Nevro (NVRO) 10-K 23 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. 14, 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	NVRO
Entity Registrant Name	NEVRO CORP
Entity Central Index Key	1,444,380
Current Fiscal Year End Date	--12-31
Entity Well-known Seasoned Issuer	Yes
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Common Stock, Shares Outstanding		29,183,202
Entity Public Float			$ 1,652

Consolidated Balance Sheets

Consolidated Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Current assets
Cash and cash equivalents	$ 41,406	$ 87,036
Short-term investments	234,951	106,634
Accounts receivable, net of allowance for doubtful accounts of $1,008 and $122 at December 31, 2016 and 2015, respectively	52,818	22,522
Inventories	85,221	62,430
Prepaid expenses and other current assets	5,895	4,009
Total current assets	420,291	282,631
Property and equipment, net	7,132	5,794
Other assets	2,354	1,852
Restricted cash	806	906
Total assets	430,583	291,183
Current liabilities
Accounts payable	16,162	21,887
Accrued liabilities	26,028	14,381
Other current liabilities	8	121
Total current liabilities	42,198	36,389
Long-term debt	138,140	19,740
Other long-term liabilities	1,211	462
Total liabilities	181,549	56,591
Commitments and contingencies (Note 5)
Stockholders’ equity
Preferred stock, $0.001 par value, 10,000,000 shares authorized at December 31, 2016 and 2015, respectively; zero shares issued and outstanding at December 31, 2016 and 2015, respectively
Common stock, $0.001 par value, 290,000,000 shares authorized at December 31, 2016 and 2015, respectively; 28,886,862 and 28,143,573 shares issued and outstanding at December 31, 2016 and 2015, respectively	29	28
Additional paid-in capital	470,869	424,147
Accumulated other comprehensive loss	(678)	(175)
Accumulated deficit	(221,186)	(189,408)
Total stockholders’ equity	249,034	234,592
Total liabilities and stockholders’ equity	$ 430,583	$ 291,183

Consolidated Balance Sheets (Pa

Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Statement Of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 1,008	$ 122
Preferred stock, par value	$ 0.001	$ 0.001
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.001	$ 0.001
Common stock, shares authorized	290,000,000	290,000,000
Common stock, shares issued	28,886,862	28,143,573
Common stock, shares outstanding	28,886,862	28,143,573

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Statement [Abstract]
Revenue	$ 228,504	$ 69,606	$ 32,573
Cost of revenue	75,433	28,120	11,278
Gross profit	153,071	41,486	21,295
Operating expenses
Research and development	33,729	21,382	19,824
Sales, general and administrative	142,423	82,471	29,777
Total operating expenses	176,152	103,853	49,601
Loss from operations	(23,081)	(62,367)	(28,306)
Interest income	1,685	575	141
Interest expense	(6,394)	(2,732)	(157)
Other income (expense), net	(1,097)	(1,741)	(1,880)
Loss on extinguishment of debt	(1,268)
Loss before income taxes	(30,155)	(66,265)	(30,202)
Provision for income taxes	1,623	1,166	478
Net loss	(31,778)	(67,431)	(30,680)
Accretion of redeemable convertible preferred stock to redemption value			(147)
Net loss attributable to common stockholders	(31,778)	(67,431)	(30,827)
Other comprehensive loss:
Changes in foreign currency translation adjustment	(163)	(178)	(147)
Changes in unrealized losses on short-term investments, net	(340)	(74)	196
Net change in other comprehensive loss	(503)	(252)	49
Comprehensive Loss	$ (32,281)	$ (67,683)	$ (30,778)
Net loss per share, basic and diluted	$ (1.12)	$ (2.54)	$ (6.94)
Weighted average number of common shares used to compute basic and diluted net loss per share	28,485,003	26,581,890	4,440,663

Consolidated Statements of Conv

Consolidated Statements of Convertible Preferred Stock, Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Mayo Foundation [Member]	Common Stock [Member]	Common Stock [Member]Mayo Foundation [Member]	Additional Paid-In Capital [Member]	Additional Paid-In Capital [Member]Mayo Foundation [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Series A Convertible Preferred Stock [Member]	Series B and C Redeemable Convertible Preferred Stock [Member]
Beginning balances at Dec. 31, 2013	$ (85,790)		$ 1		$ 5,331		$ (91,150)	$ 28	$ 47,217	$ 106,018
Beginning balances, shares at Dec. 31, 2013			1,120,416						5,437,826	9,770,222
Accretion of redeemable convertible preferred stock issuance costs										$ 147
Accretion of stock issuance costs	(147)						(147)
Conversion of preferred stock to common stock	153,382		$ 15		153,367				$ (47,217)	$ (106,165)
Conversion of preferred stock to common stock, shares			15,208,048						(5,437,826)	(9,770,222)
Issuance of common stock upon underwritten public offering, net of issuance costs	131,617	$ 523	$ 8		131,609	$ 523
Issuance of common stock upon underwritten public offering, shares			8,050,000	20,833
Exercise of common stock options	$ 964		$ 1		963
Exercise of common stock options, shares	498,565		466,194
Vesting of early exercised stock options	$ 154				154
Stock based compensation	1,998				1,998
Net loss	(30,680)						(30,680)
Other comprehensive income (loss)	49							49
Ending balances at Dec. 31, 2014	172,070		$ 25		293,945		(121,977)	77
Ending balances, shares at Dec. 31, 2014			24,865,491
Issuance of common stock upon underwritten public offering, net of issuance costs	118,439		$ 3		118,436
Issuance of common stock upon underwritten public offering, shares			2,470,587
Exercise of common stock options	$ 2,958				2,958
Exercise of common stock options, shares	751,610		774,337
Issuance of common stock under employee stock purchase plan	$ 1,430				1,430
Issuance of common stock under employee stock purchase plan, shares			33,158
Vesting of early exercised stock options	53				53
Stock based compensation	7,325				7,325
Net loss	(67,431)						(67,431)
Other comprehensive income (loss)	(252)							(252)
Ending balances at Dec. 31, 2015	234,592		$ 28		424,147		(189,408)	(175)
Ending balances, shares at Dec. 31, 2015			28,143,573
Conversion feature of convertible senior notes due 2021, net of allocated costs	31,767				31,767
Purchase of bond hedges	(45,092)				(45,092)
Sales of warrants	33,120				33,120
Exercise of common stock options	$ 6,808		$ 1		6,807
Exercise of common stock options, shares	667,494		669,337
Issuance of common stock upon release of restricted stock units			1,384
Issuance of common stock under employee stock purchase plan	$ 3,499				3,499
Issuance of common stock under employee stock purchase plan, shares			72,568
Vesting of early exercised stock options	47				47
Stock based compensation	15,760				15,760
Tax benefit from stock option deductions	814				814
Net loss	(31,778)						(31,778)
Other comprehensive income (loss)	(503)							(503)
Ending balances at Dec. 31, 2016	$ 249,034		$ 29		$ 470,869		$ (221,186)	$ (678)
Ending balances, shares at Dec. 31, 2016			28,886,862

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	$ (31,778)	$ (67,431)	$ (30,680)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	1,717	614	96
Stock-based compensation expense	15,760	7,325	1,998
Accretion of discount on short-term investments	(231)	(458)	82
Non-cash research and development expense			523
Non-cash loss on extinguishment of debt	1,156
Payment of original issue discount	(1,500)
Provision for doubtful accounts	909	90	(172)
Write-down of inventory	4,056	2,767	754
Loss on disposal of equipment	287
Non-cash interest expense	3,681	231	11
Unrealized gains (losses) on foreign currency transactions	1,854	(682)
Changes in operating assets and liabilities
Accounts receivable	(32,181)	(16,233)	167
Inventories	(27,031)	(49,407)	(5,487)
Prepaid expenses and other current assets	(1,997)	(1,197)	(1,337)
Other assets	(505)	(1,432)	(204)
Accounts payable	(5,586)	17,051	1,283
Accrued liabilities	12,136	7,987	1,763
Other long-term liabilities	750	345	55
Net cash used in operating activities	(58,503)	(100,430)	(31,148)
Cash flows from investing activities
Purchases of short-term investments	(372,309)	(190,000)	(159,265)
Proceeds from maturity of short-term investments	243,890	235,272	51,835
Changes in restricted cash	100	(606)
Purchases of property and equipment	(3,368)	(5,008)	(625)
Net cash provided by (used in) investing activities	(131,687)	39,658	(108,055)
Cash flows from financing activities
Proceeds from issuance of notes payable			19,500
Proceeds from issuance of common stock in public offering, net		118,439	131,617
Proceeds from issuance of convertible notes	172,500
Convertible notes initial issuance discount and debt issuance costs	(6,171)
Proceeds from issuance of warrants	33,120
Purchase of convertible note hedges	(45,092)
Repayment of debt	(19,500)
Proceeds from issuance of common stock to employees	10,307	4,388	964
Net cash provided by financing activities	145,164	122,827	152,081
Effect of exchange rate changes on cash and cash equivalents	(604)	(306)
Net increase (decrease) in cash and cash equivalents	(45,630)	61,749	12,878
Cash and cash equivalents
Cash and cash equivalents at beginning of period	87,036	25,287	12,409
Cash and cash equivalents at end of period	41,406	87,036	25,287
Supplemental disclosures of cash flow information
Cash paid for income taxes	492	670	243
Cash paid for interest	2,469	2,332
Significant non-cash transactions
Purchases of property and equipment in accounts payable	725	752
Vesting of early-exercised stock options	$ 47	$ 53	$ 154

