Document and Entity Information - shares	6 Months Ended
Document and Entity Information - shares	Jul. 31, 2017	Sep. 01, 2017
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jul. 31, 2017
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q2
Trading Symbol	AMBA
Entity Registrant Name	AMBARELLA INC
Entity Central Index Key	0001280263
Current Fiscal Year End Date	--01-31
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		33,214,205

Condensed Consolidated Balance Sheets (Unaudited) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Current assets:
Cash and cash equivalents	$ 309,738	$ 322,872
Marketable securities	91,077	82,522
Accounts receivable, net	38,351	38,596
Inventories	17,726	20,145
Restricted cash	9	8
Prepaid expenses and other current assets	2,810	4,392
Total current assets	459,711	468,535
Property and equipment, net	5,636	4,988
Deferred tax assets, non-current	6,299	5,774
Intangible assets, net	12,970	4,149
Goodwill	26,601	26,601
Other non-current assets	2,229	2,224
Total assets	513,446	512,271
Current liabilities:
Accounts payable	23,466	19,955
Accrued and other current liabilities	19,906	26,448
Income taxes payable	2,014	568
Deferred revenue	6,203	7,425
Total current liabilities	51,589	54,396
Other long-term liabilities	9,131	3,241
Total liabilities	60,720	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 July 31, 2017 and January 31, 2017, respectively	0	0
Ordinary shares, $0.00045 par value per share, 200,000,000 shares authorized at July 31, 2017 and January 31, 2017, respectively; 33,220,378 shares issued and outstanding at July 31, 2017; 33,369,032 shares issued and outstanding at January 31, 2017	15	15
Additional paid-in capital	204,513	212,276
Accumulated other comprehensive loss	(82)	(70)
Retained earnings	248,280	242,413
Total shareholders’ equity	452,726	454,634
Total liabilities and shareholders' equity	$ 513,446	$ 512,271

Condensed Consolidated Balance Sheets (Unaudited) (Parenthetical) - $ / shares	Jul. 31, 2017	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	33,220,378	33,369,032
Ordinary shares, shares outstanding	33,220,378	33,369,032

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Income Statement [Abstract]
Revenue	$ 71,630	$ 65,142	$ 135,765	$ 122,299
Cost of revenue	26,825	21,672	49,997	42,122
Gross profit	44,805	43,470	85,768	80,177
Operating expenses:
Research and development	27,538	23,643	54,140	48,109
Selling, general and administrative	11,962	10,565	23,706	21,458
Total operating expenses	39,500	34,208	77,846	69,567
Income from operations	5,305	9,262	7,922	10,610
Other income	224	171	377	198
Income before income taxes	5,529	9,433	8,299	10,808
Provision for income taxes	2,226	801	2,432	393
Net income	$ 3,303	$ 8,632	$ 5,867	$ 10,415
Net income per share attributable to ordinary shareholders:
Basic	$ 0.10	$ 0.27	$ 0.18	$ 0.32
Diluted	$ 0.10	$ 0.25	$ 0.17	$ 0.31
Weighted-average shares used to compute net income per share attributable to ordinary shareholders:
Basic	33,227,717	32,557,398	33,240,767	32,492,723
Diluted	34,572,927	34,175,466	34,629,004	34,063,103

Condensed Consolidated Statements of Comprehensive Income (Unaudited) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Statement Of Income And Comprehensive Income [Abstract]
Net income	$ 3,303	$ 8,632	$ 5,867	$ 10,415
Other comprehensive income (loss), net of tax:
Unrealized gains (losses) on investments	6	13	(12)	40
Other comprehensive income (loss), net of tax	6	13	(12)	40
Comprehensive income	$ 3,309	$ 8,645	$ 5,855	$ 10,455

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016
Cash flows from operating activities:
Net income	$ 5,867	$ 10,415
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	855	819
Amortization of intangible assets	1,147	23
Amortization/accretion of marketable securities	101	125
Stock-based compensation	27,407	22,767
Other non-cash items, net	43	67
Changes in operating assets and liabilities:
Accounts receivable	245	5,820
Inventories	2,419	(2,731)
Prepaid expenses and other current assets	1,618	2
Deferred tax assets	(525)	1,054
Other assets	(5)	119
Accounts payable	3,511	5,548
Accrued liabilities	(9,293)	(543)
Income taxes payable	1,446	(787)
Deferred tax liabilities	0	(58)
Deferred revenue	(1,222)	(4,613)
Other long-term liabilities	39	26
Net cash provided by operating activities	33,653	38,053
Cash flows from investing activities:
Purchase of investments	(28,049)	(50,214)
Sales of investments	4,500	19,827
Maturities of investments	14,840	19,560
Purchase of property and equipment	(1,853)	(997)
Net cash used in investing activities	(10,562)	(11,824)
Cash flows from financing activities:
Stock repurchase	(38,720)	(20,183)
Proceeds from exercise of stock options and employee stock purchase plan	3,396	2,405
Payment for software license liabilities	(901)	0
Net cash used in financing activities	(36,225)	(17,778)
Net increase (decrease) in cash and cash equivalents	(13,134)	8,451
Cash and cash equivalents at beginning of period	322,872	268,056
Cash and cash equivalents at end of period	309,738	276,507
Supplemental disclosure of cash flow information:
Cash paid for income taxes	567	637
Supplemental disclosure of noncash investing and financing activities:
Increase in liabilities related to intangible and fixed asset purchases	$ 9,193	$ 86

