Nevro (NVRO) 10-Q 6 Nov 19 2019 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Oct. 31, 2019
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Trading Symbol	NVRO
Entity Registrant Name	NEVRO CORP
Entity Central Index Key	0001444380
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Current Reporting Status	Yes
Entity Small Business	false
Entity Shell Company	false
Entity Emerging Growth Company	false
Entity Common Stock, Shares Outstanding		31,006,597
Entity File Number	001-36715
Entity Tax Identification Number	56-2568057
Entity Address, Address Line One	1800 Bridge Parkway
Entity Address, City or Town	Redwood City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94065
City Area Code	650
Local Phone Number	251-0005
Entity Interactive Data Current	Yes
Entity Incorporation, State or Country Code	DE
Security Exchange Name	NYSE
Document Quarterly Report	true
Document Transition Report	false
Title of 12(b) Security	Common Stock, $0.001 par value per share

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets
Cash and cash equivalents	$ 49,338	$ 51,266
Short-term investments	183,429	213,281
Accounts receivable, net of allowance for doubtful accounts of $925 and $824 at September 30, 2019 and December 31, 2018, respectively	70,807	80,656
Inventories	90,730	92,035
Prepaid expenses and other current assets	6,497	6,621
Total current assets	400,801	443,859
Property and equipment, net	11,721	12,801
Operating lease assets	22,348
Other assets	11,912	5,850
Restricted cash	956	606
Total assets	447,738	463,116
Current liabilities
Accounts payable	19,770	23,505
Accrued liabilities	45,048	38,790
Other current liabilities	3,509	119
Total current liabilities	68,327	62,414
Long-term debt	158,278	152,394
Long-term operating lease liabilities	21,324
Other long-term liabilities	1,712	2,825
Total liabilities	249,641	217,633
Commitments and contingencies (Note 6)
Stockholders’ equity
Preferred stock, $0.001 par value, 10,000,000 shares authorized at September 30, 2019 and December 31, 2018; zero shares issued and outstanding at September 30, 2019 and December 31, 2018
Common stock, $0.001 par value, 290,000,000 shares authorized at September 30, 2019 and December 31, 2018; 30,994,005 and 30,263,536 shares issued and outstanding at September 30, 2019 and December 31, 2018, respectively	31	30
Additional paid-in capital	594,630	552,612
Accumulated other comprehensive loss	(538)	(1,077)
Accumulated deficit	(396,026)	(306,082)
Total stockholders’ equity	198,097	245,483
Total liabilities and stockholders’ equity	$ 447,738	$ 463,116

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Statement Of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 925	$ 824
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	30,994,005	30,263,536
Common stock, shares outstanding	30,994,005	30,263,536

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 100,162	$ 95,630	$ 275,881	$ 279,345
Cost of revenue	30,222	28,382	88,789	82,175
Gross profit	69,940	67,248	187,092	197,170
Operating expenses
Research and development	13,019	12,478	42,084	34,979
Sales, general and administrative	72,905	64,007	229,806	195,331
Total operating expenses	85,924	76,485	271,890	230,310
Loss from operations	(15,984)	(9,237)	(84,798)	(33,140)
Interest income	1,603	1,275	4,641	3,423
Interest expense	(2,755)	(2,622)	(8,153)	(7,759)
Other income (expense), net	(291)	(130)	(516)	(845)
Loss before income taxes	(17,427)	(10,714)	(88,826)	(38,321)
Provision for income taxes	420	551	1,118	1,277
Net loss	(17,847)	(11,265)	(89,944)	(39,598)
Other comprehensive loss:
Changes in foreign currency translation adjustment	200	(155)	99	104
Changes in unrealized gains on short-term investments, net		269	440	191
Net change in other comprehensive loss	200	114	539	295
Comprehensive loss	$ (17,647)	$ (11,151)	$ (89,405)	$ (39,303)
Net loss per share, basic and diluted	$ (0.58)	$ (0.37)	$ (2.93)	$ (1.32)
Weighted average number of common shares used to compute basic and diluted net loss per share	30,929,938	30,123,188	30,659,117	29,997,201

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Stockholders' Equity (unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Deficit [Member]	Accumulated Other Comprehensive Income (Loss) [Member]
Beginning balances at Dec. 31, 2017	$ 249,172	$ 30	$ 508,228	$ (257,844)	$ (1,242)
Beginning balances, shares at Dec. 31, 2017		29,737,561
Adoption of accounting standard	967			967
Exercise of common stock options	1,941		1,941
Exercise of common stock options, shares		135,874
Issuance of common stock upon release of restricted stock units		73,352
Shares withheld for tax obligations	(215)		(215)
Shares withheld for tax obligations, shares		(3,019)
Stock based compensation	8,244		8,244
Net loss	(17,713)			(17,713)
Other comprehensive loss	226				226
Ending balances at Mar. 31, 2018	242,622	$ 30	518,198	(274,590)	(1,016)
Ending balances, shares at Mar. 31, 2018		29,943,768
Beginning balances at Dec. 31, 2017	249,172	$ 30	508,228	(257,844)	(1,242)
Beginning balances, shares at Dec. 31, 2017		29,737,561
Net loss	(39,598)
Other comprehensive loss	295
Ending balances at Sep. 30, 2018	244,302	$ 30	541,694	(296,475)	(947)
Ending balances, shares at Sep. 30, 2018		30,150,577
Beginning balances at Dec. 31, 2017	249,172	$ 30	508,228	(257,844)	(1,242)
Beginning balances, shares at Dec. 31, 2017		29,737,561
Net loss	(49,200)