Formation and Business of the C

Formation and Business of the Company	12 Months Ended
	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Formation and Business of the Company	1. Formation and Business of the Company We were incorporated in Minnesota on March 10, 2006 to manufacture and market innovative active implantable medical devices for the treatment of neurological disorders initially focusing on the treatment of chronic pain. Subsequently, we were reincorporated in Delaware on October 4, 2006 and relocated to California. Since inception, the Company has incurred net losses and negative cash flows from operations. During the year ended December 31, 2016, the Company incurred a net loss of $31.8 million and used $58.5 million of cash in operations. At December 31, 2016, the Company had an accumulated deficit of $221.2 million and does not expect to experience positive cash flows in the immediate future. The Company has financed operations to date primarily through private placements of equity securities, borrowings under a debt agreement, the issuance of common stock in its November 2014 initial public offering, and its June 2015 underwritten public offering, as well as its June 2016 underwritten public offering of convertible senior notes due in 2021. The Company’s ability to continue to meet its obligations and to achieve its business objectives for the foreseeable future is dependent upon, amongst other things, generating sufficient revenues and its ability to continue to control expenses, if necessary, to meet its obligations as they become due. Failure to increase sales of its products, manage discretionary expenditures or raise additional financing, if required, may adversely impact the Company’s ability to achieve its intended business objectives. Public Offerings In November 2014, the Company completed its initial public offering (IPO) of shares of its common stock and as a result, the following transactions were recorded in the Company’s consolidated financial statements during the fourth quarter of 2014: • the sale of 8,050,000 shares of common stock, including 1,050,000 from the exercise by the underwriters of their overallotment option, at an offering price of $18.00 per share, for net proceeds of $131.6 million, after deducting the underwriters’ discounts, commissions and offering costs paid by us; and • immediately prior to the completion of the IPO, all the outstanding shares of the Company’s redeemable convertible preferred stock and convertible preferred stock were converted into 15,208,048 shares of common stock. In June 2015, the Company completed an underwritten public offering of its common stock, which included shares of its common stock held by certain of its stockholders, and issued 2,470,587 shares of common stock, including 705,882 shares issued pursuant to the exercise in full by the underwriters of their option to purchase additional shares. The Company received cash proceeds of approximately $118.4 million, net of underwriting discounts and commissions and offering costs paid by the Company. In June 2016, the Company issued $150.0 million aggregate principal amount of 1.75% convertible senior notes due 2021 in a registered underwritten public offering and an additional $22.5 million aggregate principal amount of such notes pursuant to the exercise in full of the over-allotment options of the underwriters (the 2021 Notes). The interest rates are fixed at 1.75% per annum and are payable semi-annually in arrears on June 1 and December 1 of each year, commencing on December 1, 2016. The total net proceeds from the debt offering, after deducting transaction costs, were approximately $166.2 million.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the U.S. (U.S. GAAP). The consolidated financial statements include the Company’s accounts and those of its four wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated. Segments The chief operating decision maker for the Company is the Chief Executive Officer. The Chief Executive Officer reviews financial information presented on a consolidated basis, accompanied only by information about revenue by geographic region. The Company has one business activity and there are no segment managers who are held accountable for operations, operating results or plans for levels or components below the consolidated unit level, other than revenue. Accordingly, the Company has determined that it has a single reportable and operating segment structure. The Company and its Chief Executive Officer evaluate performance based primarily on revenue in the geographic locations in which the Company operates. The Company historically derived most of its revenue from sales to customers in Australia and Europe. In May 2015, the U.S. Food and Drug Administration (FDA) approved the Company’s premarket approval (PMA) application to market Senza in the United States and the Company launched sales in the United States in 2015. Revenue by geography is based on the billing address of the customer. The following table sets forth revenue by geographic area for countries with revenue accounting for 10% of more of the total revenue during the periods presented: Years Ended December 31, 2016 2015 2014 United States 76 % 35 % — % Australia * 20 % 35 % United Kingdom * 12 % 18 % Germany * 13 % 17 % * Represents less than 10% Long-lived assets and operating income outside the U.S. are not material; therefore disclosures have been limited to revenue. Foreign Currency Translation The Company’s consolidated financial statements are prepared in U.S. dollars (USD). Its foreign subsidiaries use their local currency as their functional currency and maintain their records in the local currency. Accordingly, the assets and liabilities of these subsidiaries are translated into USD using the current exchange rates in effect at the balance sheet date and equity accounts are translated into USD using historical rates. Revenues and expenses are translated using the monthly average exchange rates during the period when the transaction occurs. The resulting foreign currency translation adjustments from this process are recorded in accumulated other comprehensive income (loss) in the consolidated balance sheets. Unrealized foreign exchange gains and losses from the remeasurement of assets and liabilities denominated in currencies other than the functional currency of the reporting entity are recorded in other income (expense), net. The Company recorded net unrealized foreign currency transaction losses of $1.6 million during the year ended December 31, 2016, gains of $0.6 million during the year ended December 31, 2015 and losses of $1.1 million during the year ended December 31, 2014. Additionally, realized gains and losses resulting from transactions denominated in currencies other than the local currency are recorded in other income (expense), net. The Company recorded realized foreign currency transaction gains of $0.7 million during the year ended December 31, 2016, and losses of $2.2 million and $0.6 million during the years ended December 31, 2015 and 2014, respectively. As the Company’s international operations grow, the effect of fluctuations in currency rates will become greater, and the Company will continue to reassess its approach to managing this risk. In addition, currency fluctuations or a weakening U.S. dollar can increase the costs of the Company’s international expansion. To date, the Company has not entered into any foreign currency hedging contracts. Based on its current international structure, the Company does not plan on engaging in hedging activities in the near future. Use of Estimates The preparation of financial statements in accordance with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Significant accounting estimates and management judgments reflected in the consolidated financial statements include items such as allowances for doubtful accounts; warranty obligations; stock-based compensation; depreciation and amortization lives; inventory valuation; valuation of investments and deferred tax assets, including valuation allowances. Estimates are based on historical experience, where applicable, and other assumptions believed to be reasonable by the management. Actual results may differ from those estimates under different assumptions or conditions. Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents and investments. The majority of the Company’s cash is held by one financial institution in the United States in excess of federally insured limits. The Company maintained investments in money market funds that were not federally insured during the years ended December 31, 2016 and 2015, and held cash in foreign banks of approximately $3.3 million and $5.2 million at December 31, 2016 and 2015, respectively, that was not federally insured. The Company has not experienced any losses on its deposits of cash and cash equivalents. Through December 31, 2014, all of the Company’s revenue had been derived from sales of its products in international markets, principally Australia and Europe. In May 2015, the Company launched sales in the United States upon receiving FDA approval to market and sell its products in the United States. In the international markets in which the Company participates, the Company uses both a direct sales force and distributors to sell its products, while in the United States the Company utilizes a direct sales force. The Company performs ongoing credit evaluations of its direct customers and distributors, does not require collateral, and maintains allowances for potential credit losses on customer accounts when deemed necessary. There were no customers that accounted for 10% or more of the Company’s revenue for each of the years ended December 31, 2016, 2015 and 2014. There were no customers that accounted for 10% or more of the Company’s accounts receivable balance as of December 31, 2016 and 2015. The Company is subject to risks common to medical device companies including, but not limited to, new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, product liability, uncertainty of market acceptance of products, and the need to obtain additional financing. The Company is dependent on third party manufacturers and suppliers, in some cases sole- or single-source suppliers. There can be no assurance that the Company’s products or services will continue to be accepted in the marketplace, nor can there be any assurance that any future products or services can be developed or manufactured at an acceptable cost and with appropriate performance characteristics, or that such products or services will be successfully marketed, if at all. The Company expects to incur substantial operating losses in the near term and may need to obtain additional financing. There can be no assurance that such financing will be available or will be at terms acceptable by the Company. Fair Value of Financial Instruments Carrying amounts of certain of the Company’s financial instruments, including cash equivalents, short term investments, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities. Cash and Cash Equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less at the date of purchase to be cash equivalents. Cash and cash equivalents include money market funds in the amount of $35.5 million and $36.6 million as of December 31, 2016 and 2015, respectively. At December 31, 2016 and 2015, the Company’s cash equivalents were held in institutions in the United State and include commercial paper deposits in a money market fund which were unrestricted as to withdrawal or use. Restricted Cash Restricted cash as of December 31, 2016 and 2015 includes a letter of credit of $0.6 million representing collateral for the Company’s Redwood City, CA building lease pursuant to an agreement dated March 5, 2015. Restricted cash additionally includes certificates of deposit of $0.2 million as of December 31, 2016 and $0.3 million as of December 31, 2015, collateralizing payment of charges related to the Company’s credit cards. Investment Securities The Company classifies its investment securities as available-for-sale. The Company classifies these investment securities as short-term or long-term based on the nature of the investment, its maturity date and its availability for use in current operations. Those investments with original maturities greater than three months at the date of purchase and remaining maturities of less than 12 months are considered short-term investments. Those investments with remaining maturities greater than 12 months are also classified as short-term investments as management considers them to be available for current operations if needed. The Company’s investment securities are recorded at fair value based on the fair value hierarchy. Money market funds and treasury bonds are classified within Level 1 of the fair value hierarchy and the commercial paper and corporate notes are classified within Level 2 of the fair value hierarchy. Unrealized gains and losses, deemed temporary in nature, are reported as a separate component of accumulated other comprehensive income (loss). A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the corresponding establishment of a new cost basis for the security. Premiums (discounts) are amortized (accreted) over the life of the related security as an adjustment to yield using the straight-line interest method. Dividend and interest income are recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold. Inventories Inventories are stated at the lower of cost to purchase or manufacture the inventory or the market value of such inventory. Cost is determined using the standard cost method which approximates the first-in, first-out basis. Market value is determined as the lower of replacement cost or net realizable value. The Company regularly reviews inventory quantities in consideration of actual loss experiences, projected future demand, and remaining shelf life to record a provision for excess and obsolete inventory when appropriate. The Company’s policy is to write down inventory that has become obsolete, inventory that has a cost basis in excess of its expected lower of cost or market value, and inventory in excess of expected requirements. The estimate of excess quantities is subjective and primarily dependent on the Company’s estimates of future demand for a particular product. If the estimate of future demand is inaccurate based on actual sales, the Company may increase the write down for excess inventory for that component and record a charge to inventory impairment in the accompanying consolidated statements of operations and comprehensive loss. The Company periodically evaluates the carrying value of inventory on hand for potential excess amount over demand using the same lower of cost or market approach as that has been used to value the inventory. The Company also periodically evaluates inventory quantities in consideration of actual loss experience. As a result of these evaluations, for the years ended December 31, 2016, 2015 and 2014, the Company recognized total write downs of $4.1 million, $2.8 million and $0.8 million for its inventories. The Company’s estimation of the future demand for a particular component of the Company’s products may vary and may result in changes in estimates in any particular period. Shipping and Handling Costs Shipping and handling costs are expensed as incurred and are included in cost of revenue. Revenue Recognition The Company recognizes revenue when all of the following criteria are met: • persuasive evidence of an arrangement exists; • the sales price is fixed or determinable; • collection of the relevant receivable is reasonably assured at the time of sale; and • delivery has occurred or services have been rendered. For a majority of sales, where the Company’s sales representative delivers its product at the point of implantation at hospitals or medical facilities, the Company recognizes revenue upon completion of the procedure and authorization, which represents satisfaction of the required revenue recognition criteria. For the remaining sales, which are sent from the Company’s distribution centers directly to hospitals and medical facilities, as well as distributor sales where product is ordered in advance of an implantation procedure and a valid purchase order has been received, the Company recognizes revenue at the time of shipment of the product, which represents the point in time when the customer has taken ownership and assumed the risk of loss and the required revenue recognition criteria are satisfied. The Company’s customers are obligated to pay within specified terms regardless of when or if they ever sell or use the products. The Company does not offer rights of return or price protection and it has no post-delivery obligations. The Company periodically provides incentive offers to customers. Product revenue is recorded net of such incentive offers. Allowance for Doubtful Accounts The Company makes estimates of the collectability of accounts receivable. In doing so, the Company analyzes historical bad debt trends, customer credit worthiness, current economic trends and changes in customer payment patterns when evaluating the adequacy of the allowance for doubtful accounts. Warranty Obligations The Company has a limited one- to five-year warranty to most customers and warrants that its products will operate substantially in conformity with product specifications. The Company records an estimate for the provision for warranty claims in cost of revenue when the related revenues are recognized. This estimate is based on historical and anticipated rates of warranty claims, the cost per claim and the number of units sold. The Company regularly assesses the adequacy of its recorded warranty obligations and adjusts the amounts as necessary. Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation of property and equipment, other than leasehold improvements, is computed using the straight-line method over the assets’ estimated useful lives of three to five years. Leasehold improvements are amortized on a straight-line basis over the shorter of the estimated useful life of the asset or the life of the lease. Upon retirement or sale, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in operations. Maintenance and repairs are charged to operations as incurred. Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset or asset group might not be recoverable. When such an event occurs, management determines whether there has been impairment by comparing the anticipated undiscounted future net cash flows to the related asset group’s carrying value. If an asset is considered impaired, the asset is written down to fair value, which is determined based either on discounted cash flows or appraised value, depending on the nature of the asset. There were no impairment charges, or changes in estimated useful lives, recorded through December 31, 2016. Income Taxes The Company records income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company’s consolidated financial statements or income tax returns. In estimating future tax consequences, expected future events other than enactments or changes in the tax law or rates are considered. Valuation allowances are provided when necessary to reduce deferred tax assets to the amount expected to be realized. The Company operates in various tax jurisdictions and is subject to audit by various tax authorities. To date, taxes paid have been predominantly due to income taxes in foreign jurisdictions in which we conduct business. The Company provides for tax contingencies whenever it is deemed probable that a tax asset has been impaired or a tax liability has been incurred for events such as tax claims or changes in tax laws. Tax contingencies are based upon their technical merits, relative tax law, and the specific facts and circumstances as of each reporting period. Changes in facts and circumstances could result in material changes to the amounts recorded for such tax contingencies. The Company records uncertain tax positions on the basis of a two-step process whereby (1) a determination is made as to whether it is more likely than not that the tax positions will be sustained based on the technical merits of the position and (2) for those tax positions that meet the more-likely-than-not recognition threshold the Company recognizes the largest amount of tax benefit that is greater than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company’s policy is to recognize interest and penalties related to income taxes as a component of income tax expense. No interest or penalties related to income taxes have been recognized in the statements of operations and comprehensive loss in 2016 and 2015. Other Comprehensive Income (Loss) Other comprehensive income (loss) represents all changes in stockholders’ equity except those resulting from distributions to stockholders. The Company’s unrealized gains on short-term available-for-sale investment securities and foreign currency translation adjustments represent the components of other comprehensive income (loss) that are excluded from the reported net loss and are presented in the consolidated statements of operations and comprehensive loss. Research and Development Research and development expenses, including new product development, regulatory compliance, and clinical research, are charged to operations as incurred in the consolidated statements of operations and comprehensive loss. Such costs include personnel-related costs, including stock-based compensation, supplies, services, depreciation, allocated facilities and information services, clinical trial and related clinical manufacturing expenses, fees paid to investigative sites, and other indirect costs. Stock-Based Compensation The Company accounts for stock-based compensation arrangements with employees in accordance with Accounting Standards Codification (ASC) 718, Compensation—Stock Compensation. The Company’s determination of the fair value of stock options on the date of grant utilizes the Black-Scholes option-pricing model, and is impacted by its common stock price as well as changes in assumptions regarding a number of highly complex and subjective variables. These variables include, but are not limited to, the expected term that options will remain outstanding, the expected common stock price volatility over the term of the option awards, risk-free interest rates and expected dividends. The fair value of stock options is recognized over the period during which an optionee is required to provide services in exchange for the option award, known as the requisite service period (usually the vesting period), on a straight-line basis, with the exception of performance based stock options whose fair value is recorded as expenses when performance metrics are achieved. Stock-based compensation expense recognized at fair value includes the impact of estimated forfeitures. The Company estimates future forfeitures at the date of grant and revises the estimates, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The Company accounts for restricted stock units at their fair value, based on the closing market price of the Company’s common stock on the grant date. The fair value is amortized on a straight-line basis over the requisite service period of the awards, with the exception of performance based awards whose fair value is recorded as expenses when performance metrics are achieved. The Company estimates the fair value of the rights to purchase shares by employees under the Employee Stock Purchase Plan using the Black-Scholes option pricing formula. The Employee Stock Purchase Plan provides for consecutive six-month offering periods and the Company uses its own historical volatility data in the valuation. Equity instruments issued to non-employees are recorded at their fair value on the measurement date and are subject to periodic adjustments as the underlying equity instruments vest. The fair value of options granted to consultants is expensed when vested. The non-employee stock-based compensation expense was not material for all periods presented. Estimating the fair value of equity-settled awards as of the grant date using valuation models, such as the Black-Scholes option pricing model, is affected by assumptions regarding a number of complex variables. Changes in the assumptions can materially affect the fair value and ultimately how much stock-based compensation expense is recognized. These inputs are subjective and generally require significant analysis and judgment to develop. For all stock options granted to date, we included the volatility data based on a study of publicly traded industry peer companies. For purposes of identifying these peer companies, we considered the industry, stage of development, size and financial leverage of potential comparable companies. The risk-free interest rate is based on the yield available on U.S. Treasury zero-coupon issues similar in duration to the expected term of the equity-settled award. The Company accounts for stock-based compensation for the restricted stock units at their fair value, based on the closing market price of the Company’s common stock on the grant date. These costs are recognized on a straight-line basis over the requisite service period, which is generally the vesting term of four years. The Company recognizes a benefit from stock-based compensation as additional paid-in capital if an incremental tax benefit is realized by following the with-and-without approach. Net Loss per Share of Common Stock Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, restricted stock units and common stock options are considered to be potentially dilutive securities. Because the Company has reported a net loss in all periods presented, diluted net loss per common share is the same as basic net loss per common share for those periods. Recent Accounting Pronouncements In July 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue Recognition. Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date Revenue from Contracts with Customers (Topic 606) Identifying Performance Obligations and Licensing, In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients , related to disclosures of remaining performance obligations, as well as other amendments to guidance on collectability, non-cash consideration and the presentation of sales and other similar taxes collected from customers. In December 2016, the FASB issued ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts and Customers , related to further clarifications issued in ASU 2014-09. In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities, In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) In March 2016, the FASB issued ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August, 2016, the FASB issued ASU No. 2016-15, Classification of Certain Cash Receipts and Cash Payments (a consensus of the Emerging Issues Task Force) . The update In October 2016, the FASB issued ASU No. 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other than Inventory asset. This ASU does not apply to intra-entity transfers of inventory, where t he income tax consequences from the sale of inventory from one member of a consolidated entity to another will continue to be deferred until the inventory is sold to a third party. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, a consensus of the FASB Emerging Issues Task Force

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Fair Value Measurements	3. Fair Value Measurements Fair value is defined as the exchange price that would be received for an asset or an exit price paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The fair value hierarchy defines a three-level valuation hierarchy for disclosure of fair value measurements as follows: • Level 1 — Observable inputs, such as quoted prices in active markets for identical assets or liabilities. • Level 2 — Observable inputs other than Level 1 prices, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities. • Level 3 — Unobservable inputs that are supported by little or no market activity and that are significant to the fair value of the assets or liabilities. Cash Equivalents and Short Term Investments The Company’s cash equivalents are comprised of investments in money market funds that are classified as Level 1 of the fair value hierarchy. To value its money market funds, the Company values the funds at $1 stable net asset value, which is the quoted price in active markets for identical assets that the Company has the ability to access. The Company’s short-term investments are comprised of commercial paper, corporate notes and U.S. government agency obligations. All short-term investments have been classified within Level 1 or Level 2 of the fair value hierarchy because of the sufficient observable inputs for revaluation. The Company’s Level 2 investments are valued using third-party pricing sources. The pricing services utilize industry standard valuation models, including both income and market-based approaches, for which all significant inputs are observable, either directly or indirectly, to estimate fair value. These inputs include reported trades of any broker/dealer quotes on the same or similar investments, issuer credit spreads, benchmark investments, prepayment/default projections based on historical data and other observable inputs. The following table sets forth the Company’s financial instruments that were measured at fair value on a recurring basis, by level, within the fair value hierarchy (in thousands): Balance as of December 31, 2016 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 35,510 $ — $ — $ 35,510 Commercial paper (iii) — 160,582 — 160,582 Corporate notes (iii) — 74,369 — 74,369 Total assets $ 35,510 $ 234,951 $ — $ 270,461 Balance as of December 31, 2015 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 36,559 $ — $ — $ 36,559 Commercial paper (ii) — 129,206 — 129,206 Treasury bonds (iii) 10,617 — — 10,617 Total assets $ 47,176 $ 129,206 $ — $ 176,382 (i) Included in cash and cash equivalents on the consolidated balance sheets. (ii) Included in either cash and cash equivalents or short-term investments on the consolidated balance sheets. (iii) Included in short-term investments on the consolidated balance sheets. Convertible Senior Notes As of December 31, 2016, the fair value of the 1.75% convertible senior notes due 2021 was $183.8 million. The fair value was determined on the basis of market prices observable for similar instruments and is considered Level 2 in the fair value hierarchy.

Balance Sheet Components

Balance Sheet Components	12 Months Ended
	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Components	4. Balance Sheet Components Investments The fair value of the Company’s cash equivalents and short-term investments approximates their respective carrying amounts due to their short-term maturity. The following is a summary of the gross unrealized gains and unrealized losses on the Company’s investment securities (in thousands): December 31, 2016 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Commercial paper $ 160,729 $ 6 $ (153 ) $ 160,582 Corporate notes 74,430 3 (64 ) 74,369 Total securities $ 235,159 $ 9 $ (217 ) $ 234,951 December 31, 2015 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Commercial paper (i) $ 129,075 $ 131 $ — $ 129,206 Treasury bonds 10,616 1 — 10,617 Total securities $ 139,691 $ 132 $ — $ 139,823 (i) Includes $33.2 million of commercial paper that is classified as cash and cash equivalents on the consolidated balance sheet. Realized gains or losses from the sale of investments and other-than-temporary impairments, if any, on available-for-sale securities are reported in other income (expense), net as incurred. The cost of securities sold was determined based on the specific identification method. The Company has not recorded any realized gains, realized losses or impairment on its investments during the periods presented. The amortized costs and estimated fair values of the Company’s available-for-sale securities by contractual maturities as of December 31, 2016 were as follows (in thousands): Amortized Cost Fair Value Amounts maturing within one year $ 233,163 $ 232,955 Amounts after one year through five years 1,996 1,996 Total investment securities $ 235,159 $ 234,951 Inventories, Net (in thousands) December 31, 2016 2015 Raw materials $ 44,862 $ 37,096 Finished goods 40,359 25,334 Total inventories $ 85,221 $ 62,430 Property and Equipment, Net (in thousands) December 31, 2016 2015 Laboratory equipment $ 1,567 $ 921 Computer equipment and software 2,388 1,836 Furniture and fixtures 2,051 1,752 Leasehold improvements 1,214 1,188 Construction in process 2,274 799 Total 9,494 6,496 Less: Accumulated depreciation and amortization (2,362 ) (702 ) Property and equipment, net $ 7,132 $ 5,794 Depreciation and amortization expense for the years ended December 31, 2016, 2015 and 2014 was $1.7 million, $0.6 million and $96,000, respectively. Accrued Liabilities (in thousands) December 31, 2016 2015 Accrued payroll and related expenses $ 17,732 $ 9,857 Accrued professional fees 1,067 583 Accrued taxes 2,110 2,044 Accrued clinical and research expenses 1,545 405 Accrued interest 243 — Accrued warranty 645 394 Accrued other 2,686 1,098 Total accrued liabilities $ 26,028 $ 14,381

