A10 Networks (ATEN) 10-K 24 Feb 17 2016 FY Annual report Financial data

Document and Entity Information

Document and Entity Information - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2016	Feb. 13, 2017	Jun. 30, 2016
Document And Entity Information [Abstract]
Document Type	10-K
Amendment Flag	false
Document Period End Date	Dec. 31, 2016
Document Fiscal Year Focus	2,016
Document Fiscal Period Focus	FY
Trading Symbol	ATEN
Entity Registrant Name	A10 Networks, Inc.
Entity Central Index Key	1,580,808
Current Fiscal Year End Date	--12-31
Entity Filer Category	Accelerated Filer
Entity Common Stock, Shares Outstanding		68,346,582
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float			$ 288.7

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current Assets:
Cash and cash equivalents	$ 28,975	$ 98,117
Marketable securities	85,372	0
Accounts receivable, net of allowances of $3,619 and $4,067 as of December 31, 2016 and December 31, 2015	66,755	57,778
Inventory	15,070	18,291
Prepaid expenses and other current assets	5,137	5,064
Total current assets	201,309	179,250
Property and equipment, net	8,219	8,903
Goodwill and intangible assets	7,940	0
Other non-current assets	3,870	4,398
Total Assets	221,338	192,551
Current Liabilities:
Accounts payable	9,851	10,508
Accrued liabilities	31,525	27,757
Deferred revenue, current	61,334	49,572
Total current liabilities	102,710	87,837
Deferred revenue, non-current	31,574	23,232
Other non-current liabilities	988	1,414
Total Liabilities	135,272	112,483
Commitments and contingencies (Note 5)
Stockholder's equity :
Common stock, par value $0.00001 - 500,000 shares authorized as of December 31, 2016 and 2015; 67,873 and 64,172 shares issued and outstanding as of December 31, 2016 and 2015	1	1
Additional paid-in capital	328,869	301,886
Accumulated other comprehensive loss	(45)	0
Accumulated deficit	(242,759)	(221,819)
Total Stockholders’ Equity	86,066	80,068
Total Liabilities and Stockholders' Equity	$ 221,338	$ 192,551

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement of Financial Position [Abstract]
Allowance for doubtful accounts receivable	$ 3,619	$ 4,067
Common stock, par value (in dollars per share)	$ 0.00001	$ 0.00001
Common stock, shares authorized	500,000,000	500,000,000
Common stock, shares issued	67,873,000	64,172,000
Common stock, shares outstanding	67,873,000	64,172,000

Consolidated Statements of Oper

Consolidated Statements of Operations - USD ($) shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenue:
Products	$ 153,920	$ 138,301	$ 134,486
Services	76,083	60,654	45,021
Total revenue	230,003	198,955	179,507
Cost of revenue:
Products	37,680	33,096	31,084
Services	17,230	15,672	11,853
Total cost of revenue	54,910	48,768	42,937
Gross profit	175,093	150,187	136,570
Operating expenses:
Sales and marketing	104,360	104,531	96,837
Research and development	60,700	54,843	49,903
General and administrative	27,063	27,055	22,938
Litigation expense (benefit)	2,089	2,204	(2,837)
Total operating expenses	194,212	188,633	166,841
Loss from operations	(19,119)	(38,446)	(30,271)
Other income (expense), net:
Interest expense	(424)	(509)	(1,028)
Interest and other income (expense), net	(640)	(332)	(1,914)
Total other expense, net	(1,064)	(841)	(2,942)
Loss before income taxes	(20,183)	(39,287)	(33,213)
Provision for income taxes	757	747	1,507
Net loss	(20,940)	(40,034)	(34,720)
Accretion of redeemable convertible preferred stock dividend	0	0	(1,150)
Net loss attributable to common stockholders	$ (20,940)	$ (40,034)	$ (35,870)
Net loss per share attributable to common stockholders:
Basic and diluted (in dollars per share)	$ (0.32)	$ (0.64)	$ (0.74)
Weighted-average shares used in computing net loss per share attributable to common stockholders:
Basic and diluted (in shares)	65,701	62,428	48,682

Consolidated Statements of Comp

Consolidated Statements of Comprehensive Loss Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Statement of Comprehensive Income [Abstract]
Net loss	$ (20,940)	$ (40,034)	$ (34,720)
Other comprehensive loss, net of tax:
Unrealized loss on marketable securities	(45)	0	0
Comprehensive loss	$ (20,985)	$ (40,034)	$ (34,720)

Consolidated Statement of Stock

Consolidated Statement of Stockholders' Equity (Deficit) - USD ($) shares in Thousands, $ in Thousands	Total	Preferred StockRedeemable Convertible Preferred Stock	Preferred StockConvertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Loss
Balance at beginning of period (shares) at Dec. 31, 2013		80	30,569	10,032
Balance at beginning of period at Dec. 31, 2013	$ (134,880)	$ 81,426	$ 44,749	$ 0	$ 12,185	$ (147,065)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation expense	12,359				12,359	0
Accretion of Series D redeemable convertible preferred stock dividend	(1,150)	$ 1,150			(1,150)
Issuance of common stock in connection with initial public offering net of offering costs (shares)				9,000
Issuance of common stock in connection with initial public offering net of offering costs	120,286				120,286
Conversion of preferred stock to common stock in connection with initial public offering (shares)		80	30,569	39,997
Conversion of preferred stock to common stock in connection with initial public offering	127,325	$ (82,576)	$ (44,749)	$ 1	127,324
Common stock issued under employee equity incentive plans, net of unvested portion (shares)				2,352
Common stock issued under employee equity incentive plans, net of unvested portion	6,574				6,574
Vesting of early exercise stock options, net of repurchases (shares)				(4)
Vesting of early exercise stock options, net of repurchases	771				771
Unrealized loss on marketable securities, net of tax	0
Net loss	(34,720)					(34,720)
Balance at end of period (shares) at Dec. 31, 2014		0	0	61,377
Balance at end of period at Dec. 31, 2014	96,565	$ 0	$ 0	$ 1	278,349	(181,785)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation expense	16,861				16,861
Accretion of Series D redeemable convertible preferred stock dividend	0
Common stock issued under employee equity incentive plans, net of unvested portion (shares)				2,700
Common stock issued under employee equity incentive plans, net of unvested portion	6,232				6,232
Vesting of early exercise stock options, net of repurchases (shares)				95
Vesting of early exercise stock options, net of repurchases	444				444
Unrealized loss on marketable securities, net of tax	0
Net loss	(40,034)					(40,034)
Balance at end of period (shares) at Dec. 31, 2015		0	0	64,172
Balance at end of period at Dec. 31, 2015	80,068	$ 0	$ 0	$ 1	301,886	(221,819)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock based compensation expense	16,922				16,922
Accretion of Series D redeemable convertible preferred stock dividend	0
Common stock issued under employee equity incentive plans, net of unvested portion (shares)				3,664
Common stock issued under employee equity incentive plans, net of unvested portion	10,336				10,336
Common stock issued under asset purchase agreement (shares)				227
Common stock issued under asset purchase agreement	1,313				1,313
Vesting of early exercise stock options, net of repurchases (shares)				(37)
Vesting of early exercise stock options, net of repurchases	211				211
Repurchase and retirement of common stock (shares)				(227)
Repurchase and retirement of common stock	(1,799)				(1,799)
Unrealized loss on marketable securities, net of tax	(45)						(45)
Net loss	(20,940)					(20,940)
Balance at end of period (shares) at Dec. 31, 2016		0	0	67,873
Balance at end of period at Dec. 31, 2016	$ 86,066	$ 0	$ 0	$ 1	$ 328,869	$ (242,759)	$ (45)

Consolidated Statements of Cash

Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Cash flows from operating activities:
Net loss	$ (20,940)	$ (40,034)	$ (34,720)
Adjustments to reconcile net loss to net cash provided by (used in) operating activities:
Depreciation and amortization	8,267	8,716	10,121
Stock-based compensation	16,922	16,861	12,359
Gain on settlement of contractual liability	0	0	(6,993)
Provision for doubtful accounts and sales returns	1,731	2,531	935
Other non-cash items	875	(82)	32
Changes in operating assets and liabilities:
Accounts receivable, net	(11,319)	(5,977)	(17,281)
Inventory	892	(430)	(8,914)
Prepaid expenses and other assets	(96)	(405)	(3,017)
Accounts payable	(334)	1,109	903
Accrued liabilities	3,140	5,345	6,724
Accrued litigation expenses	(151)	6	(6,066)
Deferred revenue	20,104	15,584	15,989
Other	(313)	167	(610)
Net cash provided by (used in) operating activities	18,778	3,391	(30,538)
Cash flows from investing activities:
Proceeds from sales and maturities of marketable securities	40,628	0	0
Purchases of marketable securities	(126,231)	0	0
Purchases of property and equipment	(4,872)	(3,477)	(6,100)
Purchase of intangible asset	(1,500)	0	0
Payment for acquisition	(4,380)	0	0
Net cash used in investing activities	(96,355)	(3,477)	(6,100)
Cash flows from financing activities:
Proceeds from issuance of common stock under employee equity incentive plans, net of repurchases	10,336	6,019	7,030
Repurchase and retirement of common stock	(1,799)	0	0
Proceeds from initial public offering, net of offering costs	0	0	121,017
Principal payments on revolving credit facility	0	0	(20,000)
Other	(102)	279	(297)
Net cash provided by financing activities	8,435	6,298	107,750
Net increase (decrease) in cash and cash equivalents	(69,142)	6,212	71,112
Cash and cash equivalents - beginning of period	98,117	91,905	20,793
Cash and cash equivalents - end of period	28,975	98,117	91,905
Supplemental Disclosures:
Cash paid for income taxes, net of refunds	581	980	1,108
Cash paid for interest	194	170	503
Non-Cash Investing and Financing Activities:
Inventory transfers to property and equipment	2,360	2,840	5,379
Vesting of early exercised stock options	211	444	771
Purchases of property and equipment included in accounts payable	162	486	78
Conversion of preferred stock into common stock	0	0	127,325
Accretion of Series D redeemable convertible preferred stock	0	0	1,150
Costs related to the initial public offering included in accounts payable and accrued liabilities	0	0	75
Common stock issued under asset purchase agreement	$ 1,313	$ 0	$ 0

