Document and Entity Information - USD ($) $ in Billions	12 Months Ended
Document and Entity Information - USD ($) $ in Billions	Jan. 31, 2018	Mar. 23, 2018	Jul. 31, 2017
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Jan. 31, 2018
Document Fiscal Year Focus	2018
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		33,635,312
Entity Public Float			$ 1.5

Consolidated Balance Sheets - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Current assets:
Cash and cash equivalents	$ 346,672	$ 322,872
Marketable securities	87,919	82,522
Accounts receivable, net	31,294	38,596
Inventories	23,383	20,145
Restricted cash	9	8
Prepaid expenses and other current assets	4,006	4,392
Total current assets	493,283	468,535
Property and equipment, net	6,449	4,988
Deferred tax assets, non-current	3,642	5,774
Intangible assets, net	14,417	4,149
Goodwill	26,601	26,601
Other non-current assets	2,257	2,224
Total assets	546,649	512,271
Current liabilities:
Accounts payable	19,815	19,955
Accrued and other current liabilities	32,178	26,448
Income taxes payable	936	568
Deferred revenue, current	307	7,425
Total current liabilities	53,236	54,396
Other long-term liabilities	11,226	3,241
Total liabilities	64,462	57,637
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, 2018 and January 31, 2017, respectively	0	0
Ordinary shares, $0.00045 par value per share, 200,000,000 shares authorized at January 31, 2018 and January 31, 2017, respectively; 33,489,614 shares issued and outstanding at January 31, 2018; 33,369,032 shares issued and outstanding at January 31, 2017	15	15
Additional paid-in capital	221,186	212,276
Accumulated other comprehensive loss	(279)	(70)
Retained earnings	261,265	242,413
Total shareholders’ equity	482,187	454,634
Total liabilities and shareholders' equity	$ 546,649	$ 512,271

Consolidated Balance Sheets (Parenthetical) - $ / shares	Jan. 31, 2018	Jan. 31, 2017
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	33,489,614	33,369,032
Ordinary shares, shares outstanding	33,489,614	33,369,032

Consolidated Statements of Operations - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Income Statement [Abstract]
Revenue	$ 295,402	$ 310,297	$ 316,373
Cost of revenue	107,669	105,283	111,029
Gross profit	187,733	205,014	205,344
Operating expenses:
Research and development	115,510	101,205	82,927
Selling, general and administrative	47,792	43,446	37,738
Total operating expenses	163,302	144,651	120,665
Income from operations	24,431	60,363	84,679
Other income, net	1,298	518	530
Income before income taxes	25,729	60,881	85,209
Provision for income taxes	6,877	3,071	8,701
Net income	$ 18,852	$ 57,810	$ 76,508
Net income per share attributable to ordinary shareholders:
Basic	$ 0.57	$ 1.77	$ 2.42
Diluted	$ 0.55	$ 1.68	$ 2.27
Weighted-average shares used to compute net income per share attributable to ordinary shareholders:
Basic	33,224,803	32,671,221	31,633,936
Diluted	34,583,150	34,327,724	33,755,709

Consolidated Statements of Comprehensive Income - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 18,852	$ 57,810	$ 76,508
Other comprehensive loss, net of tax:
Unrealized losses on investments	(209)	(63)	(6)
Other comprehensive loss, net of tax	(209)	(63)	(6)
Comprehensive income	$ 18,643	$ 57,747	$ 76,502

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, 2015	$ 237,211	$ 14	$ 140,564	$ (1)	$ 96,634
Beginning 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
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
Exercise of stock options, Amount	$ 2,191	$ 0	2,191	0	0
Exercise of stock options, Shares	175,187	175,187
Vesting of restricted stock units, Amount	$ 0	$ 0	0	0	0
Vesting of restricted stock units, Shares		932,454
Employee stock purchase plan, Amount	4,646	$ 0	4,646	0	0
Employee stock purchase plan, Shares		107,736
Stock repurchase, Amount	$ (54,788)	$ 0	(54,788)	0	0
Stock repurchase, Shares	(1,094,795)	(1,094,795)
Stock-based compensation expense related to stock awards granted to employees and consultants	$ 56,861	$ 0	56,861	0	0
Net unrealized losses on investments - net of taxes	(209)	0	0	(209)	0
Net income	18,852	0	0	0	18,852
Ending Balance, Amount at Jan. 31, 2018	$ 482,187	$ 15	$ 221,186	$ (279)	$ 261,265
Ending Balance, Shares at Jan. 31, 2018	33,489,614	33,489,614

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Cash flows from operating activities:
Net income	$ 18,852	$ 57,810	$ 76,508
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	1,789	1,535	1,590
Amortization of intangible assets	2,981	50	16
Amortization/accretion of marketable securities	172	246	525
Stock-based compensation	56,861	48,832	31,094
Other non-cash items, net	164	83	155
Changes in operating assets and liabilities, net of effects of acquisitions:
Accounts receivable	7,302	812	1,262
Inventories	(3,238)	(1,978)	3,627
Prepaid expenses and other current assets	379	(216)	(572)
Deferred tax assets	2,132	853	1,291
Other non-current assets	(33)	(107)	(114)
Accounts payable	(140)	5,780	(6,880)
Accrued liabilities	1,430	2,069	4,189
Income taxes payable	368	(219)	244
Deferred tax liabilities	(40)	(89)	43
Deferred revenue	(7,026)	(2,652)	4,939
Other long-term liabilities	3,450	505	5,644
Net cash provided by operating activities	85,403	113,314	123,561
Cash flows from investing activities:
Acquisition, net of cash acquired	0	0	(29,905)
Purchase of investments	(74,863)	(115,546)	(52,786)
Sales of investments	10,900	31,078	17,732
Maturities of investments	58,050	41,435	32,248
Purchase of property and equipment	(3,687)	(2,701)	(2,085)
Net cash used in investing activities	(9,600)	(45,734)	(34,796)
Cash flows from financing activities:
Proceeds from exercise of stock options and employee stock purchase plan	7,091	7,419	9,000
Stock repurchase	(54,788)	(20,183)	0
Payment for intangible assets	(4,306)	0	0
Net cash provided by (used in) financing activities	(52,003)	(12,764)	9,000
Net increase in cash and cash equivalents	23,800	54,816	97,765
Cash and cash equivalents at beginning of period	322,872	268,056	170,291
Cash and cash equivalents at end of period	346,672	322,872	268,056
Supplemental disclosure of cash flow information:
Cash paid for income taxes	845	2,070	1,618
Supplemental disclosure of noncash investing activities:
Unpaid liabilities related to intangible and fixed assets purchases	$ 9,008	$ 481	$ 43

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Jan. 31, 2018
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 leading developer of low-power, high-definition (HD) and Ultra HD video compression and image processing solutions, and computer vision solutions. 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. Currently the Company is combining advanced computer vision technology with its state-of-the-art video to enable the next generation of intelligent cameras, advanced driver assistance systems (ADAS) and autonomous vehicles. 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 accounting principles generally accepted 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 collectability 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, assets and stock awards 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 distributor, Wintech Microelectronics Co., Ltd., or Wintech, which serves as its non-exclusive sales representative 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. 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 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 losses on deposits of its cash. The cash equivalents and marketable securities consist primarily of money market funds, 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, net in the consolidated statements of operations, and, to date, have not been material. Fair Value of Financial Instruments 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 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, 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 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, 2018, 2017 and 2016, respectively. There was no material allowance for doubtful accounts recorded as of January 31, 2018 and 2017, respectively. Inventories The Company records inventories at the lower of cost or net realizable value. 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. Any adjustments to reduce the cost of inventories to their net realizable value are recognized in earnings in the current period. 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, 2018, 2017 and 2016, 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 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. Noncancelable Software License The Company accounts for a noncancelable on premise internal-use software license as the acquisition of an intangible asset and the incurrence of a liability to the extent that all or a portion of the software licensing fees are not paid on or before the license acquisition date. The intangible asset and related liability are recorded at net present value and interest expense is recorded over the payment term. 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. As of January 31, 2018, there was no IPR&D amortized. 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, 2018. The Company tests the goodwill for impairment at least annually in the fourth fiscal quarter, 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 distributors. 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 has historically provided its distributors 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 distributors are deferred until the Company has received notification from its distributors that they have sold the Company’s products. Information reported by the Company’s distributors includes product resale price, quantity and end customer shipment information as well as remaining inventory on hand. At the time of shipment to a distributor, 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 distributor 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, 2018, 2017 and 2016, 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, 2018, 2017 and 2016, 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. As of January 31, 2018 and 2017, there was approximately $1.8 million and $0.5 million of warranty accruals recorded in the consolidated balance sheets, 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, 2018, 2017 and 2016, 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 with service or performance conditions 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 calculated based on the weighted average of historical volatilities of its own stock price and the share prices of similar companies that are publicly available for a period commensurate with the expected term. The risk-free interest rate is derived from an average of the U.S. Treasury constant maturity rates for the respective periods most closely 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. The Company uses the Lattice pricing model and performs Monte Carlo Simulation to evaluate the fair value of awards with market conditions, including assumptions of historical volatility and risk-free interest rate commensurate with the vesting term. 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 its 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, the Company 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 revenue recognition guidance provides a five-step analysis of transactions to determine when and how revenue is recognized. The guidance requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The FASB issued several updates to the guidance. The new revenue guidance may be adopted by full retrospective method, which applies retrospectively to each prior period presented, or by modified retrospective method with the cumulative effect adjustment recognized in the beginning of retained earnings as of the date of adoption. The Company elects to adopt the new guidance using the modified retrospective method. Under this transition method, the Company elects to apply this new guidance only to contracts that are not completed at the adoption date. For contracts that were modified before the adoption date, the Company elects to reflect the aggregate effect of all modifications that occur before the adoption date when identifying performance obligations, determining the transaction price, and allocating the transaction price to performance obligations. The most significant impacts of this new guidance for the Company relate to the determination of transaction price and the timing of revenue recognition for transactions with its distributors. As a result, the Company will recognize product revenue upon shipment and transfer of control to distributors (known as “sell-in” revenue recognition) rather than shipment to the end customers (known as “sell-through” revenue recognition) based on its estimate of the consideration it expects to receive. The Company also elects to exclude amounts collected from customers for all sales taxes from the transaction price. The impact of this change upon adoption was not material. Furthermore, the Company has made investments and will continuously invest in system design, changing processes and designing operational and internal control structures in order to meet the new standard requirements. 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. The Company is currently assessing the impact of the adoption of this new guidance on its financial position, results of operations and disclosures. 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 estimate of current expected credit losses (“ECL”). Under the new model, an entity is required to estimate ECL on available-for-sale (AFS) debt securities 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. 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. 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 does not believe the adoption of this new guidance will have a material impact 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 and 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 guidance will be applied prospectively and is effective for annual and interim periods beginning after December 15, 2019. 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 March 2017, the FASB issued ASU 2017-08, Receivables – Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization On Purchased Callable Debt Securities, to shorten the amortization period for the premium to the earliest call date instead of the contractual life of the instrument. This new guidance will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Entities will be required to apply the new guidance using the modified retrospective method with a cumulative-effect adjustment to retained earnings upon the adoption date. 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 2018, the FASB issued ASU 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, to permit entities to have the option to reclassify tax effects stranded in accumulated other comprehensive income as a result of tax reform to retained earnings. The FASB also gives entities the option to apply the guidance retrospectively or in the period of adoption. The guidance is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early adoption in any period is permitted. The Company does not make such election and believes that the adoption of this new guidance will not have an impact on its financial position and disclosures.

