of tax audits, if any, or their outcomes.

On July 27, 2015, in Altera Corp. v. Commissioner, the United States Tax Court issued an opinion invalidating the 2003 final Treasury regulations that requires participants in a qualified cost-sharing arrangement to share stock-based compensation. At this time, the U.S. Department of the Treasury has not withdrawn the requirement to include stock-based compensation in intercompany cost-sharing arrangements from its regulations. In February 2016, the IRS appealed the ruling to the United States Court of Appeals for the Ninth Circuit. Due to the uncertainty related to the final resolution of this issue, the Company has not recorded tax benefits in its Consolidated Statements of Operations for the year ended January 31, 2017. The Company will continue to monitor ongoing developments and potential impacts to its consolidated financial statements.

Commitments and Contingencies

12 Months Ended

Jan. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

14. Commitments and Contingencies

The Company leases its principal facilities and time-based software licenses under operating lease agreements. Net operating lease expenses for the years ended January 31, 2017, 2016 and 2015 were approximately $7.6 million, $6.8 million and $5.8 million, respectively. Future annual minimum payments under these operating agreements with initial lease terms in excess of one year are as follows:

	As of
	January 31, 2017
Fiscal Year	(in thousands)
2018	$	2,792
2019		2,234
2020		1,819
2021		814
2022		249
Total future annual minimum lease payments	$	7,908

Contract Manufacturer Commitments

The Company’s components and products are procured and built by independent contract manufacturers based on sales forecasts. These forecasts include estimates of future demand, historical trends, analysis of sales and marketing activities, and adjustment of overall market conditions. The Company regularly issues purchase orders to independent contract manufacturers which are cancelable only upon the agreement between the Company and the third-party. As of January 31, 2017 and 2016, total manufacturing purchase commitments were approximately $23.9 million and $19.7 million, respectively.

Indemnification

The Company, from time to time, in the normal course of business, indemnifies certain vendors with whom it enters into contractual relationships. The Company has agreed to hold the other party harmless against third-party claims in connection with the Company’s future products. The Company also indemnifies certain customers against third-party claims related to certain intellectual property matters. It is not possible to determine the maximum potential amount of liability under these indemnification obligations due to the limited history of prior indemnification claims and the unique facts and circumstances that are likely to be involved in each particular claim. The Company has not made payments under these obligations and no liabilities have been recorded for these obligations on the consolidated balance sheets as of January 31, 2017 and 2016, respectively.

Segment Reporting

12 Months Ended

Jan. 31, 2017

Segment Reporting [Abstract]

Segment Reporting

15. Segment Reporting

The Company operates in one reportable segment related to the development and sales of low-power, high-definition video products. The Chief Executive Officer of the Company has been identified as the Chief Operating Decision Maker (the “CODM”) and manages the Company’s operations as a whole and for the purpose of evaluating financial performance and allocating resources, the CODM reviews financial information presented on a consolidated basis accompanied by information by customer and geographic region.

Geographic Revenue

The following table sets forth the Company’s revenue by geographic region for the periods indicated:

	Year Ended January 31,
	2017		2016		2015
	(in thousands)
Hong Kong	$	276,972	$	284,722	$	196,372
Europe		13,119		8,913		6,795
United States		7,038		8,855		6,677
North America other than United States		3,687		9,953		6,076
Asia Pacific		9,481		3,930		2,358
Total revenue	$	310,297	$	316,373	$	218,278

The classification by major geographic region is based on ship-to location but in a limited number of cases it is impractical to determine the geographic source of the revenue.

As of January 31, 2017, substantially all of the Company’s long-lived assets were located in the United States and Asia Pacific region with approximate net amount of $2.1 million and $2.3 million, respectively. As of January 31, 2016, substantially all of the Company’s long-lived assets were located in the United States and Asia Pacific region with approximate net amount of $1.6 million and $1.5 million, respectively.

Major Customers

For the year ended January 31, 2017, the customers representing 10% or more of revenue and accounts receivable were Wintech, the Company’s logistics provider, and GoPro, a direct OEM customer, which accounted for approximately 60% and 19% of total revenue, respectively. The revenues for GoPro in fiscal year 2017 included only direct shipments to GoPro and did not include shipments to GoPro’s various ODMs, either directly or through Wintech. We estimated that the revenues for shipments to GoPro’s various ODMs represented an additional approximately 5% of our total revenue in fiscal 2017. The customers representing 10% or more of revenue and accounts receivable for the years ended January 31, 2016 and 2015 were Wintech and Chicony Electronics Co., Ltd., or Chicony, a direct ODM customer. The revenue from Wintech accounted for approximately 67% and 57% of total revenue in fiscal year 2016 and 2015, respectively. The revenue from Chicony accounted for approximately 21% and 32% of total revenue in fiscal year 2016 and 2015, respectively. Accounts receivable with Wintech accounted for approximately $19.3 million and $20.6 million as of January 31, 2017 and 2016, respectively. Accounts receivable with GoPro accounted for approximately $11.3 million as of January 31, 2017. Accounts receivable with Chicony accounted for approximately $11.9 million as of January 31, 2016.

- Definition

The entire disclosure for reporting segments including data and tables. Reportable segments include those that meet any of the following quantitative thresholds a) it's reported revenue, including sales to external customers and intersegment sales or transfers is 10 percent or more of the combined revenue, internal and external, of all operating segments b) the absolute amount of its reported profit or loss is 10 percent or more of the greater, in absolute amount of 1) the combined reported profit of all operating segments that did not report a loss or 2) the combined reported loss of all operating segments that did report a loss c) its assets are 10 percent or more of the combined assets of all operating segments.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8981-108599

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 41
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e9038-108599

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8971-108599

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 12
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8595-108599

Reference 5: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8380-108599

Reference 6: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 32
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8933-108599

Reference 7: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 26
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8844-108599

Reference 8: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 35
-URI http://asc.fasb.org/extlink&oid=68060357&loc=d3e8984-108599

Reference 9: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
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+ Details

Related-Party Transactions	12 Months Ended
Related-Party Transactions	Jan. 31, 2017
Related Party Transactions [Abstract]
Related-Party Transactions	16. Related-Party Transactions The Company considers an entity to be a related party if it owns more than 10% of the Company’s total voting stock at the end of each reporting period or if an officer or employee of an entity also serves on the Company’s board of directors or if it is a significant shareholder and has material business transactions with the Company. The Company leases software licenses with Cadence Design Systems, Inc. (“Cadence”). A member of the Company’s Board of Directors is also the Chief Executive Officer, President and a Director of Cadence. The Company paid $2.8 million, $2.8 million and $2.3 million of license fee for the years ended January 31, 2017, 2016 and 2015, respectively. License expense related to these agreements included in research and development expense was approximately $2.9 million, $2.7 million and $1.9 million for the years ended January 31, 2017, 2016 and 2015, respectively.

Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Jan. 31, 2017
Accounting Policies [Abstract]
Organization	Organization Ambarella, Inc. (the “Company”) was incorporated in the Cayman Islands on January 15, 2004. The Company is a developer of semiconductor processing solutions for video that enable high-definition video capture, sharing, analysis and display. The Company combines its processor design capabilities with its expertise in video and image processing, algorithms and software to provide a technology platform that is designed to be easily scalable across multiple applications and enable rapid and efficient product development. The Company’s system-on-a-chip, or SoC, designs fully integrate high-definition video processing, image processing, analysis, audio processing and system functions onto a single chip, delivering exceptional video and image quality, differentiated functionality and low power consumption. The Company sells its solutions to leading original design manufacturers, or ODMs, and original equipment manufacturers, or OEMs, globally.
Basis of Consolidation	Basis of Consolidation The Company’s fiscal year ends on January 31. The consolidated financial statements of the Company and its subsidiaries have been prepared in conformity with generally accepted accounting principles in the United States (“U.S. GAAP”). All intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expense during the reported periods. Actual results could differ from those estimates. On an ongoing basis, management evaluates its estimates and assumptions, including those related to (i) the collectibility of accounts receivable; (ii) write down of excess and obsolete inventories; (iii) intangible assets and goodwill; (iv) the estimated useful lives of long-lived assets; (v) impairment of long-lived assets and financial instruments; (vi) warranty obligations; (vii) the valuation of stock-based compensation awards and financial instruments; (viii) the probability of performance objectives achievement; (ix) the realization of tax assets and estimates of tax liabilities, including reserves for uncertain tax positions; and (x) the recognition and disclosure of contingent liabilities. These estimates and assumptions are based on historical experience and on various other factors which the Company believes to be reasonable under the circumstances. The Company may engage third-party valuation specialists to assist with estimates related to the valuation of financial instruments and assets associated with various contractual arrangements. Such estimates often require the selection of appropriate valuation methodologies and significant judgment. Actual results could differ from these estimates under different assumptions or circumstances and such differences could be material.
Concentration of Risk	Concentration of Risk The Company’s products are manufactured, assembled and tested by third-party contractors located primarily in Asia. The Company does not have long-term agreements with these contractors. A significant disruption in the operations of one or more of these contractors would impact the production of the Company’s products which could have a material adverse effect on its business, financial condition and results of operations. A substantial portion of the Company’s revenue is derived from sales through its logistics provider, Wintech Microelectronics Co., Ltd., or Wintech, which serves as its non-exclusive sales representative and logistics provider in Asia other than Japan, and through one direct OEM customer, GoPro Inc., or GoPro. Termination of the relationships with these two customers could result in a temporary or permanent loss of revenue and termination of the relationship with Wintech could result in an obligation to repurchase unsold product. Furthermore, any credit issues from these two customers could impair their abilities to make timely payment to the Company. See Note 15 for additional information regarding concentration with these two customers. Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities and accounts receivable. The Company maintains its cash primarily in checking and money market accounts with reputable financial institutions. Cash deposits held with these financial institutions may exceed the amount of insurance provided on such deposits. The Company has not experienced any material losses on deposits of its cash. The cash equivalents and marketable securities consist primarily of money market funds, demand deposits, asset-backed securities, commercial paper, U.S. government securities and debt securities of corporations which management assesses to be highly liquid, in order to limit the exposure of each investment. The Company does not hold or issue financial instruments for trading purposes. The Company performs ongoing credit evaluation of its customers and adjusts credit limits based upon payment history and customers’ credit worthiness. The Company regularly monitors collections and payments from its customers.
Foreign Currency Transactions	Foreign Currency Transactions The U.S. dollar is the functional currency for the Company and its subsidiaries. Monetary assets and liabilities denominated in non-U.S. currencies are re-measured to U.S. dollars using current exchange rates in effect at the balance sheet date. Nonmonetary assets and liabilities are re-measured to U.S. dollars using historical exchange rates. Monetary and other accounts are re-measured to U.S. dollars using average exchange rates in effect during each period. Gains or losses from foreign currency re-measurement are included in other income (loss), net in the consolidated statements of operations, and, to date, have not been material.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The fair value accounting is applied to all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed in the financial statements on a recurring basis. The carrying amounts reflected in the consolidated balance sheets for cash equivalents, accounts receivable, accounts payable, accrued liabilities and other current liabilities, approximate fair value due to the short-term nature.
Cash Equivalents and Marketable Securities	Cash Equivalents and Marketable Securities The Company considers all highly liquid investments with original maturities of less than three months at the time of purchase to be cash equivalents. Investments that are highly liquid with original maturities at the time of purchase greater than three months are considered as marketable securities. The Company classifies these investments as “available-for-sale” securities carried at fair value, based on quoted market prices of similar assets, with the unrealized gains or losses reported, net of tax, as a separate component of shareholders’ equity and included in accumulated other comprehensive income (loss) in the consolidated balance sheets. The amortization of premiums and accretion of discounts and the realized gains and losses are both recorded in other income (loss), net in the consolidated statements of operations. The Company reviews its investments for possible other-than-temporary impairments on a regular basis. If any loss on investment is believed to be other-than-temporary, a charge will be recorded and a new cost basis in the investment will be established. In evaluating whether a loss on a security is other-than-temporary, the Company considers the following factors: 1) general market conditions, 2) the duration and extent to which the fair value is less than cost, 3) the Company’s intent and ability to hold the investment. For securities in an unrealized loss position which is deemed to be other-than-temporary, the difference between the security’s then-current amortized cost basis and fair value is separated into (i) the amount of the impairment related to the credit loss (i.e., the credit loss component) and (ii) the amount of the impairment related to all other factors (i.e., the non-credit loss component). The credit loss component is recognized in earnings. The non-credit loss component is recognized in accumulated other comprehensive income (loss). Due to the relative short term nature of the investments, there have been no other-than-temporary impairments recorded to date.
Trade Accounts Receivable and Allowances for Doubtful Accounts	Trade Accounts Receivable and Allowances for Doubtful Accounts Trade accounts receivable are recorded at the invoiced amount and do not include finance charges. The Company performs ongoing credit evaluation of its customers and generally requires no collateral. The Company assesses the need for allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments by considering factors such as historical collection experience, credit quality, aging of the accounts receivable balances and current economic conditions that may affect a customer’s ability to pay. There were no material write-offs of accounts receivable for the fiscal years ended January 31, 2017, 2016 and 2015, respectively. There were no material allowance for doubtful accounts recorded as of January 31, 2017 and 2016, respectively.
Inventories	Inventories The Company records inventories at the lower of cost or market. The cost includes materials and other production costs and is computed using standard cost on a first-in, first-out basis. Inventory reserves are recorded for estimated obsolescence or unmarketable inventories based on forecast of future demand and market conditions. If actual market conditions are less favorable than projected, or if future demand for the Company’s products decrease, additional inventory write-downs may be required. Once inventory is written down, a new accounting cost basis is established and, accordingly, any associated reserve is not released until the inventory is sold or scrapped. There were no material inventory losses recognized for the fiscal years ended January 31, 2017, 2016 and 2015, respectively.
Property and Equipment	Property and Equipment Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful life for computer equipment, computer software, machinery, equipment and furniture and fixture. Leasehold improvements are amortized over the shorter of the lease term or their estimated useful lives. Repairs and maintenance are charged to expense as incurred.
Internal-Use Software	Internal-Use Software The Company capitalizes certain software that is acquired and developed solely for internal use. The capitalization costs include charges from services provided to develop software during the application development stage, costs incurred to obtain software, and certain costs from employees who are directly associated with and who directly devote time to the project. The capitalization begins when the preliminary project stage is completed and ceases no later than the point at which the project is substantially complete and ready for its intended use after all substantial testing is completed. The internal-use software is amortized over its estimated useful life. Repairs and maintenance are charged to expense as incurred.
Business Combinations and Intangible Assets	Business Combinations and Intangible Assets The Company allocates the fair value of purchase price to the assets acquired and liabilities assumed based on their estimated fair values. The excess of the fair value of purchase price over the fair values of these identifiable assets and liabilities is recorded as goodwill. When determining the fair values of assets acquired and liabilities assumed, especially with respect to intangible assets, the management makes significant estimates and assumptions. Critical estimates in valuing certain intangible assets include, but are not limited to, replacement cost. Management’s estimates of fair value are based upon assumptions believed to be reasonable, but which are inherently uncertain and unpredictable and, as a result, actual results may differ from estimates.
Goodwill and In-Process Research and Development	Goodwill and In-Process Research and Development The Company does not amortize goodwill. Acquired in-process research and development, or IPR&D, is capitalized at fair value as an intangible asset and amortization commences upon completion of the underlying projects. When a project underlying reported IPR&D is completed, the corresponding amount of IPR&D is reclassified as an amortizable purchased intangible asset and is amortized over its estimated useful life.
Impairment of Long-Lived Assets Including Goodwill and Other Acquired Intangible Assets	Impairment of Long-Lived Assets Including Goodwill and Other Acquired Intangible Assets The Company reviews property and equipment and intangible assets, excluding goodwill, for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset, or asset group, may not be recoverable. Determination of recoverability of assets to be held and used is measured by a comparison of the carrying amount of an asset, or asset group to estimated undiscounted future cash flows expected to be generated by the asset, or asset group. If the carrying amount of an asset or asset group exceeds its estimated undiscounted future cash flows, an impairment charge is recognized for the amount by which the carrying amount of the asset or asset group exceeds the estimated fair value of the asset or asset group. Fair value is determined based on the estimated discounted future cash flows expected to be generated by the asset or asset group. Events or changes in circumstances that may indicate that an asset is impaired include significant decreases in the market value of an asset, significant underperformance relative to expected historical or projected future results of operations, a change in the extent or manner in which an asset is utilized, significant declines in the estimated fair value of the overall Company for a sustained period, shifts in technology, loss of key management or personnel, changes in the Company’s operating model or strategy and competitive forces. There has been no occurrence of events to date that would trigger an impairment analysis. As such, no impairment charge has been recognized as of January 31, 2017. The Company tests the goodwill for impairment at least annually, or sooner whenever events or changes in circumstances indicate that the asset may be impaired. The Company has a single reporting unit for goodwill impairment test purposes based on its business and reporting structure. No goodwill impairment has been identified to date.
Cost Method Investment	Cost Method Investment The Company accounts for its investment in a privately held company under the cost method and reports the investment in other non-current assets in the consolidated balance sheets. The Company monitors the carrying value of the investment and records a reduction in carrying value when a decline in value is deemed to be other than temporary. To date, there have been no identified events or changes in circumstances that may have a significant adverse effect on the fair value of this investment and the Company has not recognized any impairment losses related to this investment.
Revenue Recognition	Revenue Recognition The Company generates revenue from the sales of its SoCs to OEMs or ODMs, either directly or through logistics providers. Revenue from sales directly to OEMs and ODMs is recognized upon shipment provided that persuasive evidence of an arrangement exists, legal title to the products and risk of ownership have transferred, the fee is fixed or determinable, and collection of the resulting receivable is reasonably assured. The Company provides its logistics providers with the rights to return excess levels of inventory and to future price adjustments. Given the inability to reasonably estimate these price changes and returns, revenue and costs related to shipments to logistics providers are deferred until the Company has received notification from its logistics providers that they have sold the Company’s products. Information reported by the Company’s logistics providers includes product resale price, quantity and end customer shipment information as well as remaining inventory on hand. At the time of shipment to a logistics provider, the Company records a trade receivable as there is a legally enforceable right to receive payment, reduces inventory for the value of goods shipped as legal title has passed to the logistics provider and defers the related margin as deferred revenue in the consolidated balance sheets. Any price adjustments are recorded as a change to deferred revenue at the time the adjustments are agreed upon. Arrangements with certain OEM customers provide for pricing that is dependent upon the end products into which the Company’s SoCs are used. These arrangements may also entitle the Company to a share of the product margin ultimately realized by the OEM. The minimum guaranteed amount of revenue related to the sale of products subject to these arrangements is recognized when all other elements of revenue recognition are met. Any amounts at the date of shipment invoiced in excess of the minimum guaranteed contract price are deferred until the additional amounts the Company is entitled to are fixed or determinable. Additional amounts earned by the Company resulting from margin sharing arrangements and determination of the end products into which the products are ultimately incorporated are recognized when end customer sales volume is reported to the Company. Revenue from margin sharing arrangements was not material for the fiscal years ended January 31, 2017, 2016 and 2015, respectively. The Company also enters into engineering service agreements with certain customers. These agreements may include multiple deliverables, such as software development services, licensing of intellectual property and post-contract customer support, or PCS. The Company does not sell separately any of these components and does not have Vendor Specific Objective Evidence, or VSOE, for the deliverables. Accordingly, revenues from these agreements are deferred for any amounts billed until delivery of all the elements. If the agreements include PCS, the revenues are recognized ratably over the estimated supporting periods. Revenues from engineering service agreements was not material for the fiscal years ended January 31, 2017, 2016 and 2015, respectively.