Ending balances at Dec. 31, 2018	245,483	$ 30	552,612	(306,082)	(1,077)
Ending balances, shares at Dec. 31, 2018		30,263,536
Beginning balances at Mar. 31, 2018	242,622	$ 30	518,198	(274,590)	(1,016)
Beginning balances, shares at Mar. 31, 2018		29,943,768
Exercise of common stock options	1,465		1,465
Exercise of common stock options, shares		63,351
Issuance of common stock upon release of restricted stock units		42,938
Shares withheld for tax obligations	(727)		(727)
Shares withheld for tax obligations, shares		(9,250)
Issuance of common stock under employee stock purchase plan	3,580		3,580
Issuance of common stock under employee stock purchase plan, shares		53,824
Stock based compensation	9,314		9,314
Net loss	(10,620)			(10,620)
Other comprehensive loss	(45)				(45)
Ending balances at Jun. 30, 2018	245,589	$ 30	531,830	(285,210)	(1,061)
Ending balances, shares at Jun. 30, 2018		30,094,631
Exercise of common stock options	494		494
Exercise of common stock options, shares		43,178
Issuance of common stock upon release of restricted stock units		14,060
Shares withheld for tax obligations	(83)		(83)
Shares withheld for tax obligations, shares		(1,292)
Stock based compensation	9,453		9,453
Net loss	(11,265)			(11,265)
Other comprehensive loss	114				114
Ending balances at Sep. 30, 2018	244,302	$ 30	541,694	(296,475)	(947)
Ending balances, shares at Sep. 30, 2018		30,150,577
Beginning balances at Dec. 31, 2018	245,483	$ 30	552,612	(306,082)	(1,077)
Beginning balances, shares at Dec. 31, 2018		30,263,536
Exercise of common stock options	1,928		1,928
Exercise of common stock options, shares		105,462
Issuance of common stock upon release of restricted stock units		83,008
Shares withheld for tax obligations	(154)		(154)
Shares withheld for tax obligations, shares		(4,237)
Stock based compensation	10,397		10,397
Net loss	(44,076)			(44,076)
Other comprehensive loss	521				521
Ending balances at Mar. 31, 2019	214,099	$ 30	564,783	(350,158)	(556)
Ending balances, shares at Mar. 31, 2019		30,447,769
Beginning balances at Dec. 31, 2018	245,483	$ 30	552,612	(306,082)	(1,077)
Beginning balances, shares at Dec. 31, 2018		30,263,536
Net loss	(89,944)
Other comprehensive loss	539
Ending balances at Sep. 30, 2019	198,097	$ 31	594,630	(396,026)	(538)
Ending balances, shares at Sep. 30, 2019		30,994,005
Beginning balances at Mar. 31, 2019	214,099	$ 30	564,783	(350,158)	(556)
Beginning balances, shares at Mar. 31, 2019		30,447,769
Exercise of common stock options	2,233	$ 1	2,232
Exercise of common stock options, shares		214,647
Issuance of common stock upon release of restricted stock units		95,347
Shares withheld for tax obligations	(406)		(406)
Shares withheld for tax obligations, shares		(6,530)
Issuance of common stock under employee stock purchase plan	4,095		4,095
Issuance of common stock under employee stock purchase plan, shares		119,393
Stock based compensation	9,724		9,724
Net loss	(28,021)			(28,021)
Other comprehensive loss	(182)				(182)
Ending balances at Jun. 30, 2019	201,542	$ 31	580,428	(378,179)	(738)
Ending balances, shares at Jun. 30, 2019		30,870,626
Exercise of common stock options	3,505		3,505
Exercise of common stock options, shares		83,346
Issuance of common stock upon release of restricted stock units		46,228
Shares withheld for tax obligations	(497)		(497)
Shares withheld for tax obligations, shares		(6,195)
Stock based compensation	11,194		11,194
Net loss	(17,847)			(17,847)
Other comprehensive loss	200				200
Ending balances at Sep. 30, 2019	$ 198,097	$ 31	$ 594,630	$ (396,026)	$ (538)
Ending balances, shares at Sep. 30, 2019		30,994,005

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Cash flows from operating activities
Net loss			$ (89,944)	$ (39,598)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	$ 1,112	$ 1,078	3,306	2,845
Amortization of operating lease assets			2,423
Stock-based compensation expense			31,315	27,018
Accretion of discount on short-term investments			(1,794)	(563)
Provision for doubtful accounts			106	(444)
Write-down of inventory			1,832	870
Non-cash interest expense			5,889	5,494
Unrealized (gains) losses on foreign currency transactions			(48)	910
Changes in operating assets and liabilities
Accounts receivable			9,191	(5,376)
Inventories			1,194	3,543
Prepaid expenses and other current assets			107	(1,360)
Other assets			(558)	(1,065)
Accounts payable			(3,866)	1,786
Accrued liabilities			6,267	(5,352)
Other long-term liabilities			(2,170)	584
Net cash used in operating activities			(36,750)	(10,708)	$ (5,700)
Cash flows from investing activities
Purchases of short-term investments			(178,478)	(137,867)
Proceeds from maturity of short-term investments			210,703	128,474
Investment in private company			(5,500)
Purchases of property and equipment			(2,041)	(7,876)
Net cash provided by (used in) investing activities			24,684	(17,269)
Cash flows from financing activities
Minimum tax withholding paid on behalf of employees for net share settlement			(1,057)	(1,025)
Proceeds from issuance of common stock to employees			11,761	7,480
Net cash provided by financing activities			10,704	6,455
Effect of exchange rate changes on cash and cash equivalents			(216)	(146)
Net increase (decrease) in cash, cash equivalents and restricted cash			(1,578)	(21,668)
Cash, cash equivalents and restricted cash
Cash, cash equivalents and restricted cash at beginning of period			51,872	43,651	43,651