Financial Instruments and Fair Value

12 Months Ended

Jan. 31, 2018

Investments All Other Investments [Abstract]

Financial Instruments and Fair Value

2. Financial Instruments and Fair Value

The Company invests a portion of its cash in debt securities that are denominated in United States dollars. The investment portfolio consists of money market funds, 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, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Money market funds	$	13,788	$	—	$	—		$	13,788
Commercial paper		5,480		—		—			5,480
Corporate bonds		53,175		—		(196	)		52,979
Asset-backed securities		11,048		—		(44	)		11,004
U.S. government securities		18,495		—		(39	)		18,456
Total cash equivalents and marketable securities	$	101,986	$	—	$	(279	)	$	101,707

	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, 2018		January 31, 2017
	(in thousands)
Included in cash equivalents	$	13,788	$	18,328
Included in marketable securities		87,919		82,522
Total cash equivalents and marketable securities	$	101,707	$	100,850

The contractual maturities of the investments at January 31, 2018 and 2017 were as follows:

	As of
	January 31, 2018		January 31, 2017
	(in thousands)
Due within one year	$	63,476	$	76,992
Due within one to two years		38,231		23,858
Total cash equivalents and marketable securities	$	101,707	$	100,850

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, 2018 and 2017, 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, 2018 and 2017, respectively:

	As of January 31, 2018
	Total		Level 1		Level 2		Level 3
	(in thousands)
Money market funds	$	13,788	$	13,788	$	—	$	—
Commercial paper		5,480		—		5,480		—
Corporate bonds		52,979		—		52,979		—
Asset-backed securities		11,004		—		11,004		—
U.S. government securities		18,456		—		18,456		—
Total cash equivalents and marketable securities	$	101,707	$	13,788	$	87,919	$	—

	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	$	—

Inventories

12 Months Ended

Jan. 31, 2018

Inventory Disclosure [Abstract]

Inventories

3. Inventories

Inventories at January 31, 2018 and 2017 consisted of the following:

	As of January 31,
	2018		2017
	(in thousands)
Work-in-progress	$	12,073	$	10,105
Finished goods		11,310		10,040
Total	$	23,383	$	20,145

The increase in inventory as of January 31, 2018 was primarily to support the launch of new SoCs.

Property and Equipment, Net

12 Months Ended

Jan. 31, 2018

Property Plant And Equipment [Abstract]

Property and Equipment, Net

4. Property and Equipment, net

Depreciation expense was approximately $1.8 million, $1.5 million and $1.6 million for the years ended January 31, 2018, 2017 and 2016, respectively. Property and equipment at January 31, 2018 and 2017 consisted of the following:

	As of January 31,
	2018			2017
	(in thousands)
Computer equipment and software	$	8,611		$	6,798
Machinery and equipment		4,761			3,405
Furniture and fixtures		917			797
Leasehold improvements		2,092			1,672
Construction in progress		—			755
		16,381			13,427
Less: accumulated depreciation and amortization		(9,932	)		(8,439	)
Total property and equipment, net	$	6,449		$	4,988

Intangible Assets

12 Months Ended

Jan. 31, 2018

Goodwill And Intangible Assets Disclosure [Abstract]

Intangible Assets

5. Intangible Assets

The intangible assets primarily consist of $4.1 million of IPR&D from the acquisition of VisLab S.r.l., or VisLab, in June 2015 and $10.3 million of noncancelable software licenses, net of amortization expense. Acquired IPR&D is capitalized at fair value and the 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, 2018, there was no IPR&D amortized. The Company will determine the project incorporating the VisLab IPR&D to be completed when a related chip begins mass production to address the level 3 and above advanced driving assistance systems markets.

During the twelve months ended January 31, 2018, the Company entered into certain internal-use noncancelable software license agreements in which the Company committed to pay an aggregate amount of $13.9 million through January 2020. The licenses have been capitalized as intangible assets, and the corresponding future payments have been recorded as liabilities at net present value. As of January 31, 2018, $4.3 million was recorded in accrued and other current liabilities and $4.5 million was recorded in other long-term liabilities in the consolidated balance sheets.

The carrying amounts of intangible assets as of January 31, 2018 and 2017 were as follows:

	As of January 31, 2018							As of January 31, 2017
	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
	(in thousands)
In-process research and development	$	4,100	$	—		$	4,100	$	4,100	$	—		$	4,100
Internal-use software license		13,404		(3,087	)		10,317		155		(106	)		49
Total acquired intangible assets	$	17,504	$	(3,087	)	$	14,417	$	4,255	$	(106	)	$	4,149

The amortization expense related to these software licenses was approximately $3.0 million for the fiscal year ended January 31, 2018 but was not material for the fiscal years ended January 31, 2017 and 2016, respectively. The expected annual amortization expense related to these software licenses as of January 31, 2018 is as follows:

	As of
	January 31, 2018
Fiscal Year	(in thousands)
2019	$	4,569
2020		4,473
2021		1,275
2022		—
2023		—
Thereafter		—
Total future amortization expenses:	$	10,317

There were no intangible asset impairments for the fiscal years ended January 31, 2018, 2017 and 2016, respectively.

Accrued and Other Current Liabilities

12 Months Ended

Jan. 31, 2018

Payables And Accruals [Abstract]

Accrued and Other Current Liabilities

7. Accrued and Other Current Liabilities

Accrued and other current liabilities at January 31, 2018 and 2017 consisted of the following:

	As of January 31,
	2018		2017
	(in thousands)
Accrued employee compensation	$	15,977	$	14,685
Accrued warranty		1,750		500
Accrued rebates		584		972
Accrued product development costs		6,669		7,605
Software license liabilities, current		4,346		—
Other accrued liabilities		2,852		2,686
Total accrued and other current liabilities	$	32,178	$	26,448

Deferred Revenue, Current

12 Months Ended

Jan. 31, 2018

Deferred Revenue Disclosure [Abstract]

Deferred Revenue, Current

8. Deferred Revenue, Current

Deferred revenue and related cost at January 31, 2018 and 2017 consisted of the following:

	As of January 31,
	2018		2017
	(in thousands)
Deferred revenue on product shipments	$	36	$	7,725
Deferred revenue from licenses & services		271		1,748
Deferred cost of revenue on product shipments		—		(2,048	)
Total deferred revenue, net	$	307	$	7,425

The decrease in deferred revenue on product shipments and related cost at January 31, 2018 was primarily due to the timing of shipments from the Company’s distributors.

Other Long-Term Liabilities

12 Months Ended

Jan. 31, 2018

Other Liabilities Disclosure [Abstract]

Other Long-Term Liabilities

9. Other Long-Term Liabilities

Other long-term liabilities at January 31, 2018 and 2017 consisted of the following:

	As of January 31,
	2018		2017
	(in thousands)
Unrecognized tax benefits, including interest	$	5,352	$	1,905
Deferred tax liabilities, non-current		1,293		1,333
Software license liabilities, non-current		4,484		—
Other long-term liabilities		97		3
Total other long-term liabilities	$	11,226	$	3,241

The increase in unrecognized tax benefits at January 31, 2018 was primarily due to tax positions related to certain transfer pricing arrangements.

Capital Stock

12 Months Ended

Jan. 31, 2018

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, 2018 and 2017, respectively.

Ordinary shares

200,000,000 ordinary shares were authorized at January 31, 2018 and 2017, respectively. As of January 31, 2018 and 2017, the following ordinary shares were reserved for future issuance:

	As of January 31,
	2018		2017
Shares reserved for options, restricted stock and restricted stock units		5,561,653		5,167,688
Shares reserved for employee stock purchase plan		1,561,841		1,252,465

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 through June 30, 2017. On May 31, 2017, the Company’s Board of Directors authorized the additional repurchase of up to $50.0 million of the Company’s ordinary shares over a twelve-month period commencing July 1, 2017. Repurchases may be made from time-to-time through open market purchases, 10b5-1 plans or 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. There were 1,094,795 shares repurchased during the twelve months ended January 31, 2018 for approximately $54.8 million in cash and there were 405,089 shares repurchased during the twelve months ended January 31, 2017 for approximately $20.2 million in cash. As of January 31, 2018, a total of 1,499,884 shares have been repurchased for approximately $75.0 million in cash and recorded as a reduction to equity. As of January 31, 2018, there was approximately $31.7 million available for repurchases under the repurchase program through June 30, 2018.