Cost of Revenue	Cost of Revenue Cost of revenue includes cost of materials, cost associated with packaging and assembly, testing and shipping, cost of personnel, stock-based compensation, logistics and quality assurance, warranty cost, royalty expense, write-downs of inventories and allocation of overhead.
Warranty Costs	Warranty Costs The Company typically provides warranty on its products. The Company accrues for the estimated warranty costs at the time when revenue is recognized. The warranty accruals are regularly monitored by management based upon historical experience and any specifically identified failures. While the Company engages in extensive product quality assessment, actual product failure rates, material usage or service delivery costs could differ from estimates and revisions to the estimated warranty liability would be required. The Company’s warranty accruals were not material for the fiscal years ended January 31, 2017, 2016 and 2015, respectively.
Research and Development	Research and Development Research and development costs are expensed as incurred and consist primarily of personnel costs, product development costs, which include engineering services, development software and hardware tools, license fees, costs of fabrication of masks for prototype products, other development materials costs, depreciation of equipment used in research and development and allocation of facility costs.
Selling, General and Administrative	Selling, General and Administrative Selling, general and administrative expenses consist of personnel costs, travel and trade show costs, legal expenses, other professional services and occupancy costs. Advertising expenses were not material for the fiscal years ended January 31, 2017, 2016 and 2015, respectively.
Operating Leases	Operating Leases The Company recognizes rent expense on a straight-line basis over the term of the lease. The difference between rent expense and rent payment is recorded as deferred rent and is included in accrued liabilities in the consolidated balance sheets.
Stock-Based Compensation	Stock-Based Compensation The Company measures stock-based compensation for equity awards granted to employees and directors based on the estimated fair value on the grant date, and recognizes that compensation as expense using the straight-line attribution method for service condition awards or using the graded-vesting attribution method for awards with performance conditions over the requisite service period, which is typically the vesting period of each award. The Company determines the fair value of restricted stock and restricted stock units based on the fair market value of its ordinary shares on the grant date. The Company uses the Black-Scholes option pricing model to determine the fair value of stock options. Determining the fair value of stock options on the grant date requires the input of various assumptions, including stock price of the underlying ordinary share, the exercise price of the stock option, expected volatility, expected term, risk-free interest rate and dividend rate. The expected term is calculated using the simplified method as prescribed in the guidance provided by the Securities and Exchange Commission, as neither relevant historical experience nor other relevant data are available to estimate future exercise behavior. The expected volatility is based on the historical volatilities of similar companies whose share prices are publicly available for a period commensurate with the expected term. The risk-free interest rate is derived from the average U.S. Treasury constant maturity rates during the respective periods commensurate with the expected term. The expected dividend yield is zero because the Company has not historically paid dividends and has no present intention to pay dividends. Upon adoption of ASU 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting in the first quarter of fiscal year 2017, the Company elects to account for forfeitures as they occur.
Income Taxes	Income Taxes The Company records income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in its financial statements or tax returns. In estimating future tax consequences, generally all expected future events other than enactments or changes in the tax law or rates are considered. Valuation allowances are provided when necessary to reduce deferred tax assets to the amount expected to be realized. The Company applies authoritative guidance for the accounting for uncertainty in income taxes. The guidance requires that tax effects of a position be recognized only if it is “more likely than not” to be sustained based solely on its technical merits as of the reporting date. Upon estimating the Company’s tax positions and tax benefits, the Company considers and evaluates numerous factors, which may require periodic adjustments and which may not reflect the final tax liabilities. The Company adjusts its financial statements to reflect only those tax positions that are more likely than not to be sustained under examination. As part of the process of preparing consolidated financial statements, the Company is required to estimate its taxes in each of the jurisdictions in which it operates. The Company estimates actual current tax exposure together with assessing temporary differences resulting from differing treatment of items, such as accruals and allowances not currently deductible for tax purposes. These differences result in deferred tax assets, which are included in the consolidated balance sheets. In general, deferred tax assets represent future tax benefits to be received when certain expenses previously recognized in the consolidated statements of operations become deductible expenses under applicable income tax laws, or loss or credit carryforwards are utilized. In assessing whether deferred tax assets may be realized, management considers whether it is more likely than not that some portion or all of deferred tax assets will be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income. The Company makes estimates and judgments about its future taxable income based on assumptions that are consistent with its plans and estimates. Should the actual amounts differ from estimates, the amount of valuation allowance could be materially impacted. Any adjustment to the deferred tax asset valuation allowance would be recorded in the consolidated income statement for the periods in which the adjustment is determined to be required.
Net Income Per Ordinary Share	Net Income Per Ordinary Share Basic earnings per share is computed by dividing net income available to ordinary shareholders by the weighted-average number of ordinary shares outstanding during the period. Diluted earnings per share is computed by dividing net income available to ordinary shareholders by the weighted-average number of ordinary shares outstanding during the period increased to include the number of additional ordinary shares that would have been outstanding if the potentially dilutive securities had been issued. Potentially dilutive securities include outstanding stock options, shares to be purchased under the Company’s employee stock purchase plan, unvested restricted stock and restricted stock units. The dilutive effect of potentially dilutive securities is reflected in diluted earnings per share by application of the treasury stock method.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) includes unrealized gains or losses from available-for-sale securities that are excluded from net income.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”). The new guidance clarifies the principles and develops a common revenue recognition guidance for U.S. GAAP and International Financial Reporting Standards (the “IFRS”). Under the new guidance, an entity is required to recognize an amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. This new revenue standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. Subsequently, the FASB issued the following standards related to ASU 2014-09: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (“ASU 2016-08”); ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing (“ASU 2016-10”); ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”); and ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers (“ASU 2016-20”). Accordingly, the Company must adopt ASU 2016-08, ASU 2016-10, ASU 2016-12 and ASU 2016-20 with ASU 2014-09 (collectively, the “new revenue standards”) in its first quarter of fiscal year 2019. The new revenue guidance may be applied retrospectively to each prior period presented or retrospectively with the cumulative effect recognized as of the date of adoption. The Company is currently evaluating the impact of adoption on its financial position, results of operations and disclosures. In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. In connection with each annual and interim period, management is required to assess whether there is substantial doubt about an entity’s ability to continue as a going concern within one year after the issuance date, and to provide related footnote disclosures in certain circumstances. The new guidance is effective for annual periods ending after December 15, 2016, and interim periods within annual periods beginning after December 15, 2016. Early adoption is permitted. This ASU has no impact on the Company’s financial statements or disclosures. In July 2015, the FASB issued ASU No. 2015-11, Simplifying the Measurement of Inventory. The new guidance changes the measurement principle for inventory from the lower of cost or market to lower of cost and net realizable value. Net realizable value is the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal, and transportation. It applies to entities that measure inventory using a method other than last-in, first-out (“LIFO”) and the retail inventory method (“RIM”). The new guidance will be effective for fiscal years beginning after December 15, 2016, including interim periods within those fiscal years and should be applied prospectively. Early adoption is permitted as of the beginning of an interim or annual reporting period. The Company does not believe the adoption of this new guidance will have a material impact on its financial position, results of operations and disclosures. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842). This standard requires entities that lease assets to recognize on the balance sheet the assets and liabilities for the rights and obligations created by those leases. The standard is effective for fiscal years and the interim periods within those fiscal years beginning after December 15, 2018. The guidance is required to be applied by the modified retrospective transition approach. Early adoption is permitted. The Company is currently assessing the impact of the adoption of this new guidance on its financial position, results of operations and disclosures. In March 2016, the FASB issued ASU 2016-09, Compensation – Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting, to simplify and improve the accounting for employee share-based awards. The new standard amends the accounting for employee share-based payment transactions to require recognition of the tax effects resulting from the settlement of stock-based awards as income tax benefit or expense in the income statement in the reporting period in which they occur. In addition, the tax-related cash flows resulting from share-based payments will be classified as cash flows from operating activities and cash payments made to the taxing authorities on the employees’ behalf for withheld shares will be classified as financing activities on the statement of cash flows. The new guidance also provides an accounting policy election to account for forfeitures as they occur. The Company elected to early adopt this new guidance in the first quarter of its fiscal year 2017. As a result of this adoption, the Company recorded an increase to retained earnings of $11.7 million to recognize U.S. net operating loss carryforwards attributable to tax benefits from excess stock-based compensation that had not been previously recognized and recorded a decrease to retained earnings of $0.2 million resulting from the election of accounting policy to account for forfeitures as they occur on February 1, 2016. The Company also elected to apply the presentation for cash flows related to excess tax benefits prospectively. The presentation requirements for cash flows related to employee taxes paid for withheld shares has no impact on the Company’s consolidated statements of cash flows. On February 1, 2016, the cumulative effect adjustment of these changes recognized in the beginning of retained earnings was approximately $11.5 million. In June 2016, the FASB issued ASU 2016-13, Financial Instruments – Credit Losses (Topic 326), to introduce a new impairment model for recognizing credit losses on financial instruments based on an estimated of current expected credit losses (ECL). Under the new model, available-for-sale (AFS) debt securities are required to estimate ECL only when the fair value is below the amortized cost of the asset and is no longer based on an impairment being “other-than-temporary”. The new model also requires the impairment calculation on an individual security level and requires an entity use present value of cash flows when estimating the ECL. The credit-related losses are required to be recognized through earnings and non-credit related losses are reported in other comprehensive income. The ASU will be effective for public entities in fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. Early adoption is permitted. The new guidance will require modified retrospective application to all outstanding instruments, with a cumulative effect adjustment recorded to opening retained earnings as of the beginning of the first period in which the guidance becomes effective. The Company does not believe the adoption of this new guidance will have a material impact on its consolidated financial statements. In October 2016, the FASB issued ASU 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other Than Inventory. The new guidance requires that entities recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. The new guidance will be effective for annual reporting periods beginning after December 15, 2017, including interim reporting periods within those annual reporting periods. Early adoption is permitted but should be in the first interim period. The new guidance should also be applied on a modified retrospective basis through a cumulative-effect adjustment to retained earnings as of the beginning of the period of adoption. The Company is currently assessing the impact of the adoption of this new guidance on its financial position, results of operations and disclosures. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), to require entities to show the changes in the total of cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. As a result, entities will no longer present transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. When cash, cash equivalents, restricted cash and restricted cash equivalents are presented in more than one line item on the balance sheet, the new guidance requires a reconciliation of the totals in the statement of cash flows to the related captions in the balance sheet. Entities will also have to disclose the nature of restricted cash and restricted cash equivalent balances. The new guidance will be effective for fiscal years beginning after December 15, 2017, including the interim periods within those years. Early adoption is permitted and the new guidance is applied retrospectively. The Company does not believe the adoption of this new guidance will have a material impact on its consolidated statement of cash flows and disclosures. In January 2017, the FASB issued ASU 2017-04, Intangibles – Goodwill and Other (Topic 350): Simplifying the Test of Goodwill Impairment, to eliminate the requirement to calculate the implied fair value of goodwill to measure a goodwill impairment charge. Instead, entities will record an impairment charge based on the excess of a reporting unit’s carrying amount over its fair value. This new standard will be applied prospectively and is effective for annual and interim periods beginning after December 15, 2019. Early adoption is permitted for annual and interim periods after January 1, 2017. The Company does not believe the adoption of this new guidance will have a material impact on its financial position, results of operations and disclosures.