Cash, cash equivalents and restricted cash at end of period	$ 50,294	$ 21,983	50,294	21,983	$ 51,872
Significant non-cash transactions
Purchases of property and equipment in accounts payable			$ 429	$ 55

Formation and Business of the C

Formation and Business of the Company	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Formation and Business of the Company	1. Formation and Business of the Company Nevro Corp. (the Company) was 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, the Company was reincorporated in Delaware on October 4, 2006 and relocated to California. Since inception, the Company has cumulatively incurred net losses and negative cash flows from operations. During the year ended December 31, 2018, the Company incurred a net loss of $49.2 million and used $5.7 million of cash in operations. For the nine months ended September 30, 2019, the Company incurred a net loss of $89.9 million and used $36.8 million of cash in operations. At September 30, 2019 and December 31, 2018, the Company had an accumulated deficit of $396.0 million and $306.1 million, respectively. 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, its June 2015 underwritten public offering and its June 2016 underwritten public offering of convertible senior notes due 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. 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. The accompanying interim condensed consolidated financial statements as of September 30, 2019 and for the nine months ended September 30, 2019 and 2018, and the related interim information contained within the notes to the financial statements, are unaudited. The unaudited interim condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (U.S. GAAP) for interim financial information and on the same basis as the audited financial statements included on the Company’s Annual Report on Form 10-K (Annual Report) filed with the Securities and Exchange Commission (SEC) on February 21, 2019. In the opinion of management, the accompanying unaudited interim condensed consolidated financial statements contain all adjustments (consisting of normal recurring adjustments) necessary to state fairly the Company’s financial position as of September 30, 2019, and the results of its operations and cash flows for the nine months ended September 30, 2019 and 2018. All such adjustments are of a normal and recurring nature. The interim financial data as of September 30, 2019 is not necessarily indicative of the results to be expected for the year ending December 31, 2019, or for any future period. The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto for the year ended December 31, 2018 included in the Annual Report.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of Significant Accounting Policies Basis of Presentation These condensed consolidated financial statements have been prepared in accordance with U.S. GAAP. The condensed consolidated financial statements include the Company’s accounts and those of its 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 by information about revenue by geographic region, for purposes of allocating resources and evaluating financial performance. 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. Revenue by geography is based on the billing address of the customer. The United States was the only country with revenue accounting for more than 10% of the total revenue in any of the periods presented, as follows: Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 United States 84 % 83 % 83 % 82 % Long-lived assets and operating income located outside the United States 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) on 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. Additionally, realized gains and losses resulting from transactions denominated in currencies other than the local currency are recorded in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. The Company recorded net unrealized and net realized foreign currency transaction gains (losses) during the periods presented as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Net unrealized foreign currency gain (loss) $ 190 $ (6 ) $ 690 $ (892 ) Net realized foreign currency gain (loss) (459 ) (75 ) (1,086 ) 217 As the Company’s international operations grow, its risks associated with 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 USD 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 U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Significant accounting estimates and management judgments reflected in the condensed consolidated financial statements include items such as allowances for doubtful accounts; warranty obligations; clinical accruals; stock-based compensation; depreciation and amortization periods; inventory valuation; valuation of investments; and accounting for income taxes. 