Employee Benefits and Stock-based Compensation

12 Months Ended

Jan. 31, 2018

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 condition, market condition or performance condition awards vary and are subject to approval by the board of directors; provided that the performance condition associated 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, 2017 and February 1, 2016, the Company added 1,501,606 and 1,455,001 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, 2017 and February 1, 2016, the Company added 417,112 and 404,166 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,
	2018		2017		2016
	(in thousands)
Stock-based compensation:
Cost of revenue	$	1,306	$	1,078	$	657
Research and development		34,575		29,729		19,082
Selling, general and administrative		20,980		18,025		11,355
Total stock-based compensation	$	56,861	$	48,832	$	31,094

As of January 31, 2018, total unrecognized compensation cost related to unvested stock options was $6.4 million and is expected to be recognized over a weighted-average period of 2.21 years. Total unrecognized compensation cost related to unvested restricted stock units was $100.1 million and is expected to be recognized over a weighted-average period of 2.72 years. Total unrecognized compensation cost related to unvested restricted stock awards was $3.3 million and is expected to be recognized over a weighted-average period of 1.08 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,
	2018			2017			2016
Stock Options:
Volatility		53	%		38	%		57	%
Risk-free interest rate		2.08	%		1.59	%		1.74	%
Expected term (years)		6.08			6.00		6.08
Dividend yield		0	%		0	%		0	%
Employee stock purchase plan awards:
Volatility		44	%		54	%		63	%
Risk-free interest rate		1.03	%		0.51	%		0.21	%
Expected term (years)		0.5			0.5			0.5
Dividend yield		0	%		0	%		0	%

The Company calculates expected volatility for stock options based on the weighted average of historical volatilities of its own stock price and the share prices of similar companies that are publicly available for a period commensurate with the expected term. The Company calculates expected volatility for ESPP based on its own historical stock price for a period commensurate with the offering period.

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, 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
Granted		132,250			54.66	$	28.28
Exercised		(175,187	)		12.50			$	7,446
Forfeited		(27,721	)		56.97
Expired		(21,522	)		36.31
Outstanding at January 31, 2018		1,611,344		$	24.56					4.63		$	45,868
Exercisable at January 31, 2018		1,351,181		$	18.91						3.93	$	44,868

The intrinsic value of options outstanding and exercisable is 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 $50.40 on January 31, 2018, 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, 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
Granted		1,052,235			47.11
Vested		(1,006,130	)		47.55
Forfeited		(118,497	)		54.72
Unvested at January 31, 2018		2,103,281		$	56.45

Total fair value as of the respective vesting dates of restricted stock and restricted stock units vested for the fiscal years ended January 31, 2018, 2017 and 2016 was approximately $52.1 million, $51.1 million, and $59.2 million, respectively. As of January 31, 2018, the aggregate intrinsic value of unvested restricted stock and restricted stock units was $106.0 million.

Net Income Per Ordinary Share

12 Months Ended

Jan. 31, 2018

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,
	2018		2017		2016
	(in thousands, except share and per share data)
Numerator:
Net income	$	18,852	$	57,810	$	76,508
Less: amount allocable to unvested early exercised options		—		—		—
Net income allocable to ordinary shareholders - basic	$	18,852	$	57,810	$	76,508
Undistributed earnings reallocated to ordinary shareholders		—		—		—
Net income allocable to ordinary shareholders - diluted	$	18,852	$	57,810	$	76,508
Denominator:
Weighted-average ordinary shares outstanding		33,224,803		32,671,221		31,633,992
Less: weighted-average unvested early exercised options subject to repurchase		—		—		(56	)
Weighted-average ordinary shares - basic		33,224,803		32,671,221		31,633,936
Effect of dilutive securities:
Employee stock options		961,797		1,080,864		1,245,341
Restricted stock and restricted stock units		390,145		565,068		865,863
Employee stock purchase plan		6,405		10,571		10,569
Weighted-average ordinary shares - diluted		34,583,150		34,327,724		33,755,709
Net income per ordinary share:
Basic	$	0.57	$	1.77	$	2.42
Diluted	$	0.55	$	1.68	$	2.27

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,
	2018		2017		2016
Options to purchase ordinary shares		280,907		343,936		109,958
Restricted stock and restricted stock units		907,208		891,952		163,994
Employee stock purchase plan		15,506		14,651		9,073
Early exercised options subject to repurchase		—		—		56
		1,203,621		1,250,539		283,081

Income Taxes

12 Months Ended

Jan. 31, 2018

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,
	2018		2017		2016
	(in thousands)
U.S. operations	$	2,683	$	3,092	$	3,190
Non-U.S. operations		23,046		57,789		82,019
Income before income taxes	$	25,729	$	60,881	$	85,209

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

	Year Ended January 31,
	2018			2017			2016
	(in thousands)
Current:
U.S. federal tax	$	3,321		$	818		$	5,273
U.S. state taxes		4			(212	)		541
Non-U.S. foreign taxes		1,435			1,454			1,874
		4,760			2,060			7,688
Deferred:
U.S. federal tax		2,185			1,174			1,050
U.S. state taxes		—			—			—
Non-U.S. foreign taxes		(68	)		(163	)		(37	)
		2,117			1,011			1,013
Provision for income taxes	$	6,877		$	3,071		$	8,701

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. 33.8%, 34.0% and 34.0% rates are applied to pretax income as a result of the following for the periods indicated, respectively:

	Year Ended January 31,
	2018			2017			2016
	(in thousands)
Provision at U.S. notional statutory rate	$	8,699		$	20,700		$	28,971
U.S. state taxes		2			(216	)		541
Non-U.S. foreign tax differential		(6,424	)		(18,357	)		(26,253	)
Stock-based compensation		4,645			1,605			2,896
U.S. R&D credit		(2,408	)		(2,226	)		(3,517	)
Valuation allowance		(1	)		1,901			6,090
Change in tax rate		2,252			—			—
Other		112			(336	)		(27	)
Provision for income taxes	$	6,877		$	3,071		$	8,701

On December 22, 2017, the Tax Cuts and Jobs Act (the “Tax Act”) was enacted into law in the United States. The new tax legislation contains several provisions that will impact the Company, including the reduction of the corporate income tax rate from 35% to 21%, acceleration of business asset expensing, and a reduction in the amount of executive pay that may qualify as a tax deduction, among others. The Tax Act’s new international rules, including the Global Intangible Low-Taxed Income (“GILTI”), the Base Erosion Anti-Avoidance Tax (“BEAT”), and the mandatory repatriation tax imposed on U.S. companies with certain foreign subsidiaries (the “Transition Tax”) are not expected to be applicable to the Company. However, these assessments are based on preliminary review and analysis of the Tax Act and are subject to change as the Company continues to evaluate these highly complex rules as additional interpretive guidance is issued. The decrease in the corporate income tax rate required the Company to remeasure its U.S. deferred tax assets and liabilities. The Company revalued its net deferred tax assets at December 22, 2017, which resulted in a decrease of deferred tax assets of $1.9 million and a corresponding increase in deferred tax expense.

Due to the complexities of the new tax legislation, the Securities and Exchange Commission staff (“SEC Staff”) recognized that entities may not have the necessary information available, prepared, or analyzed in reasonable detail to complete the accounting under ASC 740 for certain income tax effects of the Act in the reporting period that includes the date of enactment. Under SAB 118, an entity would use something similar to the measurement period in a business combination. That is, to the extent an entity can complete the income tax accounting effects of the Act, the completed amount is reported (“Bucket 1”). For matters that have not been completed, the entity would either (1) recognize provisional amounts to the extent that they are reasonably estimable and adjust them over time as more information becomes available (“Bucket 2”) or (2) for any specific income tax effects of the Act for which a reasonable estimate cannot be determined, continue to apply ASC 740 on the basis of the provisions of the tax laws that were in effect immediately before the Act was signed into law (i.e., the entity would not adjust current or deferred taxes for those tax effects of the Act until a reasonable estimate can be determined) (“Bucket 3”).

The measurement period begins in the period of enactment and ends when the entity obtained, prepared, and analyzed the information needed to complete the accounting requirements under ASC 740; however, the measurement period should not extend beyond one year from the enactment date. As we complete our analysis of the Tax Act, collect and prepare necessary data, and interpret any additional guidance issued by the U.S. Treasury Department, the IRS, and other standard-setting bodies, we will make adjustments to the provisional amounts. The Company expects to complete its analysis within the measurement period, which is no more than one year beyond the enactment date.

In connection with our initial analysis of the impact of the Tax Act, we have recorded provisional estimates in the period ended January 31, 2018 for the following: the revaluation of deferred tax assets and liabilities to reflect the 21 percent corporate tax rate, whether to elect to expense or depreciate new capital equipment, and the US state tax impact to the aforementioned items. The company has made reasonable estimates for each of these items; however it may be affected by other analyses related to the 2017 Act, including but not limited to, any deferred adjustments related to the filing of the Company’s 2017 federal and state tax returns and further guidance yet to be issued.

Temporary differences that gave rise to significant portions of the Company’s deferred tax assets and liabilities at January 31, 2018 and 2017 were as follows:

	As of January 31,
	2018			2017
	(in thousands)
Deferred tax assets:
Federal and state credits	$	18,176		$	14,782
Expenses not currently deductible		1,213			2,381
Stock-based compensation		2,899			3,561
Foreign deferred		229			161
Gross deferred tax assets		22,517			20,885
Valuation allowance		(18,538	)		(15,061	)
Total deferred tax assets	$	3,979		$	5,824
Deferred tax liabilities
Property and equipment		(1,655	)		(1,383	)
Foreign deferred		—			—
Net deferred tax assets	$	2,324		$	4,441

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, 2018	$	15,061		3,477		—		—	$	18,538
Year ended January 31, 2017	$	12,072		2,989		—		—	$	15,061
Year ended January 31, 2016	$	3,996		8,076		—		—	$	12,072

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, 2018 would be $6.2 million. Cumulative undistributed earnings of foreign subsidiaries for which no deferred taxes have been provided approximated $51.0 million at January 31, 2018.