Financial Instruments and Fair Value (Tables)

12 Months Ended

Jan. 31, 2017

Investments All Other Investments [Abstract]

Schedule of Available-for-Sale Securities at Fair Value

All of the investments are classified as available-for-sale securities and reported at fair value in the consolidated balance sheets as follows:

	As of January 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Money market funds	$	8,328	$	—	$	—		$	8,328
Demand deposits		10,000		—		—			10,000
Commercial paper		4,784		—		—			4,784
Corporate bonds		42,713		6		(41	)		42,678
Asset-backed securities		11,686		1		(12	)		11,675
U.S. government securities		23,409		6		(30	)		23,385
Total cash equivalents and marketable securities	$	100,920	$	13	$	(83	)	$	100,850

	As of January 31, 2016
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Money market funds	$	530	$	—	$	—		$	530
Commercial paper		2,598		—		—			2,598
Corporate bonds		21,342		7		(9	)		21,340
Asset-backed securities		4,586		—		(1	)		4,585
U.S. government securities		9,274		4		(6	)		9,272
Agency bonds		2,044		—		(2	)		2,042
Total cash equivalents and marketable securities	$	40,374	$	11	$	(18	)	$	40,367

Schedule of Cash Equivalents and Marketable Securities

	As of
	January 31, 2017		January 31, 2016
	(in thousands)
Included in cash equivalents	$	18,328	$	530
Included in marketable securities		82,522		39,837
Total cash equivalents and marketable securities	$	100,850	$	40,367

Summary of Contractual Maturities of Investments

The contractual maturities of the investments at January 31, 2017 and 2016 were as follows:

	As of
	January 31, 2017		January 31, 2016
	(in thousands)
Due within one year	$	76,992	$	33,449
Due within one to two years		23,858		6,918
Total cash equivalents and marketable securities	$	100,850	$	40,367

Schedule of Fair Value of Financial Instruments Measured on Recurring Basis

The following tables present the fair value of the financial instruments measured on a recurring basis as of January 31, 2017 and 2016, respectively:

	As of January 31, 2017
	Total		Level 1		Level 2		Level 3
	(in thousands)
Money market funds	$	8,328	$	8,328	$	—	$	—
Demand deposits		10,000		10,000		—		—
Commercial paper		4,784		—		4,784		—
Corporate bonds		42,678		—		42,678		—
Asset-backed securities		11,675		—		11,675		—
U.S. government securities		23,385		—		23,385		—
Total cash equivalents and marketable securities	$	100,850	$	18,328	$	82,522	$	—

	As of January 31, 2016
	Total		Level 1		Level 2		Level 3
	(in thousands)
Money market funds	$	530	$	530	$	—	$	—
Commercial paper		2,598		—		2,598		—
Corporate bonds		21,340		—		21,340		—
Asset-backed securities		4,585		—		4,585		—
U.S. government securities		9,272		—		9,272		—
Agency bonds		2,042		—		2,042		—
Total cash equivalents and marketable securities	$	40,367	$	530	$	39,837	$	—

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details

Inventories (Tables)

12 Months Ended

Jan. 31, 2017

Inventory Disclosure [Abstract]

Schedule of Inventory

Inventories at January 31, 2017 and 2016 consisted of the following:

	As of January 31,
	2017		2016
	(in thousands)
Work-in-progress	$	10,105	$	9,474
Finished goods		10,040		8,693
Total	$	20,145	$	18,167

Property and Equipment, Net (Tables)

12 Months Ended

Jan. 31, 2017

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment at January 31, 2017 and 2016 consisted of the following:

	As of January 31,
	2017			2016
	(in thousands)
Computer equipment and software	$	6,798		$	6,421
Machinery and equipment		3,405			2,706
Furniture and fixtures		797			492
Leasehold improvements		1,672			1,429
Construction in progress		755			253
		13,427			11,301
Less: accumulated depreciation and amortization		(8,439	)		(7,853	)
Total property and equipment, net	$	4,988		$	3,448

Accrued Liabilities (Tables)

12 Months Ended

Jan. 31, 2017

Payables And Accruals [Abstract]

Schedule of Accrued Liabilities

Accrued liabilities at January 31, 2017 and 2016 consisted of the following:

	As of January 31,
	2017		2016
	(in thousands)
Accrued employee compensation	$	14,685	$	14,512
Accrued warranty		500		234
Accrued rebates		972		824
Accrued product development costs		7,605		6,339
Other accrued liabilities		2,686		1,869
Total accrued liabilities	$	26,448	$	23,778

Deferred Revenue and Deferred Cost (Tables)

12 Months Ended

Jan. 31, 2017

Deferred Revenue Disclosure [Abstract]

Schedule of Deferred Revenue and Related Cost

Deferred revenue and related cost at January 31, 2017 and 2016 consisted of the following:

	As of January 31,
	2017			2016
	(in thousands)
Deferred revenue on product shipments	$	7,725		$	12,201
Deferred revenue from licenses & services		1,748			1,653
Deferred cost of revenue on product shipments		(2,048	)		(3,777	)
Total deferred revenue, net	$	7,425		$	10,077

Other Long-Term Liabilities (Tables)

12 Months Ended

Jan. 31, 2017

Other Liabilities Disclosure [Abstract]

Schedule of Other Long-Term Liabilities

Other long-term liabilities at January 31, 2017 and 2016 consisted of the following:

	As of January 31,
	2017		2016
	(in thousands)
Unrecognized tax benefits, including interest	$	1,905	$	10,917
Deferred tax liabilities, non-current		1,333		1,423
Other long-term liabilities		3		2
Total other long-term liabilities	$	3,241	$	12,342

Capital Stock (Tables)

12 Months Ended

Jan. 31, 2017

Equity [Abstract]

Schedule of Ordinary Shares Reserved for Future Issuance

As of January 31, 2017 and 2016, the following ordinary shares were reserved for future issuance:

	As of January 31,
	2017		2016
Shares reserved for options, restricted stock and restricted stock units		5,167,688		5,027,475
Shares reserved for employee stock purchase plan		1,252,465		974,273

Employee Benefits and Stock-based Compensation (Tables)

12 Months Ended

Jan. 31, 2017

Postemployment Benefits [Abstract]

Classification of Stock-based Compensation

The following table presents the classification of stock-based compensation for the periods indicated:

	Year Ended January 31,
	2017		2016		2015
	(in thousands)
Stock-based compensation:
Cost of revenue	$	1,078	$	657	$	343
Research and development		29,729		19,082		8,654
Selling, general and administrative		18,025		11,355		6,695
Total stock-based compensation	$	48,832	$	31,094	$	15,692

Weighted-Average Assumptions Used to Estimate Fair Value

The following table sets forth the weighted-average assumptions used to estimate the fair value of the stock options and employee stock purchase plan awards for the periods indicated:

	Year Ended January 31,
	2017			2016			2015
Stock Options:
Volatility		38	%		57	%		64	%
Risk-free interest rate		1.59	%		1.74	%		1.93	%
Expected term (years)		6.00		6.08			6.01
Dividend yield		0	%		0	%		0	%
Employee stock purchase plan awards:
Volatility		54	%		63	%		49	%
Risk-free interest rate		0.51	%		0.21	%		0.07	%
Expected term (years)		0.5			0.5			0.5
Dividend yield		0	%		0	%		0	%

Stock Option Activities

The following table summarizes stock option activities for the periods indicated:

	Option Outstanding
										Weighted-
								Total Intrinsic		Average
						Weighted-		Value of		Remaining		Aggregate
				Weighted-		Average		options		Contractual		Intrinsic
				Average		Grant-date		Exercised		Term		Value
	Shares			Exercise Price		Fair Value		(in thousands)		(in years)		(in thousands)
Outstanding at January 31, 2014		3,358,706		$	6.92
Granted		428,781			36.33	$	21.37
Exercised		(1,456,944	)		5.84			$	46,427
Forfeited		(48,634	)		13.38
Outstanding at January 31, 2015		2,281,909			13.00
Granted		179,700			71.36	$	38.81
Exercised		(567,888	)		9.11			$	37,603
Forfeited		(40,331	)		35.65
Outstanding at January 31, 2016		1,853,390			19.36
Granted		110,500			47.82	$	18.76
Exercised		(235,923	)		13.69			$	10,788
Forfeited		(16,708	)		55.07
Expired		(7,735	)		14.19
Outstanding at January 31, 2017		1,703,524		$	21.66					5.16		$	51,670
Exercisable at January 31, 2017		1,367,960		$	14.94						4.42	$	49,016

Restricted Stock and Restricted Stock Units Activities

The following table summarizes restricted stock and restricted stock units activities for the periods indicated:

				Weighted-
				Average
				Grant-Date
	Shares			Fair Value
Unvested at January 31, 2014		1,410,089		$	14.02
Granted		1,111,204			38.60
Vested		(484,296	)		17.39
Forfeited		(56,549	)		19.93
Unvested at January 31, 2015		1,980,448			26.82
Granted		1,314,387			66.14
Vested		(769,779	)		27.82
Forfeited		(29,568	)		42.11
Unvested at January 31, 2016		2,495,488			47.04
Granted		676,598			67.68
Vested		(955,230	)		39.28
Forfeited		(41,183	)		52.49
Unvested at January 31, 2017		2,175,673		$	56.76

Net Income Per Ordinary Share (Tables)

12 Months Ended

Jan. 31, 2017

Earnings Per Share [Abstract]

Computation of Basic and Diluted Net Income Per Ordinary Share

The following table sets forth the computation of basic and diluted net income per ordinary share for the periods indicated:

	Year Ended January 31,
	2017		2016			2015
	(in thousands, except share and per share data)
Numerator:
Net income	$	57,810	$	76,508		$	50,571
Less: amount allocable to unvested early exercised options		—		—			(11	)
Net income allocable to ordinary shareholders - basic	$	57,810	$	76,508		$	50,560
Undistributed earnings reallocated to ordinary shareholders		—		—			1
Net income allocable to ordinary shareholders - diluted	$	57,810	$	76,508		$	50,561
Denominator:
Weighted-average ordinary shares outstanding		32,671,221		31,633,992			29,749,354
Less: weighted-average unvested early exercised options subject to repurchase		—		(56	)		(6,701	)
Weighted-average ordinary shares - basic		32,671,221		31,633,936			29,742,653
Effect of potentially dilutive securities:
Employee stock options		1,080,864		1,245,341			1,818,401
Restricted stock and restricted stock units		565,068		865,863			704,788
Employee stock purchase plan		10,571		10,569			12,285
Weighted-average ordinary shares - diluted		34,327,724		33,755,709			32,278,127
Net income per ordinary share:
Basic	$	1.77	$	2.42		$	1.70
Diluted	$	1.68	$	2.27		$	1.57

Weighted-Average Potentially Dilutive Securities Excluded from Computation of Diluted Net Income Per Ordinary Share

The following weighted-average potentially dilutive securities were excluded from the computation of diluted net income per ordinary share as their effect would have been antidilutive:

	Year Ended January 31,
	2017		2016		2015
Options to purchase ordinary shares		343,936		109,958		217,514
Restricted stock and restricted stock units		891,952		163,994		167,702
Employee stock purchase plan		14,651		9,073		36,110
Early exercised options subject to repurchase		—		56		6,701
		1,250,539		283,081		428,027

Income Taxes (Tables)

12 Months Ended

Jan. 31, 2017

Income Tax Disclosure [Abstract]

Summary of Income before Income Taxes

Income before income taxes consisted of the following for the periods indicated:

	Year Ended January 31,
	2017		2016		2015
	(in thousands)
U.S. operations	$	3,092	$	3,190	$	1,978
Non-U.S. operations		57,789		82,019		50,058
Income before income taxes	$	60,881	$	85,209	$	52,036

Schedule of Income Tax Provision

Income tax provision consisted of the following for the periods indicated:

	Year Ended January 31,
	2017			2016			2015
	(in thousands)
Current:
U.S. federal tax	$	818		$	5,273		$	3,135
U.S. state taxes		(212	)		541			93
Non-U.S. foreign taxes		1,454			1,874			1,348
		2,060			7,688			4,576
Deferred:
U.S. federal tax		1,174			1,050			(3,208	)
U.S. state taxes		—			—			—
Non-U.S. foreign taxes		(163	)		(37	)		97
		1,011			1,013			(3,111	)
Provision for income taxes	$	3,071		$	8,701		$	1,465

Schedule of Reconciliation Between the Provision (Benefit) for Income Taxes at the Statutory Rate and the Effective Tax Rate

For purposes of the reconciliation between the provision (benefit) for income taxes at the statutory rate and the effective tax rate, a notional U.S. 34% rate is applied to pretax income as a result of the following for the periods indicated:

	Year Ended January 31,
	2017			2016			2015
	(in thousands)
Provision at U.S. notional statutory rate	$	20,700		$	28,971		$	17,692
U.S. state taxes		(216	)		541			90
Non-U.S. foreign tax differential		(18,357	)		(26,253	)		(15,644	)
Stock-based compensation		1,605			2,896			1,601
U.S. R&D credit		(2,226	)		(3,517	)		(2,298	)
Valuation allowance		1,901			6,090			—
Other		(336	)		(27	)		24
Provision for income taxes	$	3,071		$	8,701		$	1,465

Schedule of Deferred Tax Assets and Liabilities

Temporary differences that gave rise to significant portions of the Company’s deferred tax assets and liabilities at January 31, 2017 and 2016 were as follows:

	As of January 31,
	2017			2016
	(in thousands)
Deferred tax assets:
Federal and state credits	$	14,782		$	11,852
Expenses not currently deductible		2,381			2,331
Stock-based compensation		3,561			2,503
Foreign deferred		161			—
Gross deferred tax assets		20,885			16,686
Valuation allowance		(15,061	)		(12,072	)
Total deferred tax assets	$	5,824		$	4,614
Deferred tax liabilities
Property and equipment		(1,383	)		(1,378	)
Foreign deferred		—			(33	)
Net deferred tax assets	$	4,441		$	3,203

Summary of Tax Valuation Allowance

Tax valuation allowance for the periods indicated below were as follows:

							Deductions
					Additions		Charged to
	Balance at		Additional		Charged to		Expenses		Balance at
	Beginning of		Charged to		Other		or Other		End of
	Period		Expenses		Account		Accounts		Period
	(in thousands)
Tax Valuation Allowance
Year ended January 31, 2017	$	12,072		2,989		—		—	$	15,061
Year ended January 31, 2016	$	3,996		8,076		—		—	$	12,072
Year ended January 31, 2015	$	2,302		1,694		—		—	$	3,996

