Ambarella (AMBA) 10-K 30 Mar 15 2015 FY Annual report Financial data

Document_and_Entity_Informatio

Document and Entity Information (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Jan. 31, 2015	Jul. 31, 2014
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	FALSE
Document Period End Date	31-Jan-15
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	FY
Trading Symbol	AMBA
Entity Registrant Name	AMBARELLA INC
Entity Central Index Key	1280263
Current Fiscal Year End Date	-30
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding	30,837,529
Entity Public Float		$790

Consolidated_Balance_Sheets

Consolidated Balance Sheets (USD $)	Jan. 31, 2015	Jan. 31, 2014
In Thousands, unless otherwise specified
Current assets:
Cash and cash equivalents	$170,291	$143,394
Marketable securities	37,703
Accounts receivable, net	40,180	18,837
Inventories	21,693	10,452
Restricted cash	8	3
Deferred tax assets, current	1,990	1,599
Prepaid expenses and other current assets	3,506	2,951
Total current assets	275,371	177,236
Property and equipment, net	3,075	3,018
Deferred tax assets, non-current	3,936	1,134
Other assets	1,902	1,919
Total assets	284,284	183,307
Current liabilities:
Accounts payable	21,036	8,321
Accrued liabilities	18,699	11,705
Income taxes payable	748	545
Deferred tax liabilities, current	92
Deferred revenue, current	4,907	4,831
Total current liabilities	45,482	25,402
Deferred revenue, non-current	198
Other long-term liabilities	1,393	1,544
Total liabilities	47,073	26,946
Commitments and contingencies (Note 11)
Shareholders' equity:
Preference shares, $0.00045 par value per share, 20,000,000 shares authorized and no shares issued and outstanding at January 31, 2015 and January 31, 2014, respectively
Ordinary shares, $0.00045 par value per share, 200,000,000 shares authorized at January 31, 2015 and January 31, 2014, respectively; 30,837,529 shares issued and outstanding at January 31, 2015; 28,748,513 shares issued and outstanding at January 31, 2014	14	13
Additional paid-in capital	140,564	110,285
Accumulated other comprehensive income (loss)	-1
Retained earnings	96,634	46,063
Total shareholders’ equity	237,211	156,361
Total liabilities and shareholders' equity	$284,284	$183,307

Consolidated_Balance_Sheets_Pa

Consolidated Balance Sheets (Parenthetical) (USD $)	Jan. 31, 2015	Jan. 31, 2014
Statement Of Financial Position [Abstract]
Preference shares, par value	$0.00	$0.00
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	$0.00	$0.00
Ordinary shares, shares authorized	200,000,000	200,000,000
Ordinary shares, shares issued	30,837,529	28,748,513
Ordinary shares, shares outstanding	30,837,529	28,748,513

Consolidated_Statements_of_Ope

Consolidated Statements of Operations (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Income Statement [Abstract]
Revenue	$218,278	$157,608	$121,066
Cost of revenue	79,142	57,761	40,405
Gross profit	139,136	99,847	80,661
Operating expenses:
Research and development	57,978	48,777	42,829
Selling, general and administrative	29,297	23,153	17,926
Total operating expenses	87,275	71,930	60,755
Income from operations	51,861	27,917	19,906
Other income (loss), net	175	-22	136
Income before income taxes	52,036	27,895	20,042
Provision for income taxes	1,465	2,241	1,854
Net income	$50,571	$25,654	$18,188
Net income per share attributable to ordinary shareholders:
Basic	$1.70	$0.93	$0.64
Diluted	$1.57	$0.85	$0.60
Weighted-average shares used to compute net income per share attributable to ordinary shareholders:
Basic	29,742,653	27,680,778	13,511,646
Diluted	32,278,127	30,172,563	15,016,986

Consolidated_Statements_of_Com

Consolidated Statements of Comprehensive Income (Loss) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Statement Of Income And Comprehensive Income [Abstract]
Net income	$50,571	$25,654	$18,188
Other comprehensive income (loss):
Unrealized gains (losses) on investments	-1
Other comprehensive income (loss), net of tax	-1
Comprehensive income	$50,570	$25,654	$18,188

Consolidated_Statements_of_Red

Consolidated Statements of Redeemable Convertible Preference Shares and Shareholders' Equity (USD $)	Total	Outstanding Ordinary Shares [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Redeemable Convertible Preference Shares [Member]
In Thousands, except Share data
Beginning Balance, Amount at Jan. 31, 2012	$6,449	$3	$4,225		$2,221	$50,900
Beginning Balance, Shares at Jan. 31, 2012		7,600,869				13,315,727
Conversion of redeemable convertible preference shares to ordinary shares, Amount	50,900	6	50,894			-50,900
Conversion of redeemable convertible preference shares to ordinary shares, Shares		13,315,727				-13,315,727
Issuance of shares in connection with initial public offering, net of issuance cost, Amount	30,415	3	30,412
Issuance of shares in connection with initial public offering, net of issuance cost, Shares		5,804,651
Conversion of preference share warrants to ordinary share warrants	110		110
Exercise of stock options, dollar amounts net of unvested stock options exercised early, Amount	950		950
Exercise of stock options, dollar amounts net of unvested stock options exercised early, Shares	313,827	313,827
Vesting of early exercised stock options	314		314
Stock-based compensation expense related to stock awards granted to employees and consultants	4,999		4,999
Excess income tax benefit associated with stock-based compensation	7		7
Net income	18,188				18,188
Ending Balance, Amount at Jan. 31, 2013	112,332	12	91,911		20,409
Ending Balance, Shares at Jan. 31, 2013		27,035,074
Exercise of stock options, dollar amounts net of unvested stock options exercised early, Amount	6,920	1	6,919
Exercise of stock options, dollar amounts net of unvested stock options exercised early, Shares	1,160,286	1,160,286
Vesting of early exercised stock options	143		143
Vesting of restricted stock units, shares		174,888
Employee stock purchase plan, Amount	1,744		1,744
Employee stock purchase plan, Shares		341,973
Exercise of warrants to purchase ordinary shares, Amount	130		130
Exercise of warrants to purchase ordinary shares, shares		36,292
Stock-based compensation expense related to stock awards granted to employees and consultants	8,535		8,535
Excess income tax benefit associated with stock-based compensation	903		903
Net income	25,654				25,654
Ending Balance, Amount at Jan. 31, 2014	156,361	13	110,285		46,063
Ending Balance, Shares at Jan. 31, 2014	28,748,513	28,748,513
Exercise of stock options, dollar amounts net of unvested stock options exercised early, Amount	8,508	1	8,507
Exercise of stock options, dollar amounts net of unvested stock options exercised early, Shares	1,456,944	1,456,944
Vesting of early exercised stock options	59		59
Vesting of restricted stock units, shares		484,296
Employee stock purchase plan, Amount	2,735		2,735
Employee stock purchase plan, Shares		147,776
Stock-based compensation expense related to stock awards granted to employees and consultants	15,692		15,692
Excess income tax benefit associated with stock-based compensation	3,286		3,286
Net unrealized gains (losses) on investments - net of taxes	-1			-1
Net income	50,571				50,571
Ending Balance, Amount at Jan. 31, 2015	$237,211	$14	$140,564	($1)	$96,634
Ending Balance, Shares at Jan. 31, 2015	30,837,529	30,837,529

Consolidated_Statements_of_Cas

Consolidated Statements of Cash Flows (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Cash flows from operating activities:
Net income	$50,571	$25,654	$18,188
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation of property and equipment	1,335	1,096	737
Amortization/accretion of marketable securities	675
Loss on disposal of long-lived assets	21	13	4
Amortization of other intangible assets			270
Stock-based compensation	15,692	8,535	4,999
Excess income tax benefits associated with stock-based compensation	-3,286	-903	7
Other non-cash items, net	26		-149
Changes in operating assets and liabilities:
Accounts receivable	-21,343	1,316	-10,668
Inventories	-11,241	-1,534	-2,132
Prepaid expenses and other current assets	-563	-375	-1,134
Deferred tax assets	-3,193	-433	-871
Other assets	307	63	-443
Accounts payable	12,715	1,270	45
Accrued liabilities	6,686	-2,539	6,656
Income taxes payable	3,490	807	-244
Deferred tax liabilities	92
Deferred revenue	274	1,380	-4,751
Net cash provided by operating activities	52,258	34,350	10,514
Cash flows from investing activities:
Investment in a private company	-290
Purchase of investments	-59,807
Sales of investments	8,729
Maturities of investments	12,668
Net proceeds from disposal of fixed assets		13
Purchase of property and equipment	-1,361	-1,701	-1,528
Restricted Cash			514
Net cash used in investing activities	-40,061	-1,688	-1,014
Cash flows from financing activities:
Proceeds from exercise of stock options, warrants, and employee stock purchase plan, net of repurchase of stock options	11,414	9,360	1,610
Payment for initial public offering cost		-25	-1,950
Proceeds from initial public offering, net of underwriting discounts and commissions			32,390
Excess income tax benefits associated with stock-based compensation	3,286	903
Net cash provided by financing activities	14,700	10,238	32,050
Net increase in cash and cash equivalents	26,897	42,900	41,550
Cash and cash equivalents at beginning of period	143,394	100,494	58,944
Cash and cash equivalents at end of period	170,291	143,394	100,494
Supplemental disclosure of cash flow information:
Cash paid for income taxes	1,069	1,766	3,402
Supplemental disclosure of noncash investing activities:
Increase in accrued liabilities related to non-monetary assets purchases	75	24	122
Supplemental disclosure of noncash financing activities:
Increase in accrued liabilities related to non-monetary financing activities			25
Conversion of redeemable convertible preference shares to ordinary shares			50,900
Conversion of redeemable convertible preference share warrants to ordinary share warrants			$110