As of January 31, 2018 and 2017, the Company had deferred tax assets (net of deferred tax liabilities) before valuation allowance, of $20.8 million and $19.5 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 $13.8 million and $17.1 million, respectively, at January 31, 2018. 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 21%. As of January 31, 2018, the Company has recorded a valuation allowance of $18.5 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, 2018, the Company had approximately $34.1 million in unrecognized tax benefits, $22.5 million of which would affect the Company’s effective tax rate if recognized. The Company had reductions for tax positions in prior years of $11.3 million related to the effect of the corporate tax rate deduction from 35% to 21% as a result of the enactment of the Tax Act described above. The following table sets forth a reconciliation of the beginning and ending amount of unrecognized tax benefits:

	Year Ended January 31,
	2018			2017			2016
	(in thousands)
Beginning balance:	$	37,977		$	30,211		$	4,671
Additions based on tax positions related to the current year		7,892			7,830			17,169
Additions for tax positions of prior years		28			911			8,810
Reductions for tax positions in prior years		(11,313	)		—			(37	)
Settlements for prior periods		—			—			—
Lapse of applicable statute of limitations		(467	)		(975	)		(402	)
Ending balance:	$	34,117		$	37,977		$	30,211

The Company classified $5.2 million and $1.8 million of income tax liabilities as other long term liabilities as of January 31, 2018 and 2017, 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 $37,000 of interest expense and penalties related to uncertain tax positions for the year ended January 31, 2018 and 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. The Company recorded noncurrent liabilities of $139,000 and $103,000 related to interest and penalties for uncertain tax positions at January 31, 2018 and 2017, respectively.

The primary jurisdiction where our foreign earnings are derived is the Cayman Islands, where the Company is domiciled. 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 2013 to 2017 remain open to examination by U.S. federal tax authorities. The tax years 2008 to 2017 remain open to examination by U.S. state tax authorities. The tax years 2012 to 2017 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, 2018, the Company’s long-term income taxes payable, including estimated interest and penalties, was approximately $5.4 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, 2018. The Company will continue to monitor ongoing developments and potential impacts to its consolidated financial statements.

Commitments and Contingencies

12 Months Ended

Jan. 31, 2018

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

14. Commitments and Contingencies

The Company leases its principal and other facilities under operating lease agreements. Net operating lease expenses for the years ended January 31, 2018, 2017 and 2016 were approximately $5.3 million, $7.6 million and $6.8 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, 2018
Fiscal Year	(in thousands)
2019	$	2,988
2020		2,491
2021		905
2022		330
2023		83
Total future annual minimum lease payments	$	6,797

Upon adoption of Accounting Standards Update No. 2015-05, Intangible - Goodwill and Other - Internal-Use Software (Subtopic 350-40), a noncancelable on premise internal-use software license was accounted for as the acquisition of an intangible asset rather than a software license under an operating lease. For the twelve months ended January 31, 2018, there was $3.0 million of amortization expense recorded in the consolidated statements of operations related to these software licenses.

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, 2018 and 2017, total manufacturing purchase commitments were approximately $24.3 million and $23.9 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, 2018 and 2017, respectively.

Segment Reporting

12 Months Ended

Jan. 31, 2018

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 (HD), Ultra HD video compression, image processing and computer vision solutions. 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. 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 based on bill-to location for the periods indicated. Prior period revenue amounts by geographic region have been reclassified to conform to the fiscal year 2018 presentation. These reclassifications did not impact total revenues in the prior periods.

	Year Ended January 31,
	2018		2017		2016
	(in thousands)
Taiwan	$	174,486	$	185,225	$	210,677
Asia Pacific		57,862		42,461		77,976
Europe		45,185		71,556		8,879
North America other than United States		11,110		3,686		9,487
United States		6,759		7,369		9,354
Total revenue	$	295,402	$	310,297	$	316,373

As of January 31, 2018, substantially all of the Company’s property and equipment were located in the United States, Asia Pacific region and Europe with approximate net amounts of $2.7 million, $2.4 million and $1.3 million, respectively. As of January 31, 2017, substantially all of the Company’s property and equipment were located in the United States and Asia Pacific region with approximate net amounts of $2.1 million and $2.3 million, respectively.

Major Customers

For the years ended January 31, 2018 and 2017, the customers representing 10% or more of revenue and accounts receivable were Wintech, the Company’s distributor, and GoPro, a direct OEM customer. In fiscal year 2018 and 2017, Wintech accounted for approximately 59% and 60% of total revenue, respectively. In fiscal year 2018 and 2017, GoPro accounted for approximately 12% and 19% of total revenue, respectively. The customers representing 10% or more of revenue and accounts receivable for the year ended January 31, 2016 were Wintech and Chicony Electronics Co., Ltd., or Chicony, a direct ODM customer, which accounted for approximately 67% and 21% of total revenue, respectively. Accounts receivable from Wintech and GoPro accounted for approximately $9.8 million and $9.5 million as of January 31, 2018, respectively. Accounts receivable from Wintech and GoPro accounted for approximately $19.3 million and $11.3 million as of January 31, 2017, respectively.

Related-Party Transactions	12 Months Ended
Related-Party Transactions	Jan. 31, 2018
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 enters into software license agreements with Cadence Design Systems, Inc. (“Cadence”) from time to time. The Chief Executive Officer of Cadence, who is also the President and a Director of Cadence, was a member of the Company’s Board of Directors until June 7, 2017. In March 2017, the Company entered into a noncancelable software license agreement with Cadence. Under this agreement, the Company committed to pay an aggregate amount of $10.3 million through January 2020. The Company paid $3.6 million, $2.8 million and $2.8 million of license fee for the years ended January 31, 2018, 2017 and 2016, respectively. License amortization expense related to these agreements included in research and development expense was approximately $3.2 million, $2.9 million and $2.7 million for the years ended January 31, 2018, 2017 and 2016, respectively.

Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Jan. 31, 2018
Accounting Policies [Abstract]
Organization	Organization Ambarella, Inc. (the “Company”) was incorporated in the Cayman Islands on January 15, 2004. The Company is a leading developer of low-power, high-definition (HD) and Ultra HD video compression and image processing solutions, and computer vision solutions. 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. Currently the Company is combining advanced computer vision technology with its state-of-the-art video to enable the next generation of intelligent cameras, advanced driver assistance systems (ADAS) and autonomous vehicles. 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 accounting principles generally accepted 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 collectability 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, assets and stock awards 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 distributor, Wintech Microelectronics Co., Ltd., or Wintech, which serves as its non-exclusive sales representative 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. 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 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 losses on deposits of its cash. The cash equivalents and marketable securities consist primarily of money market funds, 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, net in the consolidated statements of operations, and, to date, have not been material.
Fair Value of Financial Instruments	Fair Value of Financial Instruments 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 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, 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 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, 2018, 2017 and 2016, respectively. There was no material allowance for doubtful accounts recorded as of January 31, 2018 and 2017, respectively.
Inventories	Inventories The Company records inventories at the lower of cost or net realizable value. 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. Any adjustments to reduce the cost of inventories to their net realizable value are recognized in earnings in the current period. 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, 2018, 2017 and 2016, 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 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.
Noncancelable Software License	Noncancelable Software License The Company accounts for a noncancelable on premise internal-use software license as the acquisition of an intangible asset and the incurrence of a liability to the extent that all or a portion of the software licensing fees are not paid on or before the license acquisition date. The intangible asset and related liability are recorded at net present value and interest expense is recorded over the payment term.
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. As of January 31, 2018, there was no IPR&D amortized.
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, 2018. The Company tests the goodwill for impairment at least annually in the fourth fiscal quarter, 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 distributors. 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 has historically provided its distributors 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 distributors are deferred until the Company has received notification from its distributors that they have sold the Company’s products. Information reported by the Company’s distributors includes product resale price, quantity and end customer shipment information as well as remaining inventory on hand. At the time of shipment to a distributor, 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 distributor 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, 2018, 2017 and 2016, 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, 2018, 2017 and 2016, 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. As of January 31, 2018 and 2017, there was approximately $1.8 million and $0.5 million of warranty accruals recorded in the consolidated balance sheets, 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, 2018, 2017 and 2016, 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 with service or performance conditions 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 calculated based on the weighted average of historical volatilities of its own stock price and the share prices of similar companies that are publicly available for a period commensurate with the expected term. The risk-free interest rate is derived from an average of the U.S. Treasury constant maturity rates for the respective periods most closely 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. The Company uses the Lattice pricing model and performs Monte Carlo Simulation to evaluate the fair value of awards with market conditions, including assumptions of historical volatility and risk-free interest rate commensurate with the vesting term. 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 its 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, the Company 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 revenue recognition guidance provides a five-step analysis of transactions to determine when and how revenue is recognized. The guidance requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The FASB issued several updates to the guidance. The new revenue guidance may be adopted by full retrospective method, which applies retrospectively to each prior period presented, or by modified retrospective method with the cumulative effect adjustment recognized in the beginning of retained earnings as of the date of adoption. The Company elects to adopt the new guidance using the modified retrospective method. Under this transition method, the Company elects to apply this new guidance only to contracts that are not completed at the adoption date. For contracts that were modified before the adoption date, the Company elects to reflect the aggregate effect of all modifications that occur before the adoption date when identifying performance obligations, determining the transaction price, and allocating the transaction price to performance obligations. The most significant impacts of this new guidance for the Company relate to the determination of transaction price and the timing of revenue recognition for transactions with its distributors. As a result, the Company will recognize product revenue upon shipment and transfer of control to distributors (known as “sell-in” revenue recognition) rather than shipment to the end customers (known as “sell-through” revenue recognition) based on its estimate of the consideration it expects to receive. The Company also elects to exclude amounts collected from customers for all sales taxes from the transaction price. The impact of this change upon adoption was not material. Furthermore, the Company has made investments and will continuously invest in system design, changing processes and designing operational and internal control structures in order to meet the new standard requirements. 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. The Company is currently assessing the impact of the adoption of this new guidance on its financial position, results of operations and disclosures. 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 estimate of current expected credit losses (“ECL”). Under the new model, an entity is required to estimate ECL on available-for-sale (AFS) debt securities 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. 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. 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 does not believe the adoption of this new guidance will have a material impact 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 and 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 guidance will be applied prospectively and is effective for annual and interim periods beginning after December 15, 2019. 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 March 2017, the FASB issued ASU 2017-08, Receivables – Nonrefundable Fees and Other Costs (Subtopic 310-20): Premium Amortization On Purchased Callable Debt Securities, to shorten the amortization period for the premium to the earliest call date instead of the contractual life of the instrument. This new guidance will be effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Entities will be required to apply the new guidance using the modified retrospective method with a cumulative-effect adjustment to retained earnings upon the adoption date. 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 2018, the FASB issued ASU 2018-02, Income Statement – Reporting Comprehensive Income (Topic 220): Reclassification of Certain Tax Effects from Accumulated Other Comprehensive Income, to permit entities to have the option to reclassify tax effects stranded in accumulated other comprehensive income as a result of tax reform to retained earnings. The FASB also gives entities the option to apply the guidance retrospectively or in the period of adoption. The guidance is effective for fiscal years beginning after December 15, 2018 and interim periods within those fiscal years. Early adoption in any period is permitted. The Company does not make such election and believes that the adoption of this new guidance will not have an impact on its financial position and disclosures.