Schedule of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits

The following table sets forth a reconciliation of the beginning and ending amount of unrecognized tax benefits:

	Year Ended January 31,
	2017			2016			2015
	(in thousands)
Beginning balance:	$	30,211		$	4,671		$	3,583
Additions based on tax positions related to the current year		7,830			17,169			1,284
Additions for tax positions of prior years		911			8,810			324
Reductions for tax positions in prior years		—			(37	)		—
Settlements for prior periods		—			—			(43	)
Lapse of applicable statute of limitations		(975	)		(402	)		(477	)
Ending balance:	$	37,977		$	30,211		$	4,671

Commitments and Contingencies (Tables)

12 Months Ended

Jan. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Future Annual Minimum Lease Payments

Future annual minimum payments under these operating agreements with initial lease terms in excess of one year are as follows

	As of
	January 31, 2017
Fiscal Year	(in thousands)
2018	$	2,792
2019		2,234
2020		1,819
2021		814
2022		249
Total future annual minimum lease payments	$	7,908

Segment Reporting (Tables)

12 Months Ended

Jan. 31, 2017

Segment Reporting [Abstract]

Company's Revenue by Geographic Region

The following table sets forth the Company’s revenue by geographic region for the periods indicated:

	Year Ended January 31,
	2017		2016		2015
	(in thousands)
Hong Kong	$	276,972	$	284,722	$	196,372
Europe		13,119		8,913		6,795
United States		7,038		8,855		6,677
North America other than United States		3,687		9,953		6,076
Asia Pacific		9,481		3,930		2,358
Total revenue	$	310,297	$	316,373	$	218,278

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015	Feb. 01, 2016
Summary Of Significant Accounting Policies [Line Items]
Impairment of long-lived assets	$ 0
Goodwill impairment	0
Impairment losses on investment	$ 0
Expected dividend yield	0.00%	0.00%	0.00%
Accounting Standards Update (ASU) 2016-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment of changes recognized in beginning of retained earnings				$ 11,500,000
Cumulative effect adjustment of changes recognized in beginning of retained earnings as a result of adoption of new guidance for tax benefits that were not previously recognized [Member] \| Accounting Standards Update (ASU) 2016-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment of changes recognized in beginning of retained earnings				11,700,000
Cumulative effect adjustment of changes recognized in beginning of retained earnings as a result of adoption of new guidance for accounting for forfeitures as they occur [Member] \| Accounting Standards Update (ASU) 2016-09 [Member]
Summary Of Significant Accounting Policies [Line Items]
Cumulative effect adjustment of changes recognized in beginning of retained earnings				$ (200,000)

- Definition

Amount of cumulative effect of the change in accounting principle or new accounting pronouncement on retained earnings or other components of equity or net assets in the statement of financial position as of the beginning of the earliest period presented.

+ References + Details

Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 100,920	$ 40,374
Unrealized Gains	13	11
Unrealized Losses	(83)	(18)
Fair Value	100,850	40,367
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	8,328	530
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	8,328	530
Demand deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,000
Unrealized Gains	0
Unrealized Losses	0
Fair Value	10,000
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	4,784	2,598
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	4,784	2,598
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42,713	21,342
Unrealized Gains	6	7
Unrealized Losses	(41)	(9)
Fair Value	42,678	21,340
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,686	4,586
Unrealized Gains	1	0
Unrealized Losses	(12)	(1)
Fair Value	11,675	4,585
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	23,409	9,274
Unrealized Gains	6	4
Unrealized Losses	(30)	(6)
Fair Value	$ 23,385	9,272
Agency bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		2,044
Unrealized Gains		0
Unrealized Losses		(2)
Fair Value		$ 2,042

Financial Instruments and Fair Value - Schedule of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$ 100,850	$ 40,367
Included in cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	18,328	530
Included in marketable securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$ 82,522	$ 39,837

Financial Instruments and Fair Value - Summary of Contractual Maturities of Investments (Detail) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Available For Sale Securities Debt Maturities Fair Value [Abstract]
Due within one year	$ 76,992	$ 33,449
Due within one to two years	23,858	6,918
Total cash equivalents and marketable securities	$ 100,850	$ 40,367

Inventories - Schedule of Inventory (Detail) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Inventory Disclosure [Abstract]
Work-in-progress	$ 10,105	$ 9,474
Finished goods	10,040	8,693
Total	$ 20,145	$ 18,167

Property and Equipment, Net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 13,427	$ 11,301
Less: accumulated depreciation and amortization	(8,439)	(7,853)
Total property and equipment, net	4,988	3,448
Computer equipment and software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	6,798	6,421
Machinery and equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,405	2,706
Furniture and fixtures [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	797	492
Leasehold improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,672	1,429
Construction in progress [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 755	$ 253

Acquisition - Additional Information (Detail) - USD ($) $ in Thousands	Jun. 25, 2015	Jan. 31, 2017	Jan. 31, 2016
Business Acquisition [Line Items]
Goodwill		$ 26,601	$ 26,601
Vis Lab S R L
Business Acquisition [Line Items]
Business acquisition date	Jun. 25, 2015
Cash paid for business acquisition	$ 30,000
Intangible assets acquired	4,100
Goodwill	25,300
Net assets acquired	$ 600

Goodwill and Intangible Assets - Additional Information (Detail) - USD ($)		12 Months Ended
	Jun. 25, 2015	Jan. 31, 2017	Jan. 31, 2016
Finite Lived Intangible Assets [Line Items]
Goodwill		$ 26,601,000	$ 26,601,000
Impairment of goodwill or intangible assets		0	$ 0
IPR&D
Finite Lived Intangible Assets [Line Items]
Amortization of intangible asset		$ 0
Vis Lab S R L
Finite Lived Intangible Assets [Line Items]
Business acquisition date	Jun. 25, 2015
Goodwill	$ 25,300,000
Intangible assets acquired	4,100,000
Deferred tax liabilities, intangible assets	$ 1,300,000

Accrued Liabilities - Schedule of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Payables And Accruals [Abstract]
Accrued employee compensation	$ 14,685	$ 14,512
Accrued warranty	500	234
Accrued rebates	972	824
Accrued product development costs	7,605	6,339
Other accrued liabilities	2,686	1,869
Total accrued liabilities	$ 26,448	$ 23,778

Deferred Revenue and Deferred Cost - Schedule of Deferred Revenue and Related Cost (Detail) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Deferred Revenue Disclosure [Abstract]
Deferred revenue on product shipments	$ 7,725	$ 12,201
Deferred revenue from licenses & services	1,748	1,653
Deferred cost of revenue on product shipments	(2,048)	(3,777)
Total deferred revenue, net	$ 7,425	$ 10,077

- Definition

The carrying amount of consideration received or receivable as of the balance sheet date on potential earnings that were not recognized as revenue in conformity with GAAP, and which are expected to be recognized as such within one year or the normal operating cycle, if longer, including sales, license fees, and royalties, but excluding interest income.

+ References + Details

Other Long-Term Liabilities - Schedule of Other Long-Term Liabilities (Detail) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Other Liabilities Disclosure [Abstract]
Unrecognized tax benefits, including interest	$ 1,905	$ 10,917
Deferred tax liabilities, non-current	1,333	1,423
Other long-term liabilities	3	2
Total other long-term liabilities	$ 3,241	$ 12,342

Other Long-Term Liabilities - Additional Information (Detail) - Accounting Standards Update (ASU) 2016-09 [Member] $ in Millions	Feb. 01, 2016 USD ($)
Other Liabilities Noncurrent [Line Items]
Deferred tax assets for net operating loss carryforwards	$ 11.7
Other Long Term Liabilities [Member]
Other Liabilities Noncurrent [Line Items]
Unrecognized tax benefits reduced as a result of adoption of new accounting guidance	$ 9.5

Capital Stock - Additional Information (Detail) - USD ($)			12 Months Ended
	Nov. 29, 2016	May 31, 2016	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Class Of Stock [Line Items]
Preference shares, shares authorized			20,000,000	20,000,000
Preference shares, par value			$ 0.00045	$ 0.00045
Preference shares, shares issued			0	0
Preference shares, shares outstanding			0	0
Ordinary shares, shares authorized			200,000,000	200,000,000
Stock repurchase program, expiration date	Jun. 30, 2017
Stock repurchase program, period		6 months
Stock repurchased during period, shares			405,089
Stock repurchased during period, cash			$ 20,183,000	$ 0	$ 0
Maximum
Class Of Stock [Line Items]
Amount authorized under stock repurchase program		$ 75,000,000

Capital Stock - Schedule of Ordinary Shares Reserved for Future Issuance (Detail) - shares	Jan. 31, 2017	Jan. 31, 2016
Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved	5,167,688	5,027,475
Employee stock purchase plan awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved	1,252,465	974,273