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	5. Commitments and Contingencies Operating Leases In March 2015, the Company entered into a lease agreement for approximately 50,000 square feet of office space located in Redwood City, California for a period beginning in June 2015 through May 2022 with initial annual payments of approximately $2.0 million, increasing to $2.4 million annually during the final year of the lease term. In December 2016, the Company entered into an amendment for an additional approximately 50,000 square feet of office space adjacent to the premises under the original lease (the Expansion Premises), with initial annual payments of $1.2 million, increasing to $2.9 million in the final year of the amended lease term. The lease for the Expansion Premises commences on the earlier of (i) the date the Company commences business operations in the Expansion Premises, or (ii) the date upon which the Landlord substantially completes certain improvements to, and permitting for, the Expansion Premises (the Commencement Date). The Company entered into a non-cancellable operating lease effective May 1, 2010 for facilities in Menlo Park, CA as amended in 2012 to extend the period of the lease until May 31, 2015. In March 2015, the Company extended the lease through September 30, 2015, at which time the lease terminated. In August 2014, the Company entered into a new facility lease for warehouse space beginning on August 21, 2014 through May 31, 2015, under which it is obligated to pay approximately $100,000 in lease payments over the term of the lease. In March 2015, the Company extended the warehouse lease through February 2017 under which it is obligated to pay approximately $0.3 million in lease payments over the remaining term of the lease. Rent expense for the years ended December 31, 2016, 2015 and 2014 was $2.4 million, $1.9 million and $0.7 million, respectively. Excluding the terms under the amendment for the Expansion Premises, which is subject to certain cancellation clauses, future minimum lease payments under operating leases as of December 31, 2016 are as follows (in thousands): Operating Lease Year ending December 31, 2017 $ 2,167 2018 2,185 2019 2,250 2020 2,318 2021 2,387 Thereafter 1,211 Total $ 12,518 Warranty Obligations The Company warrants that its products will operate substantially in conformity with product specifications and has a limited one- to five-year warranty to most customers. The Company established a warranty liability in June 2015. Prior to that time, replacements made under warranty were minimal and were recorded at the time that the claims were incurred. Activities related to warranty obligations were as follows (in thousands): December 31, 2016 2015 Beginning Balance $ 394 $ — Provision for warranty 902 451 Utilization (651 ) (57 ) Ending Balance $ 645 $ 394 Supply Agreements The Company has entered into supply agreements with certain of the Company’s suppliers that required certain minimum annual purchase agreements. As of December 31, 2016, the Company had minimum annual purchase commitments $25.0 million due in 2017 and $5.5 million due in each of 2018, 2019, 2020 and 2021. License Agreement In March 2006, the Company entered into an amended and restated license agreement with the Mayo Foundation for Medical Education and Research (Mayo) and Venturi Group LLC (VGL), which provides the Company access to the certain know how and licensed patents owned by Mayo and VGL for treatment of central, autonomic and peripheral nervous system disorders, including pain, using devices to modulate nerve signaling. The licenses granted are exclusive and the Company has the right to sub-license. The agreement will terminate upon the last to expire patent application, unless terminated earlier. The agreement can be terminated any time after three years from March 2006 by Mayo or VGL. Per terms of the license, the Company is required to pay royalties based on the greater of earned royalty or minimum royalty. The earned royalty will be based on a percentage of net sales of licensed products either by the Company or the sub-licensee. The minimum royalty payment will be based on royalty periods as defined in the agreement. In March 2011, the Company entered into a Phase II License Agreement with Mayo which provides the Company access to the certain know how and licensed patents owned by Mayo. The licenses granted are exclusive and the Company has the right to sub-license. The agreement will terminate upon the last to expire patent application, unless terminated earlier. Per terms of the license, the Company is required to: • Pay a retainer fee of $40,000 per annum starting March 2011 and ending February 2013; • Pay royalties based on the greater of earned royalty or minimum royalty. The earned royalty will be based on a percentage of net sales of licensed products either by the Company or the sub-licensee. The minimum annual royalty payment is $200,000. Royalties paid during the years ended December 31, 2016, 2015 and 2014 were $1.9 million, $0.6 million and $0.3 million, respectively. In November 2014, the Company issued Mayo 20,833 shares of common stock owed in connection with the IPO pursuant to the terms of the license, and recorded noncash research and development expense of $0.5 million for the fair value of the shares on the date of issuance. Contingencies From time to time, the Company may have certain contingent liabilities that arise in the ordinary course of business activities. The Company accrues a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated. There have been no contingent liabilities requiring accrual at December 31, 2016 and 2015. Indemnification The Company enters into standard indemnification arrangements in the ordinary course of business. Pursuant to these arrangements, the Company indemnifies, holds harmless, and agrees to reimburse the indemnified parties for losses suffered or incurred by the indemnified party, in connection with any trade secret, copyright, patent or other intellectual property infringement claim by any third-party with respect to the Company’s technology. The term of these indemnification agreements is generally perpetual. The maximum potential amount of future payments the Company could be required to make under these agreements is not determinable because it involves claims that may be made against the Company in the future, but have not yet been made. The Company has entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers, other than liabilities arising from willful misconduct of the individual. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited; however, the Company has director and officer insurance coverage that reduces the Company’s exposure and enables the Company to recover a portion of any future amounts paid. The Company believes the estimated fair value of these indemnification agreements in excess of applicable insurance coverage is minimal. The Company has not incurred costs to defend lawsuits or settle claims related to these indemnification agreements. No liability associated with such indemnifications has been recorded to date. Legal Matters On November 28, 2016, the Company filed a lawsuit for patent infringement against Boston Scientific Corporation and Boston Scientific Neuromodulation Corporation (collectively, Boston Scientific). The lawsuit, filed in the United States District Court for the Northern District of California, asserts that Boston Scientific is infringing the Company’s patents covering inventions relating to the Senza system and HF10 therapy. The lawsuit seeks preliminary and permanent injunctive relief against further infringement as well as damages and attorney’s fees. On December 9, 2016, Boston Scientific filed a patent infringement lawsuit alleging the Company’s manufacture, use and sale of the Senza system infringes certain of Boston Scientific’s patents covering SCS technology related to stimulation leads, rechargeable batteries and telemetry. The lawsuit, filed in the United States District Court for the District of Delaware, seeks unspecified damages and attorney’s fees, as well as preliminary and permanent injunctive relief against further infringement. As of December 31, 2016, . The Company is and may from time to time continue to be involved in various legal proceedings of a character normally incident to the ordinary course of its business, including several pending European patent oppositions at the European Patent Office (EPO) initiated by the Company’s competitors Medtronic and Boston Scientific, which the Company does not deem to be material to its business and consolidated financial statements at this stage.

Long-term Debt

Long-term Debt	12 Months Ended
	Dec. 31, 2016
Debt Disclosure [Abstract]
Long-term Debt	6. Long-term Debt 1.75% Convertible Senior Notes and Convertible Note Hedge and Warrant Transactions In June 2016, the Company issued $150.0 million aggregate principal amount of 1.75% convertible senior notes due 2021 in a registered underwritten public offering and an additional $22.5 million aggregate principal amount of such notes pursuant to the exercise in full of the over-allotment options of the underwriters (the 2021 Notes). The interest rates are fixed at 1.75% per annum and are payable semi-annually in arrears on June 1 and December 1 of each year, commencing on December 1, 2016. The total net proceeds from the debt offering, after deducting initial purchase discounts and debt issuance costs, were approximately $166.2 million. Each $1,000 principal amount of the 2021 Notes will initially be convertible into 10.3770 shares of the Company’s common stock, which is equivalent to an initial conversion price of approximately $96.37 per share, subject to adjustment upon the occurrence of specified events. The 2021 Notes will be convertible at the option of the holders at any time prior to the close of business on the business day immediately preceding December 1, 2020, only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on September 30, 2016 (and only during such calendar quarter), if the last reported sale price of the Company’s common stock for at least 20 trading days (whether or not consecutive) during a period of 30 consecutive trading days ending on the last trading day of the immediately preceding calendar quarter is greater than or equal to 130% of the conversion price on each applicable trading day; (2) during the five business day period after any ten consecutive trading day period (the measurement period) in which the trading price (as defined in the indenture to the 2021 Notes) per $1,000 principal amount of notes for each trading day of the measurement period was less than 98% of the product of the last reported sale price of the Company’s common stock and the conversion rate on each such trading day; or (3) upon the occurrence of specified corporate events. On or after December 1, 2020 until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert their 2021 Notes at any time, regardless of the foregoing circumstances. Upon conversion, the Company will pay or deliver, as the case may be, cash, shares of the Company’s common stock or a combination of cash and shares of the Company’s common stock, at the Company’s election. If the Company undergoes a fundamental change prior to the maturity date, holders of the notes may require the Company to repurchase for cash all or any portion of their notes at a repurchase price equal to 100% of the principal amount of the notes to be repurchased, plus accrued and unpaid interest to, but excluding, the fundamental change repurchase date. In addition, if specific corporate events occur prior to the applicable maturity date, the Company will increase the conversion rate for a holder who elects to convert their notes in connection with such a corporate event in certain circumstances. It is the Company’s current intent and policy to settle conversions through combination settlement with a specified dollar amount per $1,000 principal amount of notes of $1,000. During the three months ended December 31, 2016, the conditions allowing holders of the 2021 Notes to convert have not been met. The 2021 Notes are therefore not convertible during the three months ended March 31, 2017 and are classified as long-term debt. Should the sale price condition be met in a future quarter, the 2021 Notes will be convertible at the holders’ option during the immediately following quarter. As of December 31, 2016, the if-converted value of the 2021 Notes did not exceed the principal value of those notes. In accounting for the issuance of the convertible senior notes, the Company separated the 2021 Notes into liability and equity components. The carrying amount of the liability component was calculated by measuring the fair value of a similar debt instrument that does not have an associated convertible feature. The carrying amount of the equity component representing the conversion option was $32.9 million and was determined by deducting the fair value of the liability component from the par value of the 2021 Notes. The equity component is not remeasured as long as it continues to meet the conditions for equity classification. The excess of the principal amount of the liability component over its carrying amount ("debt discount") is amortized to interest expense over the term of the 2021 Notes expense at an effective interest rate of 6.29% over the contractual terms of the notes. In accounting for the debt issuance costs of $6.2 million related to the 2021 Notes, the Company allocated the total amount incurred to the liability and equity components of the 2021 Notes based on their relative values. Issuance costs attributable to the liability component were $5.0 million and will be amortized to interest expense using the effective interest method over the contractual terms of the 2021 Notes. Issuance costs attributable to the equity component were netted with the equity component in stockholders’ equity. The net carrying amount of the liability component of the 2021 Notes was as follows (in thousands): December 31, 2016 Principal $ 172,500 Unamortized discount (29,783 ) Unamortized issuance cost (4,577 ) Net carrying amount $ 138,140 The net carrying amount of the equity component of the 2021 Notes was as follows (in thousands): December 31, 2016 Debt discount related to value of conversion option $ 32,945 Debt issuance cost (1,179 ) Net carrying amount $ 31,766 The following table sets forth the interest expense recognized related to the 2021 Notes (in thousands): Year Ended December 31, 2016 Contractual interest expense $ 1,652 Amortization of debt discount 3,162 Amortization of debt issuance costs 416 Total interest expense related to the 2021 Notes $ 5,230 In connection with the offering of the 2021 Notes, the Company entered into convertible note hedge transactions with certain bank counterparties in which the Company has the option to purchase initially (subject to adjustment for certain specified events) a total of approximately 1.8 million shares of the Company’s common stock at a price of approximately $96.37 per share. The total cost of the convertible note hedge transactions was $45.1 million. In addition, the Company sold warrants to certain bank counterparties whereby the holders of the warrants have the option to purchase initially (subject to adjustment for certain specified events) a total of approximately 1.8 million shares of the Company’s common stock at a price of $127.28 per share. The Company received $33.1 million in cash proceeds from the sale of these warrants. Taken together, the purchase of the convertible note hedges and the sale of warrants are intended to offset any actual dilution from the conversion of these notes and to effectively increase the overall conversion price from $96.37 to $127.28 per share. As these transactions meet certain accounting criteria, the convertible note hedges and warrants are recorded in stockholders’ equity and are not accounted for as derivatives. The net cost of $12.0 million incurred in connection with the convertible note hedge and warrant transactions was recorded as a reduction to additional paid-in capital on the consolidated balance sheet. Capital Royalty Term Loan On October 24, 2014, the Company entered into a credit facility (the “credit facility”) with Capital Royalty Partners and certain of its affiliates (the “lenders”) under which, subject to certain conditions, the Company could enter into three term loan agreements totaling $50.0 million with the lenders on or before September 30, 2015. In June 2016, the Company paid the outstanding principal and repayment fees totaling $21.0 million to the lenders, and the credit facility terminated and is now no longer in effect. The difference between the total payment to the lenders and the net carrying amount of the obligation recorded on the balance sheet was recorded as a loss on extinguishment of debt.

Convertible Preferred Stock

Convertible Preferred Stock	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Convertible Preferred Stock	7. Convertible Preferred Stock Prior to the initial public offering, the Company had outstanding 15,208,048 shares of convertible preferred stock. Each share of preferred stock was convertible to one share of common stock. Upon the closing of the Company’s initial public offering on November 11, 2014, all shares of outstanding redeemable convertible preferred stock were automatically converted to 15,208,048 shares of the Company’s common stock. The Company recorded the Series B and C redeemable convertible preferred stock at fair value on the dates of issuance. The Company classified the Series B and C redeemable convertible preferred stock outside of stockholders’ deficit because the shares contain liquidation features that are not solely within the Company’s control. The Series B and C redeemable convertible preferred shares were originally issued with a contingent redemption feature, which allowed the holders to redeem their shares five years following the issuance date of the Series B and C redeemable preferred shares. Accordingly, the Company accreted the Series B and C redeemable convertible preferred stock for change in redemption value with a charge to accumulated deficit at the end of each reporting period. The Company has accreted $0.1 million during the year ended December 31, 2014.