Financial Instruments and Fair Value (Tables)

12 Months Ended

Jan. 31, 2018

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, 2018
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Money market funds	$	13,788	$	—	$	—		$	13,788
Commercial paper		5,480		—		—			5,480
Corporate bonds		53,175		—		(196	)		52,979
Asset-backed securities		11,048		—		(44	)		11,004
U.S. government securities		18,495		—		(39	)		18,456
Total cash equivalents and marketable securities	$	101,986	$	—	$	(279	)	$	101,707

	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

Schedule of Cash Equivalents and Marketable Securities

	As of
	January 31, 2018		January 31, 2017
	(in thousands)
Included in cash equivalents	$	13,788	$	18,328
Included in marketable securities		87,919		82,522
Total cash equivalents and marketable securities	$	101,707	$	100,850

Summary of Contractual Maturities of Investments

The contractual maturities of the investments at January 31, 2018 and 2017 were as follows:

	As of
	January 31, 2018		January 31, 2017
	(in thousands)
Due within one year	$	63,476	$	76,992
Due within one to two years		38,231		23,858
Total cash equivalents and marketable securities	$	101,707	$	100,850

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, 2018 and 2017, respectively:

	As of January 31, 2018
	Total		Level 1		Level 2		Level 3
	(in thousands)
Money market funds	$	13,788	$	13,788	$	—	$	—
Commercial paper		5,480		—		5,480		—
Corporate bonds		52,979		—		52,979		—
Asset-backed securities		11,004		—		11,004		—
U.S. government securities		18,456		—		18,456		—
Total cash equivalents and marketable securities	$	101,707	$	13,788	$	87,919	$	—

	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	$	—

- 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, 2018

Inventory Disclosure [Abstract]

Schedule of Inventory

Inventories at January 31, 2018 and 2017 consisted of the following:

	As of January 31,
	2018		2017
	(in thousands)
Work-in-progress	$	12,073	$	10,105
Finished goods		11,310		10,040
Total	$	23,383	$	20,145

Property and Equipment, Net (Tables)

12 Months Ended

Jan. 31, 2018

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

Property and equipment at January 31, 2018 and 2017 consisted of the following:

	As of January 31,
	2018			2017
	(in thousands)
Computer equipment and software	$	8,611		$	6,798
Machinery and equipment		4,761			3,405
Furniture and fixtures		917			797
Leasehold improvements		2,092			1,672
Construction in progress		—			755
		16,381			13,427
Less: accumulated depreciation and amortization		(9,932	)		(8,439	)
Total property and equipment, net	$	6,449		$	4,988

Intangible Assets (Tables)

12 Months Ended

Jan. 31, 2018

Goodwill And Intangible Assets Disclosure [Abstract]

Summary of Carrying Amounts of Intangible Assets

The carrying amounts of intangible assets as of January 31, 2018 and 2017 were as follows:

	As of January 31, 2018							As of January 31, 2017
	Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount		Gross Carrying Amount		Accumulated Amortization			Net Carrying Amount
	(in thousands)
In-process research and development	$	4,100	$	—		$	4,100	$	4,100	$	—		$	4,100
Internal-use software license		13,404		(3,087	)		10,317		155		(106	)		49
Total acquired intangible assets	$	17,504	$	(3,087	)	$	14,417	$	4,255	$	(106	)	$	4,149

Summary of Expected Annual Amortization Expense Related to Software Licenses

The expected annual amortization expense related to these software licenses as of January 31, 2018 is as follows:

	As of
	January 31, 2018
Fiscal Year	(in thousands)
2019	$	4,569
2020		4,473
2021		1,275
2022		—
2023		—
Thereafter		—
Total future amortization expenses:	$	10,317

Accrued and Other Current Liabilities (Tables)

12 Months Ended

Jan. 31, 2018

Payables And Accruals [Abstract]

Schedule of Accrued and Other Current Liabilities

Accrued and other current liabilities at January 31, 2018 and 2017 consisted of the following:

	As of January 31,
	2018		2017
	(in thousands)
Accrued employee compensation	$	15,977	$	14,685
Accrued warranty		1,750		500
Accrued rebates		584		972
Accrued product development costs		6,669		7,605
Software license liabilities, current		4,346		—
Other accrued liabilities		2,852		2,686
Total accrued and other current liabilities	$	32,178	$	26,448

Deferred Revenue, Current (Tables)

12 Months Ended

Jan. 31, 2018

Deferred Revenue Disclosure [Abstract]

Schedule of Deferred Revenue and Related Cost

Deferred revenue and related cost at January 31, 2018 and 2017 consisted of the following:

	As of January 31,
	2018		2017
	(in thousands)
Deferred revenue on product shipments	$	36	$	7,725
Deferred revenue from licenses & services		271		1,748
Deferred cost of revenue on product shipments		—		(2,048	)
Total deferred revenue, net	$	307	$	7,425

Other Long-Term Liabilities (Tables)

12 Months Ended

Jan. 31, 2018

Other Liabilities Disclosure [Abstract]

Schedule of Other Long-Term Liabilities

Other long-term liabilities at January 31, 2018 and 2017 consisted of the following:

	As of January 31,
	2018		2017
	(in thousands)
Unrecognized tax benefits, including interest	$	5,352	$	1,905
Deferred tax liabilities, non-current		1,293		1,333
Software license liabilities, non-current		4,484		—
Other long-term liabilities		97		3
Total other long-term liabilities	$	11,226	$	3,241

Capital Stock (Tables)

12 Months Ended

Jan. 31, 2018

Equity [Abstract]

Schedule of Ordinary Shares Reserved for Future Issuance

As of January 31, 2018 and 2017, the following ordinary shares were reserved for future issuance:

	As of January 31,
	2018		2017
Shares reserved for options, restricted stock and restricted stock units		5,561,653		5,167,688
Shares reserved for employee stock purchase plan		1,561,841		1,252,465

Employee Benefits and Stock-based Compensation (Tables)

12 Months Ended

Jan. 31, 2018

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,
	2018		2017		2016
	(in thousands)
Stock-based compensation:
Cost of revenue	$	1,306	$	1,078	$	657
Research and development		34,575		29,729		19,082
Selling, general and administrative		20,980		18,025		11,355
Total stock-based compensation	$	56,861	$	48,832	$	31,094

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,
	2018			2017			2016
Stock Options:
Volatility		53	%		38	%		57	%
Risk-free interest rate		2.08	%		1.59	%		1.74	%
Expected term (years)		6.08			6.00		6.08
Dividend yield		0	%		0	%		0	%
Employee stock purchase plan awards:
Volatility		44	%		54	%		63	%
Risk-free interest rate		1.03	%		0.51	%		0.21	%
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, 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
Granted		132,250			54.66	$	28.28
Exercised		(175,187	)		12.50			$	7,446
Forfeited		(27,721	)		56.97
Expired		(21,522	)		36.31
Outstanding at January 31, 2018		1,611,344		$	24.56					4.63		$	45,868
Exercisable at January 31, 2018		1,351,181		$	18.91						3.93	$	44,868

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, 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
Granted		1,052,235			47.11
Vested		(1,006,130	)		47.55
Forfeited		(118,497	)		54.72
Unvested at January 31, 2018		2,103,281		$	56.45

Net Income Per Ordinary Share (Tables)

12 Months Ended

Jan. 31, 2018

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,
	2018		2017		2016
	(in thousands, except share and per share data)
Numerator:
Net income	$	18,852	$	57,810	$	76,508
Less: amount allocable to unvested early exercised options		—		—		—
Net income allocable to ordinary shareholders - basic	$	18,852	$	57,810	$	76,508
Undistributed earnings reallocated to ordinary shareholders		—		—		—
Net income allocable to ordinary shareholders - diluted	$	18,852	$	57,810	$	76,508
Denominator:
Weighted-average ordinary shares outstanding		33,224,803		32,671,221		31,633,992
Less: weighted-average unvested early exercised options subject to repurchase		—		—		(56	)
Weighted-average ordinary shares - basic		33,224,803		32,671,221		31,633,936
Effect of dilutive securities:
Employee stock options		961,797		1,080,864		1,245,341
Restricted stock and restricted stock units		390,145		565,068		865,863
Employee stock purchase plan		6,405		10,571		10,569
Weighted-average ordinary shares - diluted		34,583,150		34,327,724		33,755,709
Net income per ordinary share:
Basic	$	0.57	$	1.77	$	2.42
Diluted	$	0.55	$	1.68	$	2.27