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 and is in excess of federally insured limits. The Company maintained investments in money market funds that were not federally insured during the periods ended September 30, 2019 and December 31, 2018. The Company also held cash in foreign banks of approximately $8.9 million at September 30, 2019 and $4.1 million at December 31, 2018 that was not federally insured. The Company has not experienced any losses on its deposits of cash and cash equivalents. The Company’s convertible note hedge transactions, entered into in connection with the 2021 Notes, subject the Company to credit risk such that the counterparties may be unable to fulfill the terms of the transactions. The associated risk is mitigated by limiting the counterparties to major financial institutions. In the international markets in which the Company participates, the Company uses a combination of a direct sales force , sales agents and independent 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. During the three and nine months ended September 30, 2019 and 2018, no single customer accounted for 10% 10% 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, manufacturing quality and scaling, continued reimbursement from third-party payors, There can be no assurance that the Company’s products or services will continue to be accepted in its existing marketplaces, 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 may choose to raise additional funds to further enhance its research and development efforts, for product expansion opportunities or to acquire a new business or products that are complementary to its business. 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 The 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 $17.3 million and $15.6 million as of September 30, 2019 and December 31, 2018, respectively. At September 30, 2019 and December 31, 2018, the Company’s cash equivalents were held at institutions in the United States and include deposits in a money market fund which was unrestricted as to withdrawal or use. Restricted Cash Restricted cash as of September 30, 2019 and December 31, 2018 consists of a letter of credit of $0.6 million representing collateral for the Company’s Redwood City, California building lease pursuant to an agreement dated March 5, 2015. Restricted cash as of September 30, 2019 additionally includes certificates of deposit of $0.4 million, representing collateral for charges related to certain of the Company’s credit cards. Investment Securities The Company classifies its investment securities as available-for-sale. 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 at the date of purchase are also classified as short-term investments as management considers them to be available for current operations if needed. The Company’s investment securities classified as available-for-sale are recorded at fair value. Unrealized gains and losses, deemed temporary in nature, are reported as a separate component of accumulated 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 net realizable value of such inventory. Cost is determined using the standard cost method which approximates the first-in, first-out basis. Net realizable value is determined as the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. 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 writes down inventory that has become obsolete, inventory that has a cost basis in excess of its expected net realizable value, and inventory that is 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 amounts over demand using the same lower of cost or net realizable value approach that has been used to value inventory. The Company also periodically evaluates inventory quantities in consideration of actual loss experience. In addition, the Company determines at times that there may be certain inventory that does not meet its product requirements. As a result of these evaluations, the Company recognized total write-downs of $0.4 million and $0.5 million for the three months ended September 30, 2019 and 2018, respectively, and $4.5 million and $0.9 million for the nine months ended September 30, 2019 and 2018, respectively. The total write-down for the nine months ended September 30, 2019 included $3.6 million related to an excess raw material charge. The Company’s estimation of the future demand for any given particular component of the Senza product may vary and may result in changes in estimates of inventory values in any particular period. Shipping and Handling Costs The Company has made the accounting policy election under ASC 606 to account for shipping and handling costs as a fulfillment activity. These costs are accrued when the related revenue is recognized. Revenue Recognition Revenue is recognized when obligations under the terms of a contract with customers are satisfied, which occurs with the transfer of control of the Company’s goods to its customers. Revenue is measured as the amount of consideration the Company expects to receive in exchange for transferring the goods. 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 the point in time when control transfers to the customers. 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, the transfer of control occurs at the time of shipment of the product. These 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. Sales, value add, and other taxes the Company collects concurrent with revenue-producing activities are excluded from revenue. The expected costs associated with warranty obligations continue to be recognized as expense when the products are sold (see Note 6). The Company periodically provides incentive offers, in the form of rebates, to customers based on their aggregate levels of purchases. 