Organization and Summary of Significant Accounting Policies	6 Months Ended
	Jul. 31, 2017
Accounting Policies [Abstract]
Organization and Summary of Significant Accounting Policies	1. Organization and Summary of Significant Accounting Policies Organization Ambarella, Inc. (the “Company”) was incorporated in the Cayman Islands on January 15, 2004. The Company is a developer of semiconductor processing solutions for video that enable high-definition video capture, sharing, analysis and display. The Company combines its processor design capabilities with its expertise in video and image processing, algorithms and software to provide a technology platform that is designed to be easily scalable across multiple applications and enable rapid and efficient product development. The Company’s system-on-a-chip (“SoC”) designs fully integrate high-definition video processing, image processing, analysis, audio processing and system functions onto a single chip, delivering exceptional video and image quality, differentiated functionality and low power consumption. The Company sells its solutions to leading original design manufacturers (“ODMs”) and original equipment manufacturers (“OEMs”) globally. Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared by the Company in accordance with the instructions to Form 10-Q pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) and, therefore, do not include all information and notes normally provided in audited financial statements. The accounting policies are described in the “Notes to Consolidated Financial Statements” in the Annual Report on Form 10-K for the 2017 fiscal year filed with the SEC on March 30, 2017 (the “Form 10-K”) and updated, as necessary, in this Form 10-Q. The year-end condensed consolidated balance sheet data presented for comparative purposes was derived from audited financial statements, but does not include all disclosures required by generally accepted accounting principles in the United States (“U.S. GAAP”). In the opinion of management, all adjustments (consisting of normal recurring accruals and adjustments) considered necessary for a fair statement have been included. The results of operations for any interim period are not necessarily indicative of, nor comparable to, the results of operations for any other interim period or for a full fiscal year. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes contained in the Form 10-K. Basis of Consolidation The Company’s fiscal year ends on January 31. The condensed consolidated financial statements of the Company and its subsidiaries have been prepared in conformity with U.S. GAAP. All intercompany transactions and balances have been eliminated upon consolidation. Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expense during the reported periods. Actual results could differ from those estimates. On an ongoing basis, management evaluates its estimates and assumptions, including those related to (i) the collectibility of accounts receivable; (ii) write down of excess and obsolete inventories; (iii) intangible assets and goodwill; (iv) the estimated useful lives of long-lived assets; (v) impairment of long-lived assets and financial instruments; (vi) warranty obligations; (vii) the valuation of stock-based compensation awards and financial instruments; (viii) the probability of performance objectives achievement; (ix) the realization of tax assets and estimates of tax liabilities, including reserves for uncertain tax positions; and (x) the recognition and disclosure of contingent liabilities. These estimates and assumptions are based on historical experience and on various other factors which the Company believes to be reasonable under the circumstances. The Company may engage third-party valuation specialists to assist with estimates related to the valuation of financial instruments and assets associated with various contractual arrangements. Such estimates often require the selection of appropriate valuation methodologies and significant judgment. Actual results could differ from these estimates under different assumptions or circumstances. Concentration of Risk The Company’s products are manufactured, assembled and tested by third-party contractors located primarily in Asia. The Company does not have long-term agreements with these contractors. A significant disruption in the operations of one or more of these contractors would impact the production of the Company’s products which could have a material adverse effect on its business, financial condition and results of operations. A substantial portion of the Company’s revenue is derived from sales through its logistics provider, Wintech Microelectronics Co., Ltd., or Wintech, which serves as its non-exclusive sales representative and logistics provider in Asia other than Japan. Termination of the relationship with Wintech could result in a temporary or permanent loss of revenue and result in an obligation to repurchase unsold product. Any Wintech credit issue could impair its ability to make timely payment to the Company. See Note 15 for additional information regarding revenue and credit concentration with this customer. 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 material losses on deposits of its cash. In order to limit the exposure of each investment, 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. The Company does not hold or issue financial instruments for trading purposes. The Company performs ongoing credit evaluations of each of its customers and adjusts credit limits based upon payment history and the customers’ credit worthiness. The Company regularly monitors collections and payments from its customers. 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 marketable securities. The Company classifies these investments as “available-for-sale” securities carried at fair value, based on quoted market prices of similar assets, with the unrealized gains or losses reported, net of tax, as a separate component of shareholders’ equity and included in accumulated other comprehensive income (loss) in the condensed consolidated balance sheets. The amortization of premiums and accretion of discounts and the realized gains and losses are both recorded in other income (loss), net in the condensed consolidated statements of operations. The Company reviews its investments for possible other-than-temporary impairments on a regular basis. If any loss on investment is believed to be other-than-temporary, a charge will be recorded and a new cost basis in the investment will be established. In evaluating whether a loss on a security is other-than-temporary, the Company considers the following factors: 1) general market conditions, 2) the duration and extent to which the fair value is less than cost, 3) the Company’s intent and ability to hold the investment. For securities in an unrealized loss position which is deemed to be other-than-temporary, the difference between the security’s then-current amortized cost basis and fair value is separated into (i) the amount of the impairment related to the credit loss (i.e., the credit loss component) and (ii) the amount of the impairment related to all other factors (i.e., the non-credit loss component). The credit loss component is recognized in earnings. The non-credit loss component is recognized in accumulated other comprehensive income (loss). Due to the relative short term nature of the investments, there have been no other-than-temporary impairments recorded to date. 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 three and six months ended July 31, 2017 and 2016, respectively. Noncancelable Internal-Use 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, 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 (“IPR&D”) are required to be tested for impairment at least annually or sooner whenever events or changes in circumstances indicate that the assets may be impaired. The Company has a single reporting unit for goodwill impairment test purposes based on its business and reporting structure. The Company does not amortize goodwill. Acquired IPR&D is capitalized at fair value as an intangible asset and amortization commences upon completion of the underlying projects. When a project underlying reported IPR&D is completed, the corresponding amount of IPR&D is reclassified as an amortizable purchased intangible asset and is amortized over its estimated useful life. Revenue Recognition The Company generates revenue from the sales of its SoCs to OEMs or ODMs, either directly or through logistics providers. Revenue from sales directly to OEMs and ODMs is recognized upon shipment provided that persuasive evidence of an arrangement exists, legal title to the products and risk of ownership have transferred, the fee is fixed or determinable, and collection of the resulting receivable is reasonably assured. The Company provides its logistics providers with the rights to return excess levels of inventory and to future price adjustments. Given the inability to reasonably estimate these price changes and returns, revenue and costs related to shipments to logistics providers are deferred until the Company has received notification from its logistics providers that they have sold the Company’s products. Information reported by the Company’s logistics providers includes product resale price, quantity and end customer shipment information as well as remaining inventory on hand. At the time of shipment to a logistics provider, the Company records a trade receivable as there is a legally enforceable right to receive payment, reduces inventory for the value of goods shipped as legal title has passed to the logistics provider and defers the related margin as deferred revenue in the condensed 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. Revenues from margin sharing arrangements were not material for the three and six months ended July 31, 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 were not material for the three and six months ended July 31, 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. 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. In estimating the Company’s tax positions and tax benefits, the Company considers and evaluates numerous factors, which may require periodic adjustments and which may not reflect the final tax liabilities. The Company adjusts its financial statements to reflect only those tax positions that are more likely than not to be sustained under examination. As part of the process of preparing condensed 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 condensed consolidated balance sheets. In general, deferred tax assets represent future tax benefits to be received when certain expenses previously recognized in the condensed consolidated statements of operations become deductible expenses under applicable income tax laws, or loss or credit carryforwards are utilized. In assessing whether deferred tax assets may be realized, management considers whether it is more likely than not that some portion or all of deferred tax assets will be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income. The Company makes estimates and judgments about its future taxable income based on assumptions that are consistent with its plans and estimates. Should the actual amounts differ from estimates, the amount of valuation allowance could be materially impacted. Any adjustment to the deferred tax asset valuation allowance would be recorded in the condensed 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 potentially dilutive securities had been issued. Potentially dilutive securities include outstanding stock options, shares to be purchased under the Company’s employee stock purchase plan, unvested restricted stock and restricted stock units. The dilutive effect of potentially dilutive securities is reflected in diluted earnings per share by application of the treasury stock method. Comprehensive Income (Loss) Comprehensive income (loss) includes unrealized gains or losses from available-for-sale securities that are excluded from net income. Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”). The new guidance clarifies the principles and develops a common revenue recognition guidance for U.S. GAAP and International Financial Reporting Standards (“IFRS”). Under the new guidance, an entity is required to recognize an amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. This new revenue standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. Subsequently, the FASB issued the following standards related to ASU 2014-09: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (“ASU 2016-08”); ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing (“ASU 2016-10”); ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”); and ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers (“ASU 2016-20”). Accordingly, the Company must adopt ASU 2016-08, ASU 2016-10, ASU 2016-12 and ASU 2016-20 with ASU 2014-09 (collectively, the “new revenue standards”) in its first quarter of fiscal year 2019. The new revenue guidance may be 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 currently anticipates adopting the new guidance using the modified retrospective method. The new guidance also requires additional disclosures about the nature, amount, timing and uncertainty of revenue and considerations arising from customer contracts, including significant judgments and estimates. While the Company is continuing to evaluate all potential impacts of the guidance, the Company expects the most significant impacts will relate to the determination of transaction price and the timing of revenue recognition for transactions with its logistics providers. 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 is currently assessing the impact of the adoption of this new guidance on its financial position, results of operations and disclosures. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), to require entities to show the changes in the total of cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. As a result, entities will no longer present transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. When cash, cash equivalents, restricted cash and restricted cash equivalents are presented in more than one line item on the balance sheet, the new guidance requires a reconciliation of the totals in the statement of cash flows to the related captions in the balance sheet. Entities will also have to disclose the nature of restricted cash and restricted cash equivalent balances. The new guidance will be effective for fiscal years beginning after December 15, 2017, including the interim periods within those years 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.

Financial Instruments and Fair Value

6 Months Ended

Jul. 31, 2017

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 U.S. 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 condensed consolidated balance sheets as follows:

	As of July 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Money market funds	$	10,232	$	—	$	—		$	10,232
Commercial paper		6,980		—		—			6,980
Corporate bonds		48,758		3		(33	)		48,728
Asset-backed securities		13,024		—		(7	)		13,017
U.S. government securities		22,397		—		(45	)		22,352
Total cash equivalents and marketable securities	$	101,391	$	3	$	(85	)	$	101,309

	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
	July 31, 2017		January 31, 2017
	(in thousands)
Included in cash equivalents	$	10,232	$	18,328
Included in marketable securities		91,077		82,522
Total cash equivalents and marketable securities	$	101,309	$	100,850

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

	As of
	July 31, 2017		January 31, 2017
	(in thousands)
Due within one year	$	86,791	$	76,992
Due within one to two years		14,518		23,858
Total cash equivalents and marketable securities	$	101,309	$	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 would 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 July 31, 2017 and January 31, 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 table presents the fair value of the financial instruments measured on a recurring basis as of July 31, 2017 and January 31, 2017:

	As of July 31, 2017
	Total		Level 1		Level 2		Level 3
	(in thousands)
Money market funds	$	10,232	$	10,232	$	—	$	—
Commercial paper		6,980		—		6,980		—
Corporate bonds		48,728		—		48,728		—
Asset-backed securities		13,017		—		13,017		—
U.S. government securities		22,352		—		22,352		—
Total cash equivalents and marketable securities	$	101,309	$	10,232	$	91,077	$	—

	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

6 Months Ended

Jul. 31, 2017

Inventory Disclosure [Abstract]

Inventories

3. Inventories

Inventory at July 31, 2017 and January 31, 2017 consisted of the following:

	As of
	July 31, 2017		January 31, 2017
	(in thousands)
Work-in-progress	$	11,156	$	10,105
Finished goods		6,570		10,040
Total	$	17,726	$	20,145

Property and Equipment, Net

6 Months Ended

Jul. 31, 2017

Property Plant And Equipment [Abstract]