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,
	2018		2017		2016
Options to purchase ordinary shares		280,907		343,936		109,958
Restricted stock and restricted stock units		907,208		891,952		163,994
Employee stock purchase plan		15,506		14,651		9,073
Early exercised options subject to repurchase		—		—		56
		1,203,621		1,250,539		283,081

Income Taxes (Tables)

12 Months Ended

Jan. 31, 2018

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,
	2018		2017		2016
	(in thousands)
U.S. operations	$	2,683	$	3,092	$	3,190
Non-U.S. operations		23,046		57,789		82,019
Income before income taxes	$	25,729	$	60,881	$	85,209

Schedule of Income Tax Provision

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

	Year Ended January 31,
	2018			2017			2016
	(in thousands)
Current:
U.S. federal tax	$	3,321		$	818		$	5,273
U.S. state taxes		4			(212	)		541
Non-U.S. foreign taxes		1,435			1,454			1,874
		4,760			2,060			7,688
Deferred:
U.S. federal tax		2,185			1,174			1,050
U.S. state taxes		—			—			—
Non-U.S. foreign taxes		(68	)		(163	)		(37	)
		2,117			1,011			1,013
Provision for income taxes	$	6,877		$	3,071		$	8,701

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. 33.8%, 34.0% and 34.0% rates are applied to pretax income as a result of the following for the periods indicated, respectively:

	Year Ended January 31,
	2018			2017			2016
	(in thousands)
Provision at U.S. notional statutory rate	$	8,699		$	20,700		$	28,971
U.S. state taxes		2			(216	)		541
Non-U.S. foreign tax differential		(6,424	)		(18,357	)		(26,253	)
Stock-based compensation		4,645			1,605			2,896
U.S. R&D credit		(2,408	)		(2,226	)		(3,517	)
Valuation allowance		(1	)		1,901			6,090
Change in tax rate		2,252			—			—
Other		112			(336	)		(27	)
Provision for income taxes	$	6,877		$	3,071		$	8,701

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, 2018 and 2017 were as follows:

	As of January 31,
	2018			2017
	(in thousands)
Deferred tax assets:
Federal and state credits	$	18,176		$	14,782
Expenses not currently deductible		1,213			2,381
Stock-based compensation		2,899			3,561
Foreign deferred		229			161
Gross deferred tax assets		22,517			20,885
Valuation allowance		(18,538	)		(15,061	)
Total deferred tax assets	$	3,979		$	5,824
Deferred tax liabilities
Property and equipment		(1,655	)		(1,383	)
Foreign deferred		—			—
Net deferred tax assets	$	2,324		$	4,441

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, 2018	$	15,061		3,477		—		—	$	18,538
Year ended January 31, 2017	$	12,072		2,989		—		—	$	15,061
Year ended January 31, 2016	$	3,996		8,076		—		—	$	12,072

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,
	2018			2017			2016
	(in thousands)
Beginning balance:	$	37,977		$	30,211		$	4,671
Additions based on tax positions related to the current year		7,892			7,830			17,169
Additions for tax positions of prior years		28			911			8,810
Reductions for tax positions in prior years		(11,313	)		—			(37	)
Settlements for prior periods		—			—			—
Lapse of applicable statute of limitations		(467	)		(975	)		(402	)
Ending balance:	$	34,117		$	37,977		$	30,211

Commitments and Contingencies (Tables)

12 Months Ended

Jan. 31, 2018

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, 2018
Fiscal Year	(in thousands)
2019	$	2,988
2020		2,491
2021		905
2022		330
2023		83
Total future annual minimum lease payments	$	6,797

Segment Reporting (Tables)

12 Months Ended

Jan. 31, 2018

Segment Reporting [Abstract]

Company's Revenue by Geographic Region Based on Bill-to Location

	Year Ended January 31,
	2018		2017		2016
	(in thousands)
Taiwan	$	174,486	$	185,225	$	210,677
Asia Pacific		57,862		42,461		77,976
Europe		45,185		71,556		8,879
North America other than United States		11,110		3,686		9,487
United States		6,759		7,369		9,354
Total revenue	$	295,402	$	310,297	$	316,373

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) - USD ($)	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Summary Of Significant Accounting Policies [Line Items]
Accumulated amortization of intangible asset	$ 3,087,000	$ 106,000
Impairment of long-lived assets	0
Goodwill impairment	0	0	$ 0
Impairment losses on investment	0
Accrued warranty	$ 1,750,000	$ 500,000
Expected dividend yield	0.00%	0.00%	0.00%
IPR&D [Member]
Summary Of Significant Accounting Policies [Line Items]
Accumulated amortization of intangible asset	$ 0	$ 0

Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 101,986	$ 100,920
Unrealized Gains	0	13
Unrealized Losses	(279)	(83)
Fair Value	101,707	100,850
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,788	8,328
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	13,788	8,328
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	5,480	4,784
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	5,480	4,784
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	53,175	42,713
Unrealized Gains	0	6
Unrealized Losses	(196)	(41)
Fair Value	52,979	42,678
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,048	11,686
Unrealized Gains	0	1
Unrealized Losses	(44)	(12)
Fair Value	11,004	11,675
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	18,495	23,409
Unrealized Gains	0	6
Unrealized Losses	(39)	(30)
Fair Value	$ 18,456	$ 23,385

Financial Instruments and Fair Value - Schedule of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$ 101,707	$ 100,850
Included in cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	13,788	18,328
Included in marketable securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$ 87,919	$ 82,522

Financial Instruments and Fair Value - Summary of Contractual Maturities of Investments (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Available For Sale Securities Debt Maturities Fair Value [Abstract]
Due within one year	$ 63,476	$ 76,992
Due within one to two years	38,231	23,858
Total cash equivalents and marketable securities	$ 101,707	$ 100,850

Inventories - Schedule of Inventory (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Inventory Disclosure [Abstract]
Work-in-progress	$ 12,073	$ 10,105
Finished goods	11,310	10,040
Total	$ 23,383	$ 20,145

Property and Equipment, Net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 16,381	$ 13,427
Less: accumulated depreciation and amortization	(9,932)	(8,439)
Total property and equipment, net	6,449	4,988
Computer equipment and software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	8,611	6,798
Machinery and equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	4,761	3,405
Furniture and fixtures [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	917	797
Leasehold improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,092	1,672
Construction in progress [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 0	$ 755

Intangible Assets - Additional Information (Detail) - USD ($)	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016	Jun. 25, 2015
Finite Lived Intangible Assets [Line Items]
Accumulated amortization of intangible asset	$ 3,087,000	$ 106,000
Committed to make license payment through January 2020	13,900,000
Liabilities associated with noncancelable internal-use software license at net present value, current	4,346,000	0
Liabilities associated with noncancelable internal-use software license at net present value, non-current	4,484,000	0
Internal-use noncancelable software license, amortization expense	3,000,000
Impairment of intangible assets	0	0	$ 0
Accrued and other current liabilities [Member]
Finite Lived Intangible Assets [Line Items]
Liabilities associated with noncancelable internal-use software license at net present value, current	4,300,000
Other long-term liabilities [Member]
Finite Lived Intangible Assets [Line Items]
Liabilities associated with noncancelable internal-use software license at net present value, non-current	4,500,000
Vis Lab SRL [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets acquired				$ 4,100,000
IPR&D [Member]
Finite Lived Intangible Assets [Line Items]
Accumulated amortization of intangible asset	0	$ 0
IPR&D [Member] \| Vis Lab SRL [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets acquired				$ 4,100,000
Noncancelable software licenses [Member]
Finite Lived Intangible Assets [Line Items]
Other intangible assets	$ 10,300,000

Intangible Assets - Summary of Carrying Amounts of Intangible Assets (Detail) - USD ($)	Jan. 31, 2018	Jan. 31, 2017
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 17,504,000	$ 4,255,000
Accumulated Amortization	(3,087,000)	(106,000)
Net Carrying Amount	14,417,000	4,149,000
In-process research and development [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	4,100,000	4,100,000
Accumulated Amortization	0	0
Net Carrying Amount	4,100,000	4,100,000
Internal-use software license [Member]
Finite Lived Intangible Assets [Line Items]
Gross Carrying Amount	13,404,000	155,000
Accumulated Amortization	(3,087,000)	(106,000)
Net Carrying Amount	$ 10,317,000	$ 49,000

Intangible Assets - Summary of Expected Annual Amortization Expense Related to Software Licenses (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Finite Lived Intangible Assets [Line Items]
Net Carrying Amount	$ 14,417	$ 4,149
Internal-use software license [Member]
Finite Lived Intangible Assets [Line Items]
2019	4,569
2020	4,473
2021	1,275
2022	0
2023	0
Thereafter	0
Net Carrying Amount	$ 10,317	$ 49

Goodwill - Additional Information (Detail) - USD ($)		12 Months Ended
Goodwill - Additional Information (Detail) - USD ($)	Jun. 25, 2015	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Finite Lived Intangible Assets [Line Items]
Goodwill		$ 26,601,000	$ 26,601,000
Goodwill impairment		$ 0	$ 0	$ 0
Vis Lab SRL [Member]
Finite Lived Intangible Assets [Line Items]
Business acquisition date	Jun. 25, 2015
Cash paid for business acquisition	$ 30,000,000
Goodwill	25,300,000
Intangible assets acquired	4,100,000
Net assets acquired	600,000
Deferred tax liabilities, intangible assets	$ 1,300,000