Stock-Based Compensation

Stock-Based Compensation	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Stock-Based Compensation	8. Stock-Based Compensation Common stock reserved for future issuance as of December 31, 2016 was as follows: December 31, 2016 Outstanding stock options and restricted stock units 3,166,782 Reserved for grants of future stock options and restricted stock units 2,202,239 Reserved for employee stock purchase plan 621,029 Total common stock reserved for future issuance 5,990,050 Stock Plans The Company’s Board of Directors, or Board, and stockholders previously approved the 2007 Stock Option Plan (the “2007 Plan”). In October 2014, the Board adopted the 2014 Equity Incentive Award Plan (the “2014 Plan” and, together with the 2007 Plan, the “Stock Plans”). As of the effective date of the 2014 Plan, the Company suspended the 2007 Plan and no additional awards may be granted under the 2007 Plan. Any shares of common stock covered by awards granted under the 2007 Plan that terminate after the effective date of the 2014 Plan by expiration, forfeiture, cancellation or other means without the issuance of such shares, will be added to the 2014 Plan reserve. Under the 2014 Plan, 1,854,166 shares of common stock were initially reserved for issuance, plus the number of shares remaining available for future awards under the 2007 Plan, as of the pricing of the IPO. The number of shares initially reserved for issuance under the 2014 Plan is subject to increase by (i) the number of shares represented by awards outstanding under the 2007 Plan that are forfeited or lapse unexercised and which following the pricing date are not issued under the 2007 Plan, and (ii) an annual increase on January 1 of each year. Under the 2014 Plan, the Company may grant awards such as incentive stock options, nonstatutory stock options, restricted stock units and stock appreciation rights. Incentive stock options (ISO) may be granted only to Company employees (including directors who are also employees). Nonqualified stock options (NSO) may be granted to Company employees, directors and consultants Stock Options Options under the 2014 Plan may be granted for periods of up to ten years and at prices no less than 100% of the estimated fair market value of the shares on the date of grant as determined by the Board, provided, however, that the exercise price of an ISO or an NSO granted to a 10% stockholder shall not be less than 110% of the estimated fair market value of the shares on the date of grant. Upon the exercise of options, the Company issues new common stock from its authorized shares. The vesting provisions of individual options vary but are generally over four years, with the exception of performance based stock options. Pursuant to the 2014 Plan, the Company granted performance based stock options to the Company’s CEO in March 2016. This performance based stock option award is subject to the CEO’s continued service to the Company through each applicable vesting date. If a performance metric is not met within the time limits specified in the award agreements, the shares subject to vesting under the vesting tranche for that performance metric will be cancelled. A summary of shares available for grant under the Stock Plans was as follows: Shares Available for Grant Balance at December 31, 2013 581,585 Additional shares reserved 1,854,166 Options granted (753,102 ) Options cancelled 12,767 Balance at December 31, 2014 1,695,416 Additional shares reserved 994,619 Options and restricted stock granted (975,688 ) Options and restricted stock cancelled 142,362 Balance at December 31, 2015 1,856,709 Additional shares reserved 1,125,742 Options and restricted stock granted (856,043 ) Options and restricted stock cancelled 75,831 Balance at December 31, 2016 2,202,239 A summary of stock option activity under the Stock Plans was as follows: Options Outstanding Weighted Average Number of Weighted Average Remaining Aggregate Options Exercise Price Contractual Term Intrinsic Value (in years) (in thousands) Outstanding at December 31, 2013 2,731,962 $ 2.88 8.0 $ 1,655 Options granted 753,102 $ 13.50 Options exercised (498,565 ) $ 2.26 $ 2,488 Options cancelled (12,767 ) $ 3.60 Outstanding at December 31, 2014 2,973,732 $ 5.77 7.9 $ 97,832 Options granted 970,238 $ 50.16 Options exercised (751,610 ) $ 3.87 $ 36,603 Options cancelled (142,072 ) $ 19.08 Outstanding at December 31, 2015 3,050,288 $ 19.74 7.8 $ 145,721 Options granted 498,564 $ 66.74 Options exercised (667,494 ) $ 10.19 $ 46,529 Options cancelled (60,131 ) $ 40.89 Outstanding at December 31, 2016 2,821,227 $ 29.85 7.4 $ 123,425 Options exercisable as of December 31, 2016 1,506,297 $ 14.69 6.4 $ 87,358 Options vested, exercisable or expected to vest as of December 31, 2016 2,739,732 $ 29.11 7.3 $ 121,743 The aggregate intrinsic value of options exercised is the difference between the estimated fair market value of the Company’s common stock at the date of exercise and the exercise price for in-the-money options. The aggregate intrinsic value of outstanding options is the difference between the closing price as of the date outstanding and the exercise price of the underlying stock options. The weighted-average grant-date fair value of options granted during the years ended December 31, 2016, 2015 and 2014 was $32.11, $25.06 and $11.33 per share, respectively. The total fair value of options vested during the years ended December 31, 2016, 2015 and 2014 was approximately $10.7 million, $5.2 million and $1.2 million, respectively, based on the grant date fair value. The options outstanding and vested under the Stock Plans by exercise price, at December 31, 2016, were as follows: Options Outstanding Options Vested Weighted Average Remaining Number Contractual Term Weighted Average Number Weighted Average Exercise Price Outstanding (in years) Exercise Price Exercisable Exercise Price $0.96 — $1.92 141,176 2.87 $ 1.48 141,176 $ 1.48 $3.60 — $3.60 1,030,002 6.01 $ 3.60 890,023 $ 3.60 $10.08 — $38.79 572,674 7.87 $ 25.89 247,046 $ 25.34 $41.83 — $54.50 573,030 8.67 $ 51.44 150,184 $ 49.67 $57.89 — $97.52 504,345 9.27 $ 71.37 77,868 $ 64.20 $0.96 — $97.52 2,821,227 7.35 $ 29.85 1,506,297 $ 14.69 Restricted Stock Units In 2015, the Company began granting restricted stock units (RSUs) under the 2014 Plan. Holders of RSUs do not have stockholder rights. Upon the release of RSUs, the Company issues new common stock from its authorized shares. RSUs generally vest four years from the date of grant. Pursuant to the 2014 Plan, the Company granted performance based RSUs to the CEO in March 2016. The performance based RSUs are subject to the CEO’s continued service to the Company through each applicable vesting date. If a performance metric is not met within the time limits specified in the RSU agreement, the shares subject to vesting under the vesting tranche for that performance metric will be canceled. A summary of RSUs activity under the Stock Plans was as follows: Number of Weighted Average Aggregate Restricted Grant Date Intrinsic Value Stock Units Fair Value (in thousands) Outstanding at December 31, 2014 — $ — $ — Restricted stock granted 5,450 $ 56.47 Restricted stock cancelled (290 ) $ 63.23 Outstanding at December 31, 2015 5,160 $ 56.09 $ 348 Restricted stock granted 357,479 $ 70.31 Restricted stock released (1,384 ) $ 56.65 $ 115 Restricted stock cancelled (15,700 ) $ 65.15 Outstanding at December 31, 2016 345,555 $ 70.39 $ 25,108 Restricted stock expected to vest as of December 31, 2016 314,061 $ 22,820 The aggregate intrinsic value of RSUs released is calculated using the fair market value of the Company’s common stock at the date of release. The aggregate intrinsic value of outstanding RSUs is calculated based on the closing price of the Company’s common stock as of the date outstanding. 2014 Employee Stock Purchase Plan In October 2014, the Board adopted the 2014 Employee Stock Purchase Plan (the ESPP). A total of 196,666 shares of common stock were initially available for future issuance under the 2014 Employee Stock Purchase Plan, subject to an annual increase on January 1 of each year. The ESPP provides eligible employees with an opportunity to purchase shares of the Company’s common stock through payroll deductions of up to 15% of their eligible compensation, subject to plan limitations. Under the ESPP, the purchase price of the Company stock is equal to 85% of the lower of its fair market value at the start and end of a six-month purchase period. A summary of ESPP activity was as follows: December 31, 2016 2015 2014 Additional shares reserved 281,435 248,654 — Shares issued 72,568 33,158 — Shares available for future issuance 621,029 412,162 196,666 Employee contributions for shares issued (in thousands) $ 3,499 $ 1,430 $ — Early Exercises Stock options previously granted under the 2007 Plan allowed the Board of Directors to grant awards to provide employee option holders the right to elect to exercise unvested options in exchange for restricted common stock. Unvested shares, which amounted to 1,836 at December 31, 2016, 14,863 at December 31, 2015 and 29,613 at December 31, 2014, were subject to a repurchase right held by the Company at the original issue price in the event the optionees’ employment was terminated either voluntarily or involuntarily. For exercises of employee options, this right lapses according to the vesting schedule designated on the associated option grant. The repurchase terms are considered to be a forfeiture provision. The shares purchased by the employees pursuant to the early exercise of stock options are not deemed to be issued or outstanding for accounting purposes until those shares vest, though they are legally issued and outstanding. In addition, cash received from employees for exercise of unvested options is treated as a refundable deposit shown as a liability on the consolidated balance sheets. As of December 31, 2016 and 2015 cash received related to unvested shares totaled $7,000 and $54,000, respectively. Amounts recorded are transferred into common stock and additional paid-in-capital as the shares vest. Other In March 2011, the Company issued 416,983 common shares under a restricted stock agreement to one of the officers of the Company at a purchase price of $1.44 per share. Under the terms of the agreement, the holder was entitled to purchase the shares in exchange for a promissory note. All the shares were purchased in March 2011 in exchange for a promissory note aggregating to $0.6 million. The restricted stock agreement granted the Company repurchase rights which lapsed upon attainment of full vesting by the stockholder. The restricted common shares vested 33% one year from the vesting start date and monthly thereafter over the next two years. The note bore interest at 0.54% per annum compounded annually. The principal amount of the note along with accrued interest was discharged on a quarterly basis in arrears on a pro rata basis over a period of three years conditioned upon the holder continuing to provide services to the Company. The Company accounted for the grant of the restricted common stock as stock-based compensation based on the fair value of the shares on the original grant date, and recognized expense over the three-year vesting period. The Company recorded stock-based compensation expenses of $48,000 for the year ended December 31, 2014. At December 31, 2014, there were no shares of common stock subject to repurchase by the Company. Employee Stock-Based Compensation The Company estimated the fair value of stock options granted to employees and shares purchased by employees under the ESPP using the Black-Scholes option valuation model. The fair value is amortized on a straight-line basis over the requisite service period of the awards, with the exception of performance based stock options whose fair value is recorded as expenses when performance metrics are achieved. The following assumptions were used in estimating the fair value: Years Ended December 31, 2016 2015 2014 Stock Options: Expected term (in years) 5.3 — 6.1 5.3 — 6.1 5.3 — 6.1 Expected volatility 47% — 49% 46% — 59% 57% — 63% Risk-free interest rate 1.3% — 1.9% 1.4% — 1.8% 1.7% — 2.0% Dividend Yield 0% 0% 0% ESPP: Expected term (in years) 0.5 0.5 — Expected volatility 46% — 53% 42% — 64% — Risk-free interest rate 0.4% — 0.6% 0.1% — 0.3% — Dividend Yield 0% 0% — Expected Term . The expected term of stock-based awards represents the weighted-average period that the stock-based awards are expected to remain outstanding. The Company has opted to use the “simplified method” for estimating the expected term of the awards, whereby the expected term equals the arithmetic average of the vesting term and the original contractual term of the awards. Starting in late 2016, the Company started to utilize its own historical data for the calculation of expected term. Expected Volatility . The Company determined the share price volatility for stock-based awards based on an analysis of the historical volatilities of a peer group of publicly traded medical device companies. In evaluating similarity, the Company considered factors such as industry, stage of life cycle and size. Starting in late 2016, the Company has started to incorporate its own stock trading volatility with those of its peer group for the calculation of volatility. Risk-Free Interest Rate. The risk-free interest rate is based on the U.S. Treasury yield in effect at the time of the grant for zero-coupon U.S. Treasury notes with remaining terms similar to the expected term of the stock-based awards. Dividend Rate. The expected dividend was assumed to be zero as the Company has never paid dividends and has no current plans to do so. Expected Forfeiture Rate. The Company is required to estimate forfeitures at the time of grant, and revise those estimates in subsequent periods if actual forfeitures differ from those estimates. The Company uses historical data to estimate pre-vesting option forfeitures and record stock-based compensation expense only for those awards that are expected to vest. To the extent actual forfeitures differ from the estimates, the difference will be recorded as a cumulative adjustment in the period that the estimates are revised. The Company accounts for RSUs at their fair value, based on the closing market price of the Company’s common stock on the grant date. The fair value is amortized on a straight-line basis over the requisite service period of the awards, with the exception of performance based awards whose fair value is recorded as an expense when performance metrics are achieved. A summary of pre-tax stock-based compensation expense by line items in the consolidated statements of operations was as follows (in thousands): Years Ended December 31, 2016 2015 2014 Cost of revenue $ 1,094 $ 621 $ 147 Research and development 3,182 1,401 661 Sales, general and administrative 11,484 5,303 1,190 Total stock-based compensation expense $ 15,760 $ 7,325 $ 1,998 The effect of recording pre-tax stock-based compensation expense recognized were as follows (in thousands): Years Ended December 31, 2016 2015 2014 Stock options $ 10,832 $ 6,679 $ 1,998 Restricted stock units 3,548 9 — Employee stock purchase plan 1,380 637 — Total stock-based compensation expense $ 15,760 $ 7,325 $ 1,998 As of December 31, 2016, total stock-based compensation expense not yet recognized, net of estimated forfeitures, were as follows: Unrecognized Weighted-Average Compensation Amortization Period (in thousands) (in years) Stock options $ 25,602 2.5 Restricted stock units 18,253 3.3 Employee stock purchase plan 757 0.4

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Income Taxes	9. Income Taxes The components of the Company’s income (loss) before income taxes were as follows: Years Ended December 31, 2016 2015 2014 (in thousands) Domestic $ (34,258 ) $ (68,919 ) $ (31,807 ) Foreign 4,103 2,654 1,605 Total income (loss) before income taxes $ (30,155 ) $ (66,265 ) $ (30,202 ) The components of income tax expense are as follows (in thousands): Years Ended December 31, 2016 2015 2014 Current: Federal $ — $ — $ — State 181 34 2 Foreign 1,442 1,132 476 Total current 1,623 1,166 478 Deferred: Federal — — — State — — — Foreign — — — Total deferred — — — Total income tax expense $ 1,623 $ 1,166 $ 478 Income tax expense differs from the amount computed by applying the statutory federal income tax rate as follows: Years Ended December 31, 2016 2015 2014 Tax at statutory federal rate 34.0 % 34.0 % 34.0 % State tax, net of federal benefit (0.4 )% 0.0 % 0.0 % Other (3.7 )% (3.5 )% (5.3 )% Foreign rate differential (0.2 )% (0.5 )% 0.2 % Tax credits 3.2 % 1.6 % 2.0 % Change in valuation allowance (38.4 )% (33.4 )% (32.5 )% Total (5.5 )% (1.8 )% (1.6 )% The tax effects of temporary differences and carryforwards that give rise to significant portions of deferred tax assets are as follows: December 31, 2016 2015 (in thousands) Net operating loss carryforwards $ 60,610 $ 56,340 Tax credits 7,655 5,236 Depreciation 26 13 Stock-based compensation 5,207 1,857 Accruals and reserves 7,559 3,617 Other 4,671 313 Deferred tax assets 85,728 67,376 Other — (345 ) Deferred tax liabilities — (345 ) Valuation allowance (85,728 ) (67,031 ) Net deferred tax assets $ — $ — The Company has established a full valuation allowance against its deferred tax assets due to the uncertainty surrounding realization of these assets. Realization of deferred tax assets is dependent upon future earnings, if any, the timing and amount of which are uncertain. Accordingly, the net deferred tax assets have been fully offset by a valuation allowance. The valuation allowance increased by $18.7 million, $23.4 million and $9.4 million for the years ended December 31, 2016, 2015 and 2014, respectively. As of December 31, 2016, the Company had net operating loss carryforwards (NOLs) for federal and state income tax purposes of approximately $224.7 million and $77.3 million, respectively. These federal and state NOLs include excess tax benefit related to stock-based compensation in the amount of $54.8 million and $23.7 million, respectively. The excess tax benefit reflected in the Company’s net operating loss carryforwards will be accounted for as a credit to stockholders’ equity, if and when realized, under current accounting. In determining if and when excess tax benefits have been realized, the Company has elected to utilize the with-and-without approach with respect to such excess tax benefits. The federal NOLs begin expiring in 2026, and the state NOLs begin expiring in 2017. As of December 31, 2016, the Company had research and development credit carryforwards of approximately $5.8 million and $5.1 million for federal and California state income tax purposes, respectively. The federal credit carryforward begins expiring in 2026, and the state credits carry forward indefinitely. Under Section 382 of the Internal Revenue Code of 1986, as amended, the Company’s ability to utilize NOLs or other tax attributes such as research tax credits, in any taxable year may be limited if the Company experiences, or has experienced, an “ownership change.” A Section 382 “ownership change” generally occurs if one or more stockholders or groups of stockholders, who own at least 5% of the Company’s stock, increase their ownership by more than 50 percentage points over their lowest ownership percentage within a rolling three-year period. Similar rules may apply under state tax laws. As a result of the Company’s June 2015 underwritten public offering, the Company experienced a Section 382 “ownership change.” The Company currently estimates that this “ownership change” will not inhibit its ability to utilize its NOLs. The Company may, in the future, experience one or more additional Section 382 “ownership changes.” If so, the Company may not be able to utilize a material portion of its NOLs and tax credits, even if the Company achieves profitability. The earnings of the Company's foreign subsidiaries are not considered indefinitely reinvested. As a result, the Company has provided for residual U.S. tax on its foreign subsidiary unremitted earnings net of a foreign tax credit deferred tax asset as of December 31, 2016. The net amount of deferred tax liability is considered insignificant. The timing of the potential remittance of these earning is uncertain at December 31, 2016. The Company had unrecognized tax benefits (UTBs) of approximately $3.4 million as of December 31, 2016. All of the deferred tax assets associated with these UTBs are fully offset by a valuation allowance. The following table summarizes the activity related to UTBs (in thousands): Balance at December 31, 2013 $ 1,065 Increases related to current year tax provisions 220 Increases related to prior year tax provisions 677 Balance at December 31, 2014 1,962 Increases related to current year tax provisions 813 Increases related to prior year tax provisions 1,069 Balance at December 31, 2015 3,844 Increases related to current year tax provisions 1,059 Decreases related to prior year tax provisions (1,519 ) Balance at December 31, 2016 $ 3,384 All of these UTBs, if recognized, would affect the effective tax rate before consideration of the valuation allowance. In accordance with ASC 740, Income Taxes The Company files U.S. federal and state income tax and foreign income tax returns with varying statues of limitations. The Company’s tax years from inception in 2006 will remain open to examination due to the carryover of the unused NOLs and tax credits. The Company does not have any tax audits or other proceedings pending. The Company does not expect any material changes to the estimated amount of liability associated with its uncertain tax positions within the next twelve months.

Net Loss Per Share Attributable

Net Loss Per Share Attributable to Common Stockholders	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Net Loss Per Share Attributable to Common Stockholders	10. Net Loss Per Share Attributable to Common Stockholders The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands, except share and per share data): Years Ended December 31, 2016 2015 2014 Net loss $ (31,778 ) $ (67,431 ) $ (30,680 ) Accretion of convertible preferred stock to redemption value — — (147 ) Net loss attributable to common stockholders, basic and diluted $ (31,778 ) $ (67,431 ) $ (30,827 ) Weighted average shares outstanding 28,492,091 26,603,512 4,486,569 Less: weighted average shares subject to repurchase (7,088 ) (21,622 ) (45,906 ) Weighted average shares used to compute basic and diluted net loss per share 28,485,003 26,581,890 4,440,663 Net loss per share attributable to common stockholders, basic and diluted $ (1.12 ) $ (2.54 ) $ (6.94 ) Basic net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding for the period. Diluted net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares and potentially dilutive securities outstanding for the period, determined using the treasury-stock method and the as-if converted method, for convertible securities, if inclusion of these is dilutive. Because the Company has reported a net loss for all periods presented, diluted net loss per common share is the same as basic net loss per common share for those periods. The following potentially dilutive securities outstanding at the end of the periods presented have been excluded from the computation of diluted shares outstanding: December 31, 2016 2015 2014 Unreleased restricted stock 345,555 5,160 — Options to purchase common stock 2,821,227 3,050,288 2,973,732 Total 3,166,782 3,055,448 2,973,732 Additionally, since the Company expects to settle the principal amount of its outstanding convertible senior notes in cash, the Company uses the treasury stock method for calculating any potential dilutive effect of the conversion spread on diluted net income per share, if applicable. The conversion spread will have a dilutive impact on diluted net income per share of common stock when the average market price of the Company’s common stock for a given period exceeds the conversion price of $96.37 per share for the 2021 Notes, which has not occurred as of December 31, 2016.

Employee Benefit Plan

Employee Benefit Plan	12 Months Ended
	Dec. 31, 2016
Postemployment Benefits [Abstract]
Employee Benefit Plan	11. Employee Benefit Plan. In 2007, the Company adopted a 401(K) plan for its employees whereby eligible employees may contribute up to the maximum amount permitted by the Internal Revenue Code of 1986, as amended. In June 2016, the Company adopted a policy to match a portion of employee contributions for all qualified employees participating in the 401(k) plan. For the year ended December 31, 2016, the Company recorded expense of $1.3 million for matching contributions.

Selected Quarterly Financial In

Selected Quarterly Financial Information	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Selected Quarterly Financial Information	12. Selected Quarterly Financial Information (Unaudited) Three Months Ended December 31, September 30, June 30, March 31, 2016 2016 2016 2016 (in thousands, except per share data) Total revenue $ 70,531 $ 60,922 $ 55,400 $ 41,651 Gross profit $ 48,839 $ 41,687 $ 36,558 $ 25,987 Loss from operations $ (6,269 ) $ (1,872 ) $ (5,923 ) $ (9,017 ) Net loss $ (9,825 ) $ (3,886 ) $ (8,779 ) $ (9,288 ) Net loss attributable to common stockholders, basic and diluted $ (9,825 ) $ (3,886 ) $ (8,779 ) $ (9,288 ) Net loss per share attributable to common stockholders, basic and diluted $ (0.34 ) $ (0.14 ) $ (0.31 ) $ (0.33 ) Shares used in computing net loss per common share, basic and diluted 28,817,333 28,542,760 28,381,253 28,194,457 Three Months Ended December 31, September 30, June 30, March 31, 2015 2015 2015 2015 (in thousands, except per share data) Total revenue $ 33,124 $ 15,402 $ 11,418 $ 9,662 Gross profit $ 20,353 $ 9,434 $ 5,910 $ 5,789 Loss from operations $ (13,144 ) $ (17,709 ) $ (19,175 ) $ (12,339 ) Net loss $ (14,191 ) $ (19,454 ) $ (19,726 ) $ (14,060 ) Net loss attributable to common stockholders, basic and diluted $ (14,191 ) $ (19,454 ) $ (19,726 ) $ (14,060 ) Net loss per share attributable to common stockholders, basic and diluted $ (0.51 ) $ (0.70 ) $ (0.77 ) $ (0.57 ) Shares used in computing net loss per common share, basic and diluted 28,003,957 27,861,523 25,564,249 24,849,229