Description of Business and Sum

Description of Business and Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business and Summary of Significant Accounting Policies	Description of Business and Summary of Significant Accounting Policies Description of Business A10 Networks, Inc. (together with our subsidiaries, the “Company”, “we”, “our” or “us”) was incorporated in California in 2004 and reincorporated in Delaware in March 2014. We are headquartered in San Jose, California and have wholly-owned subsidiaries throughout the world including Asia and Europe. Our solutions enable our customers to secure and optimize the performance of their data center and cloud applications and secure their users, applications and infrastructure from internet, web and network threats at scale. Our product portfolio consists of six advanced application delivery and security products; Application Delivery Controllers ("ADC"), Lightning Application Delivery Service (“Lightning ADS”), Carrier Grade Network Address Translation ("CGN"), Threat Protection System ("TPS"), SSL Insight (“SSLi”) and Convergent Firewall ("CFW"). They are available in a variety of form factors, such as optimized hardware appliances, bare metal software, virtual appliances, and cloud-native software. These choices make our portfolio among the most comprehensive in the industry. Basis of Presentation The accompanying consolidated financial statements include those of A10 Networks, Inc. and its subsidiaries, after elimination of all intercompany accounts and transactions. We have prepared the accompanying consolidated financial statements in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and pursuant to the rules and regulations of the United States Securities and Exchange Commission (the “SEC”). Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires us to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Those estimates and assumptions affect revenue recognition and deferred revenue, the allowance for doubtful accounts, the sales return reserve, the valuation of inventory, the fair value of marketable securities, contingencies and litigation, acquisition related purchase price allocations, accrued liabilities, and the determination of fair value of stock-based compensation. These estimates are based on information available as of the date of the consolidated financial statements; therefore, actual results could differ from management’s estimates. Significant Accounting Policies Cash and Cash Equivalents We consider all highly liquid investments with an original maturity of 90 days or less at the date of purchase to be cash equivalents. Marketable securities We classify our investments in debt and equity securities as available-for-sale and record these investments at fair value. These investments are classified as current assets and included in marketable securities on the consolidated balance sheets. Unrealized gains and losses are reported in accumulated other comprehensive income (loss), net of taxes, in stockholders’ equity. Realized gains and losses are determined based on the specific identification method and are reflected in our consolidated statements of operations. Realized gains and losses and other-than-temporary impairment charges, if any, on marketable securities are reported in interest and other income (expense), net as incurred. We regularly review our investment portfolio to identify and evaluate investments that have indicators of possible impairment. Investments are considered impaired when a decline in fair value is judged to be other-than-temporary. If the cost of an individual investment exceeds its fair value, we evaluate, among other factors, general market conditions, the duration and extent to which the fair value is less than cost, and our intent and ability to hold the investment. Once a decline in fair value is determined to be other-than-temporary, we will record an impairment charge and establish a new cost basis in the investment. Fair Value Measurement Our financial instruments consist of cash, cash equivalents, marketable securities, accounts receivable and accounts payable. Accounts receivable and accounts payable are stated at their carrying value, which approximates fair value due to the short time to the expected receipt or payment. Our cash equivalents, which include money market funds, are measured and recorded at fair value on a recurring basis. Marketable securities are comprised of certificates of deposit, corporate securities, U.S. Treasury and agency securities, commercial paper and asset-backed securities and are measured at fair value using the three-level valuation hierarchy as described below. Level 1 - Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2 - Inputs are observable, quoted prices for identical assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities. Level 3 - Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data. Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable are recorded at invoice amounts, net of allowances for doubtful accounts. We evaluate the collectability of our accounts receivable based on known collection risks and historical experience. In circumstances where we are aware of a specific customer’s inability to meet its financial obligations to us (e.g., bankruptcy filings or substantial downgrading of credit ratings), we record a specific reserve for bad debts against amounts due to reduce the net recognized receivable to the amount we reasonably believe will be collected. For all other customers, we record reserves for bad debts based on the length of time the receivables are past due and our historical experience of collections and write-offs. Inventory Inventory consists primarily of finished goods and related component parts and is stated at the lower of standard cost (which approximates actual cost on a first-in, first-out basis) or market value (estimated net realizable value). We evaluate inventory for excess and obsolete products, based on management’s assessment of future demand and market conditions. Inventory write-downs, once established, are not reversed as they establish a new cost basis for the inventory. Inventory write downs are included as a component of cost of products revenue in the accompanying consolidated statements of operations. Property and Equipment, Net Property and equipment, including leasehold improvements, are stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the related assets. Depreciation on property and equipment, excluding leasehold improvements, ranges from 1 to 3 years. Leasehold improvements are amortized on a straight-line basis over the shorter of the estimated useful lives of the assets or the remaining lease term. Amortization on leasehold improvements ranges from 2 to 8 years. Goodwill Goodwill represents the excess of purchase consideration over the fair values of assets acquired and liabilities assumed in a business combination. Goodwill is not amortized but is reviewed for possible impairment annually in the fourth quarter or more frequently if impairment indicators arise. We have one reporting unit for goodwill impairment tests, and the fair value of our reporting unit has been determined by our enterprise value. When assessing goodwill for impairment, we first perform a qualitative assessment to determine whether further impairment testing is necessary. If, as a result of its qualitative assessment, it is more-likely-than-not (i.e. greater than 50% chance) that the fair value of our reporting unit is less than its carrying amount, the quantitative impairment test will be required. Examples of events and circumstances that might indicate that a reporting unit’s fair value is less than the carrying amount include macro-economic conditions such as (i) a significant adverse change in customer demand or a severe deterioration in the entity’s operating environment and market conditions; (ii) entity-specific events such as increasing costs, declining financial performance, or loss of key personnel; or (iii) other events such as an expectation that a reporting unit will be sold or there will be a sustained decrease in the stock price on either an absolute basis or relative to peers. If it is determined, as a result of the qualitative assessment, that it is more-likely-than-not that the fair value of our reporting unit is less than its carrying amount, we perform a two-step impairment test on goodwill. The first step requires the identification of the reporting units and a comparison of the fair value of a reporting unit with its carrying amount, including goodwill. If the fair value of the reporting unit is less than its carrying value, an indication of goodwill impairment exists for the reporting unit, and the second step of the impairment test is performed to compute the amount of the impairment. Under the second step, an impairment loss is recognized for any excess of the carrying amount of the reporting unit's goodwill over the implied fair value of that goodwill. Intangible Assets Intangible assets consist primarily of developed technology, patents and acquired customer relationships resulting from acquisitions. Intangible assets are recorded at fair value and amortized on a straight-line basis over their estimated useful lives, which range from 5 to 10 years. Impairment of Long-Lived Assets We evaluate our property and equipment for impairment whenever events or changes in circumstances indicate that the carrying amount of our long-lived asset may not be recoverable. Recoverability of an asset group is measured by comparison of its carrying amount to the expected future undiscounted cash flows that the asset group is expected to generate. If it is determined that an asset group is not recoverable, an impairment loss is recorded in the amount by which the carrying amount of the asset group exceeds its fair value. Revenue Recognition We derive revenue from two sources: (i) products revenue, which includes hardware and perpetual software license revenue; and (ii) services revenue, which includes post contract support (“PCS”), subscription, professional services, and training. A substantial portion of our revenue is from sales of our products and services through distribution channel partners, such as resellers and distributors. Revenue is recognized, net of applicable taxes, when all of the following criteria are met: persuasive evidence of an arrangement exists, delivery or performance has occurred, the sales price is fixed or determinable, and collection is reasonably assured. We define each of the four criteria above as follows: • Persuasive evidence of an arrangement exists. Evidence of an arrangement consists of a purchase order issued pursuant to the terms and conditions of a master sales agreement. • Delivery or performance has occurred. We use shipping documents or written evidence of customer acceptance, when applicable, to verify delivery or performance. We recognize product revenue upon transfer of title and risk of loss, which primarily is upon shipment to customers. We do not have significant obligations for future performance, such as customer rights of return or pricing credits associated with our sales. • The sales price is fixed or determinable. We assess whether the sales price is fixed or determinable based on payment terms and whether the sales price is subject to refund or adjustment. Standard payment terms to customers range from 30 to 90 days. • Collection is reasonably assured. We assess probability of collection on a customer-by-customer basis. Our customers are subjected to a credit review process that evaluates their financial condition and ability to pay for products and services. PCS revenue includes arrangements for software support and technical support for our products. PCS is offered under renewable, fee-based contracts, which include technical support, hardware repair and replacement parts, bug fixes, patches, and unspecified upgrades on a when-and-if available basis. Revenue for PCS services is recognized on a straight-line basis over the service contract term, which is typically one year, but can be up to five years. Unearned PCS revenue is included in deferred revenue. Professional service revenue primarily consists of the fees we earn related to installation and consulting services. We recognize revenue from professional services upon delivery or completion of performance. Professional service arrangements are typically short term in nature and are largely completed within 30 to 90 days from the start of service. Multiple-Element Arrangements Our hardware with the embedded software solutions (which is a proprietary operating system that together with the hardware delivers the functionality desired by our customers), is considered a separate unit of accounting from PCS because it has value to the customer on a standalone basis and our sales arrangements do not include a right of return for delivered products. For multiple-element arrangements, we allocate revenue to each unit of accounting based on an estimated selling price at the inception of the arrangement. The total arrangement consideration is allocated to each separate unit of accounting using the relative selling price method. We limit the amount of revenue recognized for delivered elements to an amount that is not contingent upon future delivery of additional products or service. When applying the relative selling price method, we determine the selling price for each element using (i) vendor-specific objective evidence, or VSOE, of selling price, if available; (ii) third-party evidence, or TPE, of selling price, if VSOE is not available; and (iii) best estimate of selling price, or BESP, if neither VSOE nor TPE is available. • VSOE. We determine VSOE based on our historical pricing and discounting practices for the specific products and services when sold separately. In determining VSOE, we require that a substantial majority of the stand-alone selling prices fall within a reasonably narrow pricing range. • TPE. When VSOE cannot be established for deliverables in multiple-element arrangements, we apply judgment with respect to whether we can establish a selling price based on TPE. TPE is determined based on competitor prices for interchangeable products or services when sold separately to similarly situated customers. However, as our products contain a significant element of proprietary technology and our solutions offer substantially different features and functionality, the comparable pricing of products with similar functionality typically cannot be obtained. Additionally, as we are unable to reliably determine what competitors products’ selling prices are on a stand-alone basis, we are not typically able to determine TPE. • BESP. When we are unable to establish selling price using VSOE or TPE, we use BESP in our allocation of arrangement consideration. The objective of BESP is to determine the price at which we would transact a sale if the product or service was sold regularly on a standalone basis. As we have not been able to establish VSOE or TPE for our products and some of our services, we determine BESP for the purposes of allocating the arrangement, primarily based on historical transaction pricing. Historical transactions are segregated based on our pricing model and go-to-market strategy, which include factors such as the geographies in which our products and services were sold (domestic or international), offering type (product series, and level of support for PCS) and type of sales channel. The determination of BESP is made through consultation with and approval by management. We may occasionally accept returns to address customer satisfaction issues or solution-fit issues even though there is no contractual provision for such returns. We estimate returns for sales to customers based on historical returns rates applied against current-period gross revenues. Specific customer returns and allowances are considered within this estimate. Management also analyzes changes in customer demand and acceptance of products when evaluating the adequacy of returns and sales allowances. Deferred Revenue Deferred product revenue relates to arrangements where not all revenue recognition criteria have been met. Deferred services revenue primarily represents PCS contracts billed in advance and revenue is recognized ratably over the service contract term, typically 1 to 5 years. Shipping and Handling Shipping and handling charges billed to customers are included in revenue in the period shipped and the related costs are included in cost of revenue. Research and Development Costs Research and development efforts are focused on new product development and on developing additional functionality for our existing products. These expenses consist of personnel costs, and to a lesser extent, prototype materials, depreciation and certain allocated facilities and information technology costs. We expense research and development costs as incurred. Stock-Based Compensation Stock-based compensation expense is measured on the grant date based on the fair value of the award, net of estimated forfeitures, and recognized on a straight-line basis over the requisite service period. The fair value of restricted stock units (“RSUs”) is estimated using our stock price on the grant date. The fair value of options and employee stock purchase rights is estimated using the Black-Scholes model on the grant date. The Black-Scholes model determines the fair value of share-based payment awards based on assumptions including expected term, stock price volatility, and risk-free interest rate. The fair value of market-performance based restricted stock units (“MSUs”) is valued using the Monte Carlo simulation model, which uses the stock price, expected volatility and risk-free interest rate to determine the fair value. Warranty Costs Our appliance hardware and software generally carry a warranty period of 90 days . Estimates of future warranty costs are based on historical returns and the application of the historical return rates to our in-warranty installed base. Warranty costs to repair or replace items sold to customers have been insignificant for the years ended December 31, 2016 , 2015 and 2014 . Foreign Currency The functional currency of our foreign subsidiaries is the U.S. dollar. Transactions denominated in non-functional currencies are remeasured to the functional currency at the average exchange rate for the period. Non-functional currency monetary assets and liabilities are remeasured to the functional currency using the exchange rate in effect at the balance sheet date, and non-monetary assets and liabilities are remeasured at historical exchange rates. Gains and losses related to remeasurement are recorded in interest and other income (expense), net in the consolidated statements of operations. Income Taxes We account for 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 our consolidated financial statements or in our tax returns. Estimates and judgments occur in the calculation of certain tax liabilities and in the determination of the recoverability of certain deferred income tax assets, which arise from temporary differences and carryforwards. Deferred income tax assets and liabilities are measured using the currently enacted tax rates that apply to taxable income in effect for the years in which those tax assets are expected to be realized or settled. We regularly assess the likelihood that our deferred tax assets will be recovered from future taxable income and, to the extent we believe, based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through an adjustment to income tax expense. The factors used to assess the likelihood of realization of our deferred tax assets include our forecast of future taxable income and available tax planning strategies that could be implemented to realize the net deferred tax assets. Assumptions represent our best estimates and involve inherent uncertainties and the application of our judgment. We account for uncertainty in income taxes recognized in our consolidated financial statements by regularly reviewing our tax positions and benefits to be realized. We recognize tax liabilities based upon our estimate of whether, and the extent to which, additional taxes will be due when such estimates are more-likely-than-not to be sustained. An uncertain income tax position will not be recognized if it has less than a 50% likelihood of being sustained upon examination by taxing authorities. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties. Segment Information An operating segment is a component of an enterprise for which its discrete financial information is available and its operating results are regularly reviewed by chief operating decision maker for resource allocation decisions and performance assessment. Our chief operating decision maker is our Chief Executive Officer. Our Chief Executive Officer reviews financial information presented on a consolidated basis for purposes of allocating resources and assessing performance of the Company. Accordingly, we have one reportable segment and one operating segment. Vendor Business Concentration We rely on third parties to manufacture our hardware appliances and we purchase raw materials from third-party vendors. We outsourced substantially all of our manufacturing services to two independent manufacturers. In addition, we purchase certain strategic component inventory which is consigned to our third-party manufacturers. Other hardware components included in our products are sourced from various suppliers by our manufacturers and are principally industry standard parts and components that are available from multiple vendors. Concentration of Credit Risk and Significant Customers Financial instruments that potentially subject us to concentrations of credit risk consist of cash, cash equivalents, short-term investments and accounts receivable. Our cash and investments are held and invested in high-credit quality financial instruments by recognized financial institutions and therefore subject to minimum credit risk. Our accounts receivable are unsecured and represent amounts due to us based on contractual obligations of our customers. We mitigate credit risk in respect to accounts receivable by performing periodic credit evaluations based on a number of factors, including past transaction experience, evaluation of credit history and review of the invoicing terms of the contract. We generally do not require our customers to provide collateral to support accounts receivable. Significant customers, including distribution channel partners and direct customers, are those which represent more than 10% of our total revenue for each period presented, or our gross accounts receivable balance as of each respective balance sheet date. Revenue from our significant customers as a percentage of our total revenue are as follows: Years Ended December 31, 2016 2015 2014 Customer A 14% * 13% * represents less than 10% of total revenue Three customers accounted for 15% , 13% and 11% of our total gross accounts receivable as of December 31, 2016 . Two customers accounted for 27% and 11% of our gross accounts receivable as of December 31, 2015 . Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (" FASB") issued Accounting Standard Update ("ASU") No. 2014-09, Revenue from Contracts with Customers (Topic 606) , which will supersede most of the existing revenue recognition guidance under U.S. GAAP. This ASU requires an entity to recognize revenue when it transfers 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 and requires the capitalization of incremental customer acquisition costs and amortization of these costs over the contract period or estimated customer life which will result in the recognition of a contract asset on our balance sheets. This standard is effective for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. Early adoption of one year prior to the required effective date is permitted. However, we do not plan to early adopt. Accordingly, the updated standard is effective for us in the first quarter of 2018. The ASU allows for either full retrospective or modified retrospective adoption. We are still in the process of evaluating which transition method we plan to adopt with such decision depending on a number of factors, including system readiness and the magnitude of the potential impact on our financial statements. While we are continuing to assess all potential impacts of the new standard, we currently do not believe this standard will have a material impact on our consolidated financial statements and related disclosures. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This new accounting standard primarily requires lessees to recognize most leases on their balance sheets but record expenses on their income statements in a manner similar to current accounting. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. The guidance is effective for annual periods beginning after December 15, 2018 with early adoption permitted. We are currently evaluating the impact of this guidance on our financial statements. In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. The new guidance requires the recognition of the income tax effects of awards in the income statement when the awards vest or are settled, thus eliminating additional paid in capital pools. The guidance also allows for the employer to repurchase more of an employee’s shares for tax withholding purposes without triggering liability accounting. In addition, the guidance allows for a policy election to account for forfeitures as they occur rather than on an estimated basis. This guidance is effective for annual and interim reporting periods of public entities beginning after December 15, 2016 with early adoption permitted. We will be adopting this guidance in the first quarter of fiscal year 2017 and do not believe this standard will have a material impact on our consolidated financial statements.

Marketable Securities and Fair

Marketable Securities and Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Marketable Securities and Fair Value Measurements	Marketable Securities and Fair Value Measurements As of December 31, 2016 , the estimated fair value of our marketable securities, classified as available for sale, are as follows (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Certificates of deposit $ 12,499 $ 9 $ — $ 12,508 Corporate securities 42,765 9 (42 ) 42,732 U.S. Treasury and agency securities 5,190 — (14 ) 5,176 Commercial paper 11,470 1 (2 ) 11,469 Asset-backed securities 13,493 — (6 ) 13,487 $ 85,417 $ 19 $ (64 ) $ 85,372 During the year ended December 31, 2016 , we did not reclassify any amount to earnings from accumulated other comprehensive loss related to unrealized gains or losses. We did not have any marketable securities as of December 31, 2015. The following table summarizes the cost and estimated fair value of marketable securities based on contractual maturities as of December 31, 2016 (in thousands): Amortized Cost Fair Value Less than 1 year $ 53,500 $ 53,503 Mature in 1 - 3 years 31,917 31,869 $ 85,417 $ 85,372 All available-for-sale securities have been classified as current assets, based on management's ability to use the funds in current operations. Marketable securities in an unrealized loss position as of December 31, 2016 consisted of the following (in thousands): Fair Value Unrealized Losses Corporate securities $ 28,537 $ (42 ) U.S. Treasury and agency securities 5,176 (14 ) Commercial paper 8,974 (2 ) Asset-backed securities 10,664 (6 ) $ 53,351 $ (64 ) As of December 31, 2016 , no marketable securities were in a continuous unrealized loss position for more than twelve months. Based on evaluation of securities that have been in a continuous loss position, we did not recognize any other-than-temporary impairment charges for the year ended December 31, 2016 . The following is a summary of our cash, cash equivalents and marketable securities measured at fair value on a recurring basis (in thousands): December 31, 2016 December 31, 2015 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Cash $ 18,672 $ — $ — $ 18,672 $ 27,036 $ — $ — $ 27,036 Cash equivalents 10,303 — — 10,303 71,081 — — 71,081 Certificates of deposit — 12,508 — 12,508 — — — — Corporate securities — 42,732 — 42,732 — — — — U.S. Treasury and agency securities — 5,176 — 5,176 — — — — Commercial paper — 11,469 — 11,469 — — — — Asset-backed securities — 13,487 — 13,487 — — — — $ 28,975 $ 85,372 $ — $ 114,347 $ 98,117 $ — $ — $ 98,117