Organization_and_Summary_of_Si

Organization and Summary of Significant Accounting Policies	12 Months Ended
	Jan. 31, 2015
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 and display. The Company combines its processor design capabilities with its expertise in video and image processing, algorithms and software to provide a technology platform that is designed to be easily scalable across multiple applications and enable rapid and efficient product development. The Company’s system-on-a-chip, or SoC, designs fully integrate high-definition video processing, image processing, audio processing and system functions onto a single chip, delivering exceptional video and image quality, differentiated functionality and low power consumption.
	The Company sells its solutions to leading original design manufacturers, or ODMs, and original equipment manufacturers, or OEMs, globally.
	In October 2012, in connection with its initial public offering, or IPO, the Company completed the sale of 6,000,000 ordinary shares inclusive of 1,095,349 shares sold by certain shareholders of the Company. In November 2012, a total of 900,000 ordinary shares were sold to the Company’s IPO underwriters in connection with their exercise of the over-allotment option. The public offering price of the shares sold in this offering was $6.00 per share. The total net proceeds from the offering to the Company were approximately $30.4 million after deducting underwriting discounts and commissions and other offering expenses. Upon the completion of the IPO, all 13,315,727 outstanding redeemable convertible preference shares converted into ordinary shares on a one-to-one basis and all outstanding warrants to purchase redeemable convertible preference shares converted into warrants to purchase ordinary shares.
	Basis of Consolidation
	The Company’s fiscal year ends on January 31. The consolidated financial statements of the Company and its subsidiaries have been prepared in conformity with generally accepted accounting principles in the United States (“U.S. GAAP”). All intercompany transactions and balances have been eliminated in consolidation.
	Use of Estimates
	The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expense during the reported periods. Actual results could differ from those estimates.
	On an ongoing basis, management evaluates its estimates and assumptions, including those related to (i) the collectability of accounts receivable; (ii) write down for excess and obsolete inventories; (iii) the estimated useful lives of long-lived assets; (iv) impairment of long-lived assets and financial instruments; (v) warranty obligations; (vi) the valuation of stock-based compensation awards and marketable securities; (vii) the probability of performance objectives achievement; (viii) the realization of tax assets and estimates of tax liabilities, including reserves for uncertain tax positions; and (ix) 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 in Asia other than Japan, and through one large direct ODM customer, Chicony Electronics Co., Ltd., or Chicony. Termination of the relationships with these two customers could result in a temporary or permanent loss of revenue and obligation to repurchase unsold product. Furthermore, any credit issues from these two customers could impair their abilities to make timely payment to the Company. See Note 12 for additional information regarding concentration with these two customers.
	Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities and accounts receivable. The Company maintains its cash primarily in checking and money market accounts with reputable financial institutions. Cash deposits held with these financial institutions may exceed the amount of insurance provided on such deposits. The Company has not experienced any material losses on deposits of its cash. The cash equivalents and marketable securities consist primarily of money market funds, asset-backed securities, commercial paper and debt securities of corporations which management assesses to be high credit quality, in order to limit the exposure of each investment. The Company does not hold or issue financial instruments for trading purposes.
	The Company performs ongoing credit evaluations of each of its customers and adjusts credit limits based upon payment history and the customer’s credit worthiness. The Company regularly monitors collections and payments from its customers.
	Foreign Currency Transactions
	The U.S. dollar is the functional currency for the Company and its subsidiaries. Monetary assets and liabilities denominated in non-U.S. currencies are re-measured to U.S. dollars using current exchange rates in effect at the balance sheet date. Nonmonetary assets and liabilities are re-measured to U.S. dollars using historical exchange rates. Monetary and other accounts are re-measured to U.S. dollars using average exchange rates in effect during each period. Gains or losses from foreign currency re-measurement are included in other income (loss), net in the consolidated statements of operations, and, to date, have not been material.
	Fair Value of Financial Instruments
	The fair value accounting is applied to all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed in the financial statements on a recurring basis. The carrying amounts reflected in the consolidated balance sheets for cash equivalents, accounts receivable, accounts payable, accrued liabilities and other current liabilities, approximate fair value due to the short-term nature.
	Cash, Cash Equivalents and Marketable Securities
	The Company considers all highly liquid investments with original maturities of less than three months at the time of purchase to be cash equivalents. Investments that are highly liquid with original maturities at the time of purchase greater than three months are considered as marketable securities.
	The Company classifies these investments as “available-for-sale” securities carried at fair value, based on quoted market prices of similar assets, with the unrealized gains or losses reported, net of tax, as a separate component of shareholders’ equity and included in accumulated other comprehensive income (loss) in the consolidated balance sheets. The amortization of security premiums and accretion of discounts and the realized gains and losses are both recorded in other income (loss), net in the consolidated statements of operations. The Company reviews its investments for possible other-than-temporary impairments on a regular basis. If any loss on investment is believed to be other-than-temporary, a charge will be recorded and a new cost basis in the investment will be established. In evaluating whether a loss on a security is other-than-temporary, the Company considers the following factors: 1) general market conditions, 2) the duration and extent to which the fair value is less than cost, 3) the Company’s intent and ability to hold the investment.
	For securities in an unrealized loss position which is deemed to be other-than-temporary, the difference between the security’s then-current amortized cost basis and fair value is separated into (i) the amount of the impairment related to the credit loss (i.e., the credit loss component) and (ii) the amount of the impairment related to all other factors (i.e., the non-credit loss component). The credit loss component is recognized in earnings. The non-credit loss component is recognized in accumulated other comprehensive loss. Due to the relative short term nature of the investments, there have been no other-than-temporary impairments recorded to date.
	Trade Accounts Receivable and Allowances for Doubtful Accounts
	Trade accounts receivable are recorded at the invoiced amount and do not include finance charges. The Company performs ongoing credit evaluation of its customers and generally requires no collateral. The Company assesses the need for allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments by considering factors such as historical collection experience, credit quality, aging of the accounts receivable balances and current economic conditions that may affect a customer’s ability to pay. There were no write-offs of accounts receivable for fiscal years 2015, 2014 and 2013, respectively. There was no material allowance for doubtful accounts recorded as of January 31, 2015 and 2014, respectively.
	Inventories
	The Company records inventories at the lower of cost or market. The cost includes materials and other production costs and is computed using standard cost on a first-in, first-out basis. Inventory reserves are recorded for estimated obsolescence or unmarketable inventories based on forecast of future demand and market conditions. If actual market conditions are less favorable than projected, or if future demand for the Company’s products decrease, additional inventory write-downs may be required. Once inventory is written down, a new accounting cost basis has been established and, accordingly, any associated reserve is not reversed until the inventory is sold or scrapped. There have been no material inventory losses recognized to date.
	Property and Equipment
	Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful life of three years for computer equipment, computer software, machinery, equipment and furniture and fixture. Leasehold improvements are amortized over the shorter of the lease term or their estimated useful lives. Repairs and maintenance are charged to expense as incurred.
	Internal-Use Software
	The Company capitalizes certain software that is acquired and developed solely for internal use. The capitalization costs include fees for services provided to develop software during the application development stage, costs incurred to obtain software, and certain costs for employees who are directly associated with and who directly devote time to the project. The capitalization begins when the preliminary project stage is completed and ceases no later than the point at which the project is substantially complete and ready for its intended use after all substantial testing is completed. The internal-use software is amortized over its estimated useful life. Repairs and maintenance are charged to expense as incurred. As of January 31, 2015, the Company has capitalized approximately $1.6 million of internal-use software and has been recorded in property and equipment, net on the consolidated balance sheets.
	Impairment of Long-Lived Assets
	The Company records long-lived assets at cost and evaluates them for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Events or changes in circumstances that may indicate that an asset is impaired include significant decreases in the market value of an asset, significant underperformance relative to expected historical or projected future results of operations, a change in the extent or manner in which an asset is utilized, significant declines in the estimated fair value of the overall Company for a sustained period, shifts in technology, loss of key management or personnel, changes in the Company’s operating model or strategy and competitive forces. When the sum of the expected future undiscounted cash flows expected to be generated by the related asset group is less than its carrying amount, an impairment loss would be recognized. Should impairment exist, the impairment loss would be measured based on the excess of the carrying amount of the asset over the asset’s estimated fair value. There has been no occurrence of events to date that would trigger an impairment analysis. As such, no impairment charge has been recognized as of January 31, 2015.
	Cost Method Investment
	The Company accounts for its investment in a privately held company under the cost method and reports the investment in other assets in the consolidated balance sheets. The Company monitors the carrying value of the investment and records a reduction in carrying value when a decline in value is deemed to be other than temporary. To date, there have been no identified events or changes in circumstances that may have a significant adverse effect on the fair value of this investment and the Company has not recognized any impairment losses related to this investment.
	Revenue Recognition
	The Company generates revenue from the sales of its SoCs to OEMs or ODMs, either directly or through logistics providers. Revenue from sales directly to OEMs and ODMs is recognized upon shipment provided persuasive evidence of an arrangement exists, legal title to the products and risk of ownership have transferred, the fee is fixed or determinable, and collection of the resulting receivable is reasonably assured. The Company provides its logistics providers with the rights to return excess levels of inventory and to future price adjustments. Given the inability to reasonably estimate these price changes and returns, revenue and costs related to shipments to logistics providers are deferred until the Company has received notification from its logistics providers that they have sold the Company’s products. Information reported by the Company’s logistics providers includes product resale price, quantity and end customer shipment information as well as remaining inventory on hand. At the time of shipment to a logistics provider, the Company records a trade receivable as there is a legally enforceable right to receive payment, reduces inventory for the value of goods shipped as legal title has passed to the logistics provider and defers the related margin as deferred revenue in the consolidated balance sheets. Any price adjustments are recorded as a change to deferred revenue at the time the adjustments are agreed upon.
	Arrangements with certain OEM customers provide for pricing that is dependent upon the end products into which the Company’s SoCs are used. These arrangements may also entitle the Company to a share of the product margin ultimately realized by the OEM. The minimum guaranteed amount of revenue related to the sale of products subject to these arrangements is recognized when all other elements of revenue recognition are met. Any amounts at the date of shipment invoiced in excess of the minimum guaranteed contract price are deferred until the additional amounts the Company is entitled to are fixed or determinable. Additional amounts earned by the Company resulting from margin sharing arrangements and determination of the end products into which the products are ultimately incorporated are recognized when end customer sales volume is reported to the Company.
	The Company sells a limited amount of software under perpetual licenses that include post-contract customer support, or PCS. The Company does not have evidence of fair value for the PCS and, accordingly, license revenue is recognized ratably over the estimated supporting period in accordance with ASC 985, Software Revenue Recognition. The Company also enters into development agreements with certain customers. Revenue is deferred for any amounts billed prior to delivery of development services. However, if the Company retains the intellectual property generated from these development agreements, receipts and costs related to these arrangements are included in research and development expense. The revenue from those licenses and services was not material for the fiscal years ended January 31, 2015, 2014 and 2013, respectively.
	Cost of Revenue
	Cost of revenue includes cost of materials, cost associated with packaging and assembly, testing and shipping, cost of personnel, stock-based compensation, logistics and quality assurance, warranty cost, royalty expense, write-downs of inventories and allocation of overhead.
	Warranty Costs
	The Company typically provides warranty on its products. The Company accrues for the estimated warranty costs at the time when revenue is recognized. The warranty accruals are regularly monitored by management based upon historical experience and any specifically identified failures. While the Company engages in extensive product quality assessment, actual product failure rates, material usage or service delivery costs could differ from estimates and revisions to the estimated warranty liability would be required. The Company’s warranty accruals have not been material to date.
	Research and Development
	Research and development costs are expensed as incurred and consist primarily of personnel costs, product development costs, which include engineering services, development software and hardware tools, license fees, cost of fabrication of masks for prototype products, other development materials costs, depreciation of equipment used in research and development and allocation of facilities costs.
	Selling, General and Administrative
	Selling, general and administrative expense consists of personnel costs, travel and trade show costs, legal expenses, other professional services and occupancy costs. Advertising expenses have not been material to date.
	Operating Leases
	The Company recognizes rent expense on a straight-line basis over the term of the lease. The difference between rent expense and rent payment is recorded as deferred rent and is included in accrued liabilities in the consolidated balance sheets.
	Stock-Based Compensation
	The Company measures stock-based compensation for equity awards granted to employees and directors based on the estimated fair value on the grant date, and recognizes that compensation as expense using the straight-line attribution method for service condition awards or using the graded-vesting attribution method for awards with performance conditions over the requisite service period, which is typically the vesting period of each award. The Company estimates the fair value of restricted stock units, or RSUs, based on the fair market value of its ordinary shares on the grant date. The Company uses the Black-Scholes option pricing model to determine the fair value of stock options. Determining the fair value of stock options on the grant date requires the input of various assumptions, including stock price of the underlying ordinary share, the exercise price of the stock option, expected volatility, expected term, risk-free interest rate and dividend rate. The expected term is calculated using the simplified method as prescribed in the guidance provided by the Securities and Exchange Commission, as neither relevant historical experience nor other relevant data are available to estimate future exercise behavior. The expected volatility is based on the historical volatilities of similar companies whose share prices are publicly available for a period commensurate with the expected term. The risk-free interest rate is derived from the average U.S. Treasury constant maturity rates during the respective periods commensurate with the expected term. The expected dividend yield is zero because the Company has not historically paid dividends and has no present intention to pay dividends. The Company uses historical data to estimate pre-vesting award forfeitures and records stock-based compensation only for those awards that are expected to vest. Forfeitures are estimated at the time of grant and revised if necessary in subsequent periods if actual forfeitures differ from estimates.
	The Company recognizes non-employee stock-based compensation expense based on the estimated fair value of the equity instrument. The fair value of the non-employee awards is remeasured at each reporting period until services required under the arrangement are completed, which is the vesting date.
	Prior to the initial public offering, or IPO, the Company engaged an independent appraiser to assist in the valuation of its ordinary share price. The board of directors directed these regular valuations and had input into determining the relevant objective and subjective factors accounted for and relevant approaches in each valuation. After the IPO, the exercise price of stock option awards is determined by the closing price of the Company’s ordinary shares traded on The NASDAQ Global Market on the grant date.
	Income Taxes
	The Company records income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in its financial statements or tax returns. In estimating future tax consequences, generally all expected future events other than enactments or changes in the tax law or rates are considered. Valuation allowances are provided when necessary to reduce deferred tax assets to the amount expected to be realized.
	The Company applies authoritative guidance for the accounting for uncertainty in income taxes. The guidance requires that tax effects of a position be recognized only if it is “more likely than not” to be sustained based solely on its technical merits as of the reporting date. Upon estimating the Company’s tax positions and tax benefits, the Company considered and evaluated numerous factors, which may require periodic adjustments and which may not reflect the final tax liabilities. The Company adjusts its financial statements to reflect only those tax positions that are more likely than not to be sustained under examination.
	As part of the process of preparing consolidated financial statements, the Company is required to estimate its taxes in each of the jurisdictions in which it operates. The Company estimates actual current tax exposure together with assessing temporary differences resulting from differing treatment of items, such as accruals and allowances not currently deductible for tax purposes. These differences result in deferred tax assets, which are included in the consolidated balance sheets. In general, deferred tax assets represent future tax benefits to be received when certain expenses previously recognized in the consolidated statements of operations become deductible expenses under applicable income tax laws, or loss or credit carryforwards are utilized.
	In assessing whether deferred tax assets may be realized, management considers whether it is more likely than not that some portion or all of deferred tax assets will be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income.
	The Company makes estimates and judgments about its future taxable income based on assumptions that are consistent with its plans and estimates. Should the actual amounts differ from estimates, the amount of valuation allowance could be materially impacted. Any adjustment to the deferred tax asset valuation allowance would be recorded in the income statement for the periods in which the adjustment is determined to be required.
	Net Income Per Ordinary Share
	The Company applies the two-class method to calculate and present net income per ordinary share. Under the two-class method, net income is allocated between ordinary shares and other participating securities based on their participating rights. Participating securities are defined as securities that may participate in undistributed earnings with ordinary shares, whether that participation is conditioned upon the occurrence of a specified event or not. Basic net income per ordinary share is computed by dividing net income allocable to ordinary shares by the weighted-average number of ordinary shares outstanding for the period. Diluted net income per ordinary share is computed by dividing net income allocable to ordinary shares and income allocable to participating securities, to the extent they are dilutive, by the weighted-average number of ordinary shares outstanding, including the dilutive effects of participating securities on an if-converted basis plus the dilutive effects of ordinary shares. The Company’s potential dilutive ordinary share equivalents consist of incremental ordinary shares issuable upon the exercise of options, upon the issuance of shares pursuant to the Employee Stock Purchase Plan, or ESPP, upon release of vested restricted stock units, upon conversion of its redeemable convertible preference shares and upon exercise of warrants.
	The Company performs an assessment as to whether instruments granted in stock-based payment transactions are participating securities. Stock-based payment awards that have not yet vested meet the definition of a participating security provided the right to receive the dividend is non-forfeitable and non-contingent. These participating securities should be included in the computation of basic net income per ordinary share under the two-class method. The Company has concluded that its non-vested early-exercised options meet the definition of a participating security and should be included in the computation of basic net income per ordinary share.
	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 ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606). The new guidance clarifies the principles and develops a common revenue recognition guidance for U.S. GAAP and International Financial Reporting Standards (the “IFRS”). Under the new guidance, an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this core principle, an entity shall identify the contract(s) with a customer, identify the performance obligations in the contract, determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the entity satisfies a performance obligation. The new guidance is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. Early adoption is not permitted. The new revenue guidance may be applied retrospectively to each prior period presented or retrospectively with the cumulative effect recognized as of the date of adoption. The Company is currently evaluating the impact of adoption on its financial position, results of operations and disclosures.
In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. In connection with each annual and interim period, management is required to assess whether there is substantial doubt about an entity’s ability to continue as a going concern within one year after the issuance date, and to provide related footnote disclosures in certain circumstances. The new guidance is effective for annual periods ending after December 15, 2016, and interim periods within annual periods beginning after December 15, 2016. Early adoption is permitted. This ASU is not expected to have an impact on the Company’s financial statements or disclosures.