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 provides a limited one- to five-year warranty 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 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 September 30, 2019. Income Taxes During the three and nine months ended September 30, 2019 and 2018, the Company calculated its interim tax provision to record taxes incurred on a discrete basis due to the variability of taxable income in the jurisdictions in which it operates. The provision for income taxes for the three and nine months ended September 30, 2019 and 2018 is primarily comprised of foreign and state taxes based upon income earned during the period with no tax benefit recorded for the loss jurisdiction. 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. A nominal amount of interest and penalties have been recognized for the three and nine months ended September 30, 2019. No interest or penalties related to income taxes have been recognized in the statements of operations and comprehensive loss for the three and nine months ended September 30, 2018. Other Comprehensive Income (Loss) Other comprehensive income (loss) represents all changes in the stockholders’ equity except those resulting from distributions to stockholders. The Company’s changes in unrealized gains and losses on 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 have been presented in the consolidated statements of operations and comprehensive loss. Research and Development Research and development costs, 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, 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. In March 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-09, Stock Compensation (Topic 718): Improvements to Employee Shared-Based Payment Accounting , which the Company adopted on January 1, 2017. Under ASU 2016-09, entities are permitted to make an accounting policy election to either estim ate forfeitures on share-based payment awards, as previously required, or to recognize forfeitures as they occur. The Company has elected to continue to estimate forfeitures expected to occur to determine the amount of compensation cost recognized in each period. ASU 2016-09 also requires that entities recognize, on a prospective basis, all excess tax benefits and tax deficiencies as income tax expense or benefit in the income statement as discrete items in the reporting period in which they occur. The adoption did not result in a cumulative-effect adjustment to accumulated deficit as of January 1, 2017 using the modified retrospective method. Additionally, under ASU 2016-09, excess tax benefits are classified as an operating activity in the statement of cash flows. The Company has elected the presentation of excess tax benefits in the statement of cash flows using the prospective transition method. 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. Changes in the assumptions can materially affect the fair value and ultimately how much stock-based compensation expense is recognized. 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. 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 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 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 also issues stock options and restricted stock units with vesting based upon completion of performance goals. The fair value for these performance-based awards is recognized over the period during which the goals are to be achieved. Stock-based compensation expense recognized at fair value includes the impact of estimated probability that the goals would be achieved, which is assessed prior to the requisite service period for the specific goals. In March 2019, the Company granted performance stock units (PSUs) to the Company’s Chief Executive Officer. The PSUs are subject to continued service to the Company through the vesting date. The number of shares to be issued upon vesting are based on the total shareholder return of the Company’s common stock compared to the S&P Healthcare Equipment Select Industry Index (the Index), subject to an upward adjustment based on the Company’s absolute stock price performance over the specified measurement period. If the performance metrics are not met within the specified time limits, the PSUs will be canceled. The fair value of the PSUs is determined on the date of grant using a Monte Carlo simulation model, which is based on a larger number of possible stock price outcomes for the Company’s stock and the Index. The use of the Monte Carlo simulation model requires the input of certain assumptions, including the expected stock price volatility of the Company and members of the Index, correlation between changes in the stock price of the Company and members of the Index, risk-free interest rate and expected dividends, as applicable. The fair value of the PSUs is recognized over the specified measurement period on a straight-line basis. Upon adoption of ASU 2016-09 as described above, excess tax benefits or deficiencies from share-based award activity are reflected in the consolidated statements of operations as a component of the provision for income taxes, whereas they were previously recognized as additional paid-in capital. Net Loss per Share of Common Stock Basic net loss per common share is calculated by dividing net loss 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 net loss 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, the Company’s restricted stock units and options to purchase shares of common stock 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 June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments The FASB has also issued several updates to ASU No. 2016-13. The Company has not determined the potential effects of the guidance on its consolidated financial statements