Balance Sheet and Statement of

Balance Sheet and Statement of Operations Components	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Balance Sheet and Statement of Operations Components	Balance Sheets and Statement of Operations Components Allowance for Doubtful Accounts and Sales Return Reserve December 31, 2016 December 31, 2015 December 31, 2014 (in thousands) Allowance for doubtful accounts, beginning balance $ 2,887 $ 1,904 $ 1,836 Charged to expenses 1,166 1,590 76 Write-offs (1,147 ) (607 ) (8 ) Allowance for doubtful accounts, ending balance $ 2,906 $ 2,887 $ 1,904 December 31, 2016 December 31, 2015 December 31, 2014 (in thousands) Sales return reserve, beginning balance $ 1,180 $ 1,342 $ 902 Charged to revenue 565 940 858 Utilization (1,032 ) (1,102 ) (418 ) Sales return reserve, ending balance $ 713 $ 1,180 $ 1,342 Inventory December 31, December 31, (in thousands) Raw materials $ 6,669 $ 9,418 Finished goods 8,401 8,873 Total inventory $ 15,070 $ 18,291 Property and Equipment, Net Useful Life December 31, December 31, (in years) (in thousands) Equipment 1-3 $ 41,815 $ 35,836 Software 1-3 3,801 3,548 Furniture and fixtures 1-3 865 864 Leasehold improvements 2-8 2,724 2,492 Construction in progress 258 83 Property and equipment, gross 49,463 42,823 Less: accumulated depreciation and amortization (41,244 ) (33,920 ) Total property and equipment, net $ 8,219 $ 8,903 Depreciation and amortization on our property and equipment for the years ended December 31, 2016 , 2015 and 2014 was $7.6 million , $8.6 million and $10.0 million , respectively. Goodwill and Intangible Assets Activity related to goodwill for the year ended December 31, 2016 is as follows (in thousands): Balance as of December 31, 2015 $ 72 Acquisitions 1,235 Balance as of December 31, 2016 $ 1,307 Purchased intangible assets consisted of the following (in thousands): December 31, 2016 December 31, 2015 Gross Carrying Amount Accumulated Amortization Net Carrying Value Gross Carrying Amount Accumulated Amortization Net Carrying Value Developed technology $ 5,050 $ (505 ) $ 4,545 $ — $ — $ — Patents 2,936 (848 ) 2,088 1,436 (641 ) 795 Total $ 7,986 $ (1,353 ) $ 6,633 $ 3,182 $ (2,387 ) $ 795 Amortization expense related to purchased intangible assets for the years ended December 31, 2016 , 2015 and 2014 was $0.7 million , $0.1 million and $0.1 million , respectively. Purchased intangible assets are amortized over a remaining weighted average useful life of 4.6 years. Future amortization expense for purchased intangible assets as of December 31, 2016 is as follows (in thousands): Fiscal Years Ending December 31, 2017 $ 1,442 2018 1,442 2019 1,442 2020 1,442 2021 865 $ 6,633 Accrued Liabilities December 31, December 31, (in thousands) Accrued compensation and benefits $ 22,326 $ 18,134 Accrued tax liabilities 3,340 4,520 Other 5,859 5,103 Total accrued liabilities $ 31,525 $ 27,757 Deferred Revenue December 31, December 31, (in thousands) Deferred revenue: Products $ 4,182 $ 3,233 Services 88,726 69,571 Total deferred revenue 92,908 72,804 Less: current portion (61,334 ) (49,572 ) Non-current portion $ 31,574 $ 23,232 Settlement of Contractual Liability In May 2014, we reached a settlement agreement with one of our legal service providers which resulted in the reduction of a previously accrued contractual liability that totaled $12.0 million . We made a payment of $5.0 million in accordance with the terms of the settlement agreement in June 2014 and recorded a $7.0 million benefit to litigation expense (benefit) at that time.

Credit Facility

Credit Facility	12 Months Ended
	Dec. 31, 2015
Line of Credit Facility [Abstract]
Credit Facility	Credit Facility In September 2013, we entered into a credit agreement (the “2013 Credit Facility”) with Royal Bank of Canada, JPMorgan Chase Bank, N.A. and Bank of America, N.A. as lenders. The 2013 Credit Facility provided a three -year $35.0 million revolving credit facility, which included a maximum $10.0 million letter of credit facility. We were required to pay quarterly facility fees of 0.45% per annum on the average daily unused portion of the revolving credit facility. We had no outstanding borrowings under this credit facility for any period prior to its expiration on September 30, 2016. In November 2016, we entered into a loan and security agreement (the “2016 Credit Facility”) with Silicon Valley Bank (“SVB”), as the lender. The 2016 Credit Facility provides a three -year, $25.0 million revolving credit subfacility, which includes a maximum of $25.0 million letter of credit subfacility. When our net cash equals or exceeds $50.0 million , loans may be advanced under the 2016 Credit Facility up to the full $25.0 million . When our net cash falls below $50.0 million , loans may be advanced under the 2016 Credit Facility based on a borrowing base equal to a specified percentage of the value of the our eligible accounts receivable. The loans bear interest, at our option, at (i) the prime rate reported in The Wall Street Journal, minus 0.50% or (ii) a LIBOR rate determined in accordance with the 2016 Credit Facility, plus 2.50% . We are required to pay customary closing fees, commitment fees and letter of credit fees for a facility of this size and type. Our obligations under the 2016 Credit Facility are secured by substantially all of our assets, excluding our intellectual property. The 2016 Credit Facility contains customary affirmative and negative covenants. In addition, the 2016 Credit Facility requires us to maintain compliance with an adjusted quick ratio of not less than 1:50:1.00, as determined in accordance with the 2016 Credit Facility. We had no outstanding balance under the 2016 Credit Facility and were in compliance with all facility covenants as of December 31, 2016 .

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Legal Proceedings From time to time, we may be party or subject to various legal proceedings and claims, either asserted or unasserted, which arise in the ordinary course of business, including proceedings and claims that relate to intellectual property matters. Some of these proceedings involve claims that are subject to substantial uncertainties and unascertainable damages. Accordingly, except as disclosed, we have not established reserves or ranges of possible loss related to these proceedings, as at this time in the proceedings, if any, the matters do not relate to a probable loss and/or amounts cannot be reasonably estimated. On January 29, 2015, the Company, the members of our Board of Directors, our Chief Financial Officer, and the underwriters of our March 21, 2014 IPO were named as defendants in a putative class action lawsuit alleging violations of the federal Securities Act of 1933 filed in the Superior Court of the State of California, County of Santa Clara, captioned City of Warren Police and Fire Retirement System v. A10 Networks, Inc., et al., 1-15-CV-276207. Several substantially identical lawsuits were subsequently filed in the same court, bringing the same claims against the same defendants, captioned Arkansas Teacher Retirement System v. A10 Networks, Inc., et al., 1-15-CV-278575 (filed March 25, 2015) and Kaveny v. A10 Networks, Inc., et al., 1-15-CV-279006 (filed April 6, 2015). On May 29, 2015, the aforementioned putative class actions were consolidated under the caption In re A10 Networks, Inc. Shareholder Litigation, 1-15-CV-276207 (the “Class Action”). On July 31, 2015, the defendants filed demurrers to all claims, which were overruled in part on November 12, 2015. . On April 6, 2016, all parties entered into a memorandum of understanding reflecting an agreement in principle to settle all claims against all defendants asserted in the action and providing that we will make a payment of $0.8 million , net of the expected proceeds of insurance policies. The parties subsequently executed a stipulation of settlement, dated June 30, 2016, and filed a motion with the Court seeking preliminary approval of the settlement, which was granted on September 15, 2016. The payment was made in October 2016. The final fairness hearing is scheduled to be held on February 24, 2017. The settlement releases all claims asserted against all defendants and includes the dismissal of all claims against all defendants without any liability or wrongdoing attributed to them. The settlement remains subject to final court approval and other customary conditions. On June 24, 2015, our directors and certain of our officers were named as defendants in a putative derivative lawsuit filed in the Superior Court of the State of California, County of Santa Clara, captioned Hornung v. Chen, et al. , 1-15-CV-282286 (the “Derivative Action”). We were also named as a nominal defendant. The complaint seeks to allege breaches of fiduciary duties and other related claims, arising out of allegations that our officers and directors caused us to infringe patents and intellectual property, improperly approved the settlement of prior litigation, failed to adopt and implement effective internal controls, and caused us to issue false and misleading statements in connection with our IPO. Plaintiff seeks unspecified compensatory damages and other equitable relief. On January 29, 2016, the defendants filed demurrers and a motion to strike parts of the complaint as well as a motion to stay. On May 24, 2016, all parties entered into a memorandum of understanding reflecting an agreement in principle to settle all claims against all defendants asserted in the action, which provides that we implement certain corporate governance measures following final settlement approval. The parties subsequently executed a stipulation of settlement, dated August 26, 2016, and filed a motion with the Court seeking preliminary approval of the settlement. On November 22, 2016, the Court issued an order preliminarily approving the settlement. The final fairness hearing is scheduled to be held on February 24, 2017. The settlement releases all claims asserted against all defendants and includes the dismissal of all claims against all defendants without any liability or wrongdoing attributed to them. The settlement remains subject to final court approval and other customary conditions. Leases and Other Commitments We lease various operating spaces in the United States, Asia, and Europe under non-cancellable operating lease arrangements that expire on various dates through February 2022 . These arrangements require us to pay certain operating expenses, such as taxes, repairs, and insurance and contain renewal and escalation clauses. We recognize rent expense under these arrangements on a straight-line basis over the term of the lease. We have open purchase commitments with third-party contract manufacturers with facilities in Taiwan to supply nearly all of our finished goods inventories, spare parts, and accessories. These purchase orders are expected to be paid within one year of the issuance date. The following table summarizes our non-cancellable operating leases and unconditional purchase obligations as of December 31, 2016 (in thousands): Years Ending December 31, Leases and Other Contractual Obligations Purchase Commitments Total 2017 $ 2,811 $ 14,900 $ 17,711 2018 2,393 — 2,393 2019 1,992 — 1,992 2020 365 — 365 2021 79 — 79 Thereafter 7 — 7 $ 7,647 $ 14,900 $ 22,547 Rent expense was $3.5 million , $3.5 million and $3.4 million for the years ended December 31, 2016 , 2015 and 2014 , respectively. Guarantees and Indemnifications In the normal course of business, we provide indemnifications to customers against claims of intellectual property infringement made by third parties arising from the use of our products. Other guarantees or indemnification arrangements include guarantees of product and service performance, and standby letters of credit for lease facilities and corporate credit cards. We have not recorded a liability related to these indemnification and guarantee provisions and our guarantees and indemnification arrangements have not had any significant impact on our consolidated financial statements to date.