Financial_Instruments_and_Fair

Financial Instruments and Fair Value	12 Months Ended
	Jan. 31, 2015
Investments All Other Investments [Abstract]
Financial Instruments and Fair Value	2. Financial Instruments and Fair Value
	Beginning in fiscal year 2015, the Company invested a portion of its cash in marketable securities that are denominated in United States dollars. The investment portfolio consists of money market funds, asset-backed securities, commercial paper and debt securities of corporations. All of the investments are classified as available-for-sale securities and reported at fair value in the consolidated balance sheets as follows:
		As of January 31, 2015
		Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
		(in thousands)
	Money market funds	$	2,427	$	—	$	—		$	2,427
	Commercial paper		1,497		—		—			1,497
	Corporate bonds		32,356		9		(10	)		32,355
	Asset-backed securities		3,851		—		—			3,851
	Total cash equivalents and marketable securities	$	40,131	$	9	$	(10	)	$	40,130
		As of
		31-Jan-15
		(in thousands)
	Included in cash equivalents	$	2,427
	Included in marketable securities		37,703
	Total cash equivalents and marketable securities	$	40,130
	The contractual maturities of the investments at January 31, 2015 were as follows:
		As of
		31-Jan-15
		(in thousands)
	Due within one year	$	37,559
	Due within one to two years		2,571
	Total cash equivalents and marketable securities	$	40,130
	The unrealized losses on the available-for-sale securities were caused by fluctuations in market value and interest rates as a result of the economic environment. As the decline in market value was attributable to changes in market conditions and not credit quality, and because the Company neither intended to sell nor was it more likely than not that it will be required to sell these investments prior to a recovery of par value, the Company did not consider these investments to be other-than temporarily impaired as of January 31, 2015.
	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 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 asserts in active markets, or model driven valuations using significant inputs derived from or corroborated by observable market data and are classified within Level 2.
	The following table presents the fair value of the financial instruments measured on a recurring basis as of January 31, 2015:
		Total		Level 1		Level 2			Level 3
		(in thousands)
	Money market funds	$	2,427	$	2,427	$	—		$	—
	Commercial paper		1,497		—		1,497			—
	Corporate bonds		32,355		—		32,355			—
	Asset-backed securities		3,851		—		3,851			—
	Total cash equivalents and marketable securities	$	40,130	$	2,427	$	37,703		$	—

Inventories

Inventories	12 Months Ended
	Jan. 31, 2015
Inventory Disclosure [Abstract]
Inventories	3. Inventories
	Inventories at January 31, 2015 and 2014 consisted of the following:
		As of January 31,
		2015		2014
		(in thousands)
	Work-in-progress	$	13,805	$	5,119
	Finished goods		7,888		5,333
	Total	$	21,693	$	10,452

Property_and_Equipment_Net

Property and Equipment, Net	12 Months Ended
	Jan. 31, 2015
Property Plant And Equipment [Abstract]
Property and Equipment, Net	4. Property and Equipment, net
	Depreciation expense was approximately $1.3 million, $1.1 million and $0.7 million for the years ended January 31, 2015, 2014 and 2013, respectively. Property and equipment at January 31, 2015 and 2014 consisted of the following:
		As of January 31,
		2015			2014
		(in thousands)
	Computer equipment and software	$	5,310		$	4,521
	Machinery and equipment		2,234			2,114
	Furniture and fixtures		456			411
	Leasehold improvements		1,215			1,198
	Construction in progress		64			—
			9,279			8,244
	Less: accumulated depreciation and amortization		(6,204	)		(5,226	)
	Total property and equipment, net	$	3,075		$	3,018
	In March 2013, the Company entered into a lease agreement of approximately 35,000 square feet for its new headquarters located in Santa Clara, California with an initial five-year term. Pursuant to the lease agreement, the Company agreed to pay certain construction costs. As of January 31, 2014, the Company had capitalized approximately $0.7 million of leasehold improvements as a result of the construction, which is being depreciated over the term of the lease.
	In August 2012, the Company began implementation of its enterprise resources planning (“ERP”) system. As of January 31, 2015, the Company capitalized approximately $1.6 million of internal-use software related to the ERP implementation project and amortized over an estimated economic useful life of three years under a straight-line method.

Accrued_Liabilities

Accrued Liabilities	12 Months Ended
	Jan. 31, 2015
Payables And Accruals [Abstract]
Accrued Liabilities	5. Accrued Liabilities
	Accrued liabilities at January 31, 2015 and 2014 consisted of the following:
		As of January 31,
		2015		2014
		(in thousands)
	Accrued employee compensation	$	11,318	$	8,108
	Accrued warranty		203		269
	Accrued rebates		254		270
	Accrued product development costs		5,004		1,904
	Other accrued liabilities		1,920		1,154
	Total accrued liabilities	$	18,699	$	11,705

Deferred_Revenue_and_Deferred_

Deferred Revenue and Deferred Cost	12 Months Ended
	Jan. 31, 2015
Deferred Revenue Disclosure [Abstract]
Deferred Revenue and Deferred Cost	6. Deferred Revenue and Deferred Cost
	Deferred revenue and related cost at January 31, 2015 and 2014 consisted of the following:
		As of January 31,
		2015			2014
		(in thousands)
	Deferred revenue on product shipments	$	4,663		$	5,174
	Deferred revenue from licenses & services		1,610			1,023
	Deferred cost of revenue on product shipments		(1,168	)		(1,366	)
	Total deferred revenue, net	$	5,105		$	4,831

Capital_Stock

Capital Stock	12 Months Ended
	Jan. 31, 2015
Capital [Abstract]
Capital Stock	7. Capital Stock
	Initial Public Offering
	In October 2012, in connection with its initial public offering, or IPO, the Company completed the sale of 6,000,000 ordinary shares inclusive of 1,095,349 shares sold by certain shareholders of the Company. In November 2012, a total of 900,000 ordinary shares were sold to the Company’s IPO underwriters in connection with their exercise of over-allotment option. The public offering price of the shares sold in this offering was $6.00 per share. The total net proceeds from the offering to the Company were approximately $30.4 million after deducting underwriting discounts and commissions and other offering expenses. Upon the completion of the IPO, all 13,315,727 outstanding redeemable convertible preference shares converted into ordinary shares on a one-to-one basis and all outstanding warrants to purchase redeemable convertible preference shares converted into warrants to purchase ordinary shares.
	Preference shares
	After completion of the IPO, a total of 20,000,000 preference shares, with a $0.00045 par value per share, were authorized. There were no shares issued and outstanding as of January 31, 2015 and 2014, respectively.
	Warrants
	In connection with a financing agreement in 2004, the Company issued warrants to purchase 36,292 redeemable convertible preference shares at an exercise price of $3.582 per share.
	Prior to the closing of IPO, the Company utilized the Black-Scholes option pricing model to determine the fair value of the warrants, including the consideration of underlying ordinary share price, a risk-free interest rate, expected term and expected volatilities. Certain inputs used in the model were unobservable. As a result, the valuation of warrants was categorized as Level 3 in accordance with ASC 820, Fair Value Measurement. The warrants were revalued up to the closing of IPO and any change in fair value had been recorded in other income (loss).
	Upon the completion of the IPO, the warrants to purchase redeemable convertible preference shares converted to warrants to purchase ordinary shares. As a result, $110,000 of aggregate fair market value was reclassified from liabilities to shareholders’ equity. As of January 31, 2014, the warrants were fully exercised and were no longer outstanding.
	Ordinary shares
	200,000,000 ordinary shares were authorized at January 31, 2015 and 2014, respectively. As of January 31, 2015 and 2014, the following ordinary shares were reserved for future issuance:
		As of January 31,
		2015		2014
	Shares reserved for options and restricted stock units		5,055,845		5,699,530
	Shares reserved for employee stock purchase plan		667,990		456,410

Employee_Benefits_and_Stockbas

Employee Benefits and Stock-based Compensation	12 Months Ended
	Jan. 31, 2015
Postemployment Benefits [Abstract]
Employee Benefits and Stock-based Compensation	8. Employee Benefits and Stock-based Compensation
	401(k) Plan
	The Company maintains a defined contribution 401(k) plan (the “401(k) Plan”) for all of its eligible U.S. employees. Under the 401(k) Plan, eligible employees may contribute up to the Internal Revenue Service annual contribution limitation. The Company is responsible for administrative costs of the Plan. The Company has not had any matching contributions to date.
	Stock Option Plans
	2004 Stock Plan. The board of directors adopted, and the shareholders approved, the 2004 Stock Plan, as amended, (the “2004 Plan”). The 2004 Plan was last amended on August 28, 2012. The 2004 Plan provides for the grant of incentive stock options (“ISOs”) within the meaning of Section 422 of the Internal Revenue Code of 1986, as amended (the “Code”), nonstatutory stock options (“NSOs”), stock purchase rights to acquire restricted stock and restricted stock units. Upon the completion of the IPO, no additional awards will be granted under the 2004 Plan and the 2004 Plan was terminated. However, all outstanding stock options and other awards previously granted under the 2004 Plan will remain subject to the terms of the 2004 Plan.
	2012 Equity Incentive Plan. The board of directors adopted, and the shareholders approved, the 2012 Equity Incentive Plan, (the “EIP”). The EIP became effective on October 8, 2012. The EIP permits the grant of ISOs, within the meaning of Section 422 of the Code, to employees of the Company and any of the Company’s subsidiary corporations, and the grant of NSOs, stock appreciation rights, restricted stock, restricted stock units, performance units, performance shares, deferred stock units and dividend equivalents to employees, directors and consultants of the Company and any of the Company’s subsidiary corporations’ employees and consultants.
	The exercise price of ISOs granted to a holder of more than 10% of the voting power of all classes of the Company’s shares shall be no less than 110% of fair market value on the grant date. The exercise price of ISOs granted to other employees and NSOs shall be no less than 100% of fair market value on the grant date. Options granted under the Plan have a term of up to 10 years from grant date. Options granted to new employees generally vest 25% on the first anniversary service date of the grant and remainder vest ratably over the following 36 months. Vesting schedules for other option grants vary and are subject to approval by the board of directors.
	Restricted stock units, or RSUs, granted to new employees generally vest as to 1/4th of the shares on the first anniversary service date of the grant and 1/16th of the RSUs vest every 3 months thereafter, so as to be 100% vested on the fourth anniversary of the vesting commencement date. Vesting schedules for other service and performance condition awards vary and are subject to approval by the board of directors; provided that the performance RSUs shall not vest at all until the performance conditions are achieved and are subject to the RSU holder continuing to provide services to the Company through such vesting dates. The performance condition RSUs are automatically forfeited in their entirety, without any cost to or action by the Company, if there has been no achievement of the performance.
	On February 1, 2014, the Company added 1,297,555 ordinary shares to the ordinary shares reserved for issuance, pursuant to an “evergreen” provision contained in the EIP. Pursuant to such provision, on February 1st of each fiscal year, the number of ordinary shares reserved for issuance under the EIP is automatically increased by a number equal to the lesser of (i) 3,500,000 ordinary shares, (ii) four and one half percent (4.5%) of the aggregate number of ordinary shares outstanding on January 31st of the preceding fiscal year, or (iii) a lesser number of shares that may be determined by the Company’s Board of Directors.
	2012 Employee Stock Purchase Plan. The board of directors adopted, and the shareholders approved, the 2012 Employee Stock Purchase Plan, or ESPP, which became effective upon the completion of IPO. The ESPP permits eligible participants to purchase ordinary shares at a discount through contributions of up to 10% of their eligible compensation, subject to any IRS limitations. The ESPP provides for offering and purchase periods of six months in duration. The purchase price of ordinary shares is 85% of the lower of the closing market price of the Company’s ordinary shares on the first trading day of each offering period or on the purchase date.
	On February 1, 2014, the Company added 359,356 ordinary shares to the ordinary shares reserved for issuance, pursuant to an “evergreen” provision contained in the ESPP. Pursuant to such provision, on February 1st of each fiscal year, the number of ordinary shares reserved for issuance under the ESPP is automatically increased by a number equal to the lesser of (i) 1,500,000 ordinary shares, (ii) one and one quarter percent (1.25%) of the aggregate number of ordinary shares outstanding on such date, or (iii) an amount determined by the Company’s Board of Directors or a duly authorized committee of the Board of Directors.
	Early Exercise Rights. Certain employees have the rights to early exercise unvested options, subject to repurchase rights held by the Company at their original purchase price upon termination of employment until vested. As of January 31, 2015 and 2014, a total of 86,925 and 86,340 shares of unvested early exercised options were repurchased, respectively. The unvested early exercised shares subject to the Company’s repurchase rights were not material as of January 31, 2015.
	Stock-based Compensation
	The following table presents the classification of stock-based compensation for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
		(in thousands)
	Stock-based compensation:
	Cost of revenue	$	343		$	178		$	92
	Research and development		8,654			4,887			2,942
	Selling, general and administrative		6,695			3,470			1,965
	Total stock-based compensation	$	15,692		$	8,535		$	4,999
	As of January 31, 2015, total unrecognized compensation cost related to unvested stock options and unvested restricted stock units was $10.3 million and $48.7 million, respectively, and is expected to be recognized over a weighted-average period of 2.39 years and 2.90 years, respectively.
	The following table sets forth the weighted-average assumptions used to estimate the fair value of the stock options and employee stock purchase plan awards for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
	Stock Options:
	Volatility		64	%		65	%		66	%
	Risk-free interest rate		1.93	%		1.55	%		0.91	%
	Expected term (years)	6.01				6.06			6.05
	Dividend yield		0	%		0	%		0	%
	Employee stock purchase plan awards:
	Volatility		49	%		52	%		51	%
	Risk-free interest rate		0.07	%		0.04	%		0.18	%
	Expected term (years)		0.5			0.5			0.94
	Dividend yield		0	%		0	%		0	%
	The following table summarizes stock option activities for the periods indicated:
		Option Outstanding
													Weighted-
											Total Intrinsic		Average
								Weighted-			Value of		Remaining		Aggregate
					Weighted-			Average			options		Contactual		Intrinsic
					Average			Grant-date			Exercised		Term		Value
		Shares			Exercise Price			Fair Value			(in thousands)		(in years)		(in thousands)
	Outstanding at January 31, 2012		4,375,906		$	5.63
	Granted		451,071			8.79		$	5.23
	Exercised		(313,827	)		3.21					$	2,087
	Forfeited		(168,615	)		7.22
	Outstanding at January 31, 2013		4,344,535			6.07
	Granted		255,520			18.14		$	10.85
	Exercised		(1,160,286	)		5.96					$	18,217
	Forfeited		(81,063	)		10.34
	Outstanding at January 31, 2014		3,358,706			6.92
	Granted		428,781			36.33		$	21.37
	Exercised		(1,456,944	)		5.84					$	46,427
	Forfeited		(48,634	)		13.38
	Outstanding at January 31, 2015		2,281,909		$	13							6.35		$	96,547
	Exercisable at January 31, 2015		1,553,901		$	7.22								5.3	$	74,735
	Vested and expected to vest at January 31, 2015		2,239,650		$	12.68								6.3	$	95,482
	Exercisable shares include options with early exercise rights. The vested and expected-to-vest options are calculated based on vesting schedule of each grant as of the reporting date.
	The intrinsic value of options outstanding, exercisable and expected-to-vest options are calculated based on the difference between the fair market value of the Company’s ordinary shares on the reporting date and the exercise price. The closing price of the Company’s ordinary shares was $55.31 on January 31, 2015, 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 units activities for the periods indicated:
					Weighted-
					Average
				Grant-Date
	Shares			Fair Value
Unvested at January 31, 2012		—		$	—
Granted		345,171			9.99
Vested		—			—
Forfeited		(5,954	)		9.99
Unvested at January 31, 2013		339,217			9.99
Granted		1,265,472			14.78
Vested		(174,888	)		11.91
Forfeited		(19,712	)		11.97
Unvested at January 31, 2014		1,410,089			14.02
Granted		1,111,204			38.6
Vested		(484,296	)		17.39
Forfeited		(56,549	)		19.93
Unvested at January 31, 2015		1,980,448		$	26.82
As of January 31, 2015, the aggregate intrinsic value of unvested restricted stock units was $109.5 million.
Non-employee Stock-based Compensation
The fair value of awards granted to non-employees is determined on the grant date and remeasured at the end of each reporting period until such awards vest. The non-employee stock-based compensation was not material for the years ended January 31, 2015, 2014 and 2013, respectively.