Property and Equipment, Net

4. Property and Equipment, Net

Depreciation expense was approximately $0.5 million and $0.3 million for the three months ended July 31, 2017 and 2016, respectively. Depreciation expense was approximately $0.9 million and $0.8 million for the six months ended July 31, 2017 and 2016, respectively. Property and equipment at July 31, 2017 and January 31, 2017 consisted of the following:

	As of
	July 31, 2017			January 31, 2017
	(in thousands)
Computer equipment and software	$	7,352		$	6,798
Machinery and equipment		3,610			3,405
Furniture and fixtures		829			797
Leasehold improvements		1,625			1,672
Construction in progress		1,372			755
		14,788			13,427
Less: accumulated depreciation and amortization		(9,152	)		(8,439	)
Total property and equipment, net	$	5,636		$	4,988

Intangible Assets	6 Months Ended
Intangible Assets	Jul. 31, 2017
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 $8.9 million of a noncancelable software license. 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 July 31, 2017, there was no IPR&D amortized. During the six months ended July 31, 2017, the Company entered into certain noncancelable software license agreements in which the Company committed to pay an aggregate amount of $10.5 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 July 31, 2017, $3.2 million was recorded in accrued and other current liabilities and $5.9 million was recorded in other long-term liabilities in the condensed consolidated balance sheets. For the three and six months ended July 31, 2017, there was $0.8 million and $1.1 million of amortization expense recorded in the condensed consolidated statements of operations, respectively. There were no intangible asset impairments for the three and six months ended July 31, 2017 and 2016, respectively.

Goodwill	6 Months Ended
Goodwill	Jul. 31, 2017
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 three and six months ended July 31, 2017 and 2016, respectively.

Accrued and Other Current Liabilities

6 Months Ended

Jul. 31, 2017

Payables And Accruals [Abstract]

Accrued and Other Current Liabilities

7. Accrued and Other Current Liabilities

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

	As of
	July 31, 2017		January 31, 2017
	(in thousands)
Accrued employee compensation	$	11,986	$	14,685
Accrued warranty		800		500
Accrued rebates		865		972
Accrued product development costs		1,232		7,605
Software license liabilities, current		3,216		—
Other accrued liabilities		1,807		2,686
Total accrued and other current liabilities	$	19,906	$	26,448

Deferred Revenue and Deferred Cost

6 Months Ended

Jul. 31, 2017

Deferred Revenue Disclosure [Abstract]

Deferred Revenue and Deferred Cost

8. Deferred Revenue and Deferred Cost

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

	As of
	July 31, 2017			January 31, 2017
	(in thousands)
Deferred revenue from product shipments	$	7,573		$	7,725
Deferred revenue from services		1,023			1,748
Deferred cost of revenue from product shipments		(2,393	)		(2,048	)
Total deferred revenue, net	$	6,203		$	7,425

Other Long-Term Liabilities

6 Months Ended

Jul. 31, 2017

Other Liabilities Disclosure [Abstract]

Other Long-Term Liabilities

9. Other Long-Term Liabilities

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

	As of
	July 31, 2017		January 31, 2017
	(in thousands)
Unrecognized tax benefits, including interest	$	1,942	$	1,905
Deferred tax liabilities, non-current		1,333		1,333
Software license liabilities, non-current		5,851		—
Other long-term liabilities		5		3
Total other long-term liabilities	$	9,131	$	3,241

Capital Stock

6 Months Ended

Jul. 31, 2017

Equity [Abstract]

Capital Stock

10. Capital Stock

Preference shares

After completion of the Company’s initial public offering in 2012, a total of 20,000,000 preference shares, with a $0.00045 par value per share, were authorized. There were no preference shares issued and outstanding as of July 31, 2017 and January 31, 2017, respectively.

Ordinary shares

As of July 31, 2017 and January 31, 2017, a total of 200,000,000 ordinary shares were authorized.

On March 30, 2017, the Company added 1,501,606 ordinary shares to the ordinary shares reserved for issuance, pursuant to an “evergreen” provision contained in the 2012 Equity Incentive Plan (“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.

On March 30, 2017, the Company added 417,112 ordinary shares to the ordinary shares reserved for issuance, pursuant to an “evergreen” provision contained in the Amended and Restated 2012 Employee Stock Purchase Plan (“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.

As of July 31, 2017 and January 31, 2017, the following ordinary shares were reserved for future issuance under the EIP and ESPP:

	As of
	July 31, 2017		January 31, 2017
Shares reserved for options, restricted stock and restricted stock units under EIP		6,109,476		5,167,688
Shares reserved for ESPP		1,619,541		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 758,508 shares repurchased during the six months ended July 31, 2017 for approximately $38.7 million in cash. As of July 31, 2017, a total of 1,163,597 shares have been repurchased for approximately $58.9 million in cash and recorded as a reduction to equity. As of July 31, 2017, there was approximately $47.8 million available for repurchases under the repurchase program through June 30, 2018.

Stock-based Compensation

6 Months Ended

Jul. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Stock-based Compensation

11. Stock-based Compensation

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

	Three Months Ended July 31,				Six Months Ended July 31,
	2017		2016		2017		2016
	(in thousands)
Stock-based compensation:
Cost of revenue	$	332	$	246	$	635	$	491
Research and development		8,649		6,873		16,626		13,592
Selling, general and administrative		5,454		4,347		10,146		8,684
Total stock-based compensation	$	14,435	$	11,466	$	27,407	$	22,767

As of July 31, 2017, total unrecognized compensation cost related to unvested stock options was $7.4 million and is expected to be recognized over a weighted-average period of 2.05 years. Total unrecognized compensation cost related to unvested restricted stock units was $98.7 million and is expected to be recognized over a weighted-average period of 2.61 years. Total unrecognized compensation cost related to unvested restricted stock awards was $4.9 million and is expected to be recognized over a weighted-average period of 1.41 years.

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

	Three Months Ended July 31,						Six Months Ended July 31,
	2017			2016			2017			2016
Stock Options:
Volatility		53	%		38	%		53	%		38	%
Risk-free interest rate		1.88	%		1.39	%		2.08	%		1.55	%
Expected term (years)	6.08				6.08		6.07				5.96
Dividend yield		0	%		0	%		0	%		0	%
Employee stock purchase plan awards:
Volatility		—			—			39	%		67	%
Risk-free interest rate		—			—			0.89	%		0.52	%
Expected term (years)		—			—			0.5			0.5
Dividend yield		—			—			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 activity for the six months ended July 31, 2017:

	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, 2017		1,703,524		$	21.66
Granted		72,400			55.69	$	28.84
Exercised		(89,829	)		13.13			$	3,783
Forfeited		(13,818	)		56.69
Expired		(5,495	)		68.57
Outstanding at July 31, 2017		1,666,782			23.15					4.85		$	48,972
Exercisable at July 31, 2017		1,366,052		$	16.81						4.11	$	47,343

The intrinsic value of options outstanding and options 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 on July 31, 2017 was $50.05, 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 period indicated:

				Weighted-
				Average
				Grant-Date
	Shares			Fair Value
Unvested at January 31, 2017		2,175,673		$	56.76
Granted		364,861			56.79
Vested		(506,826	)		45.60
Forfeited		(70,588	)		55.15
Unvested at July 31, 2017		1,963,120		$	59.71

As of July 31, 2017, the aggregate intrinsic value of unvested restricted stock and restricted stock units was $98.3 million.

Net Income Per Ordinary Share

6 Months Ended

Jul. 31, 2017

Earnings Per Share [Abstract]

Net Income Per Ordinary Share

12. Net Income Per Ordinary Share

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

	Three Months Ended July 31,				Six Months Ended July 31,
	2017		2016		2017		2016
	(in thousands, except share and per share data)
Numerator:
Net income	$	3,303	$	8,632	$	5,867	$	10,415
Denominator:
Weighted-average ordinary shares - basic		33,227,717		32,557,398		33,240,767		32,492,723
Effect of potentially dilutive securities:
Employee stock options		984,064		1,074,331		995,107		1,062,310
Restricted stock and restricted stock units		356,253		530,279		389,498		498,128
Employee stock purchase plan		4,893		13,458		3,632		9,942
Weighted-average ordinary shares - diluted		34,572,927		34,175,466		34,629,004		34,063,103
Net income per ordinary share:
Basic	$	0.10	$	0.27	$	0.18	$	0.32
Diluted	$	0.10	$	0.25	$	0.17	$	0.31

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:

	Three Months Ended July 31,				Six Months Ended July 31,
	2017		2016		2017		2016
Options to purchase ordinary shares		271,516		471,534		266,619		476,116
Restricted stock and restricted stock units		796,472		893,341		854,799		1,047,630
Employee stock purchase plan		—		—		12,974		17,191
		1,067,988		1,364,875		1,134,392		1,540,937

Income Taxes

6 Months Ended

Jul. 31, 2017

Income Tax Disclosure [Abstract]

Income Taxes

13. Income Taxes

The following table provides details of income taxes for the periods indicated:

	Three Months Ended July 31,						Six Months Ended July 31,
	2017			2016			2017			2016
	(in thousands)
Income before income taxes	$	5,529		$	9,433		$	8,299		$	10,808
Provision for income taxes		2,226		801				2,432		393
Effective tax rate	40.3		%	8.5		%	29.3		%	3.6		%

The effective tax rate increased for the three and six months ended July 31, 2017 compared to the same periods in the prior fiscal year primarily due to a decrease in the proportion of profits generated in lower tax jurisdictions; and an increase in non-deductible stock-based compensation expense.