Accrued and Other Current Liabilities - Schedule of Accrued and Other Current Liabilities (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Payables And Accruals [Abstract]
Accrued employee compensation	$ 15,977	$ 14,685
Accrued warranty	1,750	500
Accrued rebates	584	972
Accrued product development costs	6,669	7,605
Software license liabilities, current	4,346	0
Other accrued liabilities	2,852	2,686
Total accrued and other current liabilities	$ 32,178	$ 26,448

Deferred Revenue, Current - Schedule of Deferred Revenue and Related Cost (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Deferred Revenue Disclosure [Abstract]
Deferred revenue on product shipments	$ 36	$ 7,725
Deferred revenue from licenses & services	271	1,748
Deferred cost of revenue on product shipments	0	(2,048)
Total deferred revenue, net	$ 307	$ 7,425

- 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, 2018	Jan. 31, 2017
Other Liabilities Disclosure [Abstract]
Unrecognized tax benefits, including interest	$ 5,352	$ 1,905
Deferred tax liabilities, non-current	1,293	1,333
Software license liabilities, non-current	4,484	0
Other long-term liabilities	97	3
Total other long-term liabilities	$ 11,226	$ 3,241

Capital Stock - Additional Information (Detail) - USD ($)			12 Months Ended			20 Months Ended
	May 31, 2017	May 31, 2016	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2018
Class Of Stock [Line Items]
Preference shares, shares authorized			20,000,000	20,000,000		20,000,000
Preference shares, par value			$ 0.00045	$ 0.00045		$ 0.00045
Preference shares, shares issued			0	0		0
Preference shares, shares outstanding			0	0		0
Ordinary shares, shares authorized			200,000,000	200,000,000		200,000,000
Stock repurchase program, period	12 months
Stock repurchase program, commencing date	Jul. 01, 2017
Stock repurchased during period, shares			1,094,795	405,089		1,499,884
Stock repurchased during period, cash			$ 54,788,000	$ 20,183,000	$ 0	$ 75,000,000
Amount available under stock repurchase program			$ 31,700,000			$ 31,700,000
Stock Repurchase Program $75.0 Million Authorization [Member]
Class Of Stock [Line Items]
Stock repurchase program, authorization date		May 31, 2016
Stock repurchase program, expiration date		Jun. 30, 2017
Stock Repurchase Program $50.0 Million Authorization [Member]
Class Of Stock [Line Items]
Stock repurchase program, authorization date	May 31, 2017
Stock repurchase program, expiration date	Jun. 30, 2018
Maximum [Member] \| Stock Repurchase Program $75.0 Million Authorization [Member]
Class Of Stock [Line Items]
Amount authorized under stock repurchase program		$ 75,000,000
Maximum [Member] \| Stock Repurchase Program $50.0 Million Authorization [Member]
Class Of Stock [Line Items]
Amount authorized under stock repurchase program	$ 50,000,000

Capital Stock - Schedule of Ordinary Shares Reserved for Future Issuance (Detail) - shares	Jan. 31, 2018	Jan. 31, 2017
Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved	5,561,653	5,167,688
Employee stock purchase plan awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved	1,561,841	1,252,465

Employee Benefits and Stock-based Compensation - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions			12 Months Ended
	Feb. 02, 2017	Feb. 02, 2016	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Closing price of ordinary shares			$ 50.40
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	1,501,606	1,455,001
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%
Percentage of salary contribution by employees			15.00%
Additional ordinary shares reserved for issuance	417,112	404,166
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			$ 6.4
Weighted average recognition period			2 years 2 months 15 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			$ 106.0
Total fair value of vesting dates of restricted stock and restricted stock units vested			$ 52.1	$ 51.1	$ 59.2
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 8 months 19 days
Total unrecognized compensation cost, restricted stock units			$ 100.1
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average recognition period			1 year 29 days
Total unrecognized compensation cost, restricted stock awards			$ 3.3

Employee Benefits and Stock-based Compensation - Classification of Stock-based Compensation (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Stock-based compensation:
Total stock-based compensation	$ 56,861	$ 48,832	$ 31,094
Cost of revenue [Member]
Stock-based compensation:
Total stock-based compensation	1,306	1,078	657
Research and development [Member]
Stock-based compensation:
Total stock-based compensation	34,575	29,729	19,082
Selling, general and administrative [Member]
Stock-based compensation:
Total stock-based compensation	$ 20,980	$ 18,025	$ 11,355

Employee Benefits and Stock-based Compensation - Weighted-Average Assumptions Used to Estimate Fair Value (Detail)	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
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	53.00%	38.00%	57.00%
Risk-free interest rate	2.08%	1.59%	1.74%
Expected term (years)	6 years 29 days	6 years	6 years 29 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	44.00%	54.00%	63.00%
Risk-free interest rate	1.03%	0.51%	0.21%
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, 2018	Jan. 31, 2017	Jan. 31, 2016
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding	1,703,524	1,853,390	2,281,909
Shares, Granted	132,250	110,500	179,700
Shares, Exercised	(175,187)	(235,923)	(567,888)
Shares, Forfeited	(27,721)	(16,708)	(40,331)
Shares, Expired	(21,522)	(7,735)
Shares, Outstanding	1,611,344	1,703,524	1,853,390
Shares, Exercisable	1,351,181
Weighted-Average Exercise Price, Outstanding	$ 21.66	$ 19.36	$ 13.00
Weighted-Average Exercise Price, Granted	54.66	47.82	71.36
Weighted-Average Exercise Price, Exercised	12.50	13.69	9.11
Weighted-Average Exercise Price, Forfeited	56.97	55.07	35.65
Weighted-Average Exercise Price, Expired	36.31	14.19
Weighted-Average Exercise Price, Outstanding	24.56	21.66	19.36
Weighted-Average Exercise Price, Exercisable	18.91
Weighted-Average Grant-date Fair Value, Granted	$ 28.28	$ 18.76	$ 38.81
Total Intrinsic Value of options Exercised	$ 7,446	$ 10,788	$ 37,603
Weighted-Average Remaining Contractual Term, Outstanding	4 years 7 months 17 days
Weighted-Average Remaining Contractual Term, Exercisable	3 years 11 months 4 days
Aggregate Intrinsic Value, Outstanding	$ 45,868
Aggregate Intrinsic Value, Exercisable	$ 44,868

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, 2018	Jan. 31, 2017	Jan. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Unvested, beginning balance	2,175,673	2,495,488	1,980,448
Shares, Granted	1,052,235	676,598	1,314,387
Shares, Vested	(1,006,130)	(955,230)	(769,779)
Shares, Forfeited	(118,497)	(41,183)	(29,568)
Shares, Unvested, ending balance	2,103,281	2,175,673	2,495,488
Weighted-Average Grant-Date Fair Value, Unvested, beginning balance	$ 56.76	$ 47.04	$ 26.82
Weighted-Average Grant-Date Fair Value, Granted	47.11	67.68	66.14
Weighted-Average Grant-Date Fair Value, Vested	47.55	39.28	27.82
Weighted-Average Grant-Date Fair Value, Forfeited	54.72	52.49	42.11
Weighted-Average Grant-Date Fair Value, Unvested, ending balance	$ 56.45	$ 56.76	$ 47.04

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, 2018	Jan. 31, 2017	Jan. 31, 2016
Numerator:
Net income	$ 18,852	$ 57,810	$ 76,508
Less: amount allocable to unvested early exercised options	0	0	0
Net income allocable to ordinary shareholders - basic	18,852	57,810	76,508
Undistributed earnings reallocated to ordinary shareholders	0	0	0
Net income allocable to ordinary shareholders - diluted	$ 18,852	$ 57,810	$ 76,508
Denominator:
Weighted-average ordinary shares outstanding	33,224,803	32,671,221	31,633,992
Less: weighted-average unvested early exercised options subject to repurchase	0	0	(56)
Weighted-average ordinary shares - basic	33,224,803	32,671,221	31,633,936
Effect of dilutive securities:
Employee stock options	961,797	1,080,864	1,245,341
Restricted stock and restricted stock units	390,145	565,068	865,863
Employee stock purchase plan	6,405	10,571	10,569
Weighted-average ordinary shares - diluted	34,583,150	34,327,724	33,755,709
Net income per ordinary share:
Basic	$ 0.57	$ 1.77	$ 2.42
Diluted	$ 0.55	$ 1.68	$ 2.27

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, 2018	Jan. 31, 2017	Jan. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	1,203,621	1,250,539	283,081
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	280,907	343,936	109,958
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	907,208	891,952	163,994
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	15,506	14,651	9,073
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	0	56

Income Taxes - Summary of Income before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Results Of Operations Income Before Income Taxes [Abstract]
U.S. operations	$ 2,683	$ 3,092	$ 3,190
Non-U.S. operations	23,046	57,789	82,019
Income before income taxes	$ 25,729	$ 60,881	$ 85,209

Income Taxes - Schedule of Income Tax Provision (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Current:
U.S. federal tax	$ 3,321	$ 818	$ 5,273
U.S. state taxes	4	(212)	541
Non-U.S. foreign taxes	1,435	1,454	1,874
Current income tax provision	4,760	2,060	7,688
Deferred:
U.S. federal tax	2,185	1,174	1,050
U.S. state taxes	0	0	0
Non-U.S. foreign taxes	(68)	(163)	(37)
Deferred income tax provision	2,117	1,011	1,013
Provision for income taxes	$ 6,877	$ 3,071	$ 8,701