Net_Income_Per_Ordinary_Share

Net Income Per Ordinary Share	12 Months Ended
	Jan. 31, 2015
Earnings Per Share [Abstract]
Net Income Per Ordinary Share	9. Net Income Per Ordinary Share
	The following table sets forth the computation of basic and diluted net income per ordinary share for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
		(in thousands, except share and per share data)
	Numerator:
	Net income	$	50,571		$	25,654		$	18,188
	Less: amount allocable to preference shareholders		—			—			(9,517	)
	Less: amount allocable to unvested early exercised options		(11	)		(31	)		(61	)
	Net income allocable to ordinary shareholders - basic	$	50,560		$	25,623		$	8,610
	Undistributed earnings reallocated to ordinary shareholders		1			2			432
	Net income allocable to ordinary shareholders - diluted	$	50,561		$	25,625		$	9,042
	Denominator:
	Weighted-average ordinary shares outstanding		29,749,354			27,713,998			13,599,273
	Less: weighted-average unvested early exercised options		(6,701	)		(33,220	)		(87,627	)
	subject to repurchase
	Weighted-average ordinary shares - basic		29,742,653			27,680,778			13,511,646
	Effect of potentially dilutive securities:
	Employee stock options		1,818,401			2,034,500			1,443,809
	Restricted stock units		704,788			316,350			16,930
	Employee stock purchase plan		12,285			138,461			27,230
	Warrants to purchase ordinary shares		—			2,474			6,737
	Over-allotment shares		—			—			10,634
	Weighted-average ordinary shares - diluted		32,278,127			30,172,563			15,016,986
	Net income per ordinary share:
	Basic	$	1.7		$	0.93		$	0.64
	Diluted	$	1.57		$	0.85		$	0.6
	Earnings per share (EPS) of ordinary shares was calculated using the two-class method required for participating securities. Prior to the date of the IPO, all series of redeemable convertible preference shares were considered to be participating securities due to their non-cumulative dividend rights. In connection with the Company’s IPO in October 2012, all outstanding redeemable convertible preference shares converted to ordinary shares. Net income has been allocated to the ordinary shares, redeemable convertible preference shares and unvested early exercised options based on their respective rights to share in net income and weighted-average outstanding during the periods.
	The following weighted-average potentially dilutive securities were excluded from the computation of diluted net income per ordinary share as their effect would have been antidilutive:
		Year Ended January 31,
		2015			2014			2013
	Options to purchase ordinary shares		217,514			183,859			2,053,520
	Restricted stock units		167,702			1,576			60,504
	Employee stock purchase plan		36,110			10,597			20,356
	Early exercised options subject to repurchase		6,701			33,220			87,627
	Redeemable convertible preference shares		—			—			9,131,824
	(if-converted basis)
	Warrants to purchase ordinary shares		—			—			24,889
			428,027			229,252			11,378,720

Income_Taxes

Income Taxes	12 Months Ended
	Jan. 31, 2015
Income Tax Disclosure [Abstract]
Income Taxes	10. Income Taxes
	Income before income taxes consisted of the following for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
		(in thousands)
	U.S. operations	$	1,978		$	1,990		$	3,264
	Non-U.S. operations		50,058			25,905			16,778
	Income before income taxes	$	52,036		$	27,895		$	20,042
	Income tax provision consisted of the following for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
		(in thousands)
	Current:
	U.S. federal tax	$	3,135		$	1,738		$	2,022
	U.S. state taxes		93			23			5
	Non-U.S. foreign taxes		1,348			1,058			701
			4,576			2,819			2,728
	Deferred:
	U.S. federal tax		(3,208	)		(952	)		(743	)
	U.S. state taxes		—			341			(109	)
	Non-U.S. foreign taxes		97			33			(22	)
			(3,111	)		(578	)		(874	)
	Provision for income taxes	$	1,465		$	2,241		$	1,854
	Income tax provision differed from the amounts computed by applying the U.S. federal income tax rate of 34% to pretax income as a result of the following for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
		(in thousands)
	U.S. federal tax at statutory rate	$	17,692		$	9,484		$	6,814
	U.S. state taxes		90			361			(107	)
	Non-U.S. foreign tax differential		(15,644	)		(7,674	)		(4,513	)
	Stock-based compensation		1,601			927			682
	U.S. R&D credit		(2,298	)		(858	)		(890	)
	Other		24			1			(132	)
	Provision for income taxes	$	1,465		$	2,241		$	1,854
	Temporary differences that gave rise to significant portions of the Company’s deferred tax assets and liabilities at January 31, 2015 and 2014 were as follows:
		As of January 31,
		2015			2014
		(in thousands)
	Deferred tax assets:
	Federal and state credits	$	6,465		$	2,587
	Expenses not currently deductible		1,590			1,149
	Foreign deferred		—			26
	Stock-based compensation		2,044			1,460
	Gross deferred tax assets		10,099			5,222
	Valuation allowance		(3,996	)		(2,302	)
	Total deferred tax assets	$	6,103		$	2,920
	Deferred tax liabilities
	Property and equipment		(199	)		(187	)
	Foreign deferred		(70	)		—
	Net deferred tax assets	$	5,834		$	2,733
	Tax valuation allowance for the periods indicated below were as follows:
											Deductions
								Additions			Charged to
		Balance at			Additional			Charged to			Expenses			Balance at
		Beginning of			Charged to			Other			or Other			End of
		Period			Expenses			Account			Accounts			Period
		(in thousands)
	Tax Valuation Allowance
	Year ended January 31, 2015	$	2,302			1,694			—			—		$	3,996
	Year ended January 31, 2014	$	1,243			1,059			—			—		$	2,302
	Year ended January 31, 2013	$	1,301			—			—			(58	)	$	1,243
	The Company conducts its business in several countries and regions and is subject to taxation in those jurisdictions. The Company is incorporated in the Cayman Islands with foreign subsidiaries in the U.S., China, Taiwan, and other foreign countries and regions. As such, the Company’s worldwide operating income is subject to varying tax rates and its effective tax rate is highly dependent upon the geographic distribution of its earnings or losses and the tax laws and regulations in each geographical region. Consequently, the Company has experienced lower effective tax rates as a substantial amount of its operations are conducted in lower-tax jurisdictions. If the Company’s operational structure was to change in such a manner that would increase the amount of operating income subject to taxation in higher-tax jurisdictions, or if the Company was to commence operations in jurisdictions assessing relatively higher tax rates, its effective tax rate could fluctuate significantly on a quarterly basis and/or be adversely affected. Dividend distributions received from the Company’s U.S. subsidiary and certain other foreign subsidiaries may be subject to local country withholding taxes when, and if, distributed. Deferred tax liabilities have not been recorded on unremitted earnings of certain subsidiaries because management’s intent is to indefinitely reinvest any undistributed earnings in those subsidiaries. If dividend distributions from those subsidiaries were to occur, the liability as of January 31, 2015 would be $28.6 million. Cumulative undistributed earnings of foreign subsidiaries for which no deferred taxes have been provided approximated $4.1 million at January 31, 2015.
	As of January 31, 2015 and 2014, the Company had deferred tax assets (net of deferred tax liabilities) before valuation allowance, of $9.8 million and $5.0 million, respectively. Realization of the deferred tax assets is dependent upon future taxable income, if any, the amount and timing of which are uncertain.
	The Company has Federal and California state research and development credit carryforwards of approximately $2.6 million and $5.9 million, respectively, at January 31, 2015. The Federal credits begin to expire in fiscal year 2034. The California credits can be carried forward indefinitely.
The Company reports its U.S. state deferred tax assets and related valuation allowance, net of the U.S federal tax rate of 34%. As of January 31, 2015, the Company has no valuation allowance other than state deferred tax assets as the Company has sufficient positive evidence to indicate no other valuation allowance is needed as a result of the Company’s history of profitable operations in the United States. As of January 31, 2015, the Company has a full valuation allowance against its U.S. state deferred tax assets due to uncertainty regarding the future utilization of these deferred tax assets.
Utilization of the research credit carryforwards may be subject to an annual limitation due to the ownership percentage change limitations as defined by the U.S. Internal Revenue Code Section 382, as amended, and similar state provisions. The annual limitation may result in the expiration of the U.S. Federal and state research credit carryforwards before utilization. The Company does not expect any tax credit carryforwards to expire as a result of a Section 382 limitation.
The Company applies the provisions of FASB’s guidance on accounting for uncertainty in income taxes. As of January 31, 2015, the Company had approximately $4.7 million in unrecognized tax benefits, $2.8 million of which would affect the Company’s effective tax rate if recognized. The following table sets forth a reconciliation of the beginning and ending amount of unrecognized tax benefits:
	Year Ended January 31,
	2015			2014			2013
	(in thousands)
Beginning balance:	$	3,583		$	3,018		$	2,213
Additions based on tax positions related to the		1,284			539			325
current year
Additions for tax positions of prior years		324			62			690
Settlements for prior periods		(43	)		—			—
Lapse of applicable statute of limitations		(477	)		(36	)		(210	)
Ending balance:	$	4,671		$	3,583		$	3,018
The Company classified $1.2 million and $1.3 million of income tax liabilities as other long term liabilities as of January 31, 2015 and 2014, respectively, because payment of cash or settlement is not anticipated within one year from the balance sheet date.
The Company recognizes interest and penalties related to uncertain tax positions as a component of income tax expense. The Company recorded $7,180, $37,000 and $23,000 of interest expense and penalties related to uncertain tax positions for the years ended January 31, 2015, 2014 and 2013, respectively. The Company recorded noncurrent liabilities of $160,000 and $153,000 related to interest and penalties for uncertain tax positions at January 31, 2015 and 2014, respectively.
The Company is subject to income tax in the U.S. federal jurisdiction and various state and foreign jurisdictions. The U.S. Internal Revenue Service has concluded its audit of the Company’s Federal income tax return for the fiscal year ended January 31, 2010 with no adjustments.
The Company believes that an adequate provision has been made for any adjustments that may result from tax examinations. However, the outcome of tax audits cannot be predicted with certainty. If any issues addressed in the Company’s tax audits are resolved in a manner not consistent with management’s expectations, the Company could be required to adjust its provision for income tax in the period such resolution occurs. Although timing of the resolution and/or closure of audits is highly uncertain, the Company does not believe it is reasonably possible that its unrecognized tax benefits would materially change in the next 12 months.
As of January 31, 2015, the Company’s long-term income taxes payable, including estimated interest and penalties, was approximately $1.4 million. The Company was unable to make a reasonably reliable estimate of the timing of payments in individual years due to uncertainties in the timing of tax audits, if any, or their outcomes.

Commitments_and_Contingencies

Commitments and Contingencies	12 Months Ended
	Jan. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	11. Commitments and Contingencies
	The Company leases its principal facilities and time-based software licenses under operating agreements with various expiration dates through April 2018. Net operating lease expenses for the years ended January 31, 2015, 2014 and 2013 were approximately $5.8 million, $5.0 million and $4.3 million, respectively. Future annual minimum payments under these operating agreements with initial lease terms in excess of one year are as follows:
		As of
		31-Jan-15
	Fiscal Year	(in thousands)
	2016	$	5,488
	2017		4,968
	2018		1,375
	2019		238
	2020		—
	Total future annual minimum lease payments	$	12,069
	Contract Manufacturer Commitments
	The Company’s components and products are procured and built by independent contract manufacturers based on sales forecasts. These forecasts include estimates of future demand, historical trends, analysis of sales and marketing activities, and adjustment of overall market conditions. The Company regularly issues purchase orders to independent contract manufacturers which are cancelable only upon the agreement between the Company and the third-party. As of January 31, 2015 and 2014, total manufacturing purchase commitments were approximately $27.5 million and $13.7 million, respectively.
	Indemnification
	The Company, from time to time, in the normal course of business, indemnifies certain vendors with whom it enters into contractual relationships. The Company has agreed to hold the other party harmless against third-party claims in connection with the Company’s future products. The Company also indemnifies certain customers against third party claims related to certain intellectual property matters. It is not possible to determine the maximum potential amount of liability under these indemnification obligations due to the limited history of prior indemnification claims and the unique facts and circumstances that are likely to be involved in each particular claim. The Company has not made payments under these obligations and no liabilities have been recorded for these obligations on the consolidated balance sheets as of January 31, 2015 and 2014, respectively.

Segment_Reporting

Segment Reporting	12 Months Ended
	Jan. 31, 2015
Segment Reporting [Abstract]
Segment Reporting	12. Segment Reporting
	The Company operates in one reportable segment related to the development and sales of low-power, high-definition video products. The Chief Executive Officer of the Company has been identified as the Chief Operating Decision Maker (the “CODM”) and manages the Company’s operations as a whole and for the purpose of evaluating financial performance and allocating resources, the CODM reviews financial information presented on a consolidated basis accompanied by information by customer and geographic region.
	Geographic Revenue
	The following table sets forth the Company’s revenue by geographic region for the periods indicated:
		Year Ended January 31,
		2015		2014		2013
		(in thousands)
	Hong Kong	$	196,372	$	135,382	$	104,458
	Asia Pacific		2,358		2,809		550
	United States		6,677		7,128		7,990
	North America		6,076		4,594		2,602
	Europe		6,795		7,695		5,466
	Total revenue	$	218,278	$	157,608	$	121,066
	As of January 31, 2015, substantially all of the Company’s long-lived assets were located in the United States and Asia Pacific region with approximate net amount of $1.8 million and $1.0 million, respectively. As of January 31, 2014, substantially all of the Company’s long-lived assets were located in the United States and Asia Pacific region with approximate net amount of $2.0 million and $0.9 million, respectively.
	Major Customers
	The customers representing 10% or more of revenue and accounts receivable were Wintech, the Company’s logistic provider, and Chicony, a direct ODM customer, which combined accounted for approximately 89%, 85% and 80% of total revenue for the years ended January 31, 2015, 2014 and 2013, respectively. Accounts receivable with these two customers combined accounted for approximately $36.2 million and $15.9 million as of January 31, 2015 and 2014, respectively.