Summary of Significant Accoun19

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These consolidated financial statements have been prepared in accordance with accounting principles generally accepted in the U.S. (U.S. GAAP). The consolidated financial statements include the Company’s accounts and those of its four wholly owned subsidiaries. All intercompany accounts and transactions have been eliminated.
Segments	Segments The chief operating decision maker for the Company is the Chief Executive Officer. The Chief Executive Officer reviews financial information presented on a consolidated basis, accompanied only by information about revenue by geographic region. The Company has one business activity and there are no segment managers who are held accountable for operations, operating results or plans for levels or components below the consolidated unit level, other than revenue. Accordingly, the Company has determined that it has a single reportable and operating segment structure. The Company and its Chief Executive Officer evaluate performance based primarily on revenue in the geographic locations in which the Company operates. The Company historically derived most of its revenue from sales to customers in Australia and Europe. In May 2015, the U.S. Food and Drug Administration (FDA) approved the Company’s premarket approval (PMA) application to market Senza in the United States and the Company launched sales in the United States in 2015. Revenue by geography is based on the billing address of the customer. The following table sets forth revenue by geographic area for countries with revenue accounting for 10% of more of the total revenue during the periods presented: Years Ended December 31, 2016 2015 2014 United States 76 % 35 % — % Australia * 20 % 35 % United Kingdom * 12 % 18 % Germany * 13 % 17 % * Represents less than 10% Long-lived assets and operating income outside the U.S. are not material; therefore disclosures have been limited to revenue.
Foreign Currency Translation	Foreign Currency Translation The Company’s consolidated financial statements are prepared in U.S. dollars (USD). Its foreign subsidiaries use their local currency as their functional currency and maintain their records in the local currency. Accordingly, the assets and liabilities of these subsidiaries are translated into USD using the current exchange rates in effect at the balance sheet date and equity accounts are translated into USD using historical rates. Revenues and expenses are translated using the monthly average exchange rates during the period when the transaction occurs. The resulting foreign currency translation adjustments from this process are recorded in accumulated other comprehensive income (loss) in the consolidated balance sheets. Unrealized foreign exchange gains and losses from the remeasurement of assets and liabilities denominated in currencies other than the functional currency of the reporting entity are recorded in other income (expense), net. The Company recorded net unrealized foreign currency transaction losses of $1.6 million during the year ended December 31, 2016, gains of $0.6 million during the year ended December 31, 2015 and losses of $1.1 million during the year ended December 31, 2014. Additionally, realized gains and losses resulting from transactions denominated in currencies other than the local currency are recorded in other income (expense), net. The Company recorded realized foreign currency transaction gains of $0.7 million during the year ended December 31, 2016, and losses of $2.2 million and $0.6 million during the years ended December 31, 2015 and 2014, respectively. As the Company’s international operations grow, the effect of fluctuations in currency rates will become greater, and the Company will continue to reassess its approach to managing this risk. In addition, currency fluctuations or a weakening U.S. dollar can increase the costs of the Company’s international expansion. To date, the Company has not entered into any foreign currency hedging contracts. Based on its current international structure, the Company does not plan on engaging in hedging activities in the near future.
Use of Estimates	Use of Estimates The preparation of financial statements in accordance with accounting principles generally accepted in the United States of America requires management to make estimates and assumptions that affect the amounts reported in the consolidated financial statements and accompanying notes. Significant accounting estimates and management judgments reflected in the consolidated financial statements include items such as allowances for doubtful accounts; warranty obligations; stock-based compensation; depreciation and amortization lives; inventory valuation; valuation of investments and deferred tax assets, including valuation allowances. Estimates are based on historical experience, where applicable, and other assumptions believed to be reasonable by the management. Actual results may differ from those estimates under different assumptions or conditions.
Concentration of Credit Risk and Other Risks and Uncertainties	Concentration of Credit Risk and Other Risks and Uncertainties Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash, cash equivalents and investments. The majority of the Company’s cash is held by one financial institution in the United States in excess of federally insured limits. The Company maintained investments in money market funds that were not federally insured during the years ended December 31, 2016 and 2015, and held cash in foreign banks of approximately $3.3 million and $5.2 million at December 31, 2016 and 2015, respectively, that was not federally insured. The Company has not experienced any losses on its deposits of cash and cash equivalents. Through December 31, 2014, all of the Company’s revenue had been derived from sales of its products in international markets, principally Australia and Europe. In May 2015, the Company launched sales in the United States upon receiving FDA approval to market and sell its products in the United States. In the international markets in which the Company participates, the Company uses both a direct sales force and distributors to sell its products, while in the United States the Company utilizes a direct sales force. The Company performs ongoing credit evaluations of its direct customers and distributors, does not require collateral, and maintains allowances for potential credit losses on customer accounts when deemed necessary. There were no customers that accounted for 10% or more of the Company’s revenue for each of the years ended December 31, 2016, 2015 and 2014. There were no customers that accounted for 10% or more of the Company’s accounts receivable balance as of December 31, 2016 and 2015. The Company is subject to risks common to medical device companies including, but not limited to, new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, product liability, uncertainty of market acceptance of products, and the need to obtain additional financing. The Company is dependent on third party manufacturers and suppliers, in some cases sole- or single-source suppliers. There can be no assurance that the Company’s products or services will continue to be accepted in the marketplace, nor can there be any assurance that any future products or services can be developed or manufactured at an acceptable cost and with appropriate performance characteristics, or that such products or services will be successfully marketed, if at all. The Company expects to incur substantial operating losses in the near term and may need to obtain additional financing. There can be no assurance that such financing will be available or will be at terms acceptable by the Company.
Fair Value of Financial Instruments	Fair Value of Financial Instruments Carrying amounts of certain of the Company’s financial instruments, including cash equivalents, short term investments, accounts receivable, accounts payable and accrued liabilities approximate fair value due to their relatively short maturities.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments purchased with an original maturity of three months or less at the date of purchase to be cash equivalents. Cash and cash equivalents include money market funds in the amount of $35.5 million and $36.6 million as of December 31, 2016 and 2015, respectively. At December 31, 2016 and 2015, the Company’s cash equivalents were held in institutions in the United State and include commercial paper deposits in a money market fund which were unrestricted as to withdrawal or use.
Restricted Cash	Restricted Cash Restricted cash as of December 31, 2016 and 2015 includes a letter of credit of $0.6 million representing collateral for the Company’s Redwood City, CA building lease pursuant to an agreement dated March 5, 2015. Restricted cash additionally includes certificates of deposit of $0.2 million as of December 31, 2016 and $0.3 million as of December 31, 2015, collateralizing payment of charges related to the Company’s credit cards.
Investment Securities	Investment Securities The Company classifies its investment securities as available-for-sale. The Company classifies these investment securities as short-term or long-term based on the nature of the investment, its maturity date and its availability for use in current operations. Those investments with original maturities greater than three months at the date of purchase and remaining maturities of less than 12 months are considered short-term investments. Those investments with remaining maturities greater than 12 months are also classified as short-term investments as management considers them to be available for current operations if needed. The Company’s investment securities are recorded at fair value based on the fair value hierarchy. Money market funds and treasury bonds are classified within Level 1 of the fair value hierarchy and the commercial paper and corporate notes are classified within Level 2 of the fair value hierarchy. Unrealized gains and losses, deemed temporary in nature, are reported as a separate component of accumulated other comprehensive income (loss). A decline in the fair value of any security below cost that is deemed other than temporary results in a charge to earnings and the corresponding establishment of a new cost basis for the security. Premiums (discounts) are amortized (accreted) over the life of the related security as an adjustment to yield using the straight-line interest method. Dividend and interest income are recognized when earned. Realized gains and losses are included in earnings and are derived using the specific identification method for determining the cost of securities sold.
Inventories	Inventories Inventories are stated at the lower of cost to purchase or manufacture the inventory or the market value of such inventory. Cost is determined using the standard cost method which approximates the first-in, first-out basis. Market value is determined as the lower of replacement cost or net realizable value. The Company regularly reviews inventory quantities in consideration of actual loss experiences, projected future demand, and remaining shelf life to record a provision for excess and obsolete inventory when appropriate. The Company’s policy is to write down inventory that has become obsolete, inventory that has a cost basis in excess of its expected lower of cost or market value, and inventory in excess of expected requirements. The estimate of excess quantities is subjective and primarily dependent on the Company’s estimates of future demand for a particular product. If the estimate of future demand is inaccurate based on actual sales, the Company may increase the write down for excess inventory for that component and record a charge to inventory impairment in the accompanying consolidated statements of operations and comprehensive loss. The Company periodically evaluates the carrying value of inventory on hand for potential excess amount over demand using the same lower of cost or market approach as that has been used to value the inventory. The Company also periodically evaluates inventory quantities in consideration of actual loss experience. As a result of these evaluations, for the years ended December 31, 2016, 2015 and 2014, the Company recognized total write downs of $4.1 million, $2.8 million and $0.8 million for its inventories. The Company’s estimation of the future demand for a particular component of the Company’s products may vary and may result in changes in estimates in any particular period.
Shipping and Handling Costs	Shipping and Handling Costs Shipping and handling costs are expensed as incurred and are included in cost of revenue.
Revenue Recognition	Revenue Recognition The Company recognizes revenue when all of the following criteria are met: • persuasive evidence of an arrangement exists; • the sales price is fixed or determinable; • collection of the relevant receivable is reasonably assured at the time of sale; and • delivery has occurred or services have been rendered. For a majority of sales, where the Company’s sales representative delivers its product at the point of implantation at hospitals or medical facilities, the Company recognizes revenue upon completion of the procedure and authorization, which represents satisfaction of the required revenue recognition criteria. For the remaining sales, which are sent from the Company’s distribution centers directly to hospitals and medical facilities, as well as distributor sales where product is ordered in advance of an implantation procedure and a valid purchase order has been received, the Company recognizes revenue at the time of shipment of the product, which represents the point in time when the customer has taken ownership and assumed the risk of loss and the required revenue recognition criteria are satisfied. The Company’s customers are obligated to pay within specified terms regardless of when or if they ever sell or use the products. The Company does not offer rights of return or price protection and it has no post-delivery obligations. The Company periodically provides incentive offers to customers. Product revenue is recorded net of such incentive offers.
Allowance for Doubtful Accounts	Allowance for Doubtful Accounts The Company makes estimates of the collectability of accounts receivable. In doing so, the Company analyzes historical bad debt trends, customer credit worthiness, current economic trends and changes in customer payment patterns when evaluating the adequacy of the allowance for doubtful accounts.
Warranty Obligations	Warranty Obligations The Company has a limited one- to five-year warranty to most customers and warrants that its products will operate substantially in conformity with product specifications. The Company records an estimate for the provision for warranty claims in cost of revenue when the related revenues are recognized. This estimate is based on historical and anticipated rates of warranty claims, the cost per claim and the number of units sold. The Company regularly assesses the adequacy of its recorded warranty obligations and adjusts the amounts as necessary.
Property and Equipment	Property and Equipment Property and equipment are stated at cost less accumulated depreciation and amortization. Depreciation of property and equipment, other than leasehold improvements, is computed using the straight-line method over the assets’ estimated useful lives of three to five years. Leasehold improvements are amortized on a straight-line basis over the shorter of the estimated useful life of the asset or the life of the lease. Upon retirement or sale, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is reflected in operations. Maintenance and repairs are charged to operations as incurred.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of an asset or asset group might not be recoverable. When such an event occurs, management determines whether there has been impairment by comparing the anticipated undiscounted future net cash flows to the related asset group’s carrying value. If an asset is considered impaired, the asset is written down to fair value, which is determined based either on discounted cash flows or appraised value, depending on the nature of the asset. There were no impairment charges, or changes in estimated useful lives, recorded through December 31, 2016.
Income Taxes	Income Taxes The Company records income taxes using the asset and liability method, which requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company’s consolidated financial statements or income tax returns. In estimating future tax consequences, expected future events other than enactments or changes in the tax law or rates are considered. Valuation allowances are provided when necessary to reduce deferred tax assets to the amount expected to be realized. The Company operates in various tax jurisdictions and is subject to audit by various tax authorities. To date, taxes paid have been predominantly due to income taxes in foreign jurisdictions in which we conduct business. The Company provides for tax contingencies whenever it is deemed probable that a tax asset has been impaired or a tax liability has been incurred for events such as tax claims or changes in tax laws. Tax contingencies are based upon their technical merits, relative tax law, and the specific facts and circumstances as of each reporting period. Changes in facts and circumstances could result in material changes to the amounts recorded for such tax contingencies. The Company records uncertain tax positions on the basis of a two-step process whereby (1) a determination is made as to whether it is more likely than not that the tax positions will be sustained based on the technical merits of the position and (2) for those tax positions that meet the more-likely-than-not recognition threshold the Company recognizes the largest amount of tax benefit that is greater than 50% likely to be realized upon ultimate settlement with the related tax authority. The Company’s policy is to recognize interest and penalties related to income taxes as a component of income tax expense. No interest or penalties related to income taxes have been recognized in the statements of operations and comprehensive loss in 2016 and 2015.
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) Other comprehensive income (loss) represents all changes in stockholders’ equity except those resulting from distributions to stockholders. The Company’s unrealized gains on short-term available-for-sale investment securities and foreign currency translation adjustments represent the components of other comprehensive income (loss) that are excluded from the reported net loss and are presented in the consolidated statements of operations and comprehensive loss.
Research and Development	Research and Development Research and development expenses, including new product development, regulatory compliance, and clinical research, are charged to operations as incurred in the consolidated statements of operations and comprehensive loss. Such costs include personnel-related costs, including stock-based compensation, supplies, services, depreciation, allocated facilities and information services, clinical trial and related clinical manufacturing expenses, fees paid to investigative sites, and other indirect costs.
Stock-Based Compensation	Stock-Based Compensation The Company accounts for stock-based compensation arrangements with employees in accordance with Accounting Standards Codification (ASC) 718, Compensation—Stock Compensation. The Company’s determination of the fair value of stock options on the date of grant utilizes the Black-Scholes option-pricing model, and is impacted by its common stock price as well as changes in assumptions regarding a number of highly complex and subjective variables. These variables include, but are not limited to, the expected term that options will remain outstanding, the expected common stock price volatility over the term of the option awards, risk-free interest rates and expected dividends. The fair value of stock options is recognized over the period during which an optionee is required to provide services in exchange for the option award, known as the requisite service period (usually the vesting period), on a straight-line basis, with the exception of performance based stock options whose fair value is recorded as expenses when performance metrics are achieved. Stock-based compensation expense recognized at fair value includes the impact of estimated forfeitures. The Company estimates future forfeitures at the date of grant and revises the estimates, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The Company accounts for restricted stock units at their fair value, based on the closing market price of the Company’s common stock on the grant date. The fair value is amortized on a straight-line basis over the requisite service period of the awards, with the exception of performance based awards whose fair value is recorded as expenses when performance metrics are achieved. The Company estimates the fair value of the rights to purchase shares by employees under the Employee Stock Purchase Plan using the Black-Scholes option pricing formula. The Employee Stock Purchase Plan provides for consecutive six-month offering periods and the Company uses its own historical volatility data in the valuation. Equity instruments issued to non-employees are recorded at their fair value on the measurement date and are subject to periodic adjustments as the underlying equity instruments vest. The fair value of options granted to consultants is expensed when vested. The non-employee stock-based compensation expense was not material for all periods presented. Estimating the fair value of equity-settled awards as of the grant date using valuation models, such as the Black-Scholes option pricing model, is affected by assumptions regarding a number of complex variables. Changes in the assumptions can materially affect the fair value and ultimately how much stock-based compensation expense is recognized. These inputs are subjective and generally require significant analysis and judgment to develop. For all stock options granted to date, we included the volatility data based on a study of publicly traded industry peer companies. For purposes of identifying these peer companies, we considered the industry, stage of development, size and financial leverage of potential comparable companies. The risk-free interest rate is based on the yield available on U.S. Treasury zero-coupon issues similar in duration to the expected term of the equity-settled award. The Company accounts for stock-based compensation for the restricted stock units at their fair value, based on the closing market price of the Company’s common stock on the grant date. These costs are recognized on a straight-line basis over the requisite service period, which is generally the vesting term of four years. The Company recognizes a benefit from stock-based compensation as additional paid-in capital if an incremental tax benefit is realized by following the with-and-without approach.
Net Loss per Share of Common Stock	Net Loss per Share of Common Stock Basic net loss per common share is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, restricted stock units and common stock options are considered to be potentially dilutive securities. Because the Company has reported a net loss in all periods presented, diluted net loss per common share is the same as basic net loss per common share for those periods.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In July 2015, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2015-11, Inventory (Topic 330): Simplifying the Measurement of Inventory In May 2014, the FASB issued ASU No. 2014-09, Revenue from Contracts with Customers (Topic 606) Revenue Recognition. Revenue from Contracts with Customers (Topic 606): Deferral of the Effective Date Revenue from Contracts with Customers (Topic 606) Identifying Performance Obligations and Licensing, In May 2016, the FASB issued ASU No. 2016-12, Revenue from Contracts with Customers (Topic 606): Narrow-Scope Improvements and Practical Expedients , related to disclosures of remaining performance obligations, as well as other amendments to guidance on collectability, non-cash consideration and the presentation of sales and other similar taxes collected from customers. In December 2016, the FASB issued ASU 2016-20, Technical Corrections and Improvements to Topic 606, Revenue from Contracts and Customers , related to further clarifications issued in ASU 2014-09. In January 2016, the FASB issued ASU 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities, In February 2016, the FASB issued ASU No. 2016-02, Leases (Topic 842) In March 2016, the FASB issued ASU No. 2016-09, Compensation-Stock Compensation (Topic 718): Improvements to Employee Share-Based Payment Accounting. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments In August, 2016, the FASB issued ASU No. 2016-15, Classification of Certain Cash Receipts and Cash Payments (a consensus of the Emerging Issues Task Force) . The update In October 2016, the FASB issued ASU No. 2016-16, Income Taxes (Topic 740): Intra-Entity Transfers of Assets Other than Inventory asset. This ASU does not apply to intra-entity transfers of inventory, where t he income tax consequences from the sale of inventory from one member of a consolidated entity to another will continue to be deferred until the inventory is sold to a third party. In November 2016, the FASB issued ASU No. 2016-18, Statement of Cash Flows (Topic 230): Restricted Cash, a consensus of the FASB Emerging Issues Task Force

Summary of Significant Accoun20

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2016
Accounting Policies [Abstract]
Schedule of Revenue by Major Customers by Geographic Area	The following table sets forth revenue by geographic area for countries with revenue accounting for 10% of more of the total revenue during the periods presented: Years Ended December 31, 2016 2015 2014 United States 76 % 35 % — % Australia * 20 % 35 % United Kingdom * 12 % 18 % Germany * 13 % 17 % * Represents less than 10%

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2016
Fair Value Disclosures [Abstract]
Financial Instruments Measured at Fair Value on Recurring Basis	The following table sets forth the Company’s financial instruments that were measured at fair value on a recurring basis, by level, within the fair value hierarchy (in thousands): Balance as of December 31, 2016 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 35,510 $ — $ — $ 35,510 Commercial paper (iii) — 160,582 — 160,582 Corporate notes (iii) — 74,369 — 74,369 Total assets $ 35,510 $ 234,951 $ — $ 270,461 Balance as of December 31, 2015 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 36,559 $ — $ — $ 36,559 Commercial paper (ii) — 129,206 — 129,206 Treasury bonds (iii) 10,617 — — 10,617 Total assets $ 47,176 $ 129,206 $ — $ 176,382 (i) Included in cash and cash equivalents on the consolidated balance sheets. (ii) Included in either cash and cash equivalents or short-term investments on the consolidated balance sheets. (iii) Included in short-term investments on the consolidated balance sheets.