The Company files federal and state income tax returns in the United States and in various foreign jurisdictions. The tax years 2012 to 2016 remain open to examination by U.S. federal tax authorities. The tax years 2007 to 2016 remain open to examination by U.S. state tax authorities. The tax years 2011 to 2016 remain open to examination by foreign tax authorities. Fiscal years outside of the normal statute of limitations remain open to audit by tax authorities due to tax attributes generated in those earlier years, which have been carried forward and may be audited in subsequent years when utilized.

The Company regularly assesses the likelihood of adverse outcomes resulting from potential tax examinations to determine the adequacy of its provision for income taxes. These assessments can require considerable estimates and judgments. As of July 31, 2017, the gross amount of unrecognized tax benefits was approximately $41.8 million. If the estimates of income tax liabilities prove to be less than the ultimate assessment, then a further charge to expense could be required. If events occur and the payment of these amounts ultimately proves to be unnecessary, the reversal of the liabilities could result in tax benefits being recognized in the period in which the Company determines the liabilities are no longer necessary. The Company does not anticipate significant changes to its uncertain tax positions during the next twelve months.

Commitments and Contingencies

6 Months Ended

Jul. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Commitments and Contingencies

14. Commitments and Contingencies

The Company leases its principal facilities under operating lease agreements and leases time-based software licenses from time to time. Net operating lease expense for the three months ended July 31, 2017 and 2016 was approximately $1.2 million and $1.9 million, respectively. Net operating lease expense for the six months ended July 31, 2017 and 2016 was approximately $2.9 million and $3.6 million, respectively. Future annual minimum payments under these operating leases with initial lease terms in excess of one year are as follows:

	As of
	July 31, 2017
Fiscal Year	(in thousands)
2018	$	1,483
2019		2,885
2020		2,341
2021		812
2022		247
Total future annual minimum lease payments	$	7,768

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 agreement between the Company and the third-party manufacturers. As of July 31, 2017 and January 31, 2017, total manufacturing purchase commitments were approximately $36.8 million and $23.9 million, respectively, as a result of seasonal fluctuations.

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 in the condensed consolidated balance sheets as of July 31, 2017 and January 31, 2017, respectively.

Segment Reporting

6 Months Ended

Jul. 31, 2017

Segment Reporting [Abstract]

Segment Reporting

15. Segment Reporting

The Company operates in one reportable segment related to the development and sales of low-power, high-definition video products. The Chief Executive Officer of the Company has been identified as the Chief Operating Decision Maker (the “CODM”) and manages the Company’s operations as a whole. 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.

	Three Months Ended July 31,				Six Months Ended July 31,
	2017		2016		2017		2016
	(in thousands)
Taiwan	$	48,052	$	46,803	$	94,468	$	88,905
Asia Pacific		12,291		11,577		24,050		19,163
Europe		6,444		3,282		8,344		8,634
North America other than United States		2,979		1,095		4,984		1,365
United States		1,864		2,385		3,919		4,232
Total revenue	$	71,630	$	65,142	$	135,765	$	122,299

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

Major Customers

For the three and six months ended July 31, 2017, the only customer representing 10% or more of revenue and accounts receivable was Wintech, the Company’s logistics provider, which accounted for approximately 67% and 70% of total revenue, respectively. For the three months ended July 31, 2016, the customers representing 10% or more of revenue and accounts receivable were Wintech and Chicony Electronics Co., Ltd. (“Chicony”), a direct ODM customer, which accounted for approximately 72% and 12% of total revenue, respectively. For the six months ended July 31, 2016, the only customer representing 10% or more of revenue and accounts receivable was Wintech, which accounted for approximately 73% of total revenue. Accounts receivable with Wintech accounted for approximately $23.2 million and $19.3 million as of July 31, 2017 and January 31, 2017, respectively.

Related-Party Transactions	6 Months Ended
Related-Party Transactions	Jul. 31, 2017
Related Party Transactions [Abstract]
Related-Party Transactions	16. Related-Party Transactions The Company considers an entity to be a related party if it owns more than 10% of the Company’s total voting stock at the end of each reporting period or if an officer or employee of an entity also serves on the Company’s board of directors or if it is a significant shareholder and has material business transactions with the Company. The Company 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 $0.9 million and $0.7 million to Cadence for the three months ended July 31, 2017 and 2016, respectively. The Company paid $1.0 million and $1.3 million to Cadence for the six months ended July 31, 2017 and 2016, respectively. License expenses related to these agreements included in research and development expense were approximately $0.8 million and $0.7 million for the three months ended July 31, 2017 and 2016, respectively. License expenses related to these agreements included in research and development expense were approximately $1.6 million and $1.4 million for the six months ended July 31, 2017 and 2016, respectively.

Subsequent Events	6 Months Ended
Subsequent Events	Jul. 31, 2017
Subsequent Events [Abstract]
Subsequent Events	17. Subsequent Events As of September 7, 2017, a total of 59,143 shares have been repurchased for approximately $2.7 million in cash and recorded as a reduction to equity after the balance sheet date. As of September 7, 2017, there was approximately $45.1 million available for repurchases under the repurchase program through June 30, 2018.