RelatedParty_Transactions

Related-Party Transactions	12 Months Ended
	Jan. 31, 2015
Related Party Transactions [Abstract]
Related-Party Transactions	13. 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.
	In fiscal year 2015, the Company added additional software license commitments to its existing software license agreement with Cadence Design Systems, Inc. (“Cadence”). A member of the Company’s Board of Directors is also the Chief Executive Officer, President and a Director of Cadence. Under these license commitments, the Company committed to pay an aggregate amount of $7.5 million payable through January 2017. The Company paid $2.3 million, $1.7 million and $1.8 million under these agreements for the years ended January 31, 2015, 2014 and 2013, respectively. License expenses related to these agreements included in research and development cost were approximately $1.9 million, $1.7 million and $1.8 million for the years ended January 31, 2015, 2014 and 2013, respectively.
	In addition to the related party transactions noted above, the Company recognized revenue from sales to Wintech, the Company’s logistics provider. Wintech, along with an affiliate, owned approximately 4.6% of the Company’s voting stock as of January 31, 2013, but has sold such stock and is no longer a significant shareholder of the Company as of January 31, 2015 and 2014, respectively. The Company recognized revenue from sales to Wintech of approximately $125.1 million, $88.7 million and $76.5 million for the years ended January 31, 2015, 2014 and 2013, respectively. As of January 31, 2015 and 2014, the Company had receivables from Wintech of approximately $12.1 million and $7.9 million, respectively.

Organization_and_Summary_of_Si1

Organization and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Jan. 31, 2015
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 and display. The Company combines its processor design capabilities with its expertise in video and image processing, algorithms and software to provide a technology platform that is designed to be easily scalable across multiple applications and enable rapid and efficient product development. The Company’s system-on-a-chip, or SoC, designs fully integrate high-definition video processing, image processing, audio processing and system functions onto a single chip, delivering exceptional video and image quality, differentiated functionality and low power consumption.
	The Company sells its solutions to leading original design manufacturers, or ODMs, and original equipment manufacturers, or OEMs, globally.
	In October 2012, in connection with its initial public offering, or IPO, the Company completed the sale of 6,000,000 ordinary shares inclusive of 1,095,349 shares sold by certain shareholders of the Company. In November 2012, a total of 900,000 ordinary shares were sold to the Company’s IPO underwriters in connection with their exercise of the over-allotment option. The public offering price of the shares sold in this offering was $6.00 per share. The total net proceeds from the offering to the Company were approximately $30.4 million after deducting underwriting discounts and commissions and other offering expenses. Upon the completion of the IPO, all 13,315,727 outstanding redeemable convertible preference shares converted into ordinary shares on a one-to-one basis and all outstanding warrants to purchase redeemable convertible preference shares converted into warrants to purchase ordinary shares.
Basis of Consolidation	Basis of Consolidation
	The Company’s fiscal year ends on January 31. The consolidated financial statements of the Company and its subsidiaries have been prepared in conformity with generally accepted accounting principles in the United States (“U.S. GAAP”). All intercompany transactions and balances have been eliminated in consolidation.
Use of Estimates	Use of Estimates
	The preparation of consolidated financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities at the date of the financial statements and the reported amounts of revenue and expense during the reported periods. Actual results could differ from those estimates.
	On an ongoing basis, management evaluates its estimates and assumptions, including those related to (i) the collectability of accounts receivable; (ii) write down for excess and obsolete inventories; (iii) the estimated useful lives of long-lived assets; (iv) impairment of long-lived assets and financial instruments; (v) warranty obligations; (vi) the valuation of stock-based compensation awards and marketable securities; (vii) the probability of performance objectives achievement; (viii) the realization of tax assets and estimates of tax liabilities, including reserves for uncertain tax positions; and (ix) 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 in Asia other than Japan, and through one large direct ODM customer, Chicony Electronics Co., Ltd., or Chicony. Termination of the relationships with these two customers could result in a temporary or permanent loss of revenue and obligation to repurchase unsold product. Furthermore, any credit issues from these two customers could impair their abilities to make timely payment to the Company. See Note 12 for additional information regarding concentration with these two customers.
	Financial instruments that potentially subject the Company to concentrations of credit risk consist primarily of cash, cash equivalents, marketable securities and accounts receivable. The Company maintains its cash primarily in checking and money market accounts with reputable financial institutions. Cash deposits held with these financial institutions may exceed the amount of insurance provided on such deposits. The Company has not experienced any material losses on deposits of its cash. The cash equivalents and marketable securities consist primarily of money market funds, asset-backed securities, commercial paper and debt securities of corporations which management assesses to be high credit quality, in order to limit the exposure of each investment. The Company does not hold or issue financial instruments for trading purposes.
	The Company performs ongoing credit evaluations of each of its customers and adjusts credit limits based upon payment history and the customer’s credit worthiness. The Company regularly monitors collections and payments from its customers.
Foreign Currency Transactions	Foreign Currency Transactions
	The U.S. dollar is the functional currency for the Company and its subsidiaries. Monetary assets and liabilities denominated in non-U.S. currencies are re-measured to U.S. dollars using current exchange rates in effect at the balance sheet date. Nonmonetary assets and liabilities are re-measured to U.S. dollars using historical exchange rates. Monetary and other accounts are re-measured to U.S. dollars using average exchange rates in effect during each period. Gains or losses from foreign currency re-measurement are included in other income (loss), net in the consolidated statements of operations, and, to date, have not been material.
Fair Value of Financial Instruments	Fair Value of Financial Instruments
	The fair value accounting is applied to all financial assets and liabilities and non-financial assets and liabilities that are recognized or disclosed in the financial statements on a recurring basis. The carrying amounts reflected in the consolidated balance sheets for cash equivalents, accounts receivable, accounts payable, accrued liabilities and other current liabilities, approximate fair value due to the short-term nature.
Cash, Cash Equivalents and Marketable Securities	Cash, Cash Equivalents and Marketable Securities
	The Company considers all highly liquid investments with original maturities of less than three months at the time of purchase to be cash equivalents. Investments that are highly liquid with original maturities at the time of purchase greater than three months are considered as marketable securities.
	The Company classifies these investments as “available-for-sale” securities carried at fair value, based on quoted market prices of similar assets, with the unrealized gains or losses reported, net of tax, as a separate component of shareholders’ equity and included in accumulated other comprehensive income (loss) in the consolidated balance sheets. The amortization of security premiums and accretion of discounts and the realized gains and losses are both recorded in other income (loss), net in the consolidated statements of operations. The Company reviews its investments for possible other-than-temporary impairments on a regular basis. If any loss on investment is believed to be other-than-temporary, a charge will be recorded and a new cost basis in the investment will be established. In evaluating whether a loss on a security is other-than-temporary, the Company considers the following factors: 1) general market conditions, 2) the duration and extent to which the fair value is less than cost, 3) the Company’s intent and ability to hold the investment.
	For securities in an unrealized loss position which is deemed to be other-than-temporary, the difference between the security’s then-current amortized cost basis and fair value is separated into (i) the amount of the impairment related to the credit loss (i.e., the credit loss component) and (ii) the amount of the impairment related to all other factors (i.e., the non-credit loss component). The credit loss component is recognized in earnings. The non-credit loss component is recognized in accumulated other comprehensive loss. Due to the relative short term nature of the investments, there have been no other-than-temporary impairments recorded to date.
Trade Accounts Receivable and Allowances for Doubtful Accounts	Trade Accounts Receivable and Allowances for Doubtful Accounts
	Trade accounts receivable are recorded at the invoiced amount and do not include finance charges. The Company performs ongoing credit evaluation of its customers and generally requires no collateral. The Company assesses the need for allowances for doubtful accounts for estimated losses resulting from the inability of its customers to make required payments by considering factors such as historical collection experience, credit quality, aging of the accounts receivable balances and current economic conditions that may affect a customer’s ability to pay. There were no write-offs of accounts receivable for fiscal years 2015, 2014 and 2013, respectively. There was no material allowance for doubtful accounts recorded as of January 31, 2015 and 2014, respectively.
Inventories	Inventories
	The Company records inventories at the lower of cost or market. The cost includes materials and other production costs and is computed using standard cost on a first-in, first-out basis. Inventory reserves are recorded for estimated obsolescence or unmarketable inventories based on forecast of future demand and market conditions. If actual market conditions are less favorable than projected, or if future demand for the Company’s products decrease, additional inventory write-downs may be required. Once inventory is written down, a new accounting cost basis has been established and, accordingly, any associated reserve is not reversed until the inventory is sold or scrapped. There have been no material inventory losses recognized to date.
Property and Equipment	Property and Equipment
	Property and equipment are stated at cost and depreciated using the straight-line method over the estimated useful life of three years for computer equipment, computer software, machinery, equipment and furniture and fixture. Leasehold improvements are amortized over the shorter of the lease term or their estimated useful lives. Repairs and maintenance are charged to expense as incurred.
Internal-Use Software	Internal-Use Software
	The Company capitalizes certain software that is acquired and developed solely for internal use. The capitalization costs include fees for services provided to develop software during the application development stage, costs incurred to obtain software, and certain costs for employees who are directly associated with and who directly devote time to the project. The capitalization begins when the preliminary project stage is completed and ceases no later than the point at which the project is substantially complete and ready for its intended use after all substantial testing is completed. The internal-use software is amortized over its estimated useful life. Repairs and maintenance are charged to expense as incurred. As of January 31, 2015, the Company has capitalized approximately $1.6 million of internal-use software and has been recorded in property and equipment, net on the consolidated balance sheets.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets
	The Company records long-lived assets at cost and evaluates them for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset may not be recoverable. Events or changes in circumstances that may indicate that an asset is impaired include significant decreases in the market value of an asset, significant underperformance relative to expected historical or projected future results of operations, a change in the extent or manner in which an asset is utilized, significant declines in the estimated fair value of the overall Company for a sustained period, shifts in technology, loss of key management or personnel, changes in the Company’s operating model or strategy and competitive forces. When the sum of the expected future undiscounted cash flows expected to be generated by the related asset group is less than its carrying amount, an impairment loss would be recognized. Should impairment exist, the impairment loss would be measured based on the excess of the carrying amount of the asset over the asset’s estimated fair value. There has been no occurrence of events to date that would trigger an impairment analysis. As such, no impairment charge has been recognized as of January 31, 2015.
Cost Method Investment	Cost Method Investment
	The Company accounts for its investment in a privately held company under the cost method and reports the investment in other assets in the consolidated balance sheets. The Company monitors the carrying value of the investment and records a reduction in carrying value when a decline in value is deemed to be other than temporary. To date, there have been no identified events or changes in circumstances that may have a significant adverse effect on the fair value of this investment and the Company has not recognized any impairment losses related to this investment.
Revenue Recognition	Revenue Recognition
	The Company generates revenue from the sales of its SoCs to OEMs or ODMs, either directly or through logistics providers. Revenue from sales directly to OEMs and ODMs is recognized upon shipment provided persuasive evidence of an arrangement exists, legal title to the products and risk of ownership have transferred, the fee is fixed or determinable, and collection of the resulting receivable is reasonably assured. The Company provides its logistics providers with the rights to return excess levels of inventory and to future price adjustments. Given the inability to reasonably estimate these price changes and returns, revenue and costs related to shipments to logistics providers are deferred until the Company has received notification from its logistics providers that they have sold the Company’s products. Information reported by the Company’s logistics providers includes product resale price, quantity and end customer shipment information as well as remaining inventory on hand. At the time of shipment to a logistics provider, the Company records a trade receivable as there is a legally enforceable right to receive payment, reduces inventory for the value of goods shipped as legal title has passed to the logistics provider and defers the related margin as deferred revenue in the consolidated balance sheets. Any price adjustments are recorded as a change to deferred revenue at the time the adjustments are agreed upon.
	Arrangements with certain OEM customers provide for pricing that is dependent upon the end products into which the Company’s SoCs are used. These arrangements may also entitle the Company to a share of the product margin ultimately realized by the OEM. The minimum guaranteed amount of revenue related to the sale of products subject to these arrangements is recognized when all other elements of revenue recognition are met. Any amounts at the date of shipment invoiced in excess of the minimum guaranteed contract price are deferred until the additional amounts the Company is entitled to are fixed or determinable. Additional amounts earned by the Company resulting from margin sharing arrangements and determination of the end products into which the products are ultimately incorporated are recognized when end customer sales volume is reported to the Company.
	The Company sells a limited amount of software under perpetual licenses that include post-contract customer support, or PCS. The Company does not have evidence of fair value for the PCS and, accordingly, license revenue is recognized ratably over the estimated supporting period in accordance with ASC 985, Software Revenue Recognition. The Company also enters into development agreements with certain customers. Revenue is deferred for any amounts billed prior to delivery of development services. However, if the Company retains the intellectual property generated from these development agreements, receipts and costs related to these arrangements are included in research and development expense. The revenue from those licenses and services was not material for the fiscal years ended January 31, 2015, 2014 and 2013, respectively.
Cost of Revenue	Cost of Revenue
	Cost of revenue includes cost of materials, cost associated with packaging and assembly, testing and shipping, cost of personnel, stock-based compensation, logistics and quality assurance, warranty cost, royalty expense, write-downs of inventories and allocation of overhead.
Warranty Costs	Warranty Costs
	The Company typically provides warranty on its products. The Company accrues for the estimated warranty costs at the time when revenue is recognized. The warranty accruals are regularly monitored by management based upon historical experience and any specifically identified failures. While the Company engages in extensive product quality assessment, actual product failure rates, material usage or service delivery costs could differ from estimates and revisions to the estimated warranty liability would be required. The Company’s warranty accruals have not been material to date.
Research and Development	Research and Development
	Research and development costs are expensed as incurred and consist primarily of personnel costs, product development costs, which include engineering services, development software and hardware tools, license fees, cost of fabrication of masks for prototype products, other development materials costs, depreciation of equipment used in research and development and allocation of facilities costs.
Selling, General and Administrative	Selling, General and Administrative
	Selling, general and administrative expense consists of personnel costs, travel and trade show costs, legal expenses, other professional services and occupancy costs. Advertising expenses have not been material to date.
Operating Leases	Operating Leases
	The Company recognizes rent expense on a straight-line basis over the term of the lease. The difference between rent expense and rent payment is recorded as deferred rent and is included in accrued liabilities in the consolidated balance sheets.
Stock-Based Compensation	Stock-Based Compensation
	The Company measures stock-based compensation for equity awards granted to employees and directors based on the estimated fair value on the grant date, and recognizes that compensation as expense using the straight-line attribution method for service condition awards or using the graded-vesting attribution method for awards with performance conditions over the requisite service period, which is typically the vesting period of each award. The Company estimates the fair value of restricted stock units, or RSUs, based on the fair market value of its ordinary shares on the grant date. The Company uses the Black-Scholes option pricing model to determine the fair value of stock options. Determining the fair value of stock options on the grant date requires the input of various assumptions, including stock price of the underlying ordinary share, the exercise price of the stock option, expected volatility, expected term, risk-free interest rate and dividend rate. The expected term is calculated using the simplified method as prescribed in the guidance provided by the Securities and Exchange Commission, as neither relevant historical experience nor other relevant data are available to estimate future exercise behavior. The expected volatility is based on the historical volatilities of similar companies whose share prices are publicly available for a period commensurate with the expected term. The risk-free interest rate is derived from the average U.S. Treasury constant maturity rates during the respective periods commensurate with the expected term. The expected dividend yield is zero because the Company has not historically paid dividends and has no present intention to pay dividends. The Company uses historical data to estimate pre-vesting award forfeitures and records stock-based compensation only for those awards that are expected to vest. Forfeitures are estimated at the time of grant and revised if necessary in subsequent periods if actual forfeitures differ from estimates.
	The Company recognizes non-employee stock-based compensation expense based on the estimated fair value of the equity instrument. The fair value of the non-employee awards is remeasured at each reporting period until services required under the arrangement are completed, which is the vesting date.
	Prior to the initial public offering, or IPO, the Company engaged an independent appraiser to assist in the valuation of its ordinary share price. The board of directors directed these regular valuations and had input into determining the relevant objective and subjective factors accounted for and relevant approaches in each valuation. After the IPO, the exercise price of stock option awards is determined by the closing price of the Company’s ordinary shares traded on The NASDAQ Global Market on the grant date.
Income Taxes	Income Taxes
	The Company records income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in its financial statements or tax returns. In estimating future tax consequences, generally all expected future events other than enactments or changes in the tax law or rates are considered. Valuation allowances are provided when necessary to reduce deferred tax assets to the amount expected to be realized.
	The Company applies authoritative guidance for the accounting for uncertainty in income taxes. The guidance requires that tax effects of a position be recognized only if it is “more likely than not” to be sustained based solely on its technical merits as of the reporting date. Upon estimating the Company’s tax positions and tax benefits, the Company considered and evaluated numerous factors, which may require periodic adjustments and which may not reflect the final tax liabilities. The Company adjusts its financial statements to reflect only those tax positions that are more likely than not to be sustained under examination.
	As part of the process of preparing consolidated financial statements, the Company is required to estimate its taxes in each of the jurisdictions in which it operates. The Company estimates actual current tax exposure together with assessing temporary differences resulting from differing treatment of items, such as accruals and allowances not currently deductible for tax purposes. These differences result in deferred tax assets, which are included in the consolidated balance sheets. In general, deferred tax assets represent future tax benefits to be received when certain expenses previously recognized in the consolidated statements of operations become deductible expenses under applicable income tax laws, or loss or credit carryforwards are utilized.
	In assessing whether deferred tax assets may be realized, management considers whether it is more likely than not that some portion or all of deferred tax assets will be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income.
	The Company makes estimates and judgments about its future taxable income based on assumptions that are consistent with its plans and estimates. Should the actual amounts differ from estimates, the amount of valuation allowance could be materially impacted. Any adjustment to the deferred tax asset valuation allowance would be recorded in the income statement for the periods in which the adjustment is determined to be required.
Net Income Per Ordinary Share	Net Income Per Ordinary Share
	The Company applies the two-class method to calculate and present net income per ordinary share. Under the two-class method, net income is allocated between ordinary shares and other participating securities based on their participating rights. Participating securities are defined as securities that may participate in undistributed earnings with ordinary shares, whether that participation is conditioned upon the occurrence of a specified event or not. Basic net income per ordinary share is computed by dividing net income allocable to ordinary shares by the weighted-average number of ordinary shares outstanding for the period. Diluted net income per ordinary share is computed by dividing net income allocable to ordinary shares and income allocable to participating securities, to the extent they are dilutive, by the weighted-average number of ordinary shares outstanding, including the dilutive effects of participating securities on an if-converted basis plus the dilutive effects of ordinary shares. The Company’s potential dilutive ordinary share equivalents consist of incremental ordinary shares issuable upon the exercise of options, upon the issuance of shares pursuant to the Employee Stock Purchase Plan, or ESPP, upon release of vested restricted stock units, upon conversion of its redeemable convertible preference shares and upon exercise of warrants.
	The Company performs an assessment as to whether instruments granted in stock-based payment transactions are participating securities. Stock-based payment awards that have not yet vested meet the definition of a participating security provided the right to receive the dividend is non-forfeitable and non-contingent. These participating securities should be included in the computation of basic net income per ordinary share under the two-class method. The Company has concluded that its non-vested early-exercised options meet the definition of a participating security and should be included in the computation of basic net income per ordinary share.
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 ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606). The new guidance clarifies the principles and develops a common revenue recognition guidance for U.S. GAAP and International Financial Reporting Standards (the “IFRS”). Under the new guidance, an entity should recognize revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. To achieve this core principle, an entity shall identify the contract(s) with a customer, identify the performance obligations in the contract, determine the transaction price, allocate the transaction price to the performance obligations in the contract, and recognize revenue when (or as) the entity satisfies a performance obligation. The new guidance is effective for annual reporting periods beginning after December 15, 2016, including interim periods within that reporting period. Early adoption is not permitted. The new revenue guidance may be applied retrospectively to each prior period presented or retrospectively with the cumulative effect recognized as of the date of adoption. The Company is currently evaluating the impact of adoption on its financial position, results of operations and disclosures.
	In August 2014, the FASB issued ASU No. 2014-15, Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. In connection with each annual and interim period, management is required to assess whether there is substantial doubt about an entity’s ability to continue as a going concern within one year after the issuance date, and to provide related footnote disclosures in certain circumstances. The new guidance is effective for annual periods ending after December 15, 2016, and interim periods within annual periods beginning after December 15, 2016. Early adoption is permitted. This ASU is not expected to have an impact on the Company’s financial statements or disclosures.