Balance Sheet Components (Table

Balance Sheet Components (Tables)	12 Months Ended
	Dec. 31, 2016
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Summary of Gross Unrealized Gains and Unrealized Losses of Investment Securities Excluding Investments in Money Market Funds	The following is a summary of the gross unrealized gains and unrealized losses on the Company’s investment securities (in thousands): December 31, 2016 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Commercial paper $ 160,729 $ 6 $ (153 ) $ 160,582 Corporate notes 74,430 3 (64 ) 74,369 Total securities $ 235,159 $ 9 $ (217 ) $ 234,951 December 31, 2015 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Commercial paper (i) $ 129,075 $ 131 $ — $ 129,206 Treasury bonds 10,616 1 — 10,617 Total securities $ 139,691 $ 132 $ — $ 139,823 (i) Includes $33.2 million of commercial paper that is classified as cash and cash equivalents on the consolidated balance sheet.
Summary of Amortized Costs and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturities	The amortized costs and estimated fair values of the Company’s available-for-sale securities by contractual maturities as of December 31, 2016 were as follows (in thousands): Amortized Cost Fair Value Amounts maturing within one year $ 233,163 $ 232,955 Amounts after one year through five years 1,996 1,996 Total investment securities $ 235,159 $ 234,951
Components of Inventories	Inventories, Net (in thousands) December 31, 2016 2015 Raw materials $ 44,862 $ 37,096 Finished goods 40,359 25,334 Total inventories $ 85,221 $ 62,430
Schedule of Property and Equipment, Net and Depreciation and Amortization Expense	Property and Equipment, Net (in thousands) December 31, 2016 2015 Laboratory equipment $ 1,567 $ 921 Computer equipment and software 2,388 1,836 Furniture and fixtures 2,051 1,752 Leasehold improvements 1,214 1,188 Construction in process 2,274 799 Total 9,494 6,496 Less: Accumulated depreciation and amortization (2,362 ) (702 ) Property and equipment, net $ 7,132 $ 5,794
Summary of Accrued Liabilities	Accrued Liabilities (in thousands) December 31, 2016 2015 Accrued payroll and related expenses $ 17,732 $ 9,857 Accrued professional fees 1,067 583 Accrued taxes 2,110 2,044 Accrued clinical and research expenses 1,545 405 Accrued interest 243 — Accrued warranty 645 394 Accrued other 2,686 1,098 Total accrued liabilities $ 26,028 $ 14,381

Commitments and Contingencies (

Commitments and Contingencies (Tables)	12 Months Ended
	Dec. 31, 2016
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments under Operating Leases	Excluding the terms under the amendment for the Expansion Premises, which is subject to certain cancellation clauses, future minimum lease payments under operating leases as of December 31, 2016 are as follows (in thousands): Operating Lease Year ending December 31, 2017 $ 2,167 2018 2,185 2019 2,250 2020 2,318 2021 2,387 Thereafter 1,211 Total $ 12,518
Schedule of Activities Related to Warranty Obligations	Activities related to warranty obligations were as follows (in thousands): December 31, 2016 2015 Beginning Balance $ 394 $ — Provision for warranty 902 451 Utilization (651 ) (57 ) Ending Balance $ 645 $ 394

Long-term Debt (Tables)

Long-term Debt (Tables)	12 Months Ended
	Dec. 31, 2016
Debt Instrument [Line Items]
Interest Expense Recognized Related to Convertible Notes	The following table sets forth the interest expense recognized related to the 2021 Notes (in thousands): Year Ended December 31, 2016 Contractual interest expense $ 1,652 Amortization of debt discount 3,162 Amortization of debt issuance costs 416 Total interest expense related to the 2021 Notes $ 5,230
Debt, Liability Component [Member]
Debt Instrument [Line Items]
Net Carrying Amount of Convertible Debt	The net carrying amount of the liability component of the 2021 Notes was as follows (in thousands): December 31, 2016 Principal $ 172,500 Unamortized discount (29,783 ) Unamortized issuance cost (4,577 ) Net carrying amount $ 138,140
Debt, Equity Component [Member]
Debt Instrument [Line Items]
Net Carrying Amount of Convertible Debt	The net carrying amount of the equity component of the 2021 Notes was as follows (in thousands): December 31, 2016 Debt discount related to value of conversion option $ 32,945 Debt issuance cost (1,179 ) Net carrying amount $ 31,766

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2016
Equity [Abstract]
Summary of Common Stock Reserved for Future Issuance	Common stock reserved for future issuance as of December 31, 2016 was as follows: December 31, 2016 Outstanding stock options and restricted stock units 3,166,782 Reserved for grants of future stock options and restricted stock units 2,202,239 Reserved for employee stock purchase plan 621,029 Total common stock reserved for future issuance 5,990,050
Summary of Shares Available for Grant	A summary of shares available for grant under the Stock Plans was as follows: Shares Available for Grant Balance at December 31, 2013 581,585 Additional shares reserved 1,854,166 Options granted (753,102 ) Options cancelled 12,767 Balance at December 31, 2014 1,695,416 Additional shares reserved 994,619 Options and restricted stock granted (975,688 ) Options and restricted stock cancelled 142,362 Balance at December 31, 2015 1,856,709 Additional shares reserved 1,125,742 Options and restricted stock granted (856,043 ) Options and restricted stock cancelled 75,831 Balance at December 31, 2016 2,202,239
Summary of Activity under Stock Plans	A summary of stock option activity under the Stock Plans was as follows: Options Outstanding Weighted Average Number of Weighted Average Remaining Aggregate Options Exercise Price Contractual Term Intrinsic Value (in years) (in thousands) Outstanding at December 31, 2013 2,731,962 $ 2.88 8.0 $ 1,655 Options granted 753,102 $ 13.50 Options exercised (498,565 ) $ 2.26 $ 2,488 Options cancelled (12,767 ) $ 3.60 Outstanding at December 31, 2014 2,973,732 $ 5.77 7.9 $ 97,832 Options granted 970,238 $ 50.16 Options exercised (751,610 ) $ 3.87 $ 36,603 Options cancelled (142,072 ) $ 19.08 Outstanding at December 31, 2015 3,050,288 $ 19.74 7.8 $ 145,721 Options granted 498,564 $ 66.74 Options exercised (667,494 ) $ 10.19 $ 46,529 Options cancelled (60,131 ) $ 40.89 Outstanding at December 31, 2016 2,821,227 $ 29.85 7.4 $ 123,425 Options exercisable as of December 31, 2016 1,506,297 $ 14.69 6.4 $ 87,358 Options vested, exercisable or expected to vest as of December 31, 2016 2,739,732 $ 29.11 7.3 $ 121,743
Summary of Options Outstanding and Vested under Stock Plans by Exercise Price	The options outstanding and vested under the Stock Plans by exercise price, at December 31, 2016, were as follows: Options Outstanding Options Vested Weighted Average Remaining Number Contractual Term Weighted Average Number Weighted Average Exercise Price Outstanding (in years) Exercise Price Exercisable Exercise Price $0.96 — $1.92 141,176 2.87 $ 1.48 141,176 $ 1.48 $3.60 — $3.60 1,030,002 6.01 $ 3.60 890,023 $ 3.60 $10.08 — $38.79 572,674 7.87 $ 25.89 247,046 $ 25.34 $41.83 — $54.50 573,030 8.67 $ 51.44 150,184 $ 49.67 $57.89 — $97.52 504,345 9.27 $ 71.37 77,868 $ 64.20 $0.96 — $97.52 2,821,227 7.35 $ 29.85 1,506,297 $ 14.69
Summary of Restricted Stock Units under the Stock Plan	A summary of RSUs activity under the Stock Plans was as follows: Number of Weighted Average Aggregate Restricted Grant Date Intrinsic Value Stock Units Fair Value (in thousands) Outstanding at December 31, 2014 — $ — $ — Restricted stock granted 5,450 $ 56.47 Restricted stock cancelled (290 ) $ 63.23 Outstanding at December 31, 2015 5,160 $ 56.09 $ 348 Restricted stock granted 357,479 $ 70.31 Restricted stock released (1,384 ) $ 56.65 $ 115 Restricted stock cancelled (15,700 ) $ 65.15 Outstanding at December 31, 2016 345,555 $ 70.39 $ 25,108 Restricted stock expected to vest as of December 31, 2016 314,061 $ 22,820
Schedule of Employee Stock Purchase Plan Activity	A summary of ESPP activity was as follows: December 31, 2016 2015 2014 Additional shares reserved 281,435 248,654 — Shares issued 72,568 33,158 — Shares available for future issuance 621,029 412,162 196,666 Employee contributions for shares issued (in thousands) $ 3,499 $ 1,430 $ —
Schedule of Fair Value of Employee Stock Options Using Black-Scholes Option Valuation Model	The following assumptions were used in estimating the fair value: Years Ended December 31, 2016 2015 2014 Stock Options: Expected term (in years) 5.3 — 6.1 5.3 — 6.1 5.3 — 6.1 Expected volatility 47% — 49% 46% — 59% 57% — 63% Risk-free interest rate 1.3% — 1.9% 1.4% — 1.8% 1.7% — 2.0% Dividend Yield 0% 0% 0% ESPP: Expected term (in years) 0.5 0.5 — Expected volatility 46% — 53% 42% — 64% — Risk-free interest rate 0.4% — 0.6% 0.1% — 0.3% — Dividend Yield 0% 0% —
Summary of Stock-Based Compensation Expense by Line Items in Consolidated Statements of Operations	A summary of pre-tax stock-based compensation expense by line items in the consolidated statements of operations was as follows (in thousands): Years Ended December 31, 2016 2015 2014 Cost of revenue $ 1,094 $ 621 $ 147 Research and development 3,182 1,401 661 Sales, general and administrative 11,484 5,303 1,190 Total stock-based compensation expense $ 15,760 $ 7,325 $ 1,998
Summary of Stock-Based Compensation Expense	The effect of recording pre-tax stock-based compensation expense recognized were as follows (in thousands): Years Ended December 31, 2016 2015 2014 Stock options $ 10,832 $ 6,679 $ 1,998 Restricted stock units 3,548 9 — Employee stock purchase plan 1,380 637 — Total stock-based compensation expense $ 15,760 $ 7,325 $ 1,998
Summary of Stock-Based Compensation Expense Not Yet Recognized	As of December 31, 2016, total stock-based compensation expense not yet recognized, net of estimated forfeitures, were as follows: Unrecognized Weighted-Average Compensation Amortization Period (in thousands) (in years) Stock options $ 25,602 2.5 Restricted stock units 18,253 3.3 Employee stock purchase plan 757 0.4

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2016
Income Tax Disclosure [Abstract]
Components of Income (Loss) before Income Taxes	The components of the Company’s income (loss) before income taxes were as follows: Years Ended December 31, 2016 2015 2014 (in thousands) Domestic $ (34,258 ) $ (68,919 ) $ (31,807 ) Foreign 4,103 2,654 1,605 Total income (loss) before income taxes $ (30,155 ) $ (66,265 ) $ (30,202 )
Components of Income Tax Expense	The components of income tax expense are as follows (in thousands): Years Ended December 31, 2016 2015 2014 Current: Federal $ — $ — $ — State 181 34 2 Foreign 1,442 1,132 476 Total current 1,623 1,166 478 Deferred: Federal — — — State — — — Foreign — — — Total deferred — — — Total income tax expense $ 1,623 $ 1,166 $ 478
Income Tax Expense by Applying Statutory Federal Income Tax Rate	Income tax expense differs from the amount computed by applying the statutory federal income tax rate as follows: Years Ended December 31, 2016 2015 2014 Tax at statutory federal rate 34.0 % 34.0 % 34.0 % State tax, net of federal benefit (0.4 )% 0.0 % 0.0 % Other (3.7 )% (3.5 )% (5.3 )% Foreign rate differential (0.2 )% (0.5 )% 0.2 % Tax credits 3.2 % 1.6 % 2.0 % Change in valuation allowance (38.4 )% (33.4 )% (32.5 )% Total (5.5 )% (1.8 )% (1.6 )%
Tax Effects of Temporary Differences and Carryforwards that Give Rise to Significant Portions of Deferred Tax Assets	The tax effects of temporary differences and carryforwards that give rise to significant portions of deferred tax assets are as follows: December 31, 2016 2015 (in thousands) Net operating loss carryforwards $ 60,610 $ 56,340 Tax credits 7,655 5,236 Depreciation 26 13 Stock-based compensation 5,207 1,857 Accruals and reserves 7,559 3,617 Other 4,671 313 Deferred tax assets 85,728 67,376 Other — (345 ) Deferred tax liabilities — (345 ) Valuation allowance (85,728 ) (67,031 ) Net deferred tax assets $ — $ —
Summary of Unrecognized Tax Benefits	The following table summarizes the activity related to UTBs (in thousands): Balance at December 31, 2013 $ 1,065 Increases related to current year tax provisions 220 Increases related to prior year tax provisions 677 Balance at December 31, 2014 1,962 Increases related to current year tax provisions 813 Increases related to prior year tax provisions 1,069 Balance at December 31, 2015 3,844 Increases related to current year tax provisions 1,059 Decreases related to prior year tax provisions (1,519 ) Balance at December 31, 2016 $ 3,384

Net Loss Per Share Attributab27

Net Loss Per Share Attributable to Common Stockholders (Tables)	12 Months Ended
	Dec. 31, 2016
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders	The following table summarizes the computation of basic and diluted net loss per share attributable to common stockholders of the Company (in thousands, except share and per share data): Years Ended December 31, 2016 2015 2014 Net loss $ (31,778 ) $ (67,431 ) $ (30,680 ) Accretion of convertible preferred stock to redemption value — — (147 ) Net loss attributable to common stockholders, basic and diluted $ (31,778 ) $ (67,431 ) $ (30,827 ) Weighted average shares outstanding 28,492,091 26,603,512 4,486,569 Less: weighted average shares subject to repurchase (7,088 ) (21,622 ) (45,906 ) Weighted average shares used to compute basic and diluted net loss per share 28,485,003 26,581,890 4,440,663 Net loss per share attributable to common stockholders, basic and diluted $ (1.12 ) $ (2.54 ) $ (6.94 )
Computation of Potentially Dilutive Securities Outstanding Excluded from Computation of Diluted Shares	The following potentially dilutive securities outstanding at the end of the periods presented have been excluded from the computation of diluted shares outstanding: December 31, 2016 2015 2014 Unreleased restricted stock 345,555 5,160 — Options to purchase common stock 2,821,227 3,050,288 2,973,732 Total 3,166,782 3,055,448 2,973,732

Selected Quarterly Financial 28

Selected Quarterly Financial Information (Tables)	12 Months Ended
	Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Schedule of Selected Quarterly Financial Information	Three Months Ended December 31, September 30, June 30, March 31, 2016 2016 2016 2016 (in thousands, except per share data) Total revenue $ 70,531 $ 60,922 $ 55,400 $ 41,651 Gross profit $ 48,839 $ 41,687 $ 36,558 $ 25,987 Loss from operations $ (6,269 ) $ (1,872 ) $ (5,923 ) $ (9,017 ) Net loss $ (9,825 ) $ (3,886 ) $ (8,779 ) $ (9,288 ) Net loss attributable to common stockholders, basic and diluted $ (9,825 ) $ (3,886 ) $ (8,779 ) $ (9,288 ) Net loss per share attributable to common stockholders, basic and diluted $ (0.34 ) $ (0.14 ) $ (0.31 ) $ (0.33 ) Shares used in computing net loss per common share, basic and diluted 28,817,333 28,542,760 28,381,253 28,194,457 Three Months Ended December 31, September 30, June 30, March 31, 2015 2015 2015 2015 (in thousands, except per share data) Total revenue $ 33,124 $ 15,402 $ 11,418 $ 9,662 Gross profit $ 20,353 $ 9,434 $ 5,910 $ 5,789 Loss from operations $ (13,144 ) $ (17,709 ) $ (19,175 ) $ (12,339 ) Net loss $ (14,191 ) $ (19,454 ) $ (19,726 ) $ (14,060 ) Net loss attributable to common stockholders, basic and diluted $ (14,191 ) $ (19,454 ) $ (19,726 ) $ (14,060 ) Net loss per share attributable to common stockholders, basic and diluted $ (0.51 ) $ (0.70 ) $ (0.77 ) $ (0.57 ) Shares used in computing net loss per common share, basic and diluted 28,003,957 27,861,523 25,564,249 24,849,229

Formation and Business of the29

Formation and Business of the Company - Additional Information (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Formation and Business of the Company [Line Items]
Net loss	$ (9,825)	$ (3,886)	$ (8,779)	$ (9,288)	$ (14,191)	$ (19,454)	$ (19,726)	$ (14,060)	$ (31,778)	$ (67,431)	$ (30,680)
Cash used in operations									(58,503)	(100,430)	$ (31,148)
Accumulated deficit	$ (221,186)				$ (189,408)				$ (221,186)	$ (189,408)
1.75% Convertible Senior Notes due 2021 [Member]
Formation and Business of the Company [Line Items]
Debt instrument due year									2,021