Organization and Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jul. 31, 2017
Accounting Policies [Abstract]
Organization	Organization Ambarella, Inc. (the “Company”) was incorporated in the Cayman Islands on January 15, 2004. The Company is a developer of semiconductor processing solutions for video that enable high-definition video capture, sharing, analysis and display. The Company combines its processor design capabilities with its expertise in video and image processing, algorithms and software to provide a technology platform that is designed to be easily scalable across multiple applications and enable rapid and efficient product development. The Company’s system-on-a-chip (“SoC”) designs fully integrate high-definition video processing, image processing, analysis, audio processing and system functions onto a single chip, delivering exceptional video and image quality, differentiated functionality and low power consumption. The Company sells its solutions to leading original design manufacturers (“ODMs”) and original equipment manufacturers (“OEMs”) globally.
Basis of Presentation	Basis of Presentation The accompanying unaudited condensed consolidated financial statements have been prepared by the Company in accordance with the instructions to Form 10-Q pursuant to the rules and regulations of the Securities and Exchange Commission (“SEC”) and, therefore, do not include all information and notes normally provided in audited financial statements. The accounting policies are described in the “Notes to Consolidated Financial Statements” in the Annual Report on Form 10-K for the 2017 fiscal year filed with the SEC on March 30, 2017 (the “Form 10-K”) and updated, as necessary, in this Form 10-Q. The year-end condensed consolidated balance sheet data presented for comparative purposes was derived from audited financial statements, but does not include all disclosures required by generally accepted accounting principles in the United States (“U.S. GAAP”). In the opinion of management, all adjustments (consisting of normal recurring accruals and adjustments) considered necessary for a fair statement have been included. The results of operations for any interim period are not necessarily indicative of, nor comparable to, the results of operations for any other interim period or for a full fiscal year. These unaudited condensed consolidated financial statements should be read in conjunction with the consolidated financial statements and related notes contained in the Form 10-K.
Basis of Consolidation	Basis of Consolidation The Company’s fiscal year ends on January 31. The condensed consolidated financial statements of the Company and its subsidiaries have been prepared in conformity with U.S. GAAP. All intercompany transactions and balances have been eliminated upon consolidation.
Use of Estimates	Use of Estimates The preparation of condensed consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expense during the reported periods. Actual results could differ from those estimates. On an ongoing basis, management evaluates its estimates and assumptions, including those related to (i) the collectibility of accounts receivable; (ii) write down of excess and obsolete inventories; (iii) intangible assets and goodwill; (iv) the estimated useful lives of long-lived assets; (v) impairment of long-lived assets and financial instruments; (vi) warranty obligations; (vii) the valuation of stock-based compensation awards and financial instruments; (viii) the probability of performance objectives achievement; (ix) the realization of tax assets and estimates of tax liabilities, including reserves for uncertain tax positions; and (x) the recognition and disclosure of contingent liabilities. These estimates and assumptions are based on historical experience and on various other factors which the Company believes to be reasonable under the circumstances. The Company may engage third-party valuation specialists to assist with estimates related to the valuation of financial instruments and assets associated with various contractual arrangements. Such estimates often require the selection of appropriate valuation methodologies and significant judgment. Actual results could differ from these estimates under different assumptions or circumstances.
Concentration of Risk	Concentration of Risk The Company’s products are manufactured, assembled and tested by third-party contractors located primarily in Asia. The Company does not have long-term agreements with these contractors. A significant disruption in the operations of one or more of these contractors would impact the production of the Company’s products which could have a material adverse effect on its business, financial condition and results of operations. A substantial portion of the Company’s revenue is derived from sales through its logistics provider, Wintech Microelectronics Co., Ltd., or Wintech, which serves as its non-exclusive sales representative and logistics provider in Asia other than Japan. Termination of the relationship with Wintech could result in a temporary or permanent loss of revenue and result in an obligation to repurchase unsold product. Any Wintech credit issue could impair its ability to make timely payment to the Company. See Note 15 for additional information regarding revenue and credit concentration with this customer. 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 material losses on deposits of its cash. In order to limit the exposure of each investment, 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. The Company does not hold or issue financial instruments for trading purposes. The Company performs ongoing credit evaluations of each of its customers and adjusts credit limits based upon payment history and the customers’ credit worthiness. The Company regularly monitors collections and payments from its customers.
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 marketable securities. The Company classifies these investments as “available-for-sale” securities carried at fair value, based on quoted market prices of similar assets, with the unrealized gains or losses reported, net of tax, as a separate component of shareholders’ equity and included in accumulated other comprehensive income (loss) in the condensed consolidated balance sheets. The amortization of premiums and accretion of discounts and the realized gains and losses are both recorded in other income (loss), net in the condensed consolidated statements of operations. The Company reviews its investments for possible other-than-temporary impairments on a regular basis. If any loss on investment is believed to be other-than-temporary, a charge will be recorded and a new cost basis in the investment will be established. In evaluating whether a loss on a security is other-than-temporary, the Company considers the following factors: 1) general market conditions, 2) the duration and extent to which the fair value is less than cost, 3) the Company’s intent and ability to hold the investment. For securities in an unrealized loss position which is deemed to be other-than-temporary, the difference between the security’s then-current amortized cost basis and fair value is separated into (i) the amount of the impairment related to the credit loss (i.e., the credit loss component) and (ii) the amount of the impairment related to all other factors (i.e., the non-credit loss component). The credit loss component is recognized in earnings. The non-credit loss component is recognized in accumulated other comprehensive income (loss). Due to the relative short term nature of the investments, there have been no other-than-temporary impairments recorded to date.
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 three and six months ended July 31, 2017 and 2016, respectively.
Noncancelable Internal-Use Software License	Noncancelable Internal-Use 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, 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 Goodwill and in-process research and development (“IPR&D”) are required to be tested for impairment at least annually or sooner whenever events or changes in circumstances indicate that the assets may be impaired. The Company has a single reporting unit for goodwill impairment test purposes based on its business and reporting structure. The Company does not amortize goodwill. Acquired IPR&D is capitalized at fair value as an intangible asset and amortization commences upon completion of the underlying projects. When a project underlying reported IPR&D is completed, the corresponding amount of IPR&D is reclassified as an amortizable purchased intangible asset and is amortized over its estimated useful life.
Revenue Recognition	Revenue Recognition The Company generates revenue from the sales of its SoCs to OEMs or ODMs, either directly or through logistics providers. Revenue from sales directly to OEMs and ODMs is recognized upon shipment provided that persuasive evidence of an arrangement exists, legal title to the products and risk of ownership have transferred, the fee is fixed or determinable, and collection of the resulting receivable is reasonably assured. The Company provides its logistics providers with the rights to return excess levels of inventory and to future price adjustments. Given the inability to reasonably estimate these price changes and returns, revenue and costs related to shipments to logistics providers are deferred until the Company has received notification from its logistics providers that they have sold the Company’s products. Information reported by the Company’s logistics providers includes product resale price, quantity and end customer shipment information as well as remaining inventory on hand. At the time of shipment to a logistics provider, the Company records a trade receivable as there is a legally enforceable right to receive payment, reduces inventory for the value of goods shipped as legal title has passed to the logistics provider and defers the related margin as deferred revenue in the condensed 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. Revenues from margin sharing arrangements were not material for the three and six months ended July 31, 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 were not material for the three and six months ended July 31, 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.
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. In estimating the Company’s tax positions and tax benefits, the Company considers and evaluates numerous factors, which may require periodic adjustments and which may not reflect the final tax liabilities. The Company adjusts its financial statements to reflect only those tax positions that are more likely than not to be sustained under examination. As part of the process of preparing condensed 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 condensed consolidated balance sheets. In general, deferred tax assets represent future tax benefits to be received when certain expenses previously recognized in the condensed consolidated statements of operations become deductible expenses under applicable income tax laws, or loss or credit carryforwards are utilized. In assessing whether deferred tax assets may be realized, management considers whether it is more likely than not that some portion or all of deferred tax assets will be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income. The Company makes estimates and judgments about its future taxable income based on assumptions that are consistent with its plans and estimates. Should the actual amounts differ from estimates, the amount of valuation allowance could be materially impacted. Any adjustment to the deferred tax asset valuation allowance would be recorded in the condensed 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 potentially dilutive securities had been issued. Potentially dilutive securities include outstanding stock options, shares to be purchased under the Company’s employee stock purchase plan, unvested restricted stock and restricted stock units. The dilutive effect of potentially dilutive securities is reflected in diluted earnings per share by application of the treasury stock method.
Comprehensive Income (Loss)	Comprehensive Income (Loss) Comprehensive income (loss) includes unrealized gains or losses from available-for-sale securities that are excluded from net income.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) No. 2014-09, Revenue from Contracts with Customers (Topic 606) (“ASU 2014-09”). The new guidance clarifies the principles and develops a common revenue recognition guidance for U.S. GAAP and International Financial Reporting Standards (“IFRS”). Under the new guidance, an entity is required to recognize an amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. This new revenue standard is effective for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2017. Subsequently, the FASB issued the following standards related to ASU 2014-09: ASU No. 2016-08, Revenue from Contracts with Customers (Topic 606): Principal versus Agent Considerations (“ASU 2016-08”); ASU No. 2016-10, Revenue from Contracts with Customers (Topic 606): Identifying Performance Obligations and Licensing (“ASU 2016-10”); ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients (“ASU 2016-12”); and ASU No. 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts with Customers (“ASU 2016-20”). Accordingly, the Company must adopt ASU 2016-08, ASU 2016-10, ASU 2016-12 and ASU 2016-20 with ASU 2014-09 (collectively, the “new revenue standards”) in its first quarter of fiscal year 2019. The new revenue guidance may be 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 currently anticipates adopting the new guidance using the modified retrospective method. The new guidance also requires additional disclosures about the nature, amount, timing and uncertainty of revenue and considerations arising from customer contracts, including significant judgments and estimates. While the Company is continuing to evaluate all potential impacts of the guidance, the Company expects the most significant impacts will relate to the determination of transaction price and the timing of revenue recognition for transactions with its logistics providers. 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 is currently assessing the impact of the adoption of this new guidance on its financial position, results of operations and disclosures. In November 2016, the FASB issued ASU 2016-18, Statement of Cash Flows (Topic 230), to require entities to show the changes in the total of cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. As a result, entities will no longer present transfers between cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. When cash, cash equivalents, restricted cash and restricted cash equivalents are presented in more than one line item on the balance sheet, the new guidance requires a reconciliation of the totals in the statement of cash flows to the related captions in the balance sheet. Entities will also have to disclose the nature of restricted cash and restricted cash equivalent balances. The new guidance will be effective for fiscal years beginning after December 15, 2017, including the interim periods within those years 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.