Lease Accounting

Lease Accounting	9 Months Ended
	Sep. 30, 2019
Leases [Abstract]
Lease Accounting	3. Lease Accounting Adoption of ASC 842 On January 1, 2019, the Company adopted the new accounting standard ASC 842, Leases The Company adopted the new lease standard using the transition method that allowed entities to initially apply ASC 842 at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption (the optional transition method). The Company elected the package of transitional practical expedients, such that, for leases existing prior to the adoption of ASC 842, the Company will not need to reassess whether contracts are leases, will retain historical lease classification and historical initial direct costs classification. The Company also elected the hindsight practical expedient to determine the lease term for existing leases. Operating lease assets and operating lease liabilities are recognized based on the present value of minimum lease payments over the remaining lease term. The Company uses its incremental borrowing rate based on information available when determining the lease liabilities. Lease cost is recognized on a straight-line basis over the expected lease term. Adoption of the new lease standard resulted in the recording of operating lease assets of $24.8 million and operating lease liabilities of $26.2 million. The impact of the changes made to the consolidated balance sheet as of January 1, 2019 from the adoption of ASC 842 were as follows (in thousands): Balance at Adjustments Due Balance at December 31, 2018 to ASC 842 January 1, 2019 Balance Sheet: Operating lease assets $ — $ 24,771 $ 24,771 Other current liabilities 119 2,389 2,508 Long-term operating lease liabilities — 23,805 23,805 Other long-term liabilities 2,825 (1,423 ) 1,402 The Company has operating leases for office space, warehouse, research and development facilities and equipment. Leases with terms of 12 months or less are not recorded on the balance sheet, as the related lease expenses are recognized on a straight-line basis over the lease term. The Company accounts for lease components (such as fixed payments) separately from nonlease components (such as common area expenses). As of September 30, 2019, the Company has leases with remaining terms of less than 1 year to 6 years, some of which may include options to extend the lease term for up to 5 years. The weighted average lease terms and discounts rates are as follows: September 30, 2019 Operating Lease Term and Discount Rate Weighted-average remaining lease term 5.56 years Weighted-average discount rate 7.0% As of September 30, 2019, t he maturity of lease liabilities are as follows (in thousands): Operating Leases 2019, remaining months $ 1,213 2020 4,924 2021 5,073 2022 5,258 2023 5,522 Thereafter 8,086 Total lease payments 30,076 Less: Interest (5,342 ) Present value of lease liabilities $ 24,734 Supplemental lease cost information are as follows (in thousands): Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Operating lease cost $ 1,239 $ 3,807 Supplemental balance sheet information are as follows (in thousands): September 30, 2019 Operating Leases: Operating lease assets $ 22,348 Other current liabilities $ 3,410 Long term operating lease liabilities 21,324 Total operating lease liabilities $ 24,734 Supplemental cash flow information are as follows (in thousands): Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flow from operating leases $ 1,010 $ 2,809 See Note 6 for further details of the Company’s lease commitments.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurements	4. 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. The Company’s money market funds are classified within Level 1 of the fair value hierarchy and are valued based on quoted prices in active markets for identical securities. The Company’s short-term investments are comprised of commercial paper and corporate notes. 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 and 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 September 30, 2019 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 17,279 $ — $ — $ 17,279 Agency bonds (iii) — 12,964 — 12,964 Commercial paper (ii) — 54,047 — 54,047 Corporate notes (iii) — 129,653 — 129,653 Total assets $ 17,279 $ 196,664 $ — $ 213,943 Balance as of December 31, 2018 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 15,572 $ — $ — $ 15,572 Commercial paper (ii) — 119,602 — 119,602 Corporate notes (ii) — 111,532 — 111,532 Total assets $ 15,572 $ 231,134 $ — $ 246,706 (i) Included in cash and cash equivalents on the condensed consolidated balance sheets. (i i ) Included in cash and cash equivalents or short-term investments on the condensed consolidated balance sheets. (iii) Included in short-term investments on the condensed consolidated balance sheets. Convertible Senior Notes As of September 30, 2019 and December 31, 2018, the fair value of the 1.75% convertible senior notes due 2021 was $197.5 million and $160.5 million, respectively. 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 (See Note 7).