Equity Award Plans

Equity Award Plans	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Equity Award Plans	Equity Award Plans Equity Incentive Plans 2014 Equity Incentive Plan Our 2014 Equity Incentive Plan (the “2014 Plan”) was adopted by our board of directors and approved by our stockholders in March 2014. The 2014 Plan provides for the granting of stock options, restricted stock awards, restricted stock units, stock appreciation rights, performance units and performance shares to our employees, consultants and members of our board of directors. In June 2015, our board of directors adopted and our stockholders approved an amendment and restatement of our 2014 Plan, which increased the number of shares available for issuance under the 2014 Plan by the number of shares subject to awards granted under the 2008 Stock Plan (the “2008 Plan”) that were or may in the future be canceled or otherwise forfeited or repurchased by us after March 20, 2014. A maximum of 8,310,566 shares may become available from such awards granted under the 2008 Plan for issuance under the 2014 Plan. As of December 31, 2015 , we had 3,364,304 shares available for future grant. Annually, the shares authorized for the 2014 Plan will increase by the least of (i) 8,000,000 shares, (ii) 5% of the outstanding shares of common stock on the last day of our immediately preceding fiscal year, or (iii) such other amount as determined by our board of directors. On January 1, 2016 , the number of shares in the 2014 Plan was increased by 3,211,211 shares, representing 5% of the prior year end’s common stock outstanding. In addition, 1,640,324 shares subject to awards granted under the 2008 Plan that had been canceled or otherwise forfeited or repurchased between March 21, 2014 and December 31, 2015 became available for issuance under the 2014 Plan. As of December 31, 2016 , we had 4,241,980 shares available for future grant. On January 1, 2017 , the number of shares in the 2014 Plan was increased by 3,394,376 shares, representing 5% of the prior year end’s common stock outstanding. In addition 266,799 shares subject to awards granted under the 2008 Plan that had been canceled or otherwise forfeited or repurchased during the year ended December 31, 2016 became available for issuance under the 2014 Plan. Vesting periods of awards granted under the 2014 Plan are determined by our board of directors or other committees responsible for administering the 2014 Plan (the "Plan Administrator"). The Plan Administrator determines the contractual terms of awards granted under the 2014 Plan, provided that incentive stock options and stock appreciation rights granted expire no more than ten years from the grant date. In the case of an incentive stock option granted to an employee, who at the time of grant, owns stock representing more than 10% of the total combined voting power of all classes of stock, the per share exercise price shall be no less than 110% of the fair value per share on the date of grant, and the incentive stock option shall expire no later than five years from the date of grant. For incentive stock options granted to any other employee, and nonstatutory stock options and stock appreciation rights granted to employees, consultants, or members of our board of directors, the per share exercise price shall be no less than 100% of the fair value per share on the date of grant. 2014 Employee Stock Purchase Plan The 2014 Employee Stock Purchase Plan (the "2014 Purchase Plan") was adopted by our board of directors and approved by our stockholders in March 2014. The 2014 Purchase Plan consists of a twenty-four month offering period with four six-month purchase periods in each offering period. Employees purchase shares in each purchase period at 85% of the market value of our common stock at the beginning of the offering period or the end of the purchase period, whichever is lower. If the market value of our common stock at the end of the purchase period is less than the market value at the beginning of the offering period, participants will be withdrawn from the then current offering period following their purchase of shares, and automatically will be enrolled in the immediately following offering period. Participants may contribute up to 15% of their eligible compensation, subject to certain limits. The 2014 Purchase Plan provided for an automatic share reserve increase on the first day of each fiscal year beginning 2015 by a number of shares equal to the least of (i) 3,500,000 shares, (ii) 1% of the outstanding common stock on the last day of the immediately preceding fiscal year, or (iii) such other amount as determined by our board of directors. On January 1, 2016, the number of shares in the 2014 Purchase Plan was increased by 642,242 shares, representing 1% of the prior year end’s common stock outstanding. In June 2016, our board of directors adopted, and our stockholders approved an amendment to our 2014 Purchase Plan which removed the automatic annual share increase and increased the number of shares available for issuance under the 2014 Purchase Plan by 4,000,000 shares. As of December 31, 2016 , 4,104,060 shares were available for future issuance under the 2014 Purchase Plan. Employees purchased 1,080,142 shares at an average price of $3.93 and 1,105,015 shares at an average price of $3.56 during the year ended December 31, 2016 and 2015 , respectively. The intrinsic value of shares purchased during the year ended December 31, 2016 and 2015 was $3.5 million and $3.7 million , respectively. The intrinsic value is calculated as the difference between the market value on the date of purchase and the purchase price of the shares. Early Exercise of Stock Options We have allowed certain employees and directors to exercise options granted prior to vesting. The unvested shares are subject to our repurchase right at the original purchase price. The proceeds from the early exercise of stock options initially are recorded in other non-current liabilities and reclassified to common stock as our repurchase right lapses. As of December 31, 2016 and 2015 , 14,307 and 51,884 shares were subject to repurchase at an aggregate price of $0.1 million and $0.3 million , respectively. Option Exchange Program On November 19, 2015, we commenced an option exchange which permitted certain employees and service providers to surrender certain outstanding stock options in exchange for replacement RSUs with a lesser number of shares, subject to a different vesting schedule. This option exchange was completed on December 17, 2015. A total of 344,248 options to purchase shares of common stock with a weighted-average exercise price of $13.58 per share were canceled and replaced with 109,743 RSUs with per share market value of $6.76 , on December 17, 2015. The replacement RSUs started to vest on the one-year anniversary of the grant date. We accounted for this option exchange as a stock option modification in accordance with the provisions of ASC 718 Share-Based Compensation . We are recording the incremental expense of $56,000 in addition to the remaining expense attributable to the exchanged stock options over the vesting period of the new awards. Stock-based Compensation A summary of our stock-based compensation expense is as follows (in thousands): Years Ended December 31, 2016 2015 2014 Stock-based compensation by type of award: Stock options $ 4,153 $ 5,565 $ 5,852 Restricted stock units 12,567 8,871 3,217 Employee stock purchase rights 202 2,425 3,290 $ 16,922 $ 16,861 $ 12,359 Stock-based compensation by category of expense: Cost of revenue $ 1,105 $ 1,533 $ 1,063 Sales and marketing 7,006 7,735 5,829 Research and development 5,732 5,437 3,932 General and administrative 3,079 2,156 1,535 $ 16,922 $ 16,861 $ 12,359 As of December 31, 2016 , we had $32.0 million of unrecognized stock-based compensation expense, net of estimated forfeitures, related to unvested stock-based awards which will be recognized over a weighted-average period of 2.4 years . The fair values of the options and employee stock purchase rights are estimated as of the grant date using the Black-Scholes option-pricing model with the following assumptions: Options Employee Stock Purchase Rights Years Ended December 31, Years Ended December 31, 2016 2015 2014 2016 2015 2014 Expected term (in years) 4.9 4.8 4.8 1.3 1.3 1.3 Risk-free interest rate 1.4% 1.6% 1.8% 0.8% 0.5% 0.3% Expected volatility 49% 50% 41% 42% 41% 27% Dividend rate —% —% —% —% —% —% • Expected Term . We estimate the expected life of options based on an analysis of our historical experience of employee exercise and post-vesting termination behavior considered in relation to the contractual life of the option. The expected term for the 2014 Purchase Plan is based on the term of the purchase period. • Risk-Free Interest Rate . The risk-free interest rate is based on the U.S. Treasury yield curve in effect at the time of grant for zero coupon U.S. Treasury notes with maturities approximately equal to the expected terms of stock options and shares to be issued under the 2014 Purchase Plan. • Expected Volatility . Due to the limited trading history of our own common stock, we determined the share price volatility factor based on a combination of the historical volatility of our own common stock and the historical volatility of our peer group. • Dividend Rate . The expected dividend was assumed to be zero as we have never paid dividends and have no current plans to do so. Stock Options The following table summarizes our stock option activities and related information: Number of Shares (thousands) Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (thousands) Outstanding as of December 31, 2015 9,291 $ 4.78 Granted 672 $ 5.52 Exercised (1,444 ) $ 4.22 Canceled (1) (651 ) $ 6.23 Outstanding as of December 31, 2016 7,868 $ 4.82 6.2 $ 28,931 Vested and expected to vest as of December 31, 2016 7,758 $ 4.82 6.2 $ 28,554 Vested and exercisable as of December 31, 2016 5,688 $ 4.57 5.6 $ 22,363 _____________________________________ (1) Common shares subject to awards granted under the 2008 Plan and canceled after March 21, 2014 are reallocated to the 2014 Plan’s share reserve and become available for issuance under the 2014 Plan. During the years ended 2016 and 2015 , 266,799 shares and 1,640,324 shares of the canceled stock options, respectively, were reallocated and became available for issuance under the 2014 Plan. As of December 31, 2016 , the aggregate intrinsic value represents the excess of the closing price of our common stock of $8.31 over the exercise price of the outstanding in-the-money options. The following table provides information pertaining to our stock options (in thousands, except weighted-average fair values): Years Ended December 31, 2016 2015 2014 Fair value of options granted $ 1,603 $ 869 $ 11,683 Weighted-average fair value of options granted $ 2.38 $ 2.13 $ 2.79 Intrinsic value of options exercised $ 5,990 $ 2,299 $ 14,863 Stock Awards We have granted restricted stock unit awards (“RSUs”) to our employees, consultants and members of our board of directors, and performance-based stock awards (“PSUs”) and market performance-based stock restricted stock unit awards (“MSUs”) to certain company executives. In 2014 and 2015, we granted 540,000 MSUs and 40,000 MSUs, respectively, to certain executives. These MSUs will vest if the closing price of our common stock remains above certain predetermined target prices for 20 consecutive trading days within a 4 -year period following the grant date, subject to continued service by the award holder. No MSUs were vested as of December 31, 2016 . In February 2016, we granted 547,000 PSUs with certain financial and operational targets. These PSUs are subject to service condition vesting requirements with 25% of the PSUs that become eligible to vest upon achievement of the performance targets scheduled to vest on each of the first, second, third and fourth year anniversary of the PSU grant date. None of these PSUs were vested as of December 31, 2016 . In October 2016, we granted 60,641 PSUs with certain financial and operational targets. These PSUs are subject to service condition vesting requirements with scheduled vesting dates March 2017 through June 2018 to the extent they become eligible to vest upon achievement of the performance targets. None of these PSUs were vested as of December 31, 2016 . The following table summarizes our stock award activities and related information: Number of Shares (thousands) Weighted Average Grant Date Fair Value Weighted-Average Remaining Vesting Term (Years) Aggregate Intrinsic Value (thousands) Outstanding as of December 31, 2015 3,452 $ 5.88 Granted 4,550 $ 6.50 Released (1,139 ) $ 8.16 Canceled (904 ) $ 6.56 Outstanding as of December 31, 2016 5,959 $ 5.81 1.6 $ 49,517 The aggregate intrinsic value of outstanding awards is calculated based on the closing price of our common stock of $8.31 on December 31, 2016 . The aggregate fair value of stock awards released as of the respective vesting dates was approximately $9.7 million and $5.6 million for the years ended December 31, 2016 and 2015 , respectively. Stock Repurchase Program On October 27, 2016, our board of directors authorized a share repurchase program for up to $20.0 million of our common stock over the next 12 months. Under the repurchase authorization, shares may be purchased from time to time, subject to general business and market conditions and other investment opportunities, through open market purchases, privately negotiated transactions or other means. The repurchase authorization may be commenced, suspended or discontinued at any time at our discretion. During 2016, we repurchased 226,676 shares at an average price of $7.92 as a part of publicly announced program. The repurchased shares were retired upon delivery to us.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Loss Per Share	Net Loss Per Share Basic net loss per share is computed using the weighted average number of common shares outstanding for the period. Diluted net loss per share is computed using the weighted average number of common shares outstanding for the period plus potential dilutive common shares, including stock options, RSUs and employee stock purchase rights, unless the potential common shares are anti-dilutive. Since we had net losses in the years ended December 31, 2016 , 2015 and 2014 , none of the potential dilutive common shares were included in the computation of diluted shares for these periods, as inclusion of such shares would have been anti-dilutive. The following table presents common shares related to potentially dilutive shares excluded from the calculation of diluted net loss per share as their effect would have been anti-dilutive (in thousands): Years Ended December 31, 2016 2015 2014 Stock options, RSUs and employee stock purchase rights 13,631 10,124 6,415 Common stock subject to repurchase 14 52 196 13,645 10,176 6,611

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes The geographical breakdown of loss before provision for income taxes is as follows (in thousands): Years Ended December 31, 2016 2015 2014 Domestic loss $ (22,978 ) $ (41,677 ) $ (35,593 ) Foreign income 2,795 2,390 2,380 Loss before provision for income taxes $ (20,183 ) $ (39,287 ) $ (33,213 ) The provision for income taxes consists of the following (in thousands): Years Ended December 31, 2016 2015 2014 Current provision for income taxes: State $ 41 $ 55 $ 24 Foreign 1,009 675 1,054 Total current 1,050 730 1,078 Deferred tax expense (benefit): Federal 17 — — Foreign (310 ) 17 429 Total deferred (293 ) 17 429 Provision for income taxes $ 757 $ 747 $ 1,507 The reconciliation of the statutory federal income tax and our effective income tax is as follows (in thousands): Years Ended December 31, 2016 2015 2014 Amount Percentage Amount Percentage Amount Percentage Tax at statutory rate $ (6,862 ) 34.0 % $ (13,358 ) 34.0 % $ (11,292 ) 34.0 % State tax - net of federal benefits 27 (0.1 ) 36 (0.1 ) 16 (0.1 ) Foreign rate differential (666 ) 3.3 (422 ) 1.1 231 (0.7 ) Changes in federal valuation allowance 7,141 (35.4 ) 11,926 (30.4 ) 10,547 (31.8 ) Stock-based compensation 88 (0.4 ) 1,845 (4.7 ) 1,041 (3.1 ) Other permanent items 583 (2.9 ) 415 (1.1 ) 513 (1.5 ) Expenses for uncertain tax positions 358 (1.8 ) 227 (0.6 ) 330 (1.0 ) Other 88 (0.4 ) 78 (0.1 ) 121 (0.4 ) Provision for income taxes $ 757 (3.7 )% $ 747 (1.9 )% $ 1,507 (4.6 )% The tax effects of temporary differences that give rise to significant portions of deferred tax assets (liabilities) are as follows (in thousands): December 31, December 31, Deferred tax assets: Net operating loss carryforwards $ 47,197 $ 46,317 Research and development credits, net of uncertain tax positions 12,953 9,517 Accruals, reserves, and other 21,288 17,904 Stock-based compensation 4,055 2,700 Depreciation and amortization 2,892 2,735 Gross deferred tax assets 88,385 79,173 Valuation allowance (86,935 ) (77,643 ) Total deferred tax assets 1,450 1,530 Deferred tax liabilities: Other (431 ) (805 ) Total deferred tax liabilities (431 ) (805 ) Net deferred tax assets $ 1,019 $ 725 Recognition of deferred tax assets is appropriate when realization of these assets is more likely than not. Based upon the weight of available evidence, which includes our historical operating performance and the recorded cumulative net losses in prior fiscal periods, we recorded a full valuation allowance of $86.9 million and $77.6 million against the net U.S. deferred tax assets as of December 31, 2016 and 2015 , respectively. For the years ended December 31, 2016 , 2015 and 2014 , the valuation allowance increased by $9.3 million , $14.0 million and $11.2 million , respectively. As of December 31, 2016 and 2015 , we had U.S. federal net operating loss carryforwards of $139.0 million and $130.6 million and state net operating loss carryforwards of $68.6 million and $68.4 million , respectively. We track the portion of our net operating loss attributable to stock option benefits in accordance with ASC 718 Compensation-Share Compensation , therefore, these amounts are no longer included in our gross or net deferred tax assets. The gross tax benefit of stock options totals $10.8 million at December 31, 2016 , and will only be recorded to additional paid in capital when these benefits reduce cash taxes payable. The federal net operating loss carryforwards will expire at various dates beginning in the year ending December 31, 2026 , if not utilized. The state net operating losses expire in various years ending between 2017 and 2036 , if not utilized. Additionally, as of December 31, 2016 and 2015 , we had U.S. federal research and development credit carryforwards of $8.5 million and $6.4 million and state research and development credit carryforwards of $8.8 million and $6.4 million . The federal credit carryforwards will begin to expire at various dates beginning in 2027 while the state credit carryforwards can be carried over indefinitely. Utilization of the net operating losses and credit carryforwards may be subject to an annual limitation provided for in the Internal Revenue Code Section 382 and similar state codes. Any annual limitation could result in the expiration of net operating loss and credit carryforwards before utilization. With respect to our undistributed foreign subsidiaries' earnings we consider those earnings to be indefinitely reinvested and, accordingly, no related provision for U.S. federal and state income taxes has been provided. Upon distribution of those earnings' in the form of dividends or otherwise, we may be subject to both U.S. income taxes subject to an adjustment for foreign tax credits and withholding taxes in the various countries. As of December 31, 2016 and 2015 , the undistributed earnings approximated $5.1 million and $3.9 million , respectively. The determination of the future tax consequence of the remittance of these earnings is not practicable. Uncertain Tax Positions As of December 31, 2016 and 2015 , we had gross unrecognized tax benefits of $3.3 million and $2.6 million . We have accrued net interest expense of $9,000 (i.e., there was $20,000 of gross accrued interest expense offset by $11,000 of interest released due to a lapse of statute of limitations) related to unrecognized tax benefits reflected in the consolidated financial statements for the year ended December 31, 2016 . Our policy for classifying interest and penalties associated with unrecognized income tax benefits is to include such items in income tax expense. The activity related to the unrecognized tax benefits is as follows (in thousands): Years Ended December 31, 2016 2015 2014 Gross unrecognized tax benefits—beginning balance $ 2,552 $ 2,195 $ 1,846 Increases (decrease) related to tax positions from prior years 66 (4 ) 340 Increases related to tax positions taken during current year 690 361 278 Decreases related to tax positions taken during the current year — — (269 ) Gross unrecognized tax benefits—ending balance $ 3,308 $ 2,552 $ 2,195 These amounts are related to certain deferred tax assets with a corresponding valuation allowance. As of December 31, 2016 , the total amount of unrecognized tax benefits, if recognized, that would affect the effective tax rate is $1.1 million . We believe that there will not be any significant changes in our unrecognized tax benefits in the next 12 months. We are subject to taxation in the United States, various states, and several foreign jurisdictions. Because we have net operating loss and credit carryforwards, there are open statutes of limitations in which federal, state and foreign taxing authorities may examine our tax returns for all years from 2004 through the current period. During January 2017, the Internal Revenue Service (IRS) notified us that it intends to examine the 2014 and 2015 tax returns beginning in the first quarter of 2017.

Geographic Information

Geographic Information	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Geographic Information	Geographic Information The following table is a summary of revenue by geographic regions based on ship to location (in thousands): Years Ended December 31, 2016 2015 2014 United States $ 118,750 $ 106,842 $ 85,325 Japan 52,951 35,636 45,787 Asia Pacific, excluding Japan 29,829 23,847 20,434 EMEA 23,093 27,193 19,254 Other 5,380 5,437 8,707 Total revenue $ 230,003 $ 198,955 $ 179,507 Our long-lived assets which include property and equipment, net and intangible assets, net is primarily located in the United States. No other geographic regions comprise 10% or more of long-lived assets as of December 31, 2016 and 2015 .

Related-Party Transactions

Related-Party Transactions	12 Months Ended
	Dec. 31, 2016
Related Party Transactions [Abstract]
Related-Party Transactions	Related-Party Transactions An affiliate of one of our significant stockholders is also acting as a reseller of our products. On May 27, 2015, the significant stockholder reduced its ownership of our common stock, and ceased to be a related party. During the years ended December 31, 2015 and 2014, we recognized $2.2 million and $2.8 million , respectively, revenue from this reseller.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2016
Compensation and Retirement Disclosure [Abstract]
Employee Benefit Plan	Employee Benefit Plan We adopted a profit sharing plan qualified under Section 401(k) of the Internal Revenue Code which is offered to all of our United States employees. Participants in the plan may elect to contribute up to $18,000 of their annual compensation to the plan for the 2016 calendar year. Individuals who are 50 or older may contribute an additional $6,000 of their annual income. In 2016, we matched 50% of the first 6% of the employee’s eligible compensation. We contributed $0.9 million , $0.8 million and zero during the years ended December 31, 2016 , 2015 and 2014 , respectively.