Employee Benefits and Stock-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Feb. 02, 2016	Feb. 02, 2015	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Closing price of ordinary shares			$ 49.61
2012 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Voting power of all classes of company's shares			10.00%
Additional ordinary shares reserved for issuance	1,455,001	1,387,689
2012 Equity Incentive Plan [Member] \| Scenario, plan automatically increased by the lessor of [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Annual increase in ordinary shares for available for future issuance	3,500,000	3,500,000
Annual shares increase for future issuance by percentage under 2012 equity incentive plan	4.50%	4.50%
Amended and Restated 2012 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of ordinary shares, percentage			85.00%	85.00%	85.00%
Additional ordinary shares reserved for issuance	404,166	385,469
Percentage of salary contribution by employees			15.00%
Amended and Restated 2012 Employee Stock Purchase Plan [Member] \| Scenario, plan automatically increased by the lessor of [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Annual increase in ordinary shares for available for future issuance	1,500,000	1,500,000
Annual shares increase for future issuance by percentage under 2012 employee stock purchase plan	1.25%	1.25%
Stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost, stock options			$ 8.1
Weighted average recognition period			1 year 11 months 9 days
Stock options [Member] \| 2012 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option's term of up to 10 years from grant date			10 years	10 years	10 years
Vesting schedule			Vest 25% on the first anniversary service date of the grant and remainder vest ratably over the following 36 months.
Stock options [Member] \| Incentive stock options granted to 10% ownership [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of ordinary shares, percentage			110.00%
Stock options [Member] \| Non statutory stock options and incentive stock options granted to less than 10% ownership [Member] \| Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Purchase price of ordinary shares, percentage			100.00%
Restricted Stock and Restricted Stock Units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Aggregate intrinsic value of unvested restricted stock and restricted stock units			$ 107.9
Total fair value of vesting dates of restricted stock and restricted stock units vested			$ 51.1	$ 59.2	$ 17.3
Restricted Stock and Restricted Stock Units [Member] \| 2012 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting schedule			1/4th of the shares on the first anniversary service date of the grant and 1/16th of the shares vest every 3 months thereafter, so as to be 100% vested on the fourth anniversary of the vesting commencement date
Restricted stock units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average recognition period			2 years 9 months 18 days
Total unrecognized compensation cost, restricted stock units			$ 104.1
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average recognition period			1 year 8 months 23 days
Total unrecognized compensation cost, restricted stock awards			$ 6.9

Employee Benefits and Stock-based Compensation - Classification of Stock-based Compensation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Stock-based compensation:
Total stock-based compensation	$ 48,832	$ 31,094	$ 15,692
Cost of revenue [Member]
Stock-based compensation:
Total stock-based compensation	1,078	657	343
Research and development [Member]
Stock-based compensation:
Total stock-based compensation	29,729	19,082	8,654
Selling, general and administrative [Member]
Stock-based compensation:
Total stock-based compensation	$ 18,025	$ 11,355	$ 6,695

Employee Benefits and Stock-based Compensation - Weighted-Average Assumptions Used to Estimate Fair Value (Detail)	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility	38.00%	57.00%	64.00%
Risk-free interest rate	1.59%	1.74%	1.93%
Expected term (years)	6 years	6 years 29 days	6 years 4 days
Dividend yield	0.00%	0.00%	0.00%
Employee stock purchase plan awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility	54.00%	63.00%	49.00%
Risk-free interest rate	0.51%	0.21%	0.07%
Expected term (years)	6 months	6 months	6 months
Dividend yield	0.00%	0.00%	0.00%

Employee Benefits and Stock-based Compensation - Stock Option Activities (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding	1,853,390	2,281,909	3,358,706
Shares, Granted	110,500	179,700	428,781
Shares, Exercised	(235,923)	(567,888)	(1,456,944)
Shares, Forfeited	(16,708)	(40,331)	(48,634)
Shares, Expired	(7,735)
Shares, Outstanding	1,703,524	1,853,390	2,281,909
Shares, Exercisable	1,367,960
Weighted-Average Exercise Price, Outstanding	$ 19.36	$ 13.00	$ 6.92
Weighted-Average Exercise Price, Granted	47.82	71.36	36.33
Weighted-Average Exercise Price, Exercised	13.69	9.11	5.84
Weighted-Average Exercise Price, Forfeited	55.07	35.65	13.38
Weighted-Average Exercise Price, Expired	14.19
Weighted-Average Exercise Price, Outstanding	21.66	19.36	13.00
Weighted-Average Exercise Price, Exercisable	14.94
Weighted-Average Grant-date Fair Value, Granted	$ 18.76	$ 38.81	$ 21.37
Total Intrinsic Value of options Exercised	$ 10,788	$ 37,603	$ 46,427
Weighted-Average Remaining Contractual Term, Outstanding	5 years 1 month 28 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 5 months 1 day
Aggregate Intrinsic Value, Outstanding	$ 51,670
Aggregate Intrinsic Value, Exercisable	$ 49,016

Employee Benefits and Stock-based Compensation - Restricted Stock and Restricted Stock Units Activities (Detail) - Restricted stock and restricted stock units [Member] - $ / shares	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Unvested, beginning balance	2,495,488	1,980,448	1,410,089
Shares, Granted	676,598	1,314,387	1,111,204
Shares, Vested	(955,230)	(769,779)	(484,296)
Shares, Forfeited	(41,183)	(29,568)	(56,549)
Shares, Unvested, ending balance	2,175,673	2,495,488	1,980,448
Weighted-Average Grant-Date Fair Value, Unvested, beginning balance	$ 47.04	$ 26.82	$ 14.02
Weighted-Average Grant-Date Fair Value, Granted	67.68	66.14	38.60
Weighted-Average Grant-Date Fair Value, Vested	39.28	27.82	17.39
Weighted-Average Grant-Date Fair Value, Forfeited	52.49	42.11	19.93
Weighted-Average Grant-Date Fair Value, Unvested, ending balance	$ 56.76	$ 47.04	$ 26.82

Net Income Per Ordinary Share - Computation of Basic and Diluted Net Income Per Ordinary Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Numerator:
Net income	$ 57,810	$ 76,508	$ 50,571
Less: amount allocable to unvested early exercised options	0	0	(11)
Net income allocable to ordinary shareholders - basic	57,810	76,508	50,560
Undistributed earnings reallocated to ordinary shareholders	0	0	1
Net income allocable to ordinary shareholders - diluted	$ 57,810	$ 76,508	$ 50,561
Denominator:
Weighted-average ordinary shares outstanding	32,671,221	31,633,992	29,749,354
Less: weighted-average unvested early exercised options subject to repurchase	0	(56)	(6,701)
Weighted-average ordinary shares - basic	32,671,221	31,633,936	29,742,653
Effect of potentially dilutive securities:
Employee stock options	1,080,864	1,245,341	1,818,401
Restricted stock and restricted stock units	565,068	865,863	704,788
Employee stock purchase plan	10,571	10,569	12,285
Weighted-average ordinary shares - diluted	34,327,724	33,755,709	32,278,127
Net income per ordinary share:
Basic	$ 1.77	$ 2.42	$ 1.70
Diluted	$ 1.68	$ 2.27	$ 1.57

Net Income Per Ordinary Share - Weighted-Average Potentially Dilutive Securities Excluded from Computation of Diluted Net Income Per Ordinary Share (Detail) - shares	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	1,250,539	283,081	428,027
Options to purchase ordinary shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	343,936	109,958	217,514
Restricted stock and restricted stock units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	891,952	163,994	167,702
Employee stock purchase plan awards [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	14,651	9,073	36,110
Early exercised options subject to repurchase [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	0	56	6,701

Income Taxes - Summary of Income before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Results Of Operations Income Before Income Taxes [Abstract]
U.S. operations	$ 3,092	$ 3,190	$ 1,978
Non-U.S. operations	57,789	82,019	50,058
Income before income taxes	$ 60,881	$ 85,209	$ 52,036

Income Taxes - Schedule of Income Tax Provision (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Current:
U.S. federal tax	$ 818	$ 5,273	$ 3,135
U.S. state taxes	(212)	541	93
Non-U.S. foreign taxes	1,454	1,874	1,348
Current income tax provision	2,060	7,688	4,576
Deferred:
U.S. federal tax	1,174	1,050	(3,208)
U.S. state taxes	0	0	0
Non-U.S. foreign taxes	(163)	(37)	97
Deferred income tax provision	1,011	1,013	(3,111)
Provision for income taxes	$ 3,071	$ 8,701	$ 1,465

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015	Jan. 31, 2014
Income Taxes [Line Items]
Statutory tax rate	34.00%	34.00%	34.00%
Deferred tax liabilities, not recognized	$ 5,600,000
Cumulative undistributed earnings of foreign subsidiaries	44,000,000
Gross deferred tax assets, net of deferred tax liabilities before valuation allowance	19,500,000	$ 15,300,000
Valuation allowance	15,061,000	12,072,000
Unrecognized tax benefits	37,977,000	30,211,000	$ 4,671,000	$ 3,583,000
Unrecognized tax benefits that would impact effective tax rate	30,100,000
Income tax liabilities considered as other long term liabilities	1,800,000	10,800,000
Benefit from interest accruals, reserve released due to the lapse of statute of limitations	64,000
Interest expense and penalties related to uncertain tax positions		6,000	$ 7,000
Noncurrent liabilities related to interest and penalties for uncertain tax positions	103,000	$ 166,000
Long term income taxes payable, including estimated interest and penalties	$ 1,900,000
U.S. federal tax authorities [Member] \| Earliest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2012
U.S. federal tax authorities [Member] \| Latest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2016
U.S. state tax authorities [Member] \| Earliest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2007
U.S. state tax authorities [Member] \| Latest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2016
Foreign tax authorities [Member] \| Earliest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2011
Foreign tax authorities [Member] \| Latest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2016
Federal [Member]
Income Taxes [Line Items]
Research and development credit carryforwards	$ 10,900,000
Federal credits begin to expire in fiscal year	2033
California state [Member]
Income Taxes [Line Items]
Research and development credit carryforwards	$ 13,800,000