Financial_Instruments_and_Fair1

Financial Instruments and Fair Value (Tables)	12 Months Ended
	Jan. 31, 2015
Investments All Other Investments [Abstract]
Schedule of Available-for-Sale Securities at Fair Value	All of the investments are classified as available-for-sale securities and reported at fair value in the consolidated balance sheets as follows:
		As of January 31, 2015
		Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
		(in thousands)
	Money market funds	$	2,427	$	—	$	—		$	2,427
	Commercial paper		1,497		—		—			1,497
	Corporate bonds		32,356		9		(10	)		32,355
	Asset-backed securities		3,851		—		—			3,851
	Total cash equivalents and marketable securities	$	40,131	$	9	$	(10	)	$	40,130
Schedule of Cash Equivalents and Marketable Securities
		As of
		31-Jan-15
		(in thousands)
	Included in cash equivalents	$	2,427
	Included in marketable securities		37,703
	Total cash equivalents and marketable securities	$	40,130
Summary of Contractual Maturities of Investments	The contractual maturities of the investments at January 31, 2015 were as follows:
		As of
		31-Jan-15
		(in thousands)
	Due within one year	$	37,559
	Due within one to two years		2,571
	Total cash equivalents and marketable securities	$	40,130
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 January 31, 2015:
		Total		Level 1		Level 2			Level 3
		(in thousands)
	Money market funds	$	2,427	$	2,427	$	—		$	—
	Commercial paper		1,497		—		1,497			—
	Corporate bonds		32,355		—		32,355			—
	Asset-backed securities		3,851		—		3,851			—
	Total cash equivalents and marketable securities	$	40,130	$	2,427	$	37,703		$	—

Inventories_Tables

Inventories (Tables)	12 Months Ended
	Jan. 31, 2015
Inventory Disclosure [Abstract]
Schedule of Inventory	Inventories at January 31, 2015 and 2014 consisted of the following:
		As of January 31,
		2015		2014
		(in thousands)
	Work-in-progress	$	13,805	$	5,119
	Finished goods		7,888		5,333
	Total	$	21,693	$	10,452

Property_and_Equipment_Net_Tab

Property and Equipment, Net (Tables)	12 Months Ended
	Jan. 31, 2015
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment	Property and equipment at January 31, 2015 and 2014 consisted of the following:
		As of January 31,
		2015			2014
		(in thousands)
	Computer equipment and software	$	5,310		$	4,521
	Machinery and equipment		2,234			2,114
	Furniture and fixtures		456			411
	Leasehold improvements		1,215			1,198
	Construction in progress		64			—
			9,279			8,244
	Less: accumulated depreciation and amortization		(6,204	)		(5,226	)
	Total property and equipment, net	$	3,075		$	3,018

Accrued_Liabilities_Tables

Accrued Liabilities (Tables)	12 Months Ended
	Jan. 31, 2015
Payables And Accruals [Abstract]
Schedule of Accrued Liabilities	Accrued liabilities at January 31, 2015 and 2014 consisted of the following:
		As of January 31,
		2015		2014
		(in thousands)
	Accrued employee compensation	$	11,318	$	8,108
	Accrued warranty		203		269
	Accrued rebates		254		270
	Accrued product development costs		5,004		1,904
	Other accrued liabilities		1,920		1,154
	Total accrued liabilities	$	18,699	$	11,705

Deferred_Revenue_and_Deferred_1

Deferred Revenue and Deferred Cost (Tables)	12 Months Ended
	Jan. 31, 2015
Deferred Revenue Disclosure [Abstract]
Schedule of Deferred Revenue and Related Cost	Deferred revenue and related cost at January 31, 2015 and 2014 consisted of the following:
		As of January 31,
		2015			2014
		(in thousands)
	Deferred revenue on product shipments	$	4,663		$	5,174
	Deferred revenue from licenses & services		1,610			1,023
	Deferred cost of revenue on product shipments		(1,168	)		(1,366	)
	Total deferred revenue, net	$	5,105		$	4,831

Capital_Stock_Tables

Capital Stock (Tables)	12 Months Ended
	Jan. 31, 2015
Capital [Abstract]
Schedule of Ordinary Shares Reserved for Future Issuance	As of January 31, 2015 and 2014, the following ordinary shares were reserved for future issuance:
		As of January 31,
		2015		2014
	Shares reserved for options and restricted stock units		5,055,845		5,699,530
	Shares reserved for employee stock purchase plan		667,990		456,410

Employee_Benefits_and_Stockbas1

Employee Benefits and Stock-based Compensation (Tables)	12 Months Ended
	Jan. 31, 2015
Postemployment Benefits [Abstract]
Classification of Stock-based Compensation	The following table presents the classification of stock-based compensation for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
		(in thousands)
	Stock-based compensation:
	Cost of revenue	$	343		$	178		$	92
	Research and development		8,654			4,887			2,942
	Selling, general and administrative		6,695			3,470			1,965
	Total stock-based compensation	$	15,692		$	8,535		$	4,999
Weighted-Average Assumptions Used to Estimate Fair Value	The following table sets forth the weighted-average assumptions used to estimate the fair value of the stock options and employee stock purchase plan awards for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
	Stock Options:
	Volatility		64	%		65	%		66	%
	Risk-free interest rate		1.93	%		1.55	%		0.91	%
	Expected term (years)	6.01				6.06			6.05
	Dividend yield		0	%		0	%		0	%
	Employee stock purchase plan awards:
	Volatility		49	%		52	%		51	%
	Risk-free interest rate		0.07	%		0.04	%		0.18	%
	Expected term (years)		0.5			0.5			0.94
	Dividend yield		0	%		0	%		0	%
Stock Option Activities	The following table summarizes stock option activities for the periods indicated:
		Option Outstanding
													Weighted-
											Total Intrinsic		Average
								Weighted-			Value of		Remaining		Aggregate
					Weighted-			Average			options		Contactual		Intrinsic
					Average			Grant-date			Exercised		Term		Value
		Shares			Exercise Price			Fair Value			(in thousands)		(in years)		(in thousands)
	Outstanding at January 31, 2012		4,375,906		$	5.63
	Granted		451,071			8.79		$	5.23
	Exercised		(313,827	)		3.21					$	2,087
	Forfeited		(168,615	)		7.22
	Outstanding at January 31, 2013		4,344,535			6.07
	Granted		255,520			18.14		$	10.85
	Exercised		(1,160,286	)		5.96					$	18,217
	Forfeited		(81,063	)		10.34
	Outstanding at January 31, 2014		3,358,706			6.92
	Granted		428,781			36.33		$	21.37
	Exercised		(1,456,944	)		5.84					$	46,427
	Forfeited		(48,634	)		13.38
	Outstanding at January 31, 2015		2,281,909		$	13							6.35		$	96,547
	Exercisable at January 31, 2015		1,553,901		$	7.22								5.3	$	74,735
	Vested and expected to vest at January 31, 2015		2,239,650		$	12.68								6.3	$	95,482
Restricted Stock Unit Activities	The following table summarizes restricted stock units activities for the periods indicated:
					Weighted-
					Average
					Grant-Date
		Shares			Fair Value
	Unvested at January 31, 2012		—		$	—
	Granted		345,171			9.99
	Vested		—			—
	Forfeited		(5,954	)		9.99
	Unvested at January 31, 2013		339,217			9.99
	Granted		1,265,472			14.78
	Vested		(174,888	)		11.91
	Forfeited		(19,712	)		11.97
	Unvested at January 31, 2014		1,410,089			14.02
	Granted		1,111,204			38.6
	Vested		(484,296	)		17.39
	Forfeited		(56,549	)		19.93
	Unvested at January 31, 2015		1,980,448		$	26.82

Net_Income_Per_Ordinary_Share_

Net Income Per Ordinary Share (Tables)	12 Months Ended
	Jan. 31, 2015
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Income Per Ordinary Share	The following table sets forth the computation of basic and diluted net income per ordinary share for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
		(in thousands, except share and per share data)
	Numerator:
	Net income	$	50,571		$	25,654		$	18,188
	Less: amount allocable to preference shareholders		—			—			(9,517	)
	Less: amount allocable to unvested early exercised options		(11	)		(31	)		(61	)
	Net income allocable to ordinary shareholders - basic	$	50,560		$	25,623		$	8,610
	Undistributed earnings reallocated to ordinary shareholders		1			2			432
	Net income allocable to ordinary shareholders - diluted	$	50,561		$	25,625		$	9,042
	Denominator:
	Weighted-average ordinary shares outstanding		29,749,354			27,713,998			13,599,273
	Less: weighted-average unvested early exercised options		(6,701	)		(33,220	)		(87,627	)
	subject to repurchase
	Weighted-average ordinary shares - basic		29,742,653			27,680,778			13,511,646
	Effect of potentially dilutive securities:
	Employee stock options		1,818,401			2,034,500			1,443,809
	Restricted stock units		704,788			316,350			16,930
	Employee stock purchase plan		12,285			138,461			27,230
	Warrants to purchase ordinary shares		—			2,474			6,737
	Over-allotment shares		—			—			10,634
	Weighted-average ordinary shares - diluted		32,278,127			30,172,563			15,016,986
	Net income per ordinary share:
	Basic	$	1.7		$	0.93		$	0.64
	Diluted	$	1.57		$	0.85		$	0.6
Weighted-Average Potentially Dilutive Securities Excluded from Computation of Diluted Net Income Per Ordinary Share	The following weighted-average potentially dilutive securities were excluded from the computation of diluted net income per ordinary share as their effect would have been antidilutive:
		Year Ended January 31,
		2015			2014			2013
	Options to purchase ordinary shares		217,514			183,859			2,053,520
	Restricted stock units		167,702			1,576			60,504
	Employee stock purchase plan		36,110			10,597			20,356
	Early exercised options subject to repurchase		6,701			33,220			87,627
	Redeemable convertible preference shares		—			—			9,131,824
	(if-converted basis)
	Warrants to purchase ordinary shares		—			—			24,889
			428,027			229,252			11,378,720