Financial Instruments and Fair Value (Tables)

6 Months Ended

Jul. 31, 2017

Investments All Other Investments [Abstract]

Schedule of Available-for-Sale Securities at Fair Value

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

	As of July 31, 2017
	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
	(in thousands)
Money market funds	$	10,232	$	—	$	—		$	10,232
Commercial paper		6,980		—		—			6,980
Corporate bonds		48,758		3		(33	)		48,728
Asset-backed securities		13,024		—		(7	)		13,017
U.S. government securities		22,397		—		(45	)		22,352
Total cash equivalents and marketable securities	$	101,391	$	3	$	(85	)	$	101,309

	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
	July 31, 2017		January 31, 2017
	(in thousands)
Included in cash equivalents	$	10,232	$	18,328
Included in marketable securities		91,077		82,522
Total cash equivalents and marketable securities	$	101,309	$	100,850

Summary of Contractual Maturities of Investments

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

	As of
	July 31, 2017		January 31, 2017
	(in thousands)
Due within one year	$	86,791	$	76,992
Due within one to two years		14,518		23,858
Total cash equivalents and marketable securities	$	101,309	$	100,850

Schedule of Fair Value of Financial Instruments Measured on Recurring Basis

The following table presents the fair value of the financial instruments measured on a recurring basis as of July 31, 2017 and January 31, 2017:

	As of July 31, 2017
	Total		Level 1		Level 2		Level 3
	(in thousands)
Money market funds	$	10,232	$	10,232	$	—	$	—
Commercial paper		6,980		—		6,980		—
Corporate bonds		48,728		—		48,728		—
Asset-backed securities		13,017		—		13,017		—
U.S. government securities		22,352		—		22,352		—
Total cash equivalents and marketable securities	$	101,309	$	10,232	$	91,077	$	—

	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)

6 Months Ended

Jul. 31, 2017

Inventory Disclosure [Abstract]

Schedule of Inventory

Inventory at July 31, 2017 and January 31, 2017 consisted of the following:

	As of
	July 31, 2017		January 31, 2017
	(in thousands)
Work-in-progress	$	11,156	$	10,105
Finished goods		6,570		10,040
Total	$	17,726	$	20,145

Property and Equipment, Net (Tables)

6 Months Ended

Jul. 31, 2017

Property Plant And Equipment [Abstract]

Schedule of Property and Equipment

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

	As of
	July 31, 2017			January 31, 2017
	(in thousands)
Computer equipment and software	$	7,352		$	6,798
Machinery and equipment		3,610			3,405
Furniture and fixtures		829			797
Leasehold improvements		1,625			1,672
Construction in progress		1,372			755
		14,788			13,427
Less: accumulated depreciation and amortization		(9,152	)		(8,439	)
Total property and equipment, net	$	5,636		$	4,988

Accrued and Other Current Liabilities (Tables)

6 Months Ended

Jul. 31, 2017

Payables And Accruals [Abstract]

Schedule of Accrued and Other Current Liabilities

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

	As of
	July 31, 2017		January 31, 2017
	(in thousands)
Accrued employee compensation	$	11,986	$	14,685
Accrued warranty		800		500
Accrued rebates		865		972
Accrued product development costs		1,232		7,605
Software license liabilities, current		3,216		—
Other accrued liabilities		1,807		2,686
Total accrued and other current liabilities	$	19,906	$	26,448

Deferred Revenue and Deferred Cost (Tables)

6 Months Ended

Jul. 31, 2017

Deferred Revenue Disclosure [Abstract]

Schedule of Deferred Revenue and Related Cost

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

	As of
	July 31, 2017			January 31, 2017
	(in thousands)
Deferred revenue from product shipments	$	7,573		$	7,725
Deferred revenue from services		1,023			1,748
Deferred cost of revenue from product shipments		(2,393	)		(2,048	)
Total deferred revenue, net	$	6,203		$	7,425

Other Long-Term Liabilities (Tables)

6 Months Ended

Jul. 31, 2017

Other Liabilities Disclosure [Abstract]

Schedule of Other Long-Term Liabilities

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

	As of
	July 31, 2017		January 31, 2017
	(in thousands)
Unrecognized tax benefits, including interest	$	1,942	$	1,905
Deferred tax liabilities, non-current		1,333		1,333
Software license liabilities, non-current		5,851		—
Other long-term liabilities		5		3
Total other long-term liabilities	$	9,131	$	3,241

Capital Stock (Tables)

6 Months Ended

Jul. 31, 2017

Equity [Abstract]

Schedule of Ordinary Shares Reserved for Future Issuance under EIP and ESPP

As of July 31, 2017 and January 31, 2017, the following ordinary shares were reserved for future issuance under the EIP and ESPP:

	As of
	July 31, 2017		January 31, 2017
Shares reserved for options, restricted stock and restricted stock units under EIP		6,109,476		5,167,688
Shares reserved for ESPP		1,619,541		1,252,465

Stock-based Compensation (Tables)

6 Months Ended

Jul. 31, 2017

Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]

Classification of Stock-based Compensation

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

	Three Months Ended July 31,				Six Months Ended July 31,
	2017		2016		2017		2016
	(in thousands)
Stock-based compensation:
Cost of revenue	$	332	$	246	$	635	$	491
Research and development		8,649		6,873		16,626		13,592
Selling, general and administrative		5,454		4,347		10,146		8,684
Total stock-based compensation	$	14,435	$	11,466	$	27,407	$	22,767

Weighted-Average Assumptions Used to Estimate Fair Value

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

	Three Months Ended July 31,						Six Months Ended July 31,
	2017			2016			2017			2016
Stock Options:
Volatility		53	%		38	%		53	%		38	%
Risk-free interest rate		1.88	%		1.39	%		2.08	%		1.55	%
Expected term (years)	6.08				6.08		6.07				5.96
Dividend yield		0	%		0	%		0	%		0	%
Employee stock purchase plan awards:
Volatility		—			—			39	%		67	%
Risk-free interest rate		—			—			0.89	%		0.52	%
Expected term (years)		—			—			0.5			0.5
Dividend yield		—			—			0	%		0	%

Stock Option Activity

The following table summarizes stock option activity for the six months ended July 31, 2017:

	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, 2017		1,703,524		$	21.66
Granted		72,400			55.69	$	28.84
Exercised		(89,829	)		13.13			$	3,783
Forfeited		(13,818	)		56.69
Expired		(5,495	)		68.57
Outstanding at July 31, 2017		1,666,782			23.15					4.85		$	48,972
Exercisable at July 31, 2017		1,366,052		$	16.81						4.11	$	47,343

Restricted Stock and Restricted Stock Units Activities

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

				Weighted-
				Average
				Grant-Date
	Shares			Fair Value
Unvested at January 31, 2017		2,175,673		$	56.76
Granted		364,861			56.79
Vested		(506,826	)		45.60
Forfeited		(70,588	)		55.15
Unvested at July 31, 2017		1,963,120		$	59.71

Net Income Per Ordinary Share (Tables)

6 Months Ended

Jul. 31, 2017

Earnings Per Share [Abstract]

Computation of Basic and Diluted Net Income Per Ordinary Share

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

	Three Months Ended July 31,				Six Months Ended July 31,
	2017		2016		2017		2016
	(in thousands, except share and per share data)
Numerator:
Net income	$	3,303	$	8,632	$	5,867	$	10,415
Denominator:
Weighted-average ordinary shares - basic		33,227,717		32,557,398		33,240,767		32,492,723
Effect of potentially dilutive securities:
Employee stock options		984,064		1,074,331		995,107		1,062,310
Restricted stock and restricted stock units		356,253		530,279		389,498		498,128
Employee stock purchase plan		4,893		13,458		3,632		9,942
Weighted-average ordinary shares - diluted		34,572,927		34,175,466		34,629,004		34,063,103
Net income per ordinary share:
Basic	$	0.10	$	0.27	$	0.18	$	0.32
Diluted	$	0.10	$	0.25	$	0.17	$	0.31

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:

	Three Months Ended July 31,				Six Months Ended July 31,
	2017		2016		2017		2016
Options to purchase ordinary shares		271,516		471,534		266,619		476,116
Restricted stock and restricted stock units		796,472		893,341		854,799		1,047,630
Employee stock purchase plan		—		—		12,974		17,191
		1,067,988		1,364,875		1,134,392		1,540,937

Income Taxes (Tables)

6 Months Ended

Jul. 31, 2017

Income Tax Disclosure [Abstract]

Summary of Income Taxes

The following table provides details of income taxes for the periods indicated:

	Three Months Ended July 31,						Six Months Ended July 31,
	2017			2016			2017			2016
	(in thousands)
Income before income taxes	$	5,529		$	9,433		$	8,299		$	10,808
Provision for income taxes		2,226		801				2,432		393
Effective tax rate	40.3		%	8.5		%	29.3		%	3.6		%

Commitments and Contingencies (Tables)

6 Months Ended

Jul. 31, 2017

Commitments And Contingencies Disclosure [Abstract]

Future Annual Minimum Lease Payments

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

	As of
	July 31, 2017
Fiscal Year	(in thousands)
2018	$	1,483
2019		2,885
2020		2,341
2021		812
2022		247
Total future annual minimum lease payments	$	7,768

Segment Reporting (Tables)

6 Months Ended

Jul. 31, 2017

Segment Reporting [Abstract]

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

	Three Months Ended July 31,				Six Months Ended July 31,
	2017		2016		2017		2016
	(in thousands)
Taiwan	$	48,052	$	46,803	$	94,468	$	88,905
Asia Pacific		12,291		11,577		24,050		19,163
Europe		6,444		3,282		8,344		8,634
North America other than United States		2,979		1,095		4,984		1,365
United States		1,864		2,385		3,919		4,232
Total revenue	$	71,630	$	65,142	$	135,765	$	122,299

Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 101,391	$ 100,920
Unrealized Gains	3	13
Unrealized Losses	(85)	(83)
Fair Value	101,309	100,850
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	10,232	8,328
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	10,232	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	6,980	4,784
Unrealized Gains	0	0
Unrealized Losses	0	0
Fair Value	6,980	4,784
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	48,758	42,713
Unrealized Gains	3	6
Unrealized Losses	(33)	(41)
Fair Value	48,728	42,678
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,024	11,686
Unrealized Gains	0	1
Unrealized Losses	(7)	(12)
Fair Value	13,017	11,675
U.S. government securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	22,397	23,409
Unrealized Gains	0	6
Unrealized Losses	(45)	(30)
Fair Value	$ 22,352	$ 23,385

Financial Instruments and Fair Value - Schedule of Cash Equivalents and Marketable Securities (Detail) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$ 101,309	$ 100,850
Included in cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	10,232	18,328
Included in marketable securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$ 91,077	$ 82,522

Financial Instruments and Fair Value - Summary of Contractual Maturities of Investments (Detail) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Available For Sale Securities Debt Maturities Fair Value [Abstract]
Due within one year	$ 86,791	$ 76,992
Due within one to two years	14,518	23,858
Total cash equivalents and marketable securities	$ 101,309	$ 100,850

Inventories - Schedule of Inventory (Detail) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Inventory Disclosure [Abstract]
Work-in-progress	$ 11,156	$ 10,105
Finished goods	6,570	10,040
Total	$ 17,726	$ 20,145

Property and Equipment, Net - Schedule of Property and Equipment (Detail) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 14,788	$ 13,427
Less: accumulated depreciation and amortization	(9,152)	(8,439)
Total property and equipment, net	5,636	4,988
Computer equipment and software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	7,352	6,798
Machinery and equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	3,610	3,405
Furniture and fixtures [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	829	797
Leasehold improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,625	1,672
Construction in progress [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$ 1,372	$ 755

Intangible Assets - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016	Jun. 25, 2015
Finite Lived Intangible Assets [Line Items]
Committed to make license payment through January 2020			$ 10,500,000
Noncancelable software license, amortization expense	$ 800,000		1,100,000
Impairment of intangible assets	0	$ 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	3,200,000		3,200,000
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	5,900,000		5,900,000
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]
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 license [Member]
Finite Lived Intangible Assets [Line Items]
Intangible assets acquired	$ 8,900,000		$ 8,900,000

Goodwill - Additional Information (Detail) - USD ($)		3 Months Ended		6 Months Ended
Goodwill - Additional Information (Detail) - USD ($)	Jun. 25, 2015	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016	Jan. 31, 2017
Finite Lived Intangible Assets [Line Items]
Goodwill		$ 26,601,000		$ 26,601,000		$ 26,601,000
Goodwill impairment		$ 0	$ 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	Jul. 31, 2017	Jan. 31, 2017
Payables And Accruals [Abstract]
Accrued employee compensation	$ 11,986	$ 14,685
Accrued warranty	800	500
Accrued rebates	865	972
Accrued product development costs	1,232	7,605
Software license liabilities, current	3,216	0
Other accrued liabilities	1,807	2,686
Total accrued and other current liabilities	$ 19,906	$ 26,448

Deferred Revenue and Deferred Cost - Schedule of Deferred Revenue and Related Cost (Detail) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Deferred Revenue Disclosure [Abstract]
Deferred revenue from product shipments	$ 7,573	$ 7,725
Deferred revenue from services	1,023	1,748
Deferred cost of revenue from product shipments	(2,393)	(2,048)
Total deferred revenue, net	$ 6,203	$ 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	Jul. 31, 2017	Jan. 31, 2017
Other Liabilities Disclosure [Abstract]
Unrecognized tax benefits, including interest	$ 1,942	$ 1,905
Deferred tax liabilities, non-current	1,333	1,333
Software license liabilities, non-current	5,851	0
Other long-term liabilities	5	3
Total other long-term liabilities	$ 9,131	$ 3,241

Capital Stock - Additional Information (Detail) - USD ($)				6 Months Ended		14 Months Ended
	May 31, 2017	Mar. 30, 2017	May 31, 2016	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jan. 31, 2017
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				758,508		1,163,597
Stock repurchased during period, cash				$ 38,720,000	$ 20,183,000	$ 58,900,000
Amount available under stock repurchase program				$ 47,800,000		$ 47,800,000
2012 Equity Incentive Plan [Member]
Class Of Stock [Line Items]
Additional ordinary shares reserved for issuance		1,501,606
2012 Equity Incentive Plan [Member] \| Scenario, plan automatically increased by the lessor of [Member]
Class Of Stock [Line Items]
Annual increase in ordinary shares for available for future issuance		3,500,000
Annual shares increase for future issuance by percentage under 2012 equity incentive plan		4.50%
Amended and Restated 2012 Employee Stock Purchase Plan [Member]
Class Of Stock [Line Items]
Additional ordinary shares reserved for issuance		417,112
Amended and Restated 2012 Employee Stock Purchase Plan [Member] \| Scenario, plan automatically increased by the lessor of [Member]
Class Of Stock [Line Items]
Annual increase in ordinary shares for available for future issuance		1,500,000
Annual shares increase for future issuance by percentage under 2012 employee stock purchase plan		1.25%
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 $75.0 Million Authorization [Member] \| Maximum [Member]
Class Of Stock [Line Items]
Amount authorized under stock repurchase program			$ 75,000,000
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
Stock Repurchase Program $50.0 Million Authorization [Member] \| Maximum [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 under EIP and ESPP (Detail) - shares	Jul. 31, 2017	Jan. 31, 2017
EIP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved	6,109,476	5,167,688
ESPP [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved	1,619,541	1,252,465

Stock-based Compensation - Classification of Stock-based Compensation (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Stock-based compensation:
Total stock-based compensation	$ 14,435	$ 11,466	$ 27,407	$ 22,767
Cost of revenue [Member]
Stock-based compensation:
Total stock-based compensation	332	246	635	491
Research and development [Member]
Stock-based compensation:
Total stock-based compensation	8,649	6,873	16,626	13,592
Selling, general and administrative [Member]
Stock-based compensation:
Total stock-based compensation	$ 5,454	$ 4,347	$ 10,146	$ 8,684

Stock-based Compensation - Additional Information (Detail) $ / shares in Units, $ in Millions	6 Months Ended
	Jul. 31, 2017 USD ($) $ / shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Closing price of ordinary shares \| $ / shares	$ 50.05
Stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost, stock options	$ 7.4
Weighted average recognition period	2 years 18 days
Restricted stock units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost, restricted stock units	$ 98.7
Weighted average recognition period	2 years 7 months 10 days
Restricted Stock Awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Weighted average recognition period	1 year 4 months 28 days
Total unrecognized compensation cost, restricted stock awards	$ 4.9
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	$ 98.3

Stock-based Compensation - Weighted-Average Assumptions Used to Estimate Fair Value (Detail)	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility	53.00%	38.00%	53.00%	38.00%
Risk-free interest rate	1.88%	1.39%	2.08%	1.55%
Expected term (years)	6 years 29 days	6 years 29 days	6 years 26 days	5 years 11 months 16 days
Dividend yield	0.00%	0.00%	0.00%	0.00%
Employee stock purchase plan awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility	0.00%	0.00%	39.00%	67.00%
Risk-free interest rate	0.00%	0.00%	0.89%	0.52%
Expected term (years)	0 years	0 years	6 months	6 months
Dividend yield	0.00%	0.00%	0.00%	0.00%

Stock-based Compensation - Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	6 Months Ended
	Jul. 31, 2017 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding \| shares	1,703,524
Shares, Granted \| shares	72,400
Shares, Exercised \| shares	(89,829)
Shares, Forfeited \| shares	(13,818)
Shares, Expired \| shares	(5,495)
Shares, Outstanding \| shares	1,666,782
Shares, Exercisable \| shares	1,366,052
Weighted-Average Exercise Price, Outstanding	$ 21.66
Weighted-Average Exercise Price, Granted	55.69
Weighted-Average Exercise Price, Exercised	13.13
Weighted-Average Exercise Price, Forfeited	56.69
Weighted-Average Exercise Price, Expired	68.57
Weighted-Average Exercise Price, Outstanding	23.15
Weighted-Average Exercise Price, Exercisable	16.81
Weighted-Average Grant-date Fair Value, Granted	$ 28.84
Total Intrinsic Value Of Options Exercised \| $	$ 3,783
Weighted-Average Remaining Contractual Term, Outstanding	4 years 10 months 6 days
Weighted-Average Remaining Contractual Term, Exercisable	4 years 1 month 10 days
Aggregate Intrinsic Value, Outstanding \| $	$ 48,972
Aggregate Intrinsic Value, Exercisable \| $	$ 47,343