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2019
Organization Consolidation And Presentation Of Financial Statements [Abstract]
Balance Sheet Components	5. 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, excluding investments in money market funds (in thousands): September 30, 2019 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Agency bonds $ 12,952 $ 12 $ — $ 12,964 Commercial paper (i) 53,996 51 — 54,047 Corporate notes 129,342 311 — 129,653 Total securities $ 196,290 $ 374 $ — $ 196,664 December 31, 2018 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Commercial paper (ii) $ 119,692 $ — $ (90 ) $ 119,602 Corporate notes (ii) 111,652 — (120 ) 111,532 Total securities $ 231,344 $ — $ (210 ) $ 231,134 (i) Includes $13.2 million of commercial paper that is classified as cash and cash equivalents on the condensed consolidated balance sheets. (ii) Includes $15.8 million of commercial paper and $2.0 million of corporate notes that are classified as cash and cash equivalents on the condensed consolidated balance sheets. Realized gains or losses 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 is determined based on the specific identification method. The amount of realized gains and realized losses on investments recorded for the periods presented has not been material. The contractual maturities of the Company’s investment securities as of September 30, 2019 were as follows (in thousands): Amortized Cost Fair Value Amounts maturing within one year $ 163,797 $ 164,135 Amounts maturing after one year through five years 32,493 32,529 Total investment securities $ 196,290 $ 196,664 Inventories (in thousands) September 30, December 31, 2019 2018 Raw materials $ 32,442 $ 37,453 Finished goods 58,288 54,582 Total inventories $ 90,730 $ 92,035 Property and Equipment, Net (in thousands) September 30, December 31, 2019 2018 Laboratory equipment $ 3,587 $ 2,874 Computer equipment and software 9,691 8,751 Furniture and fixtures 3,978 3,903 Leasehold improvements 4,218 4,218 Construction in process 2,309 1,811 Total 23,783 21,557 Less: Accumulated depreciation and amortization (12,062 ) (8,756 ) Property and equipment, net $ 11,721 $ 12,801 The Company recognized depreciation and amortization expense on property and equipment as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Depreciation and amortization expense $ 1,112 $ 1,078 $ 3,306 $ 2,845 Accrued Liabilities (in thousands) September 30, December 31, 2019 2018 Accrued payroll and related expenses $ 28,521 $ 26,792 Accrued professional fees 1,677 1,595 Accrued taxes 2,257 2,506 Accrued clinical and research expenses 1,958 1,105 Accrued interest 998 243 Accrued warranty 1,216 1,236 Inventory related liabilities 1,732 790 Accrued other 6,689 4,523 Total accrued liabilities $ 45,048 $ 38,790

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	6. 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 on June 30, 2015 and ending in 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 a first amendment to the lease 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 commenced on June 1, 2018 The Company entered into a separate non-cancellable facility lease for warehouse space beginning on March 1, 2017 through February 28, 2022, under which it is obligated to pay approximately $0.4 million in lease payments over the term of the lease. See Note 3 for further discussion on Lease Accounting. 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. Activities related to warranty obligations were as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Beginning balance $ 1,291 $ 943 $ 1,236 $ 708 Provision for warranty 490 597 1,426 1,681 Utilization (565 ) (447 ) (1,446 ) (1,296 ) Ending balance $ 1,216 $ 1,093 $ 1,216 $ 1,093 License Agreement In October 2006, the Company entered into an amended and restated license agreement with the Mayo Foundation for Medical Education and Research (Mayo) and the Venturi Group LLC (VGL), which provides the Company access to 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 expiration of (1) the last to expire of the licensed patents or (2) the Company’s obligations to pay royalties, whichever is later, unless terminated earlier. The agreement can be terminated by the Company, Mayo or VGL upon 60 days’ notice of a party’s material breach if such breach remains uncured after such 60-day period. Per the terms of the license, the Company is required to pay royalties based on the greater of earned royalties or a minimum royalty. The earned royalty is based on a percentage of net sales of licensed products either by the Company or the sub-licensee. The minimum royalty payment is 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. Per terms of the license, the Company is required to: • Pay a retainer fee of $40,000 per annum starting March 2011 and ending on February 2013; and • Pay royalties based on the greater of earned royalties or a minimum royalty. The earned royalties are 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. The Company recognized royalty expense during the periods indicated as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Royalty expense $ 829 $ 795 $ 2,259 $ 2,280 Contingent Consideration In February 2019, the Company entered into an agreement with a privately-held company to, among other things, provide financing in the form of a secured convertible note. The Company has the obligation to provide additional funding of up to $2.0 million and, under certain circumstances as described below, $3.0 million, respectively, in