Income Taxes - Additional Information (Detail) - USD ($)	1 Months Ended	11 Months Ended	12 Months Ended
	Jan. 31, 2018	Dec. 31, 2017	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2015
Income Taxes [Line Items]
Statutory tax rate		35.00%	33.80%	34.00%	34.00%
Decrease of deferred tax assets and corresponding increase in deferred tax expense			$ 1,900,000
Deferred tax liabilities, not recognized	$ 6,200,000		6,200,000
Cumulative undistributed earnings of foreign subsidiaries	51,000,000		51,000,000
Gross deferred tax assets, net of deferred tax liabilities before valuation allowance	20,800,000		20,800,000	$ 19,500,000
Valuation allowance	18,538,000		18,538,000	15,061,000
Unrecognized tax benefits	34,117,000		34,117,000	37,977,000	$ 30,211,000	$ 4,671,000
Unrecognized tax benefits that would impact effective tax rate	22,500,000		22,500,000
Reductions for tax positions in prior years			11,313,000	0	$ 37,000
Income tax liabilities considered as other long term liabilities	5,200,000		5,200,000	1,800,000
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			37,000
Noncurrent liabilities related to interest and penalties for uncertain tax positions	139,000		139,000	$ 103,000
Long term income taxes payable, including estimated interest and penalties	5,400,000		$ 5,400,000
U.S. federal tax authorities [Member] \| Earliest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year			2013
U.S. federal tax authorities [Member] \| Latest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year			2017
U.S. state tax authorities [Member] \| Earliest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year			2008
U.S. state tax authorities [Member] \| Latest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year			2017
Foreign tax authorities [Member] \| Earliest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year			2012
Foreign tax authorities [Member] \| Latest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year			2017
Federal [Member]
Income Taxes [Line Items]
Research and development credit carryforwards	13,800,000		$ 13,800,000
Federal credits begin to expire in fiscal year			2033
California state [Member]
Income Taxes [Line Items]
Research and development credit carryforwards	$ 17,100,000		$ 17,100,000
Scenario, Plan [Member]
Income Taxes [Line Items]
Statutory tax rate	21.00%		21.00%

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, 2018	Jan. 31, 2017	Jan. 31, 2016
Income Tax Disclosure [Abstract]
Provision at U.S. notional statutory rate	$ 8,699	$ 20,700	$ 28,971
U.S. state taxes	2	(216)	541
Non-U.S. foreign tax differential	(6,424)	(18,357)	(26,253)
Stock-based compensation	4,645	1,605	2,896
U.S. R&D credit	(2,408)	(2,226)	(3,517)
Valuation allowance	(1)	1,901	6,090
Change in tax rate	2,252	0	0
Other	112	(336)	(27)
Provision for income taxes	$ 6,877	$ 3,071	$ 8,701

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Deferred tax assets:
Federal and state credits	$ 18,176	$ 14,782
Expenses not currently deductible	1,213	2,381
Stock-based compensation	2,899	3,561
Foreign deferred	229	161
Gross deferred tax assets	22,517	20,885
Valuation allowance	(18,538)	(15,061)
Total deferred tax assets	3,979	5,824
Deferred tax liabilities
Property and equipment	(1,655)	(1,383)
Foreign deferred	0	0
Net deferred tax assets	$ 2,324	$ 4,441

Income Taxes - Summary of Tax Valuation Allowance (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	$ 15,061
Balance at End of Period	18,538	$ 15,061
Valuation Allowance of Deferred Tax Assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	15,061	12,072	$ 3,996
Additional Charged to Expenses	3,477	2,989	8,076
Additions Charged to Other Account	0	0	0
Deductions Charged to Expenses or Other Accounts	0	0	0
Balance at End of Period	$ 18,538	$ 15,061	$ 12,072

Income Taxes - Schedule of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Income Tax Disclosure [Abstract]
Beginning balance	$ 37,977	$ 30,211	$ 4,671
Additions based on tax positions related to the current year	7,892	7,830	17,169
Additions for tax positions of prior years	28	911	8,810
Reductions for tax positions in prior years	(11,313)	0	(37)
Settlements for prior periods	0	0	0
Lapse of applicable statute of limitations	(467)	(975)	(402)
Ending balance	$ 34,117	$ 37,977	$ 30,211

Commitments and Contingencies - Additional Information (Detail) - USD ($)	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Loss Contingencies [Line Items]
Net operating lease expenses	$ 5,300,000	$ 7,600,000	$ 6,800,000
Amortization of intangible assets	2,981,000	50,000	$ 16,000
Total manufacturing purchase commitments	24,300,000	23,900,000
Indemnification agreement [Member]
Loss Contingencies [Line Items]
Payments under indemnification obligations	0	0
Liabilities recorded under indemnification obligations	0	$ 0
Accounting Standards Update No. 2015-05 [Member] \| Internal-use software license [Member]
Loss Contingencies [Line Items]
Amortization of intangible assets	$ 3,000,000

Commitments and Contingencies - Future Annual Minimum Lease Payments (Detail) $ in Thousands	Jan. 31, 2018 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2019	$ 2,988
2020	2,491
2021	905
2022	330
2023	83
Total future annual minimum lease payments	$ 6,797

Segment Reporting - Additional Information (Detail) $ in Thousands	12 Months Ended
	Jan. 31, 2018 USD ($) Segment	Jan. 31, 2017 USD ($)	Jan. 31, 2016
Concentration Risk [Line Items]
Number of reportable segment \| Segment	1
Property and equipment, net	$ 6,449	$ 4,988
Accounts receivable	31,294	38,596
Wintech [Member] \| Credit concentration risk [Member]
Concentration Risk [Line Items]
Accounts receivable	9,800	19,300
GoPro [Member] \| Credit concentration risk [Member]
Concentration Risk [Line Items]
Accounts receivable	$ 9,500	$ 11,300
Sales revenue, net [Member] \| Wintech [Member] \| Customer concentration risk [Member]
Concentration Risk [Line Items]
Percentage of revenue	59.00%	60.00%	67.00%
Sales revenue, net [Member] \| GoPro [Member] \| Customer concentration risk [Member]
Concentration Risk [Line Items]
Percentage of revenue	12.00%	19.00%
Sales revenue, net [Member] \| Chicony [Member] \| Customer concentration risk [Member]
Concentration Risk [Line Items]
Percentage of revenue			21.00%
United States [Member]
Concentration Risk [Line Items]
Property and equipment, net	$ 2,700	$ 2,100
Asia Pacific [Member]
Concentration Risk [Line Items]
Property and equipment, net	2,400	$ 2,300
Europe [Member]
Concentration Risk [Line Items]
Property and equipment, net	$ 1,300

Segment Reporting - Company's Revenue by Geographic Region Based on Bill-to Location (Detail) - USD ($) $ in Thousands	12 Months Ended
	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Revenue from External Customer [Line Items]
Total revenue	$ 295,402	$ 310,297	$ 316,373
Taiwan [Member]
Revenue from External Customer [Line Items]
Total revenue	174,486	185,225	210,677
Asia Pacific [Member]
Revenue from External Customer [Line Items]
Total revenue	57,862	42,461	77,976
Europe [Member]
Revenue from External Customer [Line Items]
Total revenue	45,185	71,556	8,879
North America other than United States [Member]
Revenue from External Customer [Line Items]
Total revenue	11,110	3,686	9,487
United States [Member]
Revenue from External Customer [Line Items]
Total revenue	$ 6,759	$ 7,369	$ 9,354

Related-Party Transactions - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	12 Months Ended
	Mar. 31, 2017	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016
Related Party Transaction [Line Items]
Percentage of entity's voting stock owned by related party		10.00%
Committed to make license payment through January 2020		$ 13.9
Other Entity [Member]
Related Party Transaction [Line Items]
Committed to make license payment through January 2020	$ 10.3
Payment for license fees		3.6	$ 2.8	$ 2.8
License amortization expenses included in research and development expense		$ 3.2	$ 2.9	$ 2.7

Subsequent Events - Additional Information (Detail) - USD ($) $ in Thousands	2 Months Ended	12 Months Ended			20 Months Ended	22 Months Ended
	Mar. 29, 2018	Jan. 31, 2018	Jan. 31, 2017	Jan. 31, 2016	Jan. 31, 2018	Mar. 29, 2018
Subsequent Event [Line Items]
Stock repurchased during period, shares		1,094,795	405,089		1,499,884
Stock repurchased during period, cash		$ 54,788	$ 20,183	$ 0	$ 75,000
Amount available under stock repurchase program		$ 31,700			$ 31,700
Subsequent Event [Member]
Subsequent Event [Line Items]
Stock repurchased during period, shares	197,682					1,697,566
Stock repurchased during period, cash	$ 9,500					$ 84,500
Amount available under stock repurchase program	$ 22,200					$ 22,200

Subsequent Events	12 Months Ended
Subsequent Events	Jan. 31, 2018
Subsequent Events [Abstract]
Subsequent Events	17. Subsequent Events From February 1, 2018 to March 29, 2018, the Company repurchased a total of 197,682 shares for approximately $9.5 million in cash. As of March 29, 2018, the Company had repurchased a total of 1,697,566 shares for approximately $84.5 million in cash and there was approximately $22.2 million available for repurchases under the Company’s repurchase program through June 30, 2018.

Goodwill	12 Months Ended
Goodwill	Jan. 31, 2018
Goodwill And Intangible Assets Disclosure [Abstract]
Goodwill	6. Goodwill On June 25, 2015, the Company completed the acquisition of 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. As a result, there was $25.3 million attributed to goodwill, $4.1 million attributed to intangible assets and $0.6 million attributed to net assets acquired. 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. There were no goodwill impairments for the fiscal years ended January 31, 2018, 2017 and 2016, respectively.

Financial Instruments and Fair Value - Schedule of Fair Value of Financial Instruments Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Jan. 31, 2018	Jan. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 101,707	$ 100,850
Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	13,788	8,328
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	5,480	4,784
Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	52,979	42,678
Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	11,004	11,675
U.S. government securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	18,456	23,385
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	13,788	18,328
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	13,788	8,328
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 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	87,919	82,522
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	5,480	4,784
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	52,979	42,678
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	11,004	11,675
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	18,456	23,385
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