Appcito Acquisition

Appcito Acquisition	12 Months Ended
	Dec. 31, 2016
Business Combinations [Abstract]
Appcito Acquisition	Appcito Acquisition On June 23, 2016, we entered into an asset purchase agreement with Appcito, Inc. (“Appcito”), a privately held company engaged in providing a unified set of services for applications deployed on cloud infrastructure with facilities located in Santa Clara, California and Bangalore, India. Under the terms of the purchase agreement, we acquired substantially all of the assets of Appcito. This acquisition enhances our position as a comprehensive secure application services leader, and it represents a strategic step in our vision to help our customers become more secure and agile as they bridge traditional and cloud application environments. The total purchase consideration was $6.5 million . The fair value of the total purchase consideration was $6.3 million , which consisted of $5.0 million in cash consideration, less a holdback of $0.7 million to cover any indemnification claims within twelve months of the acquisition date, and 227,404 unregistered shares of our common stock with an aggregated fair value of $1.3 million . We allocated the total purchase consideration to the net assets acquired, including identifiable intangible assets, based on their respective fair values at the acquisition date. The following table summarizes the allocation of the purchase price to the fair value of the assets acquired (in thousands): Developed technology $ 5,050 Goodwill 1,235 Other tangible assets 58 Total assets acquired $ 6,343 Developed technology is amortized on a straight-line basis over the estimated useful life of five years . Goodwill of $1.2 million was recognized as part of this acquisition is attributable primarily to the expected synergies and other benefits from this acquisition including adding to our existing momentum around providing secure application service solutions that meet several key demands like application analytics, visibility, and centralized control. This acquisition enhances our position as a comprehensive secure application services leader, and it represents a strategic step in our vision to help our customers become more secure and agile as they bridge traditional data center and cloud application environments. This acquisition has led to the launch of the cloud-native Lightning ADS. We expect to introduce additional options spanning public and private clouds. We incurred approximately $0.2 million in legal, accounting and other professional fees related to this acquisition, all of which were expensed during the year ended December 31, 2016 . We do not consider the acquisition of Appcito to be material to our results of operations or financial position, and therefore, we are not presenting pro-forma financial information of the combined operations. This acquisition was taxable for income tax purposes, and the acquired assets have been recorded at fair value for both book and income tax purposes. Therefore, no deferred taxes have been recorded. The goodwill of $1.2 million and the $0.2 million of acquisition costs are capitalized and amortized over 15 years for income tax purposes.

Description of Business and S20

Description of Business and Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Description of Business	Description of Business A10 Networks, Inc. (together with our subsidiaries, the “Company”, “we”, “our” or “us”) was incorporated in California in 2004 and reincorporated in Delaware in March 2014. We are headquartered in San Jose, California and have wholly-owned subsidiaries throughout the world including Asia and Europe. Our solutions enable our customers to secure and optimize the performance of their data center and cloud applications and secure their users, applications and infrastructure from internet, web and network threats at scale. Our product portfolio consists of six advanced application delivery and security products; Application Delivery Controllers ("ADC"), Lightning Application Delivery Service (“Lightning ADS”), Carrier Grade Network Address Translation ("CGN"), Threat Protection System ("TPS"), SSL Insight (“SSLi”) and Convergent Firewall ("CFW"). They are available in a variety of form factors, such as optimized hardware appliances, bare metal software, virtual appliances, and cloud-native software. These choices make our portfolio among the most comprehensive in the industry.
Basis of Presentation	Basis of Presentation The accompanying consolidated financial statements include those of A10 Networks, Inc. and its subsidiaries, after elimination of all intercompany accounts and transactions. We have prepared the accompanying consolidated financial statements in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and pursuant to the rules and regulations of the United States Securities and Exchange Commission (the “SEC”).
Use of Estimates	Use of Estimates The preparation of the consolidated financial statements in conformity with U.S. GAAP requires us to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Those estimates and assumptions affect revenue recognition and deferred revenue, the allowance for doubtful accounts, the sales return reserve, the valuation of inventory, the fair value of marketable securities, contingencies and litigation, acquisition related purchase price allocations, accrued liabilities, and the determination of fair value of stock-based compensation. These estimates are based on information available as of the date of the consolidated financial statements; therefore, actual results could differ from management’s estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents We consider all highly liquid investments with an original maturity of 90 days or less at the date of purchase to be cash equivalents.
Marketable securities	Marketable securities We classify our investments in debt and equity securities as available-for-sale and record these investments at fair value. These investments are classified as current assets and included in marketable securities on the consolidated balance sheets. Unrealized gains and losses are reported in accumulated other comprehensive income (loss), net of taxes, in stockholders’ equity. Realized gains and losses are determined based on the specific identification method and are reflected in our consolidated statements of operations. Realized gains and losses and other-than-temporary impairment charges, if any, on marketable securities are reported in interest and other income (expense), net as incurred. We regularly review our investment portfolio to identify and evaluate investments that have indicators of possible impairment. Investments are considered impaired when a decline in fair value is judged to be other-than-temporary. If the cost of an individual investment exceeds its fair value, we evaluate, among other factors, general market conditions, the duration and extent to which the fair value is less than cost, and our intent and ability to hold the investment. Once a decline in fair value is determined to be other-than-temporary, we will record an impairment charge and establish a new cost basis in the investment.
Fair Value Measurement	Fair Value Measurement Our financial instruments consist of cash, cash equivalents, marketable securities, accounts receivable and accounts payable. Accounts receivable and accounts payable are stated at their carrying value, which approximates fair value due to the short time to the expected receipt or payment. Our cash equivalents, which include money market funds, are measured and recorded at fair value on a recurring basis. Marketable securities are comprised of certificates of deposit, corporate securities, U.S. Treasury and agency securities, commercial paper and asset-backed securities and are measured at fair value using the three-level valuation hierarchy as described below. Level 1 - Inputs are unadjusted, quoted prices in active markets for identical assets or liabilities at the measurement date. Level 2 - Inputs are observable, quoted prices for identical assets or liabilities in active markets, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities. Level 3 - Unobservable inputs that are significant to the measurement of the fair value of the assets or liabilities that are supported by little or no market data.
Accounts Receivable and Allowance for Doubtful Accounts	Accounts Receivable and Allowance for Doubtful Accounts Accounts receivable are recorded at invoice amounts, net of allowances for doubtful accounts. We evaluate the collectability of our accounts receivable based on known collection risks and historical experience. In circumstances where we are aware of a specific customer’s inability to meet its financial obligations to us (e.g., bankruptcy filings or substantial downgrading of credit ratings), we record a specific reserve for bad debts against amounts due to reduce the net recognized receivable to the amount we reasonably believe will be collected. For all other customers, we record reserves for bad debts based on the length of time the receivables are past due and our historical experience of collections and write-offs.
Inventory	Inventory Inventory consists primarily of finished goods and related component parts and is stated at the lower of standard cost (which approximates actual cost on a first-in, first-out basis) or market value (estimated net realizable value). We evaluate inventory for excess and obsolete products, based on management’s assessment of future demand and market conditions. Inventory write-downs, once established, are not reversed as they establish a new cost basis for the inventory. Inventory write downs are included as a component of cost of products revenue in the accompanying consolidated statements of operations.
Property and Equipment, Net	Property and Equipment, Net Property and equipment, including leasehold improvements, are stated at cost, less accumulated depreciation and amortization. Depreciation is computed using the straight-line method over the estimated useful lives of the related assets. Depreciation on property and equipment, excluding leasehold improvements, ranges from 1 to 3 years. Leasehold improvements are amortized on a straight-line basis over the shorter of the estimated useful lives of the assets or the remaining lease term. Amortization on leasehold improvements ranges from 2 to 8 years.
Goodwill	Goodwill Goodwill represents the excess of purchase consideration over the fair values of assets acquired and liabilities assumed in a business combination. Goodwill is not amortized but is reviewed for possible impairment annually in the fourth quarter or more frequently if impairment indicators arise. We have one reporting unit for goodwill impairment tests, and the fair value of our reporting unit has been determined by our enterprise value. When assessing goodwill for impairment, we first perform a qualitative assessment to determine whether further impairment testing is necessary. If, as a result of its qualitative assessment, it is more-likely-than-not (i.e. greater than 50% chance) that the fair value of our reporting unit is less than its carrying amount, the quantitative impairment test will be required. Examples of events and circumstances that might indicate that a reporting unit’s fair value is less than the carrying amount include macro-economic conditions such as (i) a significant adverse change in customer demand or a severe deterioration in the entity’s operating environment and market conditions; (ii) entity-specific events such as increasing costs, declining financial performance, or loss of key personnel; or (iii) other events such as an expectation that a reporting unit will be sold or there will be a sustained decrease in the stock price on either an absolute basis or relative to peers. If it is determined, as a result of the qualitative assessment, that it is more-likely-than-not that the fair value of our reporting unit is less than its carrying amount, we perform a two-step impairment test on goodwill. The first step requires the identification of the reporting units and a comparison of the fair value of a reporting unit with its carrying amount, including goodwill. If the fair value of the reporting unit is less than its carrying value, an indication of goodwill impairment exists for the reporting unit, and the second step of the impairment test is performed to compute the amount of the impairment. Under the second step, an impairment loss is recognized for any excess of the carrying amount of the reporting unit's goodwill over the implied fair value of that goodwill.
Intangible Assets	Intangible Assets Intangible assets consist primarily of developed technology, patents and acquired customer relationships resulting from acquisitions. Intangible assets are recorded at fair value and amortized on a straight-line basis over their estimated useful lives, which range from 5 to 10 years.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets We evaluate our property and equipment for impairment whenever events or changes in circumstances indicate that the carrying amount of our long-lived asset may not be recoverable. Recoverability of an asset group is measured by comparison of its carrying amount to the expected future undiscounted cash flows that the asset group is expected to generate. If it is determined that an asset group is not recoverable, an impairment loss is recorded in the amount by which the carrying amount of the asset group exceeds its fair value.
Revenue Recognition	Revenue Recognition We derive revenue from two sources: (i) products revenue, which includes hardware and perpetual software license revenue; and (ii) services revenue, which includes post contract support (“PCS”), subscription, professional services, and training. A substantial portion of our revenue is from sales of our products and services through distribution channel partners, such as resellers and distributors. Revenue is recognized, net of applicable taxes, when all of the following criteria are met: persuasive evidence of an arrangement exists, delivery or performance has occurred, the sales price is fixed or determinable, and collection is reasonably assured. We define each of the four criteria above as follows: • Persuasive evidence of an arrangement exists. Evidence of an arrangement consists of a purchase order issued pursuant to the terms and conditions of a master sales agreement. • Delivery or performance has occurred. We use shipping documents or written evidence of customer acceptance, when applicable, to verify delivery or performance. We recognize product revenue upon transfer of title and risk of loss, which primarily is upon shipment to customers. We do not have significant obligations for future performance, such as customer rights of return or pricing credits associated with our sales. • The sales price is fixed or determinable. We assess whether the sales price is fixed or determinable based on payment terms and whether the sales price is subject to refund or adjustment. Standard payment terms to customers range from 30 to 90 days. • Collection is reasonably assured. We assess probability of collection on a customer-by-customer basis. Our customers are subjected to a credit review process that evaluates their financial condition and ability to pay for products and services. PCS revenue includes arrangements for software support and technical support for our products. PCS is offered under renewable, fee-based contracts, which include technical support, hardware repair and replacement parts, bug fixes, patches, and unspecified upgrades on a when-and-if available basis. Revenue for PCS services is recognized on a straight-line basis over the service contract term, which is typically one year, but can be up to five years. Unearned PCS revenue is included in deferred revenue. Professional service revenue primarily consists of the fees we earn related to installation and consulting services. We recognize revenue from professional services upon delivery or completion of performance. Professional service arrangements are typically short term in nature and are largely completed within 30 to 90 days from the start of service. Multiple-Element Arrangements Our hardware with the embedded software solutions (which is a proprietary operating system that together with the hardware delivers the functionality desired by our customers), is considered a separate unit of accounting from PCS because it has value to the customer on a standalone basis and our sales arrangements do not include a right of return for delivered products. For multiple-element arrangements, we allocate revenue to each unit of accounting based on an estimated selling price at the inception of the arrangement. The total arrangement consideration is allocated to each separate unit of accounting using the relative selling price method. We limit the amount of revenue recognized for delivered elements to an amount that is not contingent upon future delivery of additional products or service. When applying the relative selling price method, we determine the selling price for each element using (i) vendor-specific objective evidence, or VSOE, of selling price, if available; (ii) third-party evidence, or TPE, of selling price, if VSOE is not available; and (iii) best estimate of selling price, or BESP, if neither VSOE nor TPE is available. • VSOE. We determine VSOE based on our historical pricing and discounting practices for the specific products and services when sold separately. In determining VSOE, we require that a substantial majority of the stand-alone selling prices fall within a reasonably narrow pricing range. • TPE. When VSOE cannot be established for deliverables in multiple-element arrangements, we apply judgment with respect to whether we can establish a selling price based on TPE. TPE is determined based on competitor prices for interchangeable products or services when sold separately to similarly situated customers. However, as our products contain a significant element of proprietary technology and our solutions offer substantially different features and functionality, the comparable pricing of products with similar functionality typically cannot be obtained. Additionally, as we are unable to reliably determine what competitors products’ selling prices are on a stand-alone basis, we are not typically able to determine TPE. • BESP. When we are unable to establish selling price using VSOE or TPE, we use BESP in our allocation of arrangement consideration. The objective of BESP is to determine the price at which we would transact a sale if the product or service was sold regularly on a standalone basis. As we have not been able to establish VSOE or TPE for our products and some of our services, we determine BESP for the purposes of allocating the arrangement, primarily based on historical transaction pricing. Historical transactions are segregated based on our pricing model and go-to-market strategy, which include factors such as the geographies in which our products and services were sold (domestic or international), offering type (product series, and level of support for PCS) and type of sales channel. The determination of BESP is made through consultation with and approval by management. We may occasionally accept returns to address customer satisfaction issues or solution-fit issues even though there is no contractual provision for such returns. We estimate returns for sales to customers based on historical returns rates applied against current-period gross revenues. Specific customer returns and allowances are considered within this estimate. Management also analyzes changes in customer demand and acceptance of products when evaluating the adequacy of returns and sales allowances.
Deferred Revenue	Deferred Revenue Deferred product revenue relates to arrangements where not all revenue recognition criteria have been met. Deferred services revenue primarily represents PCS contracts billed in advance and revenue is recognized ratably over the service contract term, typically 1 to 5 years.
Shipping and Handling	Shipping and Handling Shipping and handling charges billed to customers are included in revenue in the period shipped and the related costs are included in cost of revenue.
Research and Development Costs	Research and Development Costs Research and development efforts are focused on new product development and on developing additional functionality for our existing products. These expenses consist of personnel costs, and to a lesser extent, prototype materials, depreciation and certain allocated facilities and information technology costs. We expense research and development costs as incurred.
Stock-based Compensation	Stock-Based Compensation Stock-based compensation expense is measured on the grant date based on the fair value of the award, net of estimated forfeitures, and recognized on a straight-line basis over the requisite service period. The fair value of restricted stock units (“RSUs”) is estimated using our stock price on the grant date. The fair value of options and employee stock purchase rights is estimated using the Black-Scholes model on the grant date. The Black-Scholes model determines the fair value of share-based payment awards based on assumptions including expected term, stock price volatility, and risk-free interest rate. The fair value of market-performance based restricted stock units (“MSUs”) is valued using the Monte Carlo simulation model, which uses the stock price, expected volatility and risk-free interest rate to determine the fair value.
Warranty Costs	Warranty Costs Our appliance hardware and software generally carry a warranty period of 90 days . Estimates of future warranty costs are based on historical returns and the application of the historical return rates to our in-warranty installed base. Warranty costs to repair or replace items sold to customers have been insignificant for the years ended December 31, 2016 , 2015 and 2014 .
Foreign Currency	Foreign Currency The functional currency of our foreign subsidiaries is the U.S. dollar. Transactions denominated in non-functional currencies are remeasured to the functional currency at the average exchange rate for the period. Non-functional currency monetary assets and liabilities are remeasured to the functional currency using the exchange rate in effect at the balance sheet date, and non-monetary assets and liabilities are remeasured at historical exchange rates. Gains and losses related to remeasurement are recorded in interest and other income (expense), net in the consolidated statements of operations.
Income Taxes	Income Taxes We account for 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 our consolidated financial statements or in our tax returns. Estimates and judgments occur in the calculation of certain tax liabilities and in the determination of the recoverability of certain deferred income tax assets, which arise from temporary differences and carryforwards. Deferred income tax assets and liabilities are measured using the currently enacted tax rates that apply to taxable income in effect for the years in which those tax assets are expected to be realized or settled. We regularly assess the likelihood that our deferred tax assets will be recovered from future taxable income and, to the extent we believe, based upon the weight of available evidence, that it is more likely than not that all or a portion of deferred tax assets will not be realized, a valuation allowance is established through an adjustment to income tax expense. The factors used to assess the likelihood of realization of our deferred tax assets include our forecast of future taxable income and available tax planning strategies that could be implemented to realize the net deferred tax assets. Assumptions represent our best estimates and involve inherent uncertainties and the application of our judgment. We account for uncertainty in income taxes recognized in our consolidated financial statements by regularly reviewing our tax positions and benefits to be realized. We recognize tax liabilities based upon our estimate of whether, and the extent to which, additional taxes will be due when such estimates are more-likely-than-not to be sustained. An uncertain income tax position will not be recognized if it has less than a 50% likelihood of being sustained upon examination by taxing authorities. The provision for income taxes includes the effects of any resulting tax reserves, or unrecognized tax benefits, that are considered appropriate as well as the related net interest and penalties.
Segment Information	Segment Information An operating segment is a component of an enterprise for which its discrete financial information is available and its operating results are regularly reviewed by chief operating decision maker for resource allocation decisions and performance assessment. Our chief operating decision maker is our Chief Executive Officer. Our Chief Executive Officer reviews financial information presented on a consolidated basis for purposes of allocating resources and assessing performance of the Company. Accordingly, we have one reportable segment and one operating segment.
Vendor Business Concentration	Vendor Business Concentration We rely on third parties to manufacture our hardware appliances and we purchase raw materials from third-party vendors. We outsourced substantially all of our manufacturing services to two independent manufacturers. In addition, we purchase certain strategic component inventory which is consigned to our third-party manufacturers. Other hardware components included in our products are sourced from various suppliers by our manufacturers and are principally industry standard parts and components that are available from multiple vendors.
Concentration of Credit Risk and Significant Customers	Concentration of Credit Risk and Significant Customers Financial instruments that potentially subject us to concentrations of credit risk consist of cash, cash equivalents, short-term investments and accounts receivable. Our cash and investments are held and invested in high-credit quality financial instruments by recognized financial institutions and therefore subject to minimum credit risk. Our accounts receivable are unsecured and represent amounts due to us based on contractual obligations of our customers. We mitigate credit risk in respect to accounts receivable by performing periodic credit evaluations based on a number of factors, including past transaction experience, evaluation of credit history and review of the invoicing terms of the contract. We generally do not require our customers to provide collateral to support accounts receivable. Significant customers, including distribution channel partners and direct customers, are those which represent more than 10% of our total revenue for each period presented, or our gross accounts receivable balance as of each respective balance sheet date.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In May 2014, the Financial Accounting Standards Board (" FASB") issued Accounting Standard Update ("ASU") No. 2014-09, Revenue from Contracts with Customers (Topic 606) , which will supersede most of the existing revenue recognition guidance under U.S. GAAP. This ASU requires an entity to recognize revenue when it transfers 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 and requires the capitalization of incremental customer acquisition costs and amortization of these costs over the contract period or estimated customer life which will result in the recognition of a contract asset on our balance sheets. This standard is effective for annual reporting periods beginning after December 15, 2017, including interim periods within that reporting period. Early adoption of one year prior to the required effective date is permitted. However, we do not plan to early adopt. Accordingly, the updated standard is effective for us in the first quarter of 2018. The ASU allows for either full retrospective or modified retrospective adoption. We are still in the process of evaluating which transition method we plan to adopt with such decision depending on a number of factors, including system readiness and the magnitude of the potential impact on our financial statements. While we are continuing to assess all potential impacts of the new standard, we currently do not believe this standard will have a material impact on our consolidated financial statements and related disclosures. In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842). This new accounting standard primarily requires lessees to recognize most leases on their balance sheets but record expenses on their income statements in a manner similar to current accounting. For lessors, the guidance modifies the classification criteria and the accounting for sales-type and direct financing leases. The guidance is effective for annual periods beginning after December 15, 2018 with early adoption permitted. We are currently evaluating the impact of this guidance on our financial statements. In March 2016, the FASB issued ASU No. 2016-09, Compensation—Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. The new guidance requires the recognition of the income tax effects of awards in the income statement when the awards vest or are settled, thus eliminating additional paid in capital pools. The guidance also allows for the employer to repurchase more of an employee’s shares for tax withholding purposes without triggering liability accounting. In addition, the guidance allows for a policy election to account for forfeitures as they occur rather than on an estimated basis. This guidance is effective for annual and interim reporting periods of public entities beginning after December 15, 2016 with early adoption permitted. We will be adopting this guidance in the first quarter of fiscal year 2017 and do not believe this standard will have a material impact on our consolidated financial statements.