Income_Taxes_Tables

Income Taxes (Tables)	12 Months Ended
	Jan. 31, 2015
Income Tax Disclosure [Abstract]
Summary of Income before Income Taxes	Income before income taxes consisted of the following for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
		(in thousands)
	U.S. operations	$	1,978		$	1,990		$	3,264
	Non-U.S. operations		50,058			25,905			16,778
	Income before income taxes	$	52,036		$	27,895		$	20,042
Schedule of Income Tax Provision	Income tax provision consisted of the following for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
		(in thousands)
	Current:
	U.S. federal tax	$	3,135		$	1,738		$	2,022
	U.S. state taxes		93			23			5
	Non-U.S. foreign taxes		1,348			1,058			701
			4,576			2,819			2,728
	Deferred:
	U.S. federal tax		(3,208	)		(952	)		(743	)
	U.S. state taxes		—			341			(109	)
	Non-U.S. foreign taxes		97			33			(22	)
			(3,111	)		(578	)		(874	)
	Provision for income taxes	$	1,465		$	2,241		$	1,854
Schedule of Income Tax Provision Differed from Amounts Computed by Applying U.S. Federal Income Tax Rate	Income tax provision differed from the amounts computed by applying the U.S. federal income tax rate of 34% to pretax income as a result of the following for the periods indicated:
		Year Ended January 31,
		2015			2014			2013
		(in thousands)
	U.S. federal tax at statutory rate	$	17,692		$	9,484		$	6,814
	U.S. state taxes		90			361			(107	)
	Non-U.S. foreign tax differential		(15,644	)		(7,674	)		(4,513	)
	Stock-based compensation		1,601			927			682
	U.S. R&D credit		(2,298	)		(858	)		(890	)
	Other		24			1			(132	)
	Provision for income taxes	$	1,465		$	2,241		$	1,854
Schedule of Deferred Tax Assets and Liabilities	Temporary differences that gave rise to significant portions of the Company’s deferred tax assets and liabilities at January 31, 2015 and 2014 were as follows:
		As of January 31,
		2015			2014
		(in thousands)
	Deferred tax assets:
	Federal and state credits	$	6,465		$	2,587
	Expenses not currently deductible		1,590			1,149
	Foreign deferred		—			26
	Stock-based compensation		2,044			1,460
	Gross deferred tax assets		10,099			5,222
	Valuation allowance		(3,996	)		(2,302	)
	Total deferred tax assets	$	6,103		$	2,920
	Deferred tax liabilities
	Property and equipment		(199	)		(187	)
	Foreign deferred		(70	)		—
	Net deferred tax assets	$	5,834		$	2,733
Summary of Tax Valuation Allowance	Tax valuation allowance for the periods indicated below were as follows:
											Deductions
								Additions			Charged to
		Balance at			Additional			Charged to			Expenses			Balance at
		Beginning of			Charged to			Other			or Other			End of
		Period			Expenses			Account			Accounts			Period
		(in thousands)
	Tax Valuation Allowance
	Year ended January 31, 2015	$	2,302			1,694			—			—		$	3,996
	Year ended January 31, 2014	$	1,243			1,059			—			—		$	2,302
	Year ended January 31, 2013	$	1,301			—			—			(58	)	$	1,243
Schedule of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits	The following table sets forth a reconciliation of the beginning and ending amount of unrecognized tax benefits:
		Year Ended January 31,
		2015			2014			2013
		(in thousands)
	Beginning balance:	$	3,583		$	3,018		$	2,213
	Additions based on tax positions related to the		1,284			539			325
	current year
	Additions for tax positions of prior years		324			62			690
	Settlements for prior periods		(43	)		—			—
	Lapse of applicable statute of limitations		(477	)		(36	)		(210	)
	Ending balance:	$	4,671		$	3,583		$	3,018

Commitments_and_Contingencies_

Commitments and Contingencies (Tables)	12 Months Ended
	Jan. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Future Annual Minimum Lease Payments	Future annual minimum payments under these operating agreements with initial lease terms in excess of one year are as follows
		As of
		31-Jan-15
	Fiscal Year	(in thousands)
	2016	$	5,488
	2017		4,968
	2018		1,375
	2019		238
	2020		—
	Total future annual minimum lease payments	$	12,069

Segment_Reporting_Tables

Segment Reporting (Tables)	12 Months Ended
	Jan. 31, 2015
Segment Reporting [Abstract]
Company's Revenue by Geographic Region	The following table sets forth the Company’s revenue by geographic region for the periods indicated:
		Year Ended January 31,
		2015		2014		2013
		(in thousands)
	Hong Kong	$	196,372	$	135,382	$	104,458
	Asia Pacific		2,358		2,809		550
	United States		6,677		7,128		7,990
	North America		6,076		4,594		2,602
	Europe		6,795		7,695		5,466
	Total revenue	$	218,278	$	157,608	$	121,066

Organization_and_Summary_of_Si2

Organization and Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended			1 Months Ended
	Oct. 31, 2012	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013	Nov. 30, 2012
Summary Of Significant Accounting Policies [Line Items]
Initial public offering price per share	$6
Net proceeds from shares issued and over-allotment options exercised in connection with initial public offering after deducting underwriting discounts and commissions and other offering expenses				$30,400,000
Redeemable convertible preference shares converted to ordinary shares	13,315,727
Redeemable convertible preference shares conversion	Converted into ordinary shares on a one-to-one basis
Cash equivalents, treatment		Highly liquid investments with original maturities of less than three months at the time of purchase to be cash equivalents.
Marketable securities, treatment		Investments that are highly liquid with original maturities at the time of purchase greater than three months are considered as marketable securities.
Write-offs of accounts receivable		0	0	0
Allowance for doubtful accounts		0	0
Estimated useful life		3 years	3 years	3 years
Capitalized internal-use software		1,600,000
Impairment of long-lived assets		0
Impairment losses on investment		$0
Expected dividend yield		0.00%	0.00%	0.00%
IPO [Member]
Summary Of Significant Accounting Policies [Line Items]
Stock Issued During Period, Shares, New Issues	6,000,000
Stockholders [Member]
Summary Of Significant Accounting Policies [Line Items]
Stock Issued During Period, Shares, New Issues	1,095,349
Over Allotment Option [Member]
Summary Of Significant Accounting Policies [Line Items]
Stock Issued During Period, Shares, New Issues					900,000

Financial_Instruments_and_Fair2

Financial Instruments and Fair Value - Schedule of Available-for-Sale Securities at Fair Value (Detail) (USD $)	Jan. 31, 2015
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$40,131
Unrealized Gains	9
Unrealized Losses	-10
Fair Value	40,130
Money market funds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	2,427
Fair Value	2,427
Commercial paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	1,497
Fair Value	1,497
Corporate bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	32,356
Unrealized Gains	9
Unrealized Losses	-10
Fair Value	32,355
Asset-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,851
Fair Value	$3,851

Financial_Instruments_and_Fair3

Financial Instruments and Fair Value - Schedule of Cash Equivalents and Marketable Securities (Detail) (USD $)	Jan. 31, 2015
In Thousands, unless otherwise specified
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$40,130
Included in cash equivalents [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	2,427
Included in marketable securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Total cash equivalents and marketable securities	$37,703

Financial_Instruments_and_Fair4

Financial Instruments and Fair Value - Summary of Contractual Maturities of Investments (Detail) (USD $)	Jan. 31, 2015
In Thousands, unless otherwise specified
Available For Sale Securities Debt Maturities Fair Value [Abstract]
Due within one year	$37,559
Due within one to two years	2,571
Total cash equivalents and marketable securities	$40,130

Financial_Instruments_and_Fair5

Financial Instruments and Fair Value - Schedule of Fair Value of Financial Instruments Measured on Recurring Basis (Detail) (USD $)	Jan. 31, 2015
In Thousands, unless otherwise specified
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$40,130
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	2,427
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	37,703
Money market funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	2,427
Money market funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	2,427
Commercial paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	1,497
Commercial paper [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	1,497
Corporate bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	32,355
Corporate bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	32,355
Asset-backed securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	3,851
Asset-backed securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total cash equivalents and marketable securities	$3,851

Inventories_Schedule_of_Invent

Inventories - Schedule of Inventory (Detail) (USD $)	Jan. 31, 2015	Jan. 31, 2014
In Thousands, unless otherwise specified
Inventory Disclosure [Abstract]
Work-in-progress	$13,805	$5,119
Finished goods	7,888	5,333
Total	$21,693	$10,452

Property_and_Equipment_Net_Add

Property and Equipment, Net - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended
	Mar. 31, 2013	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
	sqft
Property Plant And Equipment [Abstract]
Depreciation of property and equipment		$1,335,000	$1,096,000	$737,000
Office facility space for new headquarters	35,000
Capitalized leasehold improvement			700,000
Initial lease term	5 years
Capitalized internal-use software		$1,600,000
Estimated economic useful life of internal-use software		3 years

Property_and_Equipment_Net_Sch

Property and Equipment, Net - Schedule of Property and Equipment (Detail) (USD $)	Jan. 31, 2015	Jan. 31, 2014
In Thousands, unless otherwise specified
Property Plant And Equipment [Line Items]
Property and equipment, gross	$9,279	$8,244
Less: accumulated depreciation and amortization	-6,204	-5,226
Total property and equipment, net	3,075	3,018
Computer equipment and software [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	5,310	4,521
Machinery and equipment [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	2,234	2,114
Furniture and fixtures [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	456	411
Leasehold improvements [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	1,215	1,198
Construction in progress [Member]
Property Plant And Equipment [Line Items]
Property and equipment, gross	$64

Accrued_Liabilities_Schedule_o

Accrued Liabilities - Schedule of Accrued Liabilities (Detail) (USD $)	Jan. 31, 2015	Jan. 31, 2014
In Thousands, unless otherwise specified
Payables And Accruals [Abstract]
Accrued employee compensation	$11,318	$8,108
Accrued warranty	203	269
Accrued rebates	254	270
Accrued product development costs	5,004	1,904
Other accrued liabilities	1,920	1,154
Total accrued liabilities	$18,699	$11,705

Deferred_Revenue_and_Deferred_2

Deferred Revenue and Deferred Cost - Schedule of Deferred Revenue and Related Cost (Detail) (USD $)	Jan. 31, 2015	Jan. 31, 2014
In Thousands, unless otherwise specified
Deferred Revenue Arrangement [Line Items]
Deferred cost of revenue on product shipments	($1,168)	($1,366)
Deferred revenue	5,105	4,831
Product shipments [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue	4,663	5,174
License and services [Member]
Deferred Revenue Arrangement [Line Items]
Deferred revenue	$1,610	$1,023

Capital_Stock_Additional_Infor

Capital Stock - Additional Information (Detail) (USD $)	1 Months Ended	12 Months Ended	1 Months Ended
	Oct. 31, 2012	Jan. 31, 2013	Nov. 30, 2012	Jan. 31, 2015	Jan. 31, 2014
Class Of Stock [Line Items]
Initial public offering price per share	$6
Net proceeds from shares issued and over-allotment options exercised in connection with initial public offering after deducting underwriting discounts and commissions and other offering expenses		$30,400,000
Redeemable convertible preference shares converted to ordinary shares	13,315,727
Preference shares, shares authorized				20,000,000	20,000,000
Preference shares, par value				$0.00	$0.00
Preference shares, shares issued				0	0
Preference shares, shares outstanding				0	0
Warrants to purchase redeemable convertible preference shares converted to warrants to purchase ordinary shares	36,292
Warrants to purchase redeemable convertible preference shares converted to warrants to purchase ordinary shares, exercise price	$3.58
Aggregate fair market value	$110,000
Total ordinary share warrants outstanding					0
Ordinary shares authorized				200,000,000	200,000,000
IPO [Member]
Class Of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	6,000,000
Stockholders [Member]
Class Of Stock [Line Items]
Stock Issued During Period, Shares, New Issues	1,095,349
Over Allotment Option [Member]
Class Of Stock [Line Items]
Stock Issued During Period, Shares, New Issues			900,000

Capital_Stock_Schedule_of_Ordi

Capital Stock - Schedule of Ordinary Shares Reserved for Future Issuance under EIP and ESPP (Detail)	Jan. 31, 2015	Jan. 31, 2014
Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved	5,055,845	5,699,530
Employee stock purchase plan awards [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares reserved	667,990	456,410

Employee_Benefits_and_Stockbas2

Employee Benefits and Stock-based Compensation - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, except Share data, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013	Feb. 01, 2014
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unvested early exercised options repurchased	86,925	86,340
Closing price of ordinary shares	55.31
2012 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Voting power of all classes of company's shares	10.00%	10.00%	10.00%
Additional ordinary shares reserved for issuance				1,297,555
2012 Equity Incentive Plan [Member] | Scenario, plan automatically increased by the lessor of [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Annual increase in ordinary shares for available for future issuance				3,500,000
Annual shares increase for future issuance by percentage under 2012 equity plan				4.50%
2012 Employee Stock Purchase Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price of stock options as percentage of fair market value at grant date	85.00%	85.00%	85.00%
Percentage of salary contribution by employees	10.00%	10.00%	10.00%
Additional ordinary shares reserved for issuance				359,356
2012 Employee Stock Purchase Plan [Member] | Scenario, plan automatically increased by the lessor of [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Annual increase in ordinary shares for available for future issuance				1,500,000
Annual shares increase for future issuance by percentage under 2012 employee stock purchase plan				1.25%
Stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost, stock options	10.3
Weighted average recognition period	2 years 4 months 21 days
Stock options [Member] | 2012 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Option's term of up to 10 years from grant date	10 years	10 years	10 years
Vesting schedule	Vest 25% on the first anniversary date of the grant and remainder vest ratably over the following 36 months.	Vest 25% on the first anniversary date of the grant and remainder vest ratably over the following 36 months.	Vest 25% on the first anniversary date of the grant and remainder vest ratably over the following 36 months.
Stock options [Member] | Incentive stock options granted to 10% ownership [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price of stock options as percentage of fair market value at grant date	110.00%
Stock options [Member] | Non statutory stock options and incentive stock options granted to less than 10% ownership [Member] | Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Exercise price of stock options as percentage of fair market value at grant date	100.00%
Restricted stock units [Member] | 2012 Equity Incentive Plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Vesting schedule	1/4th of the shares on the first anniversary service date of the grant and 1/16th of the RSUs vest every 3 months thereafter, so as to be 100% vested on the fourth anniversary of the vesting commencement date.	1/4th of the shares on the first anniversary service date of the grant and 1/16th of the RSUs vest every 3 months thereafter, so as to be 100% vested on the fourth anniversary of the vesting commencement date.	1/4th of the shares on the first anniversary service date of the grant and 1/16th of the RSUs vest every 3 months thereafter, so as to be 100% vested on the fourth anniversary of the vesting commencement date.
Restricted stock units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total unrecognized compensation cost, restricted stock units	48.7
Weighted average recognition period	2 years 10 months 24 days
Aggregate intrinsic value of unvested restricted stock units	109.5