Formation and Business of the30

Formation and Business of the Company - Additional Information - Public Offering (Detail) - USD ($)	1 Months Ended			12 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Nov. 30, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued		2,470,587
Net proceeds from common stock		$ 118,400,000	$ 131,600,000
1.75% Convertible Senior Notes due 2021 [Member]
Subsidiary, Sale of Stock [Line Items]
Aggregate principal amount of convertible senior notes	$ 150,000,000
Debt instrument interest rate	1.75%			1.75%
Debt instrument due year				2,021
Additional aggregate principal amount of convertible senior notes	$ 22,500,000
Debt instrument frequency of payment				semi-annually in arrears on June 1 and December 1 of each year, commencing on December 1, 2016
Net proceeds from the debt offering after deducting transaction costs	$ 166,200,000
Common Stock [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued					2,470,587	8,050,000
IPO [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued			8,050,000
Common stock, shares issued price per share			$ 18
IPO [Member] | Common Stock [Member]
Subsidiary, Sale of Stock [Line Items]
Shares issued upon conversion of redeemable convertible preferred stock and convertible preferred stock			15,208,048
Over Allotment Option [Member]
Subsidiary, Sale of Stock [Line Items]
Common stock, shares issued		705,882	1,050,000

Summary of Significant Accoun31

Summary of Significant Accounting Policies - Additional Information (Detail)	12 Months Ended
	Dec. 31, 2016USD ($)SubsidiaryBusinessCustomer	Dec. 31, 2015USD ($)Customer	Dec. 31, 2014USD ($)Customer
Summary Of Significant Accounting Policies [Line Items]
Number of wholly owned subsidiaries | Subsidiary	4
Number of business activities | Business	1
Net unrealized foreign currency transaction gains (losses)	$ (1,600,000)	$ 600,000	$ (1,100,000)
Realized foreign currency transaction gains (losses)	700,000	(2,200,000)	(600,000)
Cash held in foreign banks	3,300,000	5,200,000
Money market funds	35,500,000	36,600,000
Restricted cash	806,000	906,000
Write down of inventory	$ 4,056,000	2,767,000	$ 754,000
Standard product warranty, description	Limited one- to five-year warranty
Impairment charges	$ 0
Interest or penalties recognized	$ 0	0
Employee stock purchase plan offering period	6 months
RSU's [Member]
Summary Of Significant Accounting Policies [Line Items]
Vesting term	4 years
Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	3 years
Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Estimated useful life of property and equipment	5 years
Letter of Credit [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 600,000	600,000
Certificate of Deposit [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash	$ 200,000	$ 300,000
Customer Concentration Risk [Member] | Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage	10.00%	10.00%	10.00%
Number of customers accounted more than 10% concentration risk | Customer	0	0	0
Credit Concentration Risk [Member] | Accounts Receivable [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage	10.00%	10.00%
Number of customers accounted more than 10% concentration risk | Customer	0	0

Summary of Significant Accoun32

Summary of Significant Accounting Policies - Schedule of Revenue by Major Customers by Geographic Area (Detail) - Revenue [Member] - Geographic Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
United States [Member]
Concentration Risk [Line Items]
Revenue	76.00%	35.00%
Australia [Member]
Concentration Risk [Line Items]
Revenue		20.00%	35.00%
United Kingdom [Member]
Concentration Risk [Line Items]
Revenue		12.00%	18.00%
Germany [Member]
Concentration Risk [Line Items]
Revenue		13.00%	17.00%

Summary of Significant Accoun33

Summary of Significant Accounting Policies - Schedule of Revenue by Major Customers by Geographic Area (Parenthetical) (Detail) - Revenue [Member] - Geographic Concentration Risk [Member]	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
United States [Member]
Concentration Risk [Line Items]
Revenue	76.00%	35.00%
Australia [Member]
Concentration Risk [Line Items]
Revenue		20.00%	35.00%
Australia [Member] | Maximum [Member]
Concentration Risk [Line Items]
Revenue	10.00%
United Kingdom [Member]
Concentration Risk [Line Items]
Revenue		12.00%	18.00%
United Kingdom [Member] | Maximum [Member]
Concentration Risk [Line Items]
Revenue	10.00%
Germany [Member]
Concentration Risk [Line Items]
Revenue		13.00%	17.00%
Germany [Member] | Maximum [Member]
Concentration Risk [Line Items]
Revenue	10.00%

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Jun. 30, 2016
1.75% Convertible Senior Notes due 2021 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate	1.75%	1.75%
Debt instrument due year	2,021
Fair value of notes	$ 183.8
Fair Value, Measurements, Recurring [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Net asset value of market funds	$ 1

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 270,461	$ 176,382
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	35,510	47,176
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	234,951	129,206
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	35,510	36,559
Money Market Funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	35,510	36,559
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	160,582	129,206
Commercial Paper [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	160,582	129,206
Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	74,369
Corporate Notes [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	$ 74,369
Treasury Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		10,617
Treasury Bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		$ 10,617

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Gross Unrealized Gains and Unrealized Losses of Investment Securities in Cash on Hand and Money Market Funds (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	$ 235,159	$ 139,691
Gross Unrealized Holding Gains	9	132
Gross Unrealized Holding Losses	(217)
Aggregate Fair Value	234,951	139,823
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	160,729	129,075
Gross Unrealized Holding Gains	6	131
Gross Unrealized Holding Losses	(153)
Aggregate Fair Value	160,582	129,206
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	74,430
Gross Unrealized Holding Gains	3
Gross Unrealized Holding Losses	(64)
Aggregate Fair Value	$ 74,369
Treasury Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		10,616
Gross Unrealized Holding Gains		1
Aggregate Fair Value		$ 10,617

Balance Sheet Components - Su37

Balance Sheet Components - Summary of Gross Unrealized Gains and Unrealized Losses of Investment Securities in Cash on Hand and Money Market Funds (Parenthetical) (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	$ 41,406	$ 87,036	$ 25,287	$ 12,409
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents		$ 33,200

Balance Sheet Components - Addi

Balance Sheet Components - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Balance Sheet Components [Abstract]
Realized gains or losses on investments	$ 0	$ 0
Depreciation and amortization expense	$ 1,717,000	$ 614,000	$ 96,000

Balance Sheet Components - Su39

Balance Sheet Components - Summary of Amortized Costs and Estimated Fair Value of Available-for-Sale Securities by Contractual Maturities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Investments Debt And Equity Securities [Abstract]
Amortized Cost, Amounts maturing within one year	$ 233,163
Amortized Cost, Amounts after one year through five years	1,996
Amortized Cost	235,159	$ 139,691
Fair Value, Amounts maturing within one year	232,955
Fair Value, Amounts after one year through five years	1,996
Fair Value, Total investment securities	$ 234,951	$ 139,823

Balance Sheet Components - Comp

Balance Sheet Components - Components of Inventories (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Inventory Disclosure [Abstract]
Raw materials	$ 44,862	$ 37,096
Finished goods	40,359	25,334
Total inventories	$ 85,221	$ 62,430

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 9,494	$ 6,496
Less: Accumulated depreciation and amortization	(2,362)	(702)
Property and equipment, net	7,132	5,794
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,567	921
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,388	1,836
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	2,051	1,752
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	1,214	1,188
Construction in Process [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,274	$ 799

Balance Sheet Components - Su42

Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Payables And Accruals [Abstract]
Accrued payroll and related expenses	$ 17,732	$ 9,857
Accrued professional fees	1,067	583
Accrued taxes	2,110	2,044
Accrued clinical and research expenses	1,545	405
Accrued interest	243
Accrued warranty	645	394
Accrued other	2,686	1,098
Total accrued liabilities	$ 26,028	$ 14,381

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)	May 31, 2015USD ($)	Feb. 28, 2017USD ($)	Jun. 30, 2015shares	Nov. 30, 2014USD ($)shares	Dec. 31, 2016USD ($)ft²	Dec. 31, 2015USD ($)	Dec. 31, 2014USD ($)	Mar. 31, 2015USD ($)ft²
Other Commitments [Line Items]
Lease expense, payment due					$ 2,167,000
Rent expense					$ 2,400,000	$ 1,900,000	$ 700,000
Standard product warranty, description					Limited one- to five-year warranty
Retainer fees					$ 33,729,000	21,382,000	19,824,000
Common stock, shares issued | shares			2,470,587
Noncash research and development expense							523,000
Contingent liabilities					0	0
Indemnification Agreement [Member]
Other Commitments [Line Items]
Contingent liabilities					0
Patent Infringement [Member]
Other Commitments [Line Items]
Contingent liabilities					0
Licensing Agreements [Member]
Other Commitments [Line Items]
Annual royalty payment					$ 1,900,000	$ 600,000	$ 300,000
Mayo And VGL [Member] | Licensing Agreements [Member]
Other Commitments [Line Items]
License agreement, terms					The agreement will terminate upon the last to expire patent application, unless terminated earlier. The agreement can be terminated any time after three years from March 2006 by Mayo or VGL.
Mayo Foundation [Member] | Licensing Agreements [Member]
Other Commitments [Line Items]
Retainer fees					$ 40,000
Common stock, shares issued | shares				20,833
Noncash research and development expense				$ 500,000
Mayo Foundation [Member] | Licensing Agreements [Member] | Minimum [Member]
Other Commitments [Line Items]
Annual royalty payment					200,000
Supply Agreements [Member]
Other Commitments [Line Items]
Purchase commitment, amount due in 2017					25,000,000
Purchase commitment, amount due in 2018					5,500,000
Purchase commitment, amount due in 2019					5,500,000
Purchase commitment, amount due in 2020					5,500,000
Purchase commitment, amount due in 2021					$ 5,500,000
Redwood Office Agreement [Member]
Other Commitments [Line Items]
Lease agreement, commencement period					2015-03
Area of office space | ft²								50,000
Lease agreement, effective date					Jun. 30, 2015
Lease agreement, expiration period					2022-05
Lease expense, payment due								$ 2,000,000
Annual lease expense payable in May 2022								$ 2,400,000
Redwood Office Agreement Additional Expansion Premises [Member]
Other Commitments [Line Items]
Area of office space | ft²					50,000
Lease expense, payment due					$ 1,200,000
Annual lease expense payable in final year of lease term					$ 2,900,000
Commencement date description					The lease for the Expansion Premises commences on the earlier of (i) the date the Company commences business operations in the Expansion Premises, or (ii) the date upon which the Landlord substantially completes certain improvements to, and permitting for, the Expansion Premises (the “Commencement Date”).
Menlo Park Agreement, Original [Member]
Other Commitments [Line Items]
Lease agreement, effective date					May 1, 2010
Lease agreement, expiration date					May 31, 2015
Menlo Park Agreement, Extended [Member]
Other Commitments [Line Items]
Lease agreement, commencement period					2015-03
Lease agreement, expiration date					Sep. 30, 2015
Lease agreement, lease expense	$ 100,000
Facility Lease Agreement, Original [Member]
Other Commitments [Line Items]
Lease agreement, commencement period					2014-08
Lease agreement, effective date					Aug. 21, 2014
Lease agreement, expiration date					May 31, 2015
Facility Lease Agreement, Extended [Member]
Other Commitments [Line Items]
Lease agreement, commencement period					2015-03
Lease agreement, expiration period					2017-02
Facility Lease Agreement, Extended [Member] | Scenario Forecast [Member]
Other Commitments [Line Items]
Lease agreement, lease expense		$ 300,000

Commitments and Contingencies44

Commitments and Contingencies - Schedule of Future Minimum Lease Payments under Operating Leases (Detail) $ in Thousands	Dec. 31, 2016USD ($)
Leases [Abstract]
2,017	$ 2,167
2,018	2,185
2,019	2,250
2,020	2,318
2,021	2,387
Thereafter	1,211
Total	$ 12,518

Commitments and Contingencies45

Commitments and Contingencies - Schedule of Activities Related to Warranty Obligations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Commitments And Contingencies Disclosure [Abstract]
Beginning Balance	$ 394
Provision for warranty	902	$ 451
Utilization	(651)	(57)
Ending Balance	$ 645	$ 394

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Detail)	Oct. 24, 2014USD ($)Term_loan	Jun. 30, 2016USD ($)d$ / sharesshares	Dec. 31, 2016USD ($)
Debt Instrument [Line Items]
Proceeds from issuance of warrants			$ 33,120,000
Repayment of outstanding principal and fees			$ 19,500,000
Credit Facility [Member]
Debt Instrument [Line Items]
Number of term loan agreements | Term_loan	3
1.75% Convertible Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Aggregate principal amount of convertible senior notes		$ 150,000,000
Debt instrument interest rate		1.75%	1.75%
Debt instrument due year			2,021
Additional aggregate principal amount of convertible senior notes		$ 22,500,000
Debt instrument frequency of payment			semi-annually in arrears on June 1 and December 1 of each year, commencing on December 1, 2016
Net proceeds from the debt offering after deducting transaction costs		166,200,000
Convertible notes principal amount		$ 1,000
Convertible notes, shares issued | shares		10.3770
Convertible notes, type of equity security issued			common stock
Convertible notes, conversion price | $ / shares		$ 96.37
Debt instrument convertible, percentage of conversion price		130.00%
Percentage of repurchase price, which is equal to principal amount of convertible notes		100.00%
Debt instrument combination settlement		$ 1,000
Debt conversion, converted instrument amount		$ 32,900,000
Debt instrument, effective interest rate		6.29%
Debt issuance costs attributable to the liability and equity component, total amount		$ 6,200,000
Debt issuance costs attributable to the liability component		$ 5,000,000
Number of shares purchased under convertible note hedge transactions | shares		1,800,000
Purchase price of the shares issued under convertible note hedge transactions | $ / shares		$ 96.37
Total cost of the convertible note hedge transactions		$ 45,100,000
Proceeds from issuance of warrants		33,100,000
Net cost of reduction to additional paid-in capital		$ 12,000,000
1.75% Convertible Senior Notes due 2021 [Member] | Warrant
Debt Instrument [Line Items]
Number of shares issued for warrants under convertible note hedge transactions | shares		1,800,000
Purchase price of the shares issued under convertible note hedge transactions | $ / shares		$ 127.28
1.75% Convertible Senior Notes due 2021 [Member] | 130% for Applicable Conversion Price [Member]
Debt Instrument [Line Items]
Debt instrument convertible trading days | d		20
Debt instrument convertible consecutive trading days		30 days
1.75% Convertible Senior Notes due 2021 [Member] | 98% Applicable Conversion Price [Member]
Debt Instrument [Line Items]
Debt instrument convertible trading days | d		5
Debt instrument convertible consecutive trading days		10 days
1.75% Convertible Senior Notes due 2021 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of closing sale price of common stock		98.00%
1.75% Convertible Senior Notes due 2021 [Member] | Maximum [Member] | Warrant
Debt Instrument [Line Items]
Overall conversion price | $ / shares		$ 127.28
1.75% Convertible Senior Notes due 2021 [Member] | Minimum [Member] | Warrant
Debt Instrument [Line Items]
Overall conversion price | $ / shares		$ 96.37
Capital Royalty Term Loan [Member] | Credit Facility [Member]
Debt Instrument [Line Items]
Credit facility borrowing capacity	$ 50,000,000
Credit facility expiration date			Sep. 30, 2015
Repayment of outstanding principal and fees		$ 21,000,000

Long-term Debt - Net Carrying A

Long-term Debt - Net Carrying Amount of Liability Component of Convertible Debt (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Jun. 30, 2016	Dec. 31, 2015
Debt Instrument [Line Items]
Net carrying amount	$ 138,140		$ 19,740
1.75% Convertible Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Unamortized issuance cost		$ (5,000)
1.75% Convertible Senior Notes due 2021 [Member] | Debt, Liability Component [Member]
Debt Instrument [Line Items]
Principal	172,500
Unamortized discount	(29,783)
Unamortized issuance cost	(4,577)
Net carrying amount	$ 138,140

Long-term Debt - Net Carrying48

Long-term Debt - Net Carrying Amount of Equity Component of Convertible Debt (Detail) - 1.75% Convertible Senior Notes due 2021 [Member] - USD ($) $ in Thousands	Dec. 31, 2016	Jun. 30, 2016
Debt Instrument [Line Items]
Net carrying amount		$ 32,900
Debt, Equity Component [Member]
Debt Instrument [Line Items]
Debt discount related to value of conversion option	$ 32,945
Debt issuance cost	(1,179)
Net carrying amount	$ 31,766

Long-term Debt - Interest Expen

Long-term Debt - Interest Expense Recognized Related to Convertible Notes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Amortization of debt issuance costs	$ 3,681	$ 231	$ 11
1.75% Convertible Senior Notes due 2021 [Member]
Debt Instrument [Line Items]
Contractual interest expense	1,652
Amortization of debt discount	3,162
Amortization of debt issuance costs	416
Total interest expense related to the 2021 Notes	$ 5,230

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Detail) - USD ($) $ in Thousands	Nov. 11, 2014	Dec. 31, 2016	Dec. 31, 2014	Dec. 31, 2015	Nov. 10, 2014
Class of Stock [Line Items]
Convertible preferred stock outstanding		0		0	15,208,048
Accretion of redeemable convertible preferred stock for change in redemption value			$ 147
Series B and C Redeemable Convertible Preferred Stock [Member]
Class of Stock [Line Items]
Redeemable convertible preferred shares, conversion period		5 years
Accretion of redeemable convertible preferred stock for change in redemption value			$ 100
IPO [Member]
Class of Stock [Line Items]
Convertible preferred stock converted to common stock	15,208,048
Common Stock [Member]
Class of Stock [Line Items]
Common stock shares issued for each convertible preferred stock	1

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Common Stock Reserved for Future Issuance (Detail)	Dec. 31, 2016shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding stock options and restricted stock units	3,166,782
Reserved for grants of future stock options and restricted stock units	2,202,239
Reserved for employee stock purchase plan	621,029
Total common stock reserved for future issuance	5,990,050