Stock-based Compensation - Restricted Stock and Restricted Stock Units Activities (Detail) - Restricted stock and restricted stock units [Member]	6 Months Ended
	Jul. 31, 2017 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Unvested, beginning balance \| shares	2,175,673
Shares, Granted \| shares	364,861
Shares, Vested \| shares	(506,826)
Shares, Forfeited \| shares	(70,588)
Shares, Unvested, ending balance \| shares	1,963,120
Weighted-Average Grant-Date Fair Value, Unvested, beginning balance \| $ / shares	$ 56.76
Weighted-Average Grant-Date Fair Value, Granted \| $ / shares	56.79
Weighted-Average Grant-Date Fair Value, Vested \| $ / shares	45.60
Weighted-Average Grant-Date Fair Value, Forfeited \| $ / shares	55.15
Weighted-Average Grant-Date Fair Value, Unvested, ending balance \| $ / shares	$ 59.71

Net Income Per Ordinary Share - Computation of Basic and Diluted Net Income Per Ordinary Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Numerator:
Net income	$ 3,303	$ 8,632	$ 5,867	$ 10,415
Denominator:
Weighted-average ordinary shares - basic	33,227,717	32,557,398	33,240,767	32,492,723
Effect of potentially dilutive securities:
Employee stock options	984,064	1,074,331	995,107	1,062,310
Restricted stock and restricted stock units	356,253	530,279	389,498	498,128
Employee stock purchase plan	4,893	13,458	3,632	9,942
Weighted-average ordinary shares - diluted	34,572,927	34,175,466	34,629,004	34,063,103
Net income per ordinary share:
Basic	$ 0.10	$ 0.27	$ 0.18	$ 0.32
Diluted	$ 0.10	$ 0.25	$ 0.17	$ 0.31

Net Income Per Ordinary Share - Weighted-Average Potentially Dilutive Securities Excluded from Computation of Diluted Net Income Per Ordinary Share (Detail) - shares	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	1,067,988	1,364,875	1,134,392	1,540,937
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	271,516	471,534	266,619	476,116
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	796,472	893,341	854,799	1,047,630
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	0	0	12,974	17,191

Income Taxes - Summary of Income Taxes (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Income Tax Disclosure [Abstract]
Income before income taxes	$ 5,529	$ 9,433	$ 8,299	$ 10,808
Provision for income taxes	$ 2,226	$ 801	$ 2,432	$ 393
Effective tax rate	40.30%	8.50%	29.30%	3.60%

Income Taxes - Additional Information (Detail) $ in Millions	6 Months Ended
	Jul. 31, 2017 USD ($)
Income Taxes [Line Items]
Unrecognized tax benefits	$ 41.8
U.S. federal tax authorities [Member] \| Earliest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2012
U.S. federal tax authorities [Member] \| Latest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2016
U.S. state tax authorities [Member] \| Earliest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2007
U.S. state tax authorities [Member] \| Latest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2016
Foreign tax authorities [Member] \| Earliest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2011
Foreign tax authorities [Member] \| Latest tax year [Member]
Income Taxes [Line Items]
Income tax examination, year	2016

Commitments and Contingencies - Additional Information (Detail) - USD ($)	3 Months Ended		6 Months Ended		12 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016	Jan. 31, 2017
Loss Contingencies [Line Items]
Net operating lease expense	$ 1,200,000	$ 1,900,000	$ 2,900,000	$ 3,600,000
Total manufacturing purchase commitments	36,800,000		36,800,000		$ 23,900,000
Indemnification agreement [Member]
Loss Contingencies [Line Items]
Payments under indemnification obligations			0		0
Liabilities recorded under indemnification obligations	$ 0		$ 0		$ 0

Commitments and Contingencies - Future Annual Minimum Lease Payments (Detail) $ in Thousands	Jul. 31, 2017 USD ($)
Commitments And Contingencies Disclosure [Abstract]
2018	$ 1,483
2019	2,885
2020	2,341
2021	812
2022	247
Total future annual minimum lease payments	$ 7,768

Segment Reporting - Additional Information (Detail) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017 USD ($)	Jul. 31, 2016	Jul. 31, 2017 USD ($) Segment	Jul. 31, 2016	Jan. 31, 2017 USD ($)
Concentration Risk [Line Items]
Number of reportable segment \| Segment			1
Property and equipment, net	$ 5,636		$ 5,636		$ 4,988
Accounts receivable	38,351		38,351		38,596
Wintech [Member] \| Credit concentration risk [Member]
Concentration Risk [Line Items]
Accounts receivable	$ 23,200		$ 23,200		$ 19,300
Sales revenue, net [Member] \| Wintech [Member] \| Customer concentration risk [Member]
Concentration Risk [Line Items]
Percentage of revenue	67.00%	72.00%	70.00%	73.00%
Sales revenue, net [Member] \| Wintech [Member] \| Customer concentration risk [Member] \| Minimum [Member]
Concentration Risk [Line Items]
Percentage of revenue or accounts receivable	10.00%	10.00%	10.00%	10.00%
Sales revenue, net [Member] \| Chicony [Member] \| Customer concentration risk [Member]
Concentration Risk [Line Items]
Percentage of revenue		12.00%
Sales revenue, net [Member] \| Chicony [Member] \| Customer concentration risk [Member] \| Minimum [Member]
Concentration Risk [Line Items]
Percentage of revenue or accounts receivable		10.00%
Accounts receivable [Member] \| Wintech [Member] \| Credit concentration risk [Member] \| Minimum [Member]
Concentration Risk [Line Items]
Percentage of revenue or accounts receivable	10.00%	10.00%	10.00%	10.00%
Accounts receivable [Member] \| Chicony [Member] \| Credit concentration risk [Member] \| Minimum [Member]
Concentration Risk [Line Items]
Percentage of revenue or accounts receivable		10.00%
United States [Member]
Concentration Risk [Line Items]
Property and equipment, net	$ 2,300		$ 2,300
Asia Pacific [Member]
Concentration Risk [Line Items]
Property and equipment, net	$ 2,400		$ 2,400

Segment Reporting - Company's Revenue by Geographic Region Based on Bill-to Location (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Revenue from External Customer [Line Items]
Total revenue	$ 71,630	$ 65,142	$ 135,765	$ 122,299
Taiwan [Member]
Revenue from External Customer [Line Items]
Total revenue	48,052	46,803	94,468	88,905
Asia Pacific [Member]
Revenue from External Customer [Line Items]
Total revenue	12,291	11,577	24,050	19,163
Europe [Member]
Revenue from External Customer [Line Items]
Total revenue	6,444	3,282	8,344	8,634
North America other than United States [Member]
Revenue from External Customer [Line Items]
Total revenue	2,979	1,095	4,984	1,365
United States [Member]
Revenue from External Customer [Line Items]
Total revenue	$ 1,864	$ 2,385	$ 3,919	$ 4,232

Related-Party Transactions - Additional Information (Detail) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2017	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017	Jul. 31, 2016
Related Party Transaction [Line Items]
Percentage of entity's voting stock owned by related party		10.00%		10.00%
Committed to make license payment through January 2020				$ 10.5
Other Entity [Member]
Related Party Transaction [Line Items]
Committed to make license payment through January 2020	$ 10.3
Payment for license fees		$ 0.9	$ 0.7	1.0	$ 1.3
License expenses included in research and development expense		$ 0.8	$ 0.7	$ 1.6	$ 1.4

Subsequent Events - Additional Information (Detail) - USD ($) $ in Thousands		1 Months Ended	6 Months Ended		14 Months Ended
	May 31, 2017	Sep. 07, 2017	Jul. 31, 2017	Jul. 31, 2016	Jul. 31, 2017
Subsequent Event [Line Items]
Stock repurchased during period, shares			758,508		1,163,597
Stock repurchased during period, cash			$ 38,720	$ 20,183	$ 58,900
Amount available under stock repurchase program			$ 47,800		$ 47,800
Subsequent Event [Member]
Subsequent Event [Line Items]
Stock repurchased during period, shares		59,143
Stock repurchased during period, cash		$ 2,700
Amount available under stock repurchase program		$ 45,100
Stock Repurchase Program $50.0 Million Authorization [Member]
Subsequent Event [Line Items]
Stock repurchase program, expiration date	Jun. 30, 2018

Financial Instruments and Fair Value - Schedule of Fair Value of Financial Instruments Measured on Recurring Basis (Detail) - USD ($) $ in Thousands	Jul. 31, 2017	Jan. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$ 101,309	$ 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	10,232	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	6,980	4,784
Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	48,728	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	13,017	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	22,352	23,385
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	10,232	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	10,232	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	91,077	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	6,980	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	48,728	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	13,017	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	22,352	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