Description of Business and S21

Description of Business and Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Revenue as Percentage of Total Revenue and Accounts Receivable as Percentage of Total Net Accounts Receivable	Revenue from our significant customers as a percentage of our total revenue are as follows: Years Ended December 31, 2016 2015 2014 Customer A 14% * 13% * represents less than 10% of total revenue

Marketable Securities and Fai22

Marketable Securities and Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	As of December 31, 2016 , the estimated fair value of our marketable securities, classified as available for sale, are as follows (in thousands): Amortized Cost Gross Unrealized Gains Gross Unrealized Losses Fair Value Certificates of deposit $ 12,499 $ 9 $ — $ 12,508 Corporate securities 42,765 9 (42 ) 42,732 U.S. Treasury and agency securities 5,190 — (14 ) 5,176 Commercial paper 11,470 1 (2 ) 11,469 Asset-backed securities 13,493 — (6 ) 13,487 $ 85,417 $ 19 $ (64 ) $ 85,372
Investments Classified by Contractual Maturity Date	The following table summarizes the cost and estimated fair value of marketable securities based on contractual maturities as of December 31, 2016 (in thousands): Amortized Cost Fair Value Less than 1 year $ 53,500 $ 53,503 Mature in 1 - 3 years 31,917 31,869 $ 85,417 $ 85,372
Schedule of Unrealized Loss on Investments	Marketable securities in an unrealized loss position as of December 31, 2016 consisted of the following (in thousands): Fair Value Unrealized Losses Corporate securities $ 28,537 $ (42 ) U.S. Treasury and agency securities 5,176 (14 ) Commercial paper 8,974 (2 ) Asset-backed securities 10,664 (6 ) $ 53,351 $ (64 )
Schedule of Fair Value of Assets Measured on Recurring Basis	The following is a summary of our cash, cash equivalents and marketable securities measured at fair value on a recurring basis (in thousands): December 31, 2016 December 31, 2015 Level 1 Level 2 Level 3 Total Level 1 Level 2 Level 3 Total Cash $ 18,672 $ — $ — $ 18,672 $ 27,036 $ — $ — $ 27,036 Cash equivalents 10,303 — — 10,303 71,081 — — 71,081 Certificates of deposit — 12,508 — 12,508 — — — — Corporate securities — 42,732 — 42,732 — — — — U.S. Treasury and agency securities — 5,176 — 5,176 — — — — Commercial paper — 11,469 — 11,469 — — — — Asset-backed securities — 13,487 — 13,487 — — — — $ 28,975 $ 85,372 $ — $ 114,347 $ 98,117 $ — $ — $ 98,117

Balance Sheet and Statement o23

Balance Sheet and Statement of Operations Components (Tables)	12 Months Ended
	Dec. 31, 2016
Property, Plant and Equipment [Abstract]
Allowance for Doubtful Accounts and Sales Return Reserve	Allowance for Doubtful Accounts and Sales Return Reserve December 31, 2016 December 31, 2015 December 31, 2014 (in thousands) Allowance for doubtful accounts, beginning balance $ 2,887 $ 1,904 $ 1,836 Charged to expenses 1,166 1,590 76 Write-offs (1,147 ) (607 ) (8 ) Allowance for doubtful accounts, ending balance $ 2,906 $ 2,887 $ 1,904 December 31, 2016 December 31, 2015 December 31, 2014 (in thousands) Sales return reserve, beginning balance $ 1,180 $ 1,342 $ 902 Charged to revenue 565 940 858 Utilization (1,032 ) (1,102 ) (418 ) Sales return reserve, ending balance $ 713 $ 1,180 $ 1,342
Schedule of Inventory	Inventory December 31, December 31, (in thousands) Raw materials $ 6,669 $ 9,418 Finished goods 8,401 8,873 Total inventory $ 15,070 $ 18,291
Schedule of Property and Equipment, Net	Property and Equipment, Net Useful Life December 31, December 31, (in years) (in thousands) Equipment 1-3 $ 41,815 $ 35,836 Software 1-3 3,801 3,548 Furniture and fixtures 1-3 865 864 Leasehold improvements 2-8 2,724 2,492 Construction in progress 258 83 Property and equipment, gross 49,463 42,823 Less: accumulated depreciation and amortization (41,244 ) (33,920 ) Total property and equipment, net $ 8,219 $ 8,903
Schedule of Goodwill	Activity related to goodwill for the year ended December 31, 2016 is as follows (in thousands): Balance as of December 31, 2015 $ 72 Acquisitions 1,235 Balance as of December 31, 2016 $ 1,307
Schedule of Intangible Assets	Purchased intangible assets consisted of the following (in thousands): December 31, 2016 December 31, 2015 Gross Carrying Amount Accumulated Amortization Net Carrying Value Gross Carrying Amount Accumulated Amortization Net Carrying Value Developed technology $ 5,050 $ (505 ) $ 4,545 $ — $ — $ — Patents 2,936 (848 ) 2,088 1,436 (641 ) 795 Total $ 7,986 $ (1,353 ) $ 6,633 $ 3,182 $ (2,387 ) $ 795
Schedule of Amortization Expense	Future amortization expense for purchased intangible assets as of December 31, 2016 is as follows (in thousands): Fiscal Years Ending December 31, 2017 $ 1,442 2018 1,442 2019 1,442 2020 1,442 2021 865 $ 6,633
Schedule of Accrued Liabilities	Accrued Liabilities December 31, December 31, (in thousands) Accrued compensation and benefits $ 22,326 $ 18,134 Accrued tax liabilities 3,340 4,520 Other 5,859 5,103 Total accrued liabilities $ 31,525 $ 27,757
Schedule of Deferred Revenue	Deferred Revenue December 31, December 31, (in thousands) Deferred revenue: Products $ 4,182 $ 3,233 Services 88,726 69,571 Total deferred revenue 92,908 72,804 Less: current portion (61,334 ) (49,572 ) Non-current portion $ 31,574 $ 23,232

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments and Contingencies Disclosure [Abstract]
Schedule of Future Noncancelable Minimum Operating Lease Payments	The following table summarizes our non-cancellable operating leases and unconditional purchase obligations as of December 31, 2016 (in thousands): Years Ending December 31, Leases and Other Contractual Obligations Purchase Commitments Total 2017 $ 2,811 $ 14,900 $ 17,711 2018 2,393 — 2,393 2019 1,992 — 1,992 2020 365 — 365 2021 79 — 79 Thereafter 7 — 7 $ 7,647 $ 14,900 $ 22,547

Equity Award Plans (Tables)

Equity Award Plans (Tables)	12 Months Ended
	Dec. 31, 2016
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Summary of Stock-based Compensation	A summary of our stock-based compensation expense is as follows (in thousands): Years Ended December 31, 2016 2015 2014 Stock-based compensation by type of award: Stock options $ 4,153 $ 5,565 $ 5,852 Restricted stock units 12,567 8,871 3,217 Employee stock purchase rights 202 2,425 3,290 $ 16,922 $ 16,861 $ 12,359 Stock-based compensation by category of expense: Cost of revenue $ 1,105 $ 1,533 $ 1,063 Sales and marketing 7,006 7,735 5,829 Research and development 5,732 5,437 3,932 General and administrative 3,079 2,156 1,535 $ 16,922 $ 16,861 $ 12,359
ESPP Valuation Assumptions	The fair values of the options and employee stock purchase rights are estimated as of the grant date using the Black-Scholes option-pricing model with the following assumptions: Options Employee Stock Purchase Rights Years Ended December 31, Years Ended December 31, 2016 2015 2014 2016 2015 2014 Expected term (in years) 4.9 4.8 4.8 1.3 1.3 1.3 Risk-free interest rate 1.4% 1.6% 1.8% 0.8% 0.5% 0.3% Expected volatility 49% 50% 41% 42% 41% 27% Dividend rate —% —% —% —% —% —%
Stock Options Valuation Assumptions	The fair values of the options and employee stock purchase rights are estimated as of the grant date using the Black-Scholes option-pricing model with the following assumptions: Options Employee Stock Purchase Rights Years Ended December 31, Years Ended December 31, 2016 2015 2014 2016 2015 2014 Expected term (in years) 4.9 4.8 4.8 1.3 1.3 1.3 Risk-free interest rate 1.4% 1.6% 1.8% 0.8% 0.5% 0.3% Expected volatility 49% 50% 41% 42% 41% 27% Dividend rate —% —% —% —% —% —%
Summary of Activity under Stock Option Plans	The following table summarizes our stock option activities and related information: Number of Shares (thousands) Weighted-Average Exercise Price Weighted-Average Remaining Contractual Term (Years) Aggregate Intrinsic Value (thousands) Outstanding as of December 31, 2015 9,291 $ 4.78 Granted 672 $ 5.52 Exercised (1,444 ) $ 4.22 Canceled (1) (651 ) $ 6.23 Outstanding as of December 31, 2016 7,868 $ 4.82 6.2 $ 28,931 Vested and expected to vest as of December 31, 2016 7,758 $ 4.82 6.2 $ 28,554 Vested and exercisable as of December 31, 2016 5,688 $ 4.57 5.6 $ 22,363 _____________________________________ (1) Common shares subject to awards granted under the 2008 Plan and canceled after March 21, 2014 are reallocated to the 2014 Plan’s share reserve and become available for issuance under the 2014 Plan. During the years ended 2016 and 2015 , 266,799 shares and 1,640,324 shares of the canceled stock options, respectively, were reallocated and became available for issuance under the 2014 Plan.
Stock Option Information	The following table provides information pertaining to our stock options (in thousands, except weighted-average fair values): Years Ended December 31, 2016 2015 2014 Fair value of options granted $ 1,603 $ 869 $ 11,683 Weighted-average fair value of options granted $ 2.38 $ 2.13 $ 2.79 Intrinsic value of options exercised $ 5,990 $ 2,299 $ 14,863
Summary of Restricted Stock Units Activity	The following table summarizes our stock award activities and related information: Number of Shares (thousands) Weighted Average Grant Date Fair Value Weighted-Average Remaining Vesting Term (Years) Aggregate Intrinsic Value (thousands) Outstanding as of December 31, 2015 3,452 $ 5.88 Granted 4,550 $ 6.50 Released (1,139 ) $ 8.16 Canceled (904 ) $ 6.56 Outstanding as of December 31, 2016 5,959 $ 5.81 1.6 $ 49,517

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Summary of Outstanding Shares of Common Stock Equivalents	The following table presents common shares related to potentially dilutive shares excluded from the calculation of diluted net loss per share as their effect would have been anti-dilutive (in thousands): Years Ended December 31, 2016 2015 2014 Stock options, RSUs and employee stock purchase rights 13,631 10,124 6,415 Common stock subject to repurchase 14 52 196 13,645 10,176 6,611