Employee_Benefits_and_Stockbas3

Employee Benefits and Stock-based Compensation - Classification of Stock-based Compensation (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Stock-based compensation:
Total stock-based compensation	$15,692	$8,535	$4,999
Cost of revenue [Member]
Stock-based compensation:
Total stock-based compensation	343	178	92
Research and development [Member]
Stock-based compensation:
Total stock-based compensation	8,654	4,887	2,942
Selling, general and administrative [Member]
Stock-based compensation:
Total stock-based compensation	$6,695	$3,470	$1,965

Employee_Benefits_and_Stockbas4

Employee Benefits and Stock-based Compensation - Weighted-Average Assumptions Used to Estimate Fair Value (Detail)	12 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Dividend yield	0.00%	0.00%	0.00%
Stock options [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility	64.00%	65.00%	66.00%
Risk-free interest rate	1.93%	1.55%	0.91%
Expected term (years)	6 years 4 days	6 years 22 days	6 years 18 days
Dividend yield	0.00%	0.00%	0.00%
Employee stock purchase plan [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Volatility	49.00%	52.00%	51.00%
Risk-free interest rate	0.07%	0.04%	0.18%
Expected term (years)	6 months	6 months	11 months 9 days
Dividend yield	0.00%	0.00%	0.00%

Employee_Benefits_and_Stockbas5

Employee Benefits and Stock-based Compensation - Stock Option Activities (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Shares, Outstanding	3,358,706	4,344,535	4,375,906
Shares, Granted	428,781	255,520	451,071
Shares, Exercised	-1,456,944	-1,160,286	-313,827
Shares, Forfeited	-48,634	-81,063	-168,615
Shares, Outstanding	2,281,909	3,358,706	4,344,535
Shares, Exercisable	1,553,901
Shares, Vested and expected to vest	2,239,650
Weighted-Average Exercise Price, Outstanding	$6.92	$6.07	$5.63
Weighted-Average Exercise Price, Granted	$36.33	$18.14	$8.79
Weighted-Average Exercise Price, Exercised	$5.84	$5.96	$3.21
Weighted-Average Exercise Price, Forfeited	$13.38	$10.34	$7.22
Weighted-Average Exercise Price, Outstanding	$13	$6.92	$6.07
Weighted-Average Exercise Price, Exercisable	$7.22
Weighted-Average Exercise Price, Vested and expected to vest	$12.68
Weighted-Average Grant-date Fair Value, Granted	$21.37	$10.85	$5.23
Total Intrinsic Value of options Exercised, Exercised	$46,427	$18,217	$2,087
Weighted-Average Remaining Contractual Term, Outstanding	6 years 4 months 6 days
Weighted-Average Remaining Contractual Term, Exercisable	5 years 3 months 18 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	6 years 3 months 18 days
Aggregate Intrinsic Value, Outstanding	96,547
Aggregate Intrinsic Value, Exercisable	74,735
Aggregate Intrinsic Value, Vested and expected to vest	$95,482

Employee_Benefits_and_Stockbas6

Employee Benefits and Stock-based Compensation - Restricted Stock Units Activities (Detail) (Restricted stock units [Member], USD $)	12 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Restricted stock units [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Shares, Unvested, beginning balance	1,410,089	339,217
Shares, Granted	1,111,204	1,265,472	345,171
Shares, Vested	-484,296	-174,888
Shares, Forfeited	-56,549	-19,712	-5,954
Shares, Unvested, ending balance	1,980,448	1,410,089	339,217
Weighted-Average Grant-Date Fair Value, Unvested, beginning balance	$14.02	$9.99
Weighted-Average Grant-Date Fair Value, Granted	$38.60	$14.78	$9.99
Weighted-Average Grant-Date Fair Value, Vested	$17.39	$11.91
Weighted-Average Grant-Date Fair Value, Forfeited	$19.93	$11.97	$9.99
Weighted-Average Grant-Date Fair Value, Unvested, ending balance	$26.82	$14.02	$9.99

Net_Income_Per_Ordinary_Share_1

Net Income Per Ordinary Share - Computation of Basic and Diluted Net Income Per Ordinary Share (Detail) (USD $)	12 Months Ended
In Thousands, except Share data, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Numerator:
Net income	$50,571	$25,654	$18,188
Less: amount allocable to preference shareholders			-9,517
Less: amount allocable to unvested early exercised options	-11	-31	-61
Net income allocable to ordinary shareholders - basic	50,560	25,623	8,610
Undistributed earnings reallocated to ordinary shareholders	1	2	432
Net income allocable to ordinary shareholders - diluted	$50,561	$25,625	$9,042
Denominator:
Weighted-average ordinary shares outstanding	29,749,354	27,713,998	13,599,273
Less: weighted-average unvested early exercised options subject to repurchase	-6,701	-33,220	-87,627
Weighted-average ordinary shares - basic	29,742,653	27,680,778	13,511,646
Effect of potentially dilutive securities:
Employee stock options	1,818,401	2,034,500	1,443,809
Restricted stock units	704,788	316,350	16,930
Employee stock purchase plan	12,285	138,461	27,230
Warrants to purchase ordinary shares		2,474	6,737
Over-allotment shares			10,634
Weighted-average ordinary shares - diluted	32,278,127	30,172,563	15,016,986
Net income per ordinary share:
Basic	$1.70	$0.93	$0.64
Diluted	$1.57	$0.85	$0.60

Net_Income_Per_Ordinary_Share_2

Net Income Per Ordinary Share - Weighted-Average Potentially Dilutive Securities Excluded from Computation of Diluted Net Income Per Ordinary Share (Detail)	12 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	428,027	229,252	11,378,720
Stock options [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	217,514	183,859	2,053,520
Restricted stock units [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	167,702	1,576	60,504
Employee stock purchase plan [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	36,110	10,597	20,356
Early exercised options subject to repurchase [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share	6,701	33,220	87,627
Redeemable Convertible Preference Shares [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Antidilutive shares excluded from computation of earnings per share			9,131,824
Warrants 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			24,889

Income_Taxes_Summary_of_Income

Income Taxes - Summary of Income before Income Taxes (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Results Of Operations Income Before Income Taxes [Abstract]
U.S. operations	$1,978	$1,990	$3,264
Non-U.S. operations	50,058	25,905	16,778
Income before income taxes	$52,036	$27,895	$20,042

Income_Taxes_Schedule_of_Incom

Income Taxes - Schedule of Income Tax Provision (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Current:
U.S. federal tax	$3,135	$1,738	$2,022
U.S. state taxes	93	23	5
Non-U.S. foreign taxes	1,348	1,058	701
Current income tax provision	4,576	2,819	2,728
Deferred:
U.S. federal tax	-3,208	-952	-743
U.S. state taxes		341	-109
Non-U.S. foreign taxes	97	33	-22
Deferred income tax provision	-3,111	-578	-874
Provision for income taxes	$1,465	$2,241	$1,854

Income_Taxes_Additional_Inform

Income Taxes - Additional Information (Detail) (USD $)	12 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013	Feb. 01, 2014	Feb. 01, 2013	Feb. 01, 2012
Income Taxes [Line Items]
U.S. federal income tax rate	34.00%	34.00%	34.00%
Cumulative undistributed earnings of foreign subsidiaries	$28,600,000
Deferred tax liabilities, not recognized	4,100,000
Gross deferred tax assets, net of deferred tax liabilities before valuation allowance	9,800,000	5,000,000
Unrecognized tax benefits	4,671,000	3,583,000	3,018,000	3,583,000	3,018,000	2,213,000
Unrecognized tax benefits that would impact effective tax rate	2,800,000
Income tax liabilities considered as other long term liabilities	1,200,000	1,300,000
Interest expense and penalties related to uncertain tax positions	7,180	37,000	23,000
Noncurrent liabilities related to interest and penalties for uncertain tax positions	160,000	153,000
Long term income taxes payable, including estimated interest and penalties	1,400,000
Federal [Member]
Income Taxes [Line Items]
Research and development credit carryforwards	2,600,000
Federal credits begin to expire in fiscal year	2034
California state [Member]
Income Taxes [Line Items]
Research and development credit carryforwards	$5,900,000

Income_Taxes_Schedule_of_Incom1

Income Taxes - Schedule of Income Tax Provision Differed from Amounts Computed by Applying U.S. Federal Income Tax Rate (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Income Tax Disclosure [Abstract]
U.S. federal tax at statutory rate	$17,692	$9,484	$6,814
U.S. state taxes	90	361	-107
Non-U.S. foreign tax differential	-15,644	-7,674	-4,513
Stock-based compensation	1,601	927	682
U.S. R&D credit	-2,298	-858	-890
Other	24	1	-132
Provision for income taxes	$1,465	$2,241	$1,854

Income_Taxes_Schedule_of_Defer

Income Taxes - Schedule of Deferred Tax Assets and Liabilities (Detail) (USD $)	Jan. 31, 2015	Jan. 31, 2014
In Thousands, unless otherwise specified
Deferred tax assets:
Federal and state credits	$6,465	$2,587
Expenses not currently deductible	1,590	1,149
Foreign deferred		26
Stock-based compensation	2,044	1,460
Gross deferred tax assets	10,099	5,222
Valuation allowance	-3,996	-2,302
Total deferred tax assets	6,103	2,920
Deferred tax liabilities
Property and equipment	-199	-187
Foreign deferred	-70
Net deferred tax assets	$5,834	$2,733

Income_Taxes_Summary_of_Tax_Va

Income Taxes - Summary of Tax Valuation Allowance (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at End of Period	$3,996	$2,302
Valuation Allowance of Deferred Tax Assets [Member]
Valuation and Qualifying Accounts Disclosure [Line Items]
Balance at Beginning of Period	2,302	1,243	1,301
Additional Charged to Expenses	1,694	1,059
Deductions Charged to Expenses or Other Accounts			-58
Balance at End of Period	$3,996	$2,302	$1,243

Income_Taxes_Schedule_of_Recon

Income Taxes - Schedule of Reconciliation of Beginning and Ending Amount of Unrecognized Tax Benefits (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Income Tax Disclosure [Abstract]
Beginning balance	$3,583	$3,018	$2,213
Additions based on tax positions related to the current year	1,284	539	325
Additions for tax positions of prior years	324	62	690
Settlements for prior periods	-43
Lapse of applicable statute of limitations	-477	-36	-210
Ending balance	$4,671	$3,583	$3,018

Commitments_and_Contingencies_1

Commitments and Contingencies - Additional Information (Detail) (USD $)	12 Months Ended
	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Loss Contingencies [Line Items]
Net operating lease expenses	$5,800,000	$5,000,000	$4,300,000
Total manufacturing purchase commitments	27,500,000	13,700,000
Indemnification agreement [Member]
Loss Contingencies [Line Items]
Payments under indemnification obligations	0	0
Liabilities recorded under indemnification obligations	$0	$0

Commitments_and_Contingencies_2

Commitments and Contingencies - Future Annual Minimum Lease Payments (Detail) (USD $)	Jan. 31, 2015
In Thousands, unless otherwise specified
Commitments And Contingencies Disclosure [Abstract]
2016	$5,488
2017	4,968
2018	1,375
2019	238
2020	0
Total future annual minimum lease payments	$12,069

Segment_Reporting_Additional_I

Segment Reporting - Additional Information (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Concentration Risk [Line Items]
Number of reportable segment	1
Long-lived assets	3,075	3,018
Accounts receivable	40,180	18,837
Wintech And Chicony [Member]
Concentration Risk [Line Items]
Accounts receivable	36,200	15,900
Wintech And Chicony [Member] | Sales revenue, net [Member] | Customer concentration risk [Member]
Concentration Risk [Line Items]
Percentage of revenue	89.00%	85.00%	80.00%
Wintech And Chicony [Member] | Sales revenue, net [Member] | Customer concentration risk [Member] | Minimum [Member]
Concentration Risk [Line Items]
Percentage of revenue or accounts receivable	10.00%	10.00%	10.00%
Wintech And Chicony [Member] | Accounts receivable [Member] | Credit concentration risk [Member] | Minimum [Member]
Concentration Risk [Line Items]
Percentage of revenue or accounts receivable	10.00%	10.00%	10.00%
United States [Member]
Concentration Risk [Line Items]
Long-lived assets	1,800	2,000
Asia Pacific [Member]
Concentration Risk [Line Items]
Long-lived assets	1,000	900

Segment_Reporting_Companys_Rev

Segment Reporting - Company's Revenue by Geographic Region (Detail) (USD $)	12 Months Ended
In Thousands, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Revenue from External Customer [Line Items]
Total revenue	$218,278	$157,608	$121,066
Hong Kong [Member]
Revenue from External Customer [Line Items]
Total revenue	196,372	135,382	104,458
Asia Pacific [Member]
Revenue from External Customer [Line Items]
Total revenue	2,358	2,809	550
United States [Member]
Revenue from External Customer [Line Items]
Total revenue	6,677	7,128	7,990
North America [Member]
Revenue from External Customer [Line Items]
Total revenue	6,076	4,594	2,602
Europe [Member]
Revenue from External Customer [Line Items]
Total revenue	$6,795	$7,695	$5,466

RelatedParty_Transactions_Addi

Related-Party Transactions - Additional Information (Detail) (USD $)	12 Months Ended
In Millions, unless otherwise specified	Jan. 31, 2015	Jan. 31, 2014	Jan. 31, 2013
Related party [Member]
Related Party Transaction [Line Items]
Percentage of entity's voting stock owned by related party	10.00%	10.00%	10.00%
Other Entity [Member]
Related Party Transaction [Line Items]
Commitment to make license payment through January 2017	$7.50
Payment for license fees	2.3	1.7	1.8
License expenses commitments included in research and development cost	1.9	1.7	1.8
Investor [Member]
Related Party Transaction [Line Items]
Percentage of investor own voting stock			4.60%
Recognized revenue from related party	125.1	88.7	76.5
Account receivables from related party	$12.10	$7.90