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Detail) - USD ($)	1 Months Ended	12 Months Ended
	Mar. 31, 2011	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Oct. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance		5,990,050
Weighted-average grant-date fair value of options granted		$ 32.11	$ 25.06	$ 11.33
Fair value of options vested		$ 10,700,000	$ 5,200,000	$ 1,200,000
Employee stock purchase plan offering period		6 months
Stock options unvested shares		1,836	14,863	29,613
Cash received from unvested shares		$ 7,000	$ 54,000
Stock based compensation expenses		$ 15,760,000	$ 7,325,000	$ 1,998,000
Common stock repurchased				0
Interest rate per annum	0.54%
Promissory note discharge period	3 years
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option purchase price, percentage of fair value		85.00%
Number of shares available for sale					196,666
Maximum employee subscription rate		15.00%
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of stock issued under employee stock purchase plan and restricted stock	416,983
Closing price per share of common stock	$ 1.44
Promissory note, aggregate value	$ 600,000
Stock based compensation expenses				$ 48,000
Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common shares vested period, percentage	33.00%
Share-based Compensation Award, Tranche Two [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common shares vested period, percentage	33.00%
Share-based Compensation Award, Tranche Three [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Restricted common shares vested period, percentage	33.00%
2007 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Additional awards authorized under plan		0
2014 Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for future issuance					1,854,166
Plan modification description		The number of shares initially reserved for issuance under the 2014 Plan is subject to increase by (i) the number of shares represented by awards outstanding under the 2007 Plan that are forfeited or lapse unexercised and which following the pricing date are not issued under the 2007 Plan, and (ii) an annual increase on January 1 of each year.
2014 Plan [Member] | ISO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shareholder granted option		10.00%
2014 Plan [Member] | NSO [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of shareholder granted option		10.00%
2014 Plan [Member] | Share-based Compensation Award, Tranche One [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Vesting term		4 years
2014 Plan [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options expiration period		10 years
Option purchase price, percentage of fair value		110.00%
2014 Plan [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Option purchase price, percentage of fair value		100.00%

Stock-Based Compensation - Su53

Stock-Based Compensation - Summary of Shares Available for Grant (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant, Granted	(498,564)	(970,238)	(753,102)
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant, Beginning balances	1,856,709	1,695,416	581,585
Shares Available for Grant, Additional shares reserved	1,125,742	994,619	1,854,166
Shares Available for Grant, Granted			(753,102)
Shares Available for Grant, Forfeited or cancelled			12,767
Shares Available for Grant, Ending balances	2,202,239	1,856,709	1,695,416
Employee Stock Option and Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares Available for Grant, Options and other than options granted	(856,043)	(975,688)
Shares Available for Grant, Options and other than options forfeited or cancelled	75,831	142,362

Stock-Based Compensation - Su54

Stock-Based Compensation - Summary of Activity under Stock Plans (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Sharebased Compensation Arrangement By Sharebased Payment Award Options Outstanding Weighted Average Exercise Price And Additional Disclosures [Abstract]
Number of Options, Outstanding Beginning balances	3,050,288	2,973,732	2,731,962
Number of Options, Options granted	498,564	970,238	753,102
Number of Options, Options exercised	(667,494)	(751,610)	(498,565)
Number of Options, Options cancelled	(60,131)	(142,072)	(12,767)
Number of Options, Outstanding Ending balances	2,821,227	3,050,288	2,973,732	2,731,962
Number of Options, Options exercisable	1,506,297
Number of Options, Options vested, exercisable or expected to vest	2,739,732
Weighted Average Exercise Price, Beginning balances	$ 19.74	$ 5.77	$ 2.88
Weighted Average Exercise Price, Options granted	66.74	50.16	13.50
Weighted Average Exercise Price, Options exercised	10.19	3.87	2.26
Weighted Average Exercise Price, Options cancelled	40.89	19.08	3.60
Weighted Average Exercise Price, Ending balances	29.85	$ 19.74	$ 5.77	$ 2.88
Weighted Average Exercise Price, Options exercisable	14.69
Weighted Average Exercise Price, Options vested, exercisable or expected to vest	$ 29.11
Options Outstanding, Weighted-Average Remaining Contractual Term	7 years 4 months 24 days	7 years 9 months 18 days	7 years 10 months 24 days	8 years
Options exercisable, Weighted-Average Remaining Contractual Term	6 years 4 months 24 days
Options vested, exercisable or expected to vest, Weighted Average Remaining Contractual Term	7 years 3 months 18 days
Options Outstanding, Aggregate Intrinsic Value, Beginning balances	$ 145,721	$ 97,832	$ 1,655
Options exercised, Aggregate Intrinsic Value	46,529	36,603	2,488
Options Outstanding, Aggregate Intrinsic Value, Ending balances	123,425	$ 145,721	$ 97,832	$ 1,655
Options exercisable, Aggregate Intrinsic Value	87,358
Options vested, exercisable or expected to vest, Aggregate Intrinsic Value	$ 121,743

Stock-Based Compensation - Su55

Stock-Based Compensation - Summary of Options Outstanding and Vested Under Stock Plans by Exercise Price (Detail)	12 Months Ended
	Dec. 31, 2016$ / sharesshares
$0.96 - $1.92 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Exercise Price Lower Range Limit	$ 0.96
Options Outstanding, Exercise Price Upper Range Limit	$ 1.92
Number of Options Outstanding | shares	141,176
Options Outstanding, Weighted Average Remaining Contractual Life (in Years)	2 years 10 months 13 days
Options Outstanding, Weighted Average Exercise Price	$ 1.48
Options Vested, Number Exercisable | shares	141,176
Options Vested, Weighted Average Exercise Price	$ 1.48
$3.60 - $3.60 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Exercise Price Lower Range Limit	3.60
Options Outstanding, Exercise Price Upper Range Limit	$ 3.60
Number of Options Outstanding | shares	1,030,002
Options Outstanding, Weighted Average Remaining Contractual Life (in Years)	6 years 4 days
Options Outstanding, Weighted Average Exercise Price	$ 3.60
Options Vested, Number Exercisable | shares	890,023
Options Vested, Weighted Average Exercise Price	$ 3.60
$10.08 - $38.79 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Exercise Price Lower Range Limit	10.08
Options Outstanding, Exercise Price Upper Range Limit	$ 38.79
Number of Options Outstanding | shares	572,674
Options Outstanding, Weighted Average Remaining Contractual Life (in Years)	7 years 10 months 13 days
Options Outstanding, Weighted Average Exercise Price	$ 25.89
Options Vested, Number Exercisable | shares	247,046
Options Vested, Weighted Average Exercise Price	$ 25.34
$41.83 - $54.50 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Exercise Price Lower Range Limit	41.83
Options Outstanding, Exercise Price Upper Range Limit	$ 54.50
Number of Options Outstanding | shares	573,030
Options Outstanding, Weighted Average Remaining Contractual Life (in Years)	8 years 8 months 1 day
Options Outstanding, Weighted Average Exercise Price	$ 51.44
Options Vested, Number Exercisable | shares	150,184
Options Vested, Weighted Average Exercise Price	$ 49.67
$57.89 - $97.52 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Exercise Price Lower Range Limit	57.89
Options Outstanding, Exercise Price Upper Range Limit	$ 97.52
Number of Options Outstanding | shares	504,345
Options Outstanding, Weighted Average Remaining Contractual Life (in Years)	9 years 3 months 7 days
Options Outstanding, Weighted Average Exercise Price	$ 71.37
Options Vested, Number Exercisable | shares	77,868
Options Vested, Weighted Average Exercise Price	$ 64.20
$0.96 - $97.52 [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Options Outstanding, Exercise Price Lower Range Limit	0.96
Options Outstanding, Exercise Price Upper Range Limit	$ 97.52
Number of Options Outstanding | shares	2,821,227
Options Outstanding, Weighted Average Remaining Contractual Life (in Years)	7 years 4 months 6 days
Options Outstanding, Weighted Average Exercise Price	$ 29.85
Options Vested, Number Exercisable | shares	1,506,297
Options Vested, Weighted Average Exercise Price	$ 14.69

Stock-Based Compensation - Su56

Stock-Based Compensation - Summary of Restricted Stock Units Under Stock Plan (Detail) - Restricted Stock Units [Member] - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Number of Restricted Stock Units, Outstanding Beginning Balance	5,160
Number of Restricted Stock Units, Restricted stock granted	357,479	5,450
Number of Restricted Stock Units, Restricted stock released	(1,384)
Number of Restricted Stock Units, Restricted stock cancelled	(15,700)	(290)
Number of Restricted Stock Units, Outstanding Ending Balance	345,555	5,160
Number of Restricted Stock Units, Restricted stock expected to vest	314,061
Weighted Average Grant Date Fair Value Outstanding, Beginning Balance	$ 56.09
Weighted Average Grant Date Fair Value, Granted	70.31	$ 56.47
Weighted Average Grant Date Fair Value, Released	56.65
Weighted Average Grant Date Fair Value, Cancelled	65.15	63.23
Weighted Average Grant Date Fair Value Outstanding, Ending Balance	$ 70.39	$ 56.09
Aggregate Intrinsic Value Outstanding, Beginning Balance	$ 348
Aggregate Intrinsic Value, Released	115
Aggregate Intrinsic Value Outstanding, Ending Balance	25,108	$ 348
Aggregate Intrinsic Value, Expected to vest	$ 22,820

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Employee Stock Purchase Plan Activity (Detail) - ESPP [Member] - 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]
Additional shares reserved	281,435	248,654
Shares issued	72,568	33,158
Shares available for future issuance	621,029	412,162	196,666
Employee contributions for shares issued	$ 3,499	$ 1,430

Stock-Based Compensation - Sc58

Stock-Based Compensation - Schedule of Fair Value of Employee Stock Options Using Black-Scholes Option Valuation Model (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility, minimum	47.00%	46.00%	57.00%
Expected volatility, maximum	49.00%	59.00%	63.00%
Risk-free interest rate, minimum	1.30%	1.40%	1.70%
Risk-free interest rate, maximum	1.90%	1.80%	2.00%
Dividend Yield	0.00%	0.00%	0.00%
Stock Options [Member] | Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 3 months 18 days	5 years 3 months 18 days	5 years 3 months 18 days
Stock Options [Member] | Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 1 month 6 days	6 years 1 month 6 days	6 years 1 month 6 days
ESPP [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 months	6 months
Expected volatility, minimum	46.00%	42.00%
Expected volatility, maximum	53.00%	64.00%
Risk-free interest rate, minimum	0.40%	0.10%
Risk-free interest rate, maximum	0.60%	0.30%
Dividend Yield	0.00%	0.00%

Stock-Based Compensation - Su59

Stock-Based Compensation - Summary of Stock-Based Compensation Expense by Line Items in Consolidated Statements of Operations (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 15,760	$ 7,325	$ 1,998
Cost of Revenue [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	1,094	621	147
Research and Development [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	3,182	1,401	661
Selling, General and Administrative [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 11,484	$ 5,303	$ 1,190

Stock-Based Compensation - Su60

Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 15,760	$ 7,325	$ 1,998
Stock Options [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	10,832	6,679	$ 1,998
Restricted Stock Units [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	3,548	9
Employee Stock Purchase Plan [Member]
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Stock-based compensation expense	$ 1,380	$ 637

Stock-Based Compensation - Su61

Stock-Based Compensation - Summary of Stock-Based Compensation Expense Not Yet Recognized (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2016USD ($)
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation	$ 25,602
Weighted-Average Amortization Period (in years)	2 years 6 months
Restricted Stock Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation	$ 18,253
Weighted-Average Amortization Period (in years)	3 years 3 months 18 days
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized Compensation	$ 757
Weighted-Average Amortization Period (in years)	4 months 24 days

Income Taxes - Components of In

Income Taxes - Components of Income (Loss) before Income Taxes (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Domestic	$ (34,258)	$ (68,919)	$ (31,807)
Foreign	4,103	2,654	1,605
Loss before income taxes	$ (30,155)	$ (66,265)	$ (30,202)

Income Taxes - Components of 63

Income Taxes - Components of Income Tax Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current:
Federal		$ 0	$ 0
State	$ 181	34	2
Foreign	1,442	1,132	476
Total current	1,623	1,166	478
Deferred:
Federal		0	0
State		0	0
Foreign		0	0
Total deferred		0	0
Total income tax expense	$ 1,623	$ 1,166	$ 478

Income Taxes - Income Tax Expen

Income Taxes - Income Tax Expense by Applying Statutory Federal Income Tax Rate (Detail)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Tax at statutory federal rate	34.00%	34.00%	34.00%
State tax, net of federal benefit	(0.40%)	0.00%	0.00%
Other	(3.70%)	(3.50%)	(5.30%)
Foreign rate differential	(0.20%)	(0.50%)	0.20%
Tax credits	3.20%	1.60%	2.00%
Change in valuation allowance	(38.40%)	(33.40%)	(32.50%)
Total	(5.50%)	(1.80%)	(1.60%)

Income Taxes - Tax Effects of T

Income Taxes - Tax Effects of Temporary Differences and Carryforwards That Give Rise to Significant Portions of Deferred Tax Assets (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Income Tax Disclosure [Abstract]
Net operating loss carryforwards	$ 60,610	$ 56,340
Tax credits	7,655	5,236
Depreciation	26	13
Stock-based compensation	5,207	1,857
Accruals and reserves	7,559	3,617
Other	4,671	313
Deferred tax assets	85,728	67,376
Other		(345)
Deferred tax liabilities		(345)
Valuation allowance	$ (85,728)	(67,031)
Net deferred tax assets		$ 0

Income Taxes - Additional Infor

Income Taxes - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Income Taxes [Line Items]
Increase in valuation allowance	$ 18,700,000	$ 23,400,000	$ 9,400,000
Research and development credit carry forwards	33,729,000	21,382,000	19,824,000
Unrecognized tax benefits	3,384,000	3,844,000	1,962,000	$ 1,065,000
Accrued interest and penalties	0	$ 0	$ 0
California state [Member]
Income Taxes [Line Items]
Research and development credit carry forwards	5,100,000
Federal [Member]
Income Taxes [Line Items]
Net operating loss carryforward	$ 224,700,000
Net operating loss expiration date	2,026
Excess tax benefit related to stock-based compensation	$ 54,800,000
Research and development credit carry forwards	5,800,000
State and Local Jurisdiction [Member]
Income Taxes [Line Items]
Net operating loss carryforward	$ 77,300,000
Net operating loss expiration date	2,017
Excess tax benefit related to stock-based compensation	$ 23,700,000

Income Taxes - Summary of Unrec

Income Taxes - Summary of Unrecognized Tax Benefits (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Beginning balance	$ 3,844	$ 1,962	$ 1,065
Increases related to current year tax provisions	1,059	813	220
Increases related to prior year tax provisions		1,069	677
Decreases related to prior year tax provisions	(1,519)
Ending balance	$ 3,384	$ 3,844	$ 1,962

Net Loss Per Share Attributab68

Net Loss Per Share Attributable to Common Stockholders - Computation of Basic and Diluted Net Loss per Share Attributable to Common Stockholders (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Earnings Per Share [Abstract]
Net loss	$ (9,825)	$ (3,886)	$ (8,779)	$ (9,288)	$ (14,191)	$ (19,454)	$ (19,726)	$ (14,060)	$ (31,778)	$ (67,431)	$ (30,680)
Accretion of convertible preferred stock to redemption value											(147)
Net loss attributable to common stockholders	$ (9,825)	$ (3,886)	$ (8,779)	$ (9,288)	$ (14,191)	$ (19,454)	$ (19,726)	$ (14,060)	$ (31,778)	$ (67,431)	$ (30,827)
Weighted average shares outstanding									28,492,091	26,603,512	4,486,569
Less: weighted average shares subject to repurchase									(7,088)	(21,622)	(45,906)
Weighted average shares used to compute basic and diluted net loss per share	28,817,333	28,542,760	28,381,253	28,194,457	28,003,957	27,861,523	25,564,249	24,849,229	28,485,003	26,581,890	4,440,663
Net loss per share attributable to common stockholders, basic and diluted	$ (0.34)	$ (0.14)	$ (0.31)	$ (0.33)	$ (0.51)	$ (0.70)	$ (0.77)	$ (0.57)	$ (1.12)	$ (2.54)	$ (6.94)

Net Loss Per Share Attributab69

Net Loss Per Share Attributable to Common Stockholders - Computation of Potentially Dilutive Securities Outstanding Excluded from Computation of Diluted Shares (Detail) - shares	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted shares outstanding	3,166,782	3,055,448	2,973,732
Unreleased Restricted Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted shares outstanding	345,555	5,160
Options to Purchase Common Stock [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted shares outstanding	2,821,227	3,050,288	2,973,732

Net Loss Per Share Attributab70

Net Loss Per Share Attributable to Common Stockholders - Additional Information (Detail)	Dec. 31, 2016$ / shares
1.75% Convertible Senior Notes due 2021 [Member]
Earnings Per Share Diluted [Line Items]
Convertible notes, conversion price	$ 96.37

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Detail) $ in Millions	12 Months Ended
	Dec. 31, 2016USD ($)
Postemployment Benefits [Abstract]
Expense for matching contributions	$ 1.3

Selected Quarterly Financial 72

Selected Quarterly Financial Information - Schedule of Selected Quarterly Financial Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Quarterly Financial Information Disclosure [Abstract]
Total revenue	$ 70,531	$ 60,922	$ 55,400	$ 41,651	$ 33,124	$ 15,402	$ 11,418	$ 9,662	$ 228,504	$ 69,606	$ 32,573
Gross profit	48,839	41,687	36,558	25,987	20,353	9,434	5,910	5,789	153,071	41,486	21,295
Loss from operations	(6,269)	(1,872)	(5,923)	(9,017)	(13,144)	(17,709)	(19,175)	(12,339)	(23,081)	(62,367)	(28,306)
Net loss	(9,825)	(3,886)	(8,779)	(9,288)	(14,191)	(19,454)	(19,726)	(14,060)	(31,778)	(67,431)	(30,680)
Net loss attributable to common stockholders, basic and diluted	$ (9,825)	$ (3,886)	$ (8,779)	$ (9,288)	$ (14,191)	$ (19,454)	$ (19,726)	$ (14,060)	$ (31,778)	$ (67,431)	$ (30,827)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.34)	$ (0.14)	$ (0.31)	$ (0.33)	$ (0.51)	$ (0.70)	$ (0.77)	$ (0.57)	$ (1.12)	$ (2.54)	$ (6.94)
Shares used in computing net loss per common share, basic and diluted	28,817,333	28,542,760	28,381,253	28,194,457	28,003,957	27,861,523	25,564,249	24,849,229	28,485,003	26,581,890	4,440,663