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Schedule of Income before Income Tax, Domestic and Foreign	The geographical breakdown of loss before provision for income taxes is as follows (in thousands): Years Ended December 31, 2016 2015 2014 Domestic loss $ (22,978 ) $ (41,677 ) $ (35,593 ) Foreign income 2,795 2,390 2,380 Loss before provision for income taxes $ (20,183 ) $ (39,287 ) $ (33,213 )
Schedule of Components of Income Tax Expense (Benefit)	The provision for income taxes consists of the following (in thousands): Years Ended December 31, 2016 2015 2014 Current provision for income taxes: State $ 41 $ 55 $ 24 Foreign 1,009 675 1,054 Total current 1,050 730 1,078 Deferred tax expense (benefit): Federal 17 — — Foreign (310 ) 17 429 Total deferred (293 ) 17 429 Provision for income taxes $ 757 $ 747 $ 1,507
Schedule of Effective Income Tax Rate Reconciliation	The reconciliation of the statutory federal income tax and our effective income tax is as follows (in thousands): Years Ended December 31, 2016 2015 2014 Amount Percentage Amount Percentage Amount Percentage Tax at statutory rate $ (6,862 ) 34.0 % $ (13,358 ) 34.0 % $ (11,292 ) 34.0 % State tax - net of federal benefits 27 (0.1 ) 36 (0.1 ) 16 (0.1 ) Foreign rate differential (666 ) 3.3 (422 ) 1.1 231 (0.7 ) Changes in federal valuation allowance 7,141 (35.4 ) 11,926 (30.4 ) 10,547 (31.8 ) Stock-based compensation 88 (0.4 ) 1,845 (4.7 ) 1,041 (3.1 ) Other permanent items 583 (2.9 ) 415 (1.1 ) 513 (1.5 ) Expenses for uncertain tax positions 358 (1.8 ) 227 (0.6 ) 330 (1.0 ) Other 88 (0.4 ) 78 (0.1 ) 121 (0.4 ) Provision for income taxes $ 757 (3.7 )% $ 747 (1.9 )% $ 1,507 (4.6 )%
Schedule of Deferred Tax Assets and Liabilities	The tax effects of temporary differences that give rise to significant portions of deferred tax assets (liabilities) are as follows (in thousands): December 31, December 31, Deferred tax assets: Net operating loss carryforwards $ 47,197 $ 46,317 Research and development credits, net of uncertain tax positions 12,953 9,517 Accruals, reserves, and other 21,288 17,904 Stock-based compensation 4,055 2,700 Depreciation and amortization 2,892 2,735 Gross deferred tax assets 88,385 79,173 Valuation allowance (86,935 ) (77,643 ) Total deferred tax assets 1,450 1,530 Deferred tax liabilities: Other (431 ) (805 ) Total deferred tax liabilities (431 ) (805 ) Net deferred tax assets $ 1,019 $ 725
Summary of Income Tax Contingencies	The activity related to the unrecognized tax benefits is as follows (in thousands): Years Ended December 31, 2016 2015 2014 Gross unrecognized tax benefits—beginning balance $ 2,552 $ 2,195 $ 1,846 Increases (decrease) related to tax positions from prior years 66 (4 ) 340 Increases related to tax positions taken during current year 690 361 278 Decreases related to tax positions taken during the current year — — (269 ) Gross unrecognized tax benefits—ending balance $ 3,308 $ 2,552 $ 2,195

Geographic Information (Tables)

Geographic Information (Tables)	12 Months Ended
	Dec. 31, 2016
Segment Reporting [Abstract]
Schedule of Total Revenue Based on Customer's Location	The following table is a summary of revenue by geographic regions based on ship to location (in thousands): Years Ended December 31, 2016 2015 2014 United States $ 118,750 $ 106,842 $ 85,325 Japan 52,951 35,636 45,787 Asia Pacific, excluding Japan 29,829 23,847 20,434 EMEA 23,093 27,193 19,254 Other 5,380 5,437 8,707 Total revenue $ 230,003 $ 198,955 $ 179,507

Appcito Acquisition (Tables)

Appcito Acquisition (Tables)	12 Months Ended
	Dec. 31, 2016
Business Combinations [Abstract]
Schedule of Purchase Price Allocation	The following table summarizes the allocation of the purchase price to the fair value of the assets acquired (in thousands): Developed technology $ 5,050 Goodwill 1,235 Other tangible assets 58 Total assets acquired $ 6,343

Description of Business and S30

Description of Business and Summary of Significant Accounting Policies - Additional Information (Details)	12 Months Ended
	Dec. 31, 2016segmentsolution
Property, Plant and Equipment [Line Items]
Number of software based advanced application networking and network security solutions | solution	6
Warranty period (in days)	90 days
Number of reportable segments	1
Number of operating segments	1
Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	1 year
Estimated useful life, finite-lived assets (in years)	5 years
Period of recognition of deferred revenue (in years)	1 year
Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	3 years
Estimated useful life, finite-lived assets (in years)	10 years
Period of recognition of deferred revenue (in years)	5 years
Leasehold improvements | Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	2 years
Leasehold improvements | Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	8 years

Description of Business and S31

Description of Business and Summary of Significant Accounting Policies - Schedule of Revenue as Percentage of Total Revenue and Accounts Receivable as Percentage of Total Net Accounts Receivable (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Customer A | Revenue
Entity Wide Revenue Major Customer [Line Items]
Percentage representation of significant customers	14.00%		13.00%
Customer B | Accounts Receivable, Net
Entity Wide Revenue Major Customer [Line Items]
Percentage representation of significant customers	15.00%	27.00%
Customer C | Accounts Receivable, Net
Entity Wide Revenue Major Customer [Line Items]
Percentage representation of significant customers	13.00%	11.00%
Customer D | Accounts Receivable, Net
Entity Wide Revenue Major Customer [Line Items]
Percentage representation of significant customers	11.00%

Marketable Securities and Fai32

Marketable Securities and Fair Value Measurements - Estimate of Fair Value of Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 85,417
Gross Unrealized Gains	19
Gross Unrealized Losses	(64)
Fair Value	85,372
Certificates of deposit
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	12,499
Gross Unrealized Gains	9
Gross Unrealized Losses	0
Fair Value	12,508	$ 0
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	42,765
Gross Unrealized Gains	9
Gross Unrealized Losses	(42)
Fair Value	42,732	0
U.S. Treasury and agency securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	5,190
Gross Unrealized Gains	0
Gross Unrealized Losses	(14)
Fair Value	5,176	0
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	11,470
Gross Unrealized Gains	1
Gross Unrealized Losses	(2)
Fair Value	11,469	0
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	13,493
Gross Unrealized Gains	0
Gross Unrealized Losses	(6)
Fair Value	$ 13,487	$ 0

Marketable Securities and Fai33

Marketable Securities and Fair Value Measurements - Contractual Maturities (Details) $ in Thousands	Dec. 31, 2016USD ($)
Amortized Cost
Less than 1 year	$ 53,500
Mature in 1 - 3 years	31,917
Amortized Cost	85,417
Fair Value
Less than 1 year	53,503
Mature in 1 - 3 years	31,869
Fair Value	$ 85,372

Marketable Securities and Fai34

Marketable Securities and Fair Value Measurements - Securities in Unrealized Loss Position (Details) $ in Thousands	Dec. 31, 2016USD ($)
Schedule of Available-for-sale Securities [Line Items]
Continuous loss position, Fair value	$ 53,351
Continuous loss position, Unrealized losses	(64)
Corporate securities
Schedule of Available-for-sale Securities [Line Items]
Continuous loss position, Fair value	28,537
Continuous loss position, Unrealized losses	(42)
U.S. Treasury and agency securities
Schedule of Available-for-sale Securities [Line Items]
Continuous loss position, Fair value	5,176
Continuous loss position, Unrealized losses	(14)
Commercial paper
Schedule of Available-for-sale Securities [Line Items]
Continuous loss position, Fair value	8,974
Continuous loss position, Unrealized losses	(2)
Asset-backed securities
Schedule of Available-for-sale Securities [Line Items]
Continuous loss position, Fair value	10,664
Continuous loss position, Unrealized losses	$ (6)

Marketable Securities and Fai35

Marketable Securities and Fair Value Measurements - Schedule of Fair Value of Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financial Assets
Marketable Securities	$ 85,372
Total	114,347	$ 98,117
Level I
Financial Assets
Total	28,975	98,117
Level II
Financial Assets
Total	85,372	0
Level III
Financial Assets
Total	0	0
Cash
Financial Assets
Cash and Cash Equivalents	18,672	27,036
Cash | Level I
Financial Assets
Cash and Cash Equivalents	18,672	27,036
Cash | Level II
Financial Assets
Cash and Cash Equivalents	0	0
Cash | Level III
Financial Assets
Cash and Cash Equivalents	0	0
Cash equivalents
Financial Assets
Cash and Cash Equivalents	10,303	71,081
Cash equivalents | Level I
Financial Assets
Cash and Cash Equivalents	10,303	71,081
Cash equivalents | Level II
Financial Assets
Cash and Cash Equivalents	0	0
Cash equivalents | Level III
Financial Assets
Cash and Cash Equivalents	0	0
Certificates of deposit
Financial Assets
Marketable Securities	12,508	0
Certificates of deposit | Level I
Financial Assets
Marketable Securities	0	0
Certificates of deposit | Level II
Financial Assets
Marketable Securities	12,508	0
Certificates of deposit | Level III
Financial Assets
Marketable Securities	0	0
Corporate securities
Financial Assets
Marketable Securities	42,732	0
Corporate securities | Level I
Financial Assets
Marketable Securities	0	0
Corporate securities | Level II
Financial Assets
Marketable Securities	42,732	0
Corporate securities | Level III
Financial Assets
Marketable Securities	0	0
U.S. Treasury and agency securities
Financial Assets
Marketable Securities	5,176	0
U.S. Treasury and agency securities | Level I
Financial Assets
Marketable Securities	0	0
U.S. Treasury and agency securities | Level II
Financial Assets
Marketable Securities	5,176	0
U.S. Treasury and agency securities | Level III
Financial Assets
Marketable Securities	0	0
Commercial paper
Financial Assets
Marketable Securities	11,469	0
Commercial paper | Level I
Financial Assets
Marketable Securities	0	0
Commercial paper | Level II
Financial Assets
Marketable Securities	11,469	0
Commercial paper | Level III
Financial Assets
Marketable Securities	0	0
Asset-backed securities
Financial Assets
Marketable Securities	13,487	0
Asset-backed securities | Level I
Financial Assets
Marketable Securities	0	0
Asset-backed securities | Level II
Financial Assets
Marketable Securities	13,487	0
Asset-backed securities | Level III
Financial Assets
Marketable Securities	$ 0	$ 0

Balance Sheet and Statement o36

Balance Sheet and Statement of Operations Components - Schedule of Allowance for Doubtful Accounts and Sales Return Reserve (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Allowance for Doubtful Accounts
Valuation Allowance [Line Items]
Beginning Balance	$ 2,887	$ 1,904	$ 1,836
Charged to expenses	1,166	1,590	76
Write-offs	(1,147)	(607)	(8)
Ending Balance	2,906	2,887	1,904
Allowance for Sales Returns
Valuation Allowance [Line Items]
Beginning Balance	1,180	1,342	902
Charged to revenue	565	940	858
Write-offs	(1,032)	(1,102)	(418)
Ending Balance	$ 713	$ 1,180	$ 1,342

Balance Sheet and Statement o37

Balance Sheet and Statement of Operations Components - Schedule of Inventory (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Raw materials	$ 6,669	$ 9,418
Finished goods	8,401	8,873
Total inventory	$ 15,070	$ 18,291

Balance Sheet and Statement o38

Balance Sheet and Statement of Operations Components - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 49,463	$ 42,823
Less: accumulated depreciation and amortization	(41,244)	(33,920)
Total property and equipment, net	8,219	8,903
Equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	41,815	35,836
Software
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,801	3,548
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	865	864
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,724	2,492
Construction in progress
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 258	$ 83
Minimum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	1 year
Minimum | Equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	1 year
Minimum | Software
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	1 year
Minimum | Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	1 year
Minimum | Leasehold improvements
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	2 years
Maximum
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	3 years
Maximum | Equipment
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	3 years
Maximum | Software
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	3 years
Maximum | Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	3 years
Maximum | Leasehold improvements
Property, Plant and Equipment [Line Items]
Estimated Useful Life (in Years)	8 years

Balance Sheet and Statement o39

Balance Sheet and Statement of Operations Components - Goodwill Roll Forward (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)
Goodwill [Roll Forward]
Beginning balance	$ 72
Acquisitions	1,235
Ending balance	$ 1,307

Balance Sheet and Statement o40

Balance Sheet and Statement of Operations Components - Purchased Intangible Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	$ 7,986	$ 3,182
Accumulated Amortization	(1,353)	(2,387)
Net Carrying Value	6,633	795
Developed technology
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	5,050	0
Accumulated Amortization	(505)	0
Net Carrying Value	4,545	0
Patents
Finite-Lived Intangible Assets [Line Items]
Gross Carrying Amount	2,936	1,436
Accumulated Amortization	(848)	(641)
Net Carrying Value	$ 2,088	$ 795

Balance Sheet and Statement o41

Balance Sheet and Statement of Operations Components - Future Amortization Expense (Details) $ in Thousands	Dec. 31, 2016USD ($)
Property, Plant and Equipment [Abstract]
2,017	$ 1,442
2,018	1,442
2,019	1,442
2,020	1,442
2,021	865
Total	$ 6,633

Balance Sheet and Statement o42

Balance Sheet and Statement of Operations Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Abstract]
Accrued compensation and benefits	$ 22,326	$ 18,134
Accrued tax liabilities	3,340	4,520
Other	5,859	5,103
Total accrued liabilities	$ 31,525	$ 27,757

Balance Sheet and Statement o43

Balance Sheet and Statement of Operations Components - Schedule of Deferred Revenue (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	$ 92,908	$ 72,804
Less: current portion	(61,334)	(49,572)
Non-current portion	31,574	23,232
Products
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	4,182	3,233
Services
Deferred Revenue Arrangement [Line Items]
Total deferred revenue	$ 88,726	$ 69,571

Balance Sheet and Statement o44

Balance Sheet and Statement of Operations Components - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	Jun. 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Mar. 31, 2014
Property, Plant and Equipment [Abstract]
Depreciation and amortization property and equipment		$ 7,600	$ 8,600	$ 10,000
Amortization of assets		$ 700	100	100
Weighted average useful life (in years)		4 years 7 months
Contractual liability					$ 12,000
Payments related to settlement	$ 5,000
Benefit to litigation expense	$ 7,000	$ 0	$ 0	$ 6,993

Credit Facility (Details)

Credit Facility (Details)	1 Months Ended		12 Months Ended
	Nov. 30, 2016USD ($)	Sep. 30, 2013USD ($)	Dec. 31, 2016USD ($)	Sep. 30, 2016USD ($)
Revolving Credit Facility
Line of Credit Facility [Line Items]
Debt instrument term	3 years	3 years
Maximum borrowing capacity	$ 25,000,000	$ 35,000,000
Debt covenant, net cash equals or exceeds, amount	50,000,000
Debt covenant, net cash falls below, amount	$ 50,000,000
Quarterly facility fees			0.45%
Amount outstanding			$ 0	$ 0
Minimum adjusted quick ratio under debt compliance			1.50
Revolving Credit Facility | Prime Rate
Line of Credit Facility [Line Items]
Variable interest rate	0.50%
Revolving Credit Facility | LIBOR
Line of Credit Facility [Line Items]
Variable interest rate	2.50%
Letter of Credit
Line of Credit Facility [Line Items]
Maximum borrowing capacity	$ 25,000,000	$ 10,000,000