Income Taxes - Schedule of Reconciliation Between the Provision (Benefit) for Income Taxes at the Statutory Rate and the Effective Tax Rate (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Income Tax Disclosure [Abstract]
Provision at U.S. notional statutory rate	$ 20,700	$ 28,971	$ 17,692
U.S. state taxes	(216)	541	90
Non-U.S. foreign tax differential	(18,357)	(26,253)	(15,644)
Stock-based compensation	1,605	2,896	1,601
U.S. R&D credit	(2,226)	(3,517)	(2,298)
Valuation allowance	1,901	6,090	0
Other	(336)	(27)	24
Provision for income taxes	$ 3,071	$ 8,701	$ 1,465

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Deferred tax assets:
Federal and state credits	$ 14,782	$ 11,852
Expenses not currently deductible	2,381	2,331
Stock-based compensation	3,561	2,503
Foreign deferred	161	0
Gross deferred tax assets	20,885	16,686
Valuation allowance	(15,061)	(12,072)
Total deferred tax assets	5,824	4,614
Deferred tax liabilities
Property and equipment	(1,383)	(1,378)
Foreign deferred	0	(33)
Net deferred tax assets	$ 4,441	$ 3,203

Income Taxes - Summary of Tax Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 12,072
Balance at End of Period	15,061	$ 12,072
Valuation Allowance of Deferred Tax Assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	12,072	3,996	$ 2,302
Additional Charged to Expenses	2,989	8,076	1,694
Additions Charged to Other Account	0	0	0
Deductions Charged to Expenses or Other Accounts	0	0	0
Balance at End of Period	$ 15,061	$ 12,072	$ 3,996

Income Taxes - Schedule of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Income Tax Disclosure [Abstract]
Beginning balance	$ 30,211	$ 4,671	$ 3,583
Additions based on tax positions related to the current year	7,830	17,169	1,284
Additions for tax positions of prior years	911	8,810	324
Reductions for tax positions in prior years	0	(37)	0
Settlements for prior periods	0	0	(43)
Lapse of applicable statute of limitations	(975)	(402)	(477)
Ending balance	$ 37,977	$ 30,211	$ 4,671

Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Loss Contingencies [Line Items]
Net operating lease expenses	$ 7,600,000	$ 6,800,000	$ 5,800,000
Total manufacturing purchase commitments	23,900,000	19,700,000
Indemnification agreement [Member]
Loss Contingencies [Line Items]
Payments under indemnification obligations	0	0
Liabilities recorded under indemnification obligations	$ 0	$ 0

Commitments and Contingencies - Future Annual Minimum Lease Payments (Detail) $ in Thousands	Jan. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018	$ 2,792
2019	2,234
2020	1,819
2021	814
2022	249
Total future annual minimum lease payments	$ 7,908

Segment Reporting - Additional Information (Detail) $ in Thousands	12 Months Ended
	Jan. 31, 2017 USD ($) Segment	Jan. 31, 2016 USD ($)	Jan. 31, 2015
Concentration Risk [Line Items]
Number of reportable segment \| Segment	1
Property and equipment, net	$ 4,988	$ 3,448
Accounts receivable	38,596	39,408
Wintech [Member] \| Credit concentration risk [Member]
Concentration Risk [Line Items]
Accounts receivable	19,300	20,600
GoPro [Member] \| Credit concentration risk [Member]
Concentration Risk [Line Items]
Accounts receivable	$ 11,300
Chicony [Member] \| Credit concentration risk [Member]
Concentration Risk [Line Items]
Accounts receivable		$ 11,900
Sales revenue, net [Member] \| Wintech and GoPro [Member] \| Customer concentration risk [Member] \| Minimum [Member]
Concentration Risk [Line Items]
Percentage of revenue or accounts receivable	10.00%
Sales revenue, net [Member] \| Wintech [Member] \| Customer concentration risk [Member]
Concentration Risk [Line Items]
Percentage of revenue	60.00%	67.00%	57.00%
Sales revenue, net [Member] \| GoPro [Member] \| Customer concentration risk [Member]
Concentration Risk [Line Items]
Percentage of revenue	19.00%
Sales revenue, net [Member] \| Wintech And Chicony [Member] \| Customer concentration risk [Member] \| Minimum [Member]
Concentration Risk [Line Items]
Percentage of revenue or accounts receivable		10.00%	10.00%
Sales revenue, net [Member] \| GoPro’s various ODMs [Member] \| Customer concentration risk [Member]
Concentration Risk [Line Items]
Percentage of revenue	5.00%
Sales revenue, net [Member] \| Chicony [Member] \| Customer concentration risk [Member]
Concentration Risk [Line Items]
Percentage of revenue		21.00%	32.00%
Accounts receivable [Member] \| Wintech and GoPro [Member] \| Credit concentration risk [Member] \| Minimum [Member]
Concentration Risk [Line Items]
Percentage of revenue or accounts receivable	10.00%
Accounts receivable [Member] \| Wintech And Chicony [Member] \| Credit concentration risk [Member] \| Minimum [Member]
Concentration Risk [Line Items]
Percentage of revenue or accounts receivable		10.00%	10.00%
United States [Member]
Concentration Risk [Line Items]
Property and equipment, net	$ 2,100	$ 1,600
Asia Pacific [Member]
Concentration Risk [Line Items]
Property and equipment, net	$ 2,300	$ 1,500

Segment Reporting - Company's Revenue by Geographic Region (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Revenue from External Customer [Line Items]
Total revenue	$ 310,297	$ 316,373	$ 218,278
Hong Kong [Member]
Revenue from External Customer [Line Items]
Total revenue	276,972	284,722	196,372
Europe [Member]
Revenue from External Customer [Line Items]
Total revenue	13,119	8,913	6,795
United States [Member]
Revenue from External Customer [Line Items]
Total revenue	7,038	8,855	6,677
North America other than United States [Member]
Revenue from External Customer [Line Items]
Total revenue	3,687	9,953	6,076
Asia Pacific [Member]
Revenue from External Customer [Line Items]
Total revenue	$ 9,481	$ 3,930	$ 2,358

Related-Party Transactions - Additional Information (Detail) - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Related Party Transaction [Line Items]
Percentage of entity's voting stock owned by related party	10.00%
Other Entity [Member]
Related Party Transaction [Line Items]
Payment for license fees	$ 2.8	$ 2.8	$ 2.3
License expenses included in research and development expense	$ 2.9	$ 2.7	$ 1.9

Subsequent Events - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Mar. 30, 2017	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Subsequent Event [Line Items]
Stock repurchased during period, shares		405,089
Stock repurchased during period, cash		$ 20,183	$ 0	$ 0
Subsequent Event [Member]
Subsequent Event [Line Items]
Stock repurchased during period, shares	162,738
Stock repurchased during period, cash	$ 8,800
Shares repurchased	567,827
Shares repurchased in cash	$ 29,000

Subsequent Events	12 Months Ended
Subsequent Events	Jan. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	17. Subsequent Events In March 2017, the Company repurchased a total of 162,738 shares for approximately $8.8 million in cash. As of March 30, 2017, the Company had repurchased a total of 567,827 shares for approximately $29.0 million in cash under the Company’s repurchase program.

Financial Instruments and Fair Value - Schedule of Fair Value of Financial Instruments Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Jan. 31, 2017	Jan. 31, 2016
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 100,850	$ 40,367
Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	8,328	530
Demand deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	10,000
Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	4,784	2,598
Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	42,678	21,340
Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	11,675	4,585
U.S. government securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	23,385	9,272
Agency bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		2,042
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	18,328	530
Level 1 [Member] \| Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	8,328	530
Level 1 [Member] \| Demand deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	10,000
Level 1 [Member] \| Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Level 1 [Member] \| Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Level 1 [Member] \| Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Level 1 [Member] \| U.S. government securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Level 1 [Member] \| Agency bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		0
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	82,522	39,837
Level 2 [Member] \| Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Level 2 [Member] \| Demand deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0
Level 2 [Member] \| Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	4,784	2,598
Level 2 [Member] \| Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	42,678	21,340
Level 2 [Member] \| Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	11,675	4,585
Level 2 [Member] \| U.S. government securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	23,385	9,272
Level 2 [Member] \| Agency bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		2,042
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Level 3 [Member] \| Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Level 3 [Member] \| Demand deposits [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0
Level 3 [Member] \| Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Level 3 [Member] \| Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Level 3 [Member] \| Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	0	0
Level 3 [Member] \| U.S. government securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 0	0
Level 3 [Member] \| Agency bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities		$ 0