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details) - USD ($) $ in Millions	Apr. 06, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Loss Contingencies [Line Items]
Rent expense		$ 3.5	$ 3.5	$ 3.4
City of Warren Police and Fire Retirement System v. A10 Networks
Loss Contingencies [Line Items]
Litigation settlement	$ (0.8)

Commitments and Contingencies47

Commitments and Contingencies - Lease Obligations and Other Commitments (Details) $ in Thousands	Dec. 31, 2016USD ($)
Operating Leased Assets [Line Items]
2,017	$ 17,711
2,018	2,393
2,019	1,992
2,020	365
2,021	79
Thereafter	7
Total	22,547
Leases and Other Contractual Obligations
Operating Leased Assets [Line Items]
2,017	2,811
2,018	2,393
2,019	1,992
2,020	365
2,021	79
Thereafter	7
Total	7,647
Purchase Commitments
Operating Leased Assets [Line Items]
2,017	14,900
2,018	0
2,019	0
2,020	0
2,021	0
Thereafter	0
Total	$ 14,900

Equity Award Plans - 2014 Equit

Equity Award Plans - 2014 Equity Incentive Plan/ESPP (Details) - USD ($) $ / shares in Units, $ in Thousands	Jan. 01, 2017	Jan. 01, 2016	Dec. 17, 2015	Jun. 10, 2015	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares authorized to be repurchased (in shares)						14,307	51,884
Aggregate price of shares authorized to be repurchased						$ 100	$ 300
Canceled (in shares)						651,000
Canceled (in dollars per share)						$ 6.23
2014 Stock Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future grant						4,241,980	3,364,304
Percentage of outstanding shares of common stock		5.00%				5.00%
Options granted, exercisable term (in years)						5 years
2014 Stock Incentive Plan | Prior Common Stock Outstanding
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized for future issuance	3,394,376	3,211,211
2014 Stock Incentive Plan | Reallocated 2008 Equity Plan Shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional shares authorized for future issuance						266,799	1,640,324
2014 Stock Incentive Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for reallocation				8,310,566
Additional shares reserved for future issuance							8,000,000
Percentage of outstanding shares of common stock							5.00%
Options granted, exercisable term (in years)						10 years
Total combined voting power of all classes of stock						10.00%
2014 Stock Incentive Plan | Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of exercise price of fair value per share on grant date						110.00%
2014 Stock Incentive Plan | Minimum | Non Statutory Stock Option Award
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of exercise price of fair value per share on grant date						100.00%
2014 Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of shares available for future grant						4,104,060
Additional shares authorized for future issuance		642,242			4,000,000
Acquisition price at lower of fair market value, percentage						85.00%
Percentage of eligible compensation through payroll deductions						15.00%
2014 Employee Stock Purchase Plan | ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares purchased during period						1,080,142	1,105,015
Average share price of shares purchased (in dollars per share)						$ 3.93	$ 3.56
Aggregate intrinsic value of shares purchased						$ 3,500	$ 3,700
2014 Employee Stock Purchase Plan | Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of outstanding shares of common stock							1.00%
Additional shares authorized for future issuance							3,500,000
Option Exchange Program
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Canceled (in shares)			344,248
Canceled (in dollars per share)			$ 13.58
Other than options granted (in shares)			109,743
Granted (in dollars per share)			$ 6.76
Incremental share based compensation expense						$ 56

Equity Award Plans - Schedule o

Equity Award Plans - Schedule of Stock-based Compensation Awards Granted under Stock Option Plan in Consolidated Statements of Operations (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 16,922	$ 16,861	$ 12,359
Cost of revenue
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	1,105	1,533	1,063
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	7,006	7,735	5,829
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	5,732	5,437	3,932
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	3,079	2,156	1,535
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	4,153	5,565	5,852
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	12,567	8,871	3,217
Employee stock purchase rights
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation	$ 202	$ 2,425	$ 3,290

Equity Award Plans - Summary of

Equity Award Plans - Summary of Valuation Assumptions (Details)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	4 years 10 months 25 days	4 years 9 months 18 days	4 years 9 months 25 days
Risk-free interest rate	1.40%	1.60%	1.80%
Volatility	49.00%	50.00%	41.00%
Dividend rate	0.00%	0.00%	0.00%
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	1 year 3 months 20 days	1 year 3 months 20 days	1 year 3 months 20 days
Risk-free interest rate	0.80%	0.50%	0.30%
Volatility	42.00%	41.00%	27.00%
Dividend rate	0.00%	0.00%	0.00%

Equity Award Plans - Summary 51

Equity Award Plans - Summary of Activity under Stock Option Plans (Details) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)$ / sharesshares
Number of Shares Underlying Outstanding Options
Outstanding options, Beginning balance (in shares) | shares	9,291
Granted (in shares) | shares	672
Exercised (in shares) | shares	(1,444)
Canceled (in shares) | shares	(651)
Outstanding options, Ending balance (in shares) | shares	7,868
Vested and expected to vest at end of period (in shares) | shares	7,758
Vested and exercisable (in shares) | shares	5,688
Weighted-Average Exercise Price
Beginning balance (in dollars per share) | $ / shares	$ 4.78
Granted (in dollars per share) | $ / shares	5.52
Exercised (in dollars per share) | $ / shares	4.22
Canceled (in dollars per share) | $ / shares	6.23
Ending balance (in dollars per share) | $ / shares	4.82
Vested and expected to vest at end of period (in dollars per share) | $ / shares	4.82
Vested and exercisable at end of period (in dollars per share) | $ / shares	$ 4.57
Weighted-average remaining contractual term (in years)	6 years 2 months 12 days
Weighted average remaining contractual term, Vested and expected to vest at end of period (in years)	6 years 2 months 12 days
Weighted average remaining contractual term, Vested and exercisable at end of period (in years)	5 years 7 months 6 days
Aggregate Intrinsic Value | $	$ 28,931
Aggregate Intrinsic Value, Vested and expected to vest at end of period | $	28,554
Aggregate Intrinsic Value, Vested and exercisable at end of period | $	$ 22,363

Equity Award Plans - Informatio

Equity Award Plans - Information About Stock Options (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Fair value of options granted	$ 1,603	$ 869	$ 11,683
Weighted-average fair value of options granted (in dollars per share)	$ 2.38	$ 2.13	$ 2.79
Intrinsic value of options exercised	$ 5,990	$ 2,299	$ 14,863

Equity Award Plans - Summary 53

Equity Award Plans - Summary of RSU activity (Details) - RSUs $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)$ / sharesshares
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at beginning of period (in shares) | shares	3,452
Granted (in shares) | shares	4,550
Released (in shares) | shares	(1,139)
Canceled (in shares) | shares	(904)
Outstanding at end of period (in shares) | shares	5,959
Weighted Average Grant Date Fair Value
Outstanding at beginning of period (in dollars per share) | $ / shares	$ 5.88
Granted (in dollars per share) | $ / shares	6.50
Released (in dollars per share) | $ / shares	8.16
Canceled (in dollars per share) | $ / shares	6.56
Outstanding at end of period (in dollars per share) | $ / shares	$ 5.81
Weighted-Average Remaining Vesting Term (Years)	1 year 7 months 13 days
Aggregate Intrinsic Value (thousands) | $	$ 49,517

Equity Award Plans - Stock Awar

Equity Award Plans - Stock Awards (Details) - USD ($)	1 Months Ended		12 Months Ended
	Oct. 31, 2016	Feb. 29, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Oct. 27, 2016
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total compensation expense related to unvested awards granted, not yet recognized			$ 32,000,000
Total compensation expense related to unvested awards granted, not yet recognized weighted-average period for recognition			2 years 4 months 12 days
Share price (in dollars per share)			$ 8.31
MSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)				40,000	540,000
Consecutive trading days			20 days
Target price measurement period			4 years
PSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)	60,641	547,000
Vesting percentage		25.00%
RSUs
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Granted (in shares)			4,550,000
Fair value of vested shares			$ 9,700,000	$ 5,600,000
Common Stock
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Amount authorized to be repurchased						$ 20,000,000
Number of shares repurchased during period			226,676
Average price per share of shares repurchased (in dollars per share)			$ 7.92

Net Loss Per Share - Summary of

Net Loss Per Share - Summary of Outstanding Shares of Common Stock Equivalents (Detail) - shares shares in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share Diluted [Line Items]
Anti-dilutive securities excluded from computation of diluted net income per share	13,645	10,176	6,611
Stock options, RSUs and employee stock purchase rights
Earnings Per Share Diluted [Line Items]
Anti-dilutive securities excluded from computation of diluted net income per share	13,631	10,124	6,415
Common Stock Subject to Repurchase
Earnings Per Share Diluted [Line Items]
Anti-dilutive securities excluded from computation of diluted net income per share	14	52	196

Income Taxes - Schedule of Inco

Income Taxes - Schedule of Income before Income Tax, by Geographic Region (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Domestic loss	$ (22,978)	$ (41,677)	$ (35,593)
Foreign income	2,795	2,390	2,380
Loss before income taxes	$ (20,183)	$ (39,287)	$ (33,213)

Income Taxes - Components of In

Income Taxes - Components of Income Tax Expense (Benefit) (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current provision for income taxes:
State	$ 41	$ 55	$ 24
Foreign	1,009	675	1,054
Total current	1,050	730	1,078
Deferred tax expense (benefit):
Federal	17	0	0
Foreign	(310)	17	429
Total deferred	(293)	17	429
Provision for income taxes	$ 757	$ 747	$ 1,507

Income Taxes - Effective Income

Income Taxes - Effective Income Tax Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Tax at statutory rate	$ (6,862)	$ (13,358)	$ (11,292)
Tax at statutory rate (percent)	34.00%	34.00%	34.00%
State tax - net of federal benefits	$ 27	$ 36	$ 16
State tax - net of federal benefits (percent)	(0.10%)	(0.10%)	(0.10%)
Foreign rate differential	$ (666)	$ (422)	$ 231
Foreign rate differential (percent)	3.30%	1.10%	(0.70%)
Changes in federal valuation allowance	$ 7,141	$ 11,926	$ 10,547
Changes in valuation allowance (percent)	(35.40%)	(30.40%)	(31.80%)
Stock-based compensation	$ 88	$ 1,845	$ 1,041
Stock-based compensation (percent)	(0.40%)	(4.70%)	(3.10%)
Other permanent items	$ 583	$ 415	$ 513
Other permanent items (percent)	(2.90%)	(1.10%)	(1.50%)
Expenses for uncertain tax positions	$ 358	$ 227	$ 330
Expenses for uncertain tax positions (percent)	(1.80%)	(0.60%)	(1.00%)
Other	$ 88	$ 78	$ 121
Other (percent)	(0.40%)	(0.10%)	(0.40%)
Provision for income taxes	$ 757	$ 747	$ 1,507
Provision for income taxes (percent)	(3.70%)	(1.90%)	(4.60%)

Income Taxes - Deferred Tax Ass

Income Taxes - Deferred Tax Assets and Liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Deferred tax assets:
Net operating loss carryforwards	$ 47,197	$ 46,317
Research and development credits, net of uncertain tax positions	12,953	9,517
Accruals, reserves, and other	21,288	17,904
Stock-based compensation	4,055	2,700
Depreciation and amortization	2,892	2,735
Gross deferred tax assets	88,385	79,173
Valuation allowance	(86,935)	(77,643)
Total deferred tax assets	1,450	1,530
Deferred tax liabilities:
Others	(431)	(805)
Total deferred tax liabilities	(431)	(805)
Net deferred tax assets	$ 1,019	$ 725

Income Taxes - Unrecognized Tax

Income Taxes - Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Gross unrecognized tax benefits—beginning balance	$ 2,552	$ 2,195	$ 1,846
Increases (decrease) related to tax positions from prior years	66	(4)	340
Increases related to tax positions taken during current year	690	361	278
Decreases related to tax positions taken during the current year	0	0	(269)
Gross unrecognized tax benefits—ending balance	$ 3,308	$ 2,552	$ 2,195

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Operating Loss Carryforwards [Line Items]
Valuation allowance	$ 86,935	$ 77,643
Increase in valuation allowance	9,300	14,000	$ 11,200
Undistributed earnings of foreign subsidiaries	5,100	3,900
Unrecognized tax benefits	3,308	2,552	2,195	$ 1,846
Accrued interest related to unrecognized tax benefits	9
Gross accrued interest expense	66	(4)	$ 340
Unrecognized tax benefits that would affect the effective tax rate	1,100
U.S. Federal
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	139,000	130,600
State
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	68,600	68,400
Research and Development Credit Carryforward | U.S. Federal
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	8,500	6,400
Research and Development Credit Carryforward | State
Operating Loss Carryforwards [Line Items]
Tax credit carryforward	8,800	$ 6,400
Stock Options
Operating Loss Carryforwards [Line Items]
Operating loss carryforwards	10,800
Interest Expense [Member]
Operating Loss Carryforwards [Line Items]
Gross accrued interest expense	20
Interest released due to lapse of statue of limitations	$ 11

Geographic Information - Schedu

Geographic Information - Schedule of Total Revenue Based on Customer's Location (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Segment Reporting Information [Line Items]
Total revenue	$ 230,003	$ 198,955	$ 179,507
United States
Segment Reporting Information [Line Items]
Total revenue	118,750	106,842	85,325
Japan
Segment Reporting Information [Line Items]
Total revenue	52,951	35,636	45,787
Asia Pacific, excluding Japan
Segment Reporting Information [Line Items]
Total revenue	29,829	23,847	20,434
EMEA
Segment Reporting Information [Line Items]
Total revenue	23,093	27,193	19,254
Other
Segment Reporting Information [Line Items]
Total revenue	$ 5,380	$ 5,437	$ 8,707

Related-Party Transactions (Det

Related-Party Transactions (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014
Related Party Transactions [Abstract]
Revenue from related parties	$ 2.2	$ 2.8

Employee Benefit Plan (Details)

Employee Benefit Plan (Details) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Compensation and Retirement Disclosure [Abstract]
Percent match	50.00%
Percent of employee's compensation	6.00%
Contribution amount	$ 900,000	$ 800,000	$ 0

Appcito Acquisition (Details)

Appcito Acquisition (Details) - USD ($) $ in Thousands	Jun. 23, 2016	Jun. 30, 2016	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Business Acquisition [Line Items]
Cash consideration			$ 4,380	$ 0	$ 0
Estimated useful life (in years)			4 years 7 months
Goodwill			$ 1,307	$ 72
Appcito, Inc.
Business Acquisition [Line Items]
Total purchase price consideration	$ 6,500
Fair value of the purchase price consideration	6,300
Cash consideration	5,000
Holdback held to cover indemnification claims	$ 700
Unregistered shares of common stock issued (shares)	227,404
Fair value of common stock issued	$ 1,300
Goodwill	$ 1,235
Legal, accounting and other professional fees incurred		$ 200
Amortization period of acquisition costs (in years)	15 years
Developed technology | Appcito, Inc.
Business Acquisition [Line Items]
Estimated useful life (in years)	5 years

Appcito Acquisition - Purchase

Appcito Acquisition - Purchase Price Allocation (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Jun. 23, 2016	Dec. 31, 2015
Business Acquisition [Line Items]
Goodwill	$ 1,307		$ 72
Appcito, Inc.
Business Acquisition [Line Items]
Developed technology		$ 5,050
Goodwill		1,235
Other tangible assets		58
Total assets acquired		$ 6,343