the form of two separate additional secured convertible notes. The Company expects the first obligation of up to $2.0 million to occur within twelve months of September 30, 2019. The second obligation of up to $3.0 million takes effect only after the Company exercises its option to make a further investment in the privately-held company that is based on certain development targets. The agreement additionally provides the Company with the exclusive right, but not the obligation, to acquire the privately-held company. As of September 30, 2019, the value of the secured convertible note, measured at amortized cost, is $5.7 million, while the value of certain rights in relation to the agreement, measured at cost and monitored for impairment on an ongoing basis, is $1.0 million. These amounts are reported in Other Assets on the Condensed Consolidated Balance Sheet. The accretion of amortized cost is recorded in Interest Income, while any changes in value from impairment assessment are recorded in Other Income (Expense) in the Consolidated Statements of Operations and Comprehensive Income. The Company concluded that the privately-held company is a variable interest entity, however the Company is not the primary beneficiary as it does not retain power to direct the activities that most significantly impact its economic performance. Contingencies From time to time, the Company may have certain contingent liabilities that arise in the ordinary course of business activities related to, for example, employment matters and patent issues. 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 were no contingent liabilities requiring accrual at September 30, 2019 and December 31, 2018. 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 applicabl e insurance coverage is minimal. 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 U.S. District Court for the Northern District of California (the Court), asserts that Boston Scientific is infringing seven of 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 July 24, 2018, the Court issued an order on claim construction and summary judgment. In the order, the Court ruled that six asserted method claims in three of the Company’s asserted patents were patent eligible and not invalid as indefinite. Specifically, the claims upheld in the ruling were claims 11, 21 and 23 of U.S. Patent No. 8,359,102; claim 18 of U.S. Patent No. 8,792,988; and claims 1 and 5 of U.S. Patent No. 8,768,472. Collectively, these six claims cover methods for delivering SCS therapy at frequencies between 1.5 kHz and 100 kHz. The Court, however, found that Boston Scientific is not currently infringing the six upheld method claims. Specifically, the Court found that Boston Scientific's sale of the Spectra WaveWriter systems for commercial use in the United States does not infringe the upheld method claims because the Spectra WaveWriter systems cannot be programmed to generate signals above 1.2 kHz. With regard to the use of the Spectra WaveWriter and the Precision with MultiWave systems in patients that have completed the ACCELERATE clinical trial, the Court found such use to fall within the safe harbor provision of 35 U.S.C. § 271(e). The Court further held that 35 U.S.C. § 271(f) does not apply to method claims, and therefore the sale of the Precision with MultiWave systems in Europe does not infringe the upheld method claims. The Court also found that the asserted system claims in four of the Company's asserted patents were invalid as indefinite. Specifically, the Court invalidated claims 18, 34, and 55 of U.S. Patent No. 9,327,125; claims 5 and 34 of U.S. Patent No. 9,333,357; claims 7, 12, 35, 37, and 58 of U.S. Patent No. 8,712,533; and claims 1 and 22 of U.S. Patent No. 9,480,842. On July 27, 2018, the parties submitted a joint statement to the Court wherein Boston Scientific asserted to the Court that, with respect to whether any U.S. launch of a high-rate product (such as the Precision with MultiWave and Spectra WaveWriter models used in the ACCELERATE study or any other system that is programmable at any frequency in the range 1.5 to 100 kHz) is imminent, Boston Scientific, as of now, has not decided whether to launch such a product; has not established a timeline for when such a decision might be made, if ever; and has not determined what frequencies would be enabled if it were to decide to launch such a product in the future. Boston Scientific further confirmed its public statements that the ACCELERATE study has been extended into 2019, with an estimated study completion date between April 2019 and November 2019. On the basis of the foregoing, the parties agreed to dismissal on ripeness grounds of Nevro’s declaratory judgment claims without prejudice, each side to bear its own fees and costs as to these claims, and jointly requested that the Court enter such a dismissal. The dismissal was thereafter entered as a court order on July 31, 2018. The Company and Boston Scientific are each appealing portions of the Court’s July 24 th On December 9, 2016, Boston Scientific filed a patent infringement lawsuit alleging the Company’s manufacture, use and sale of the Senza system infringes ten of Boston Scientific’s patents covering spinal cord stimulation technology related to stimulation leads, rechargeable batteries and telemetry. The lawsuit, filed in the U.S. 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. During this litigation, Boston Scientific unilaterally dismissed their assertions with regard to two of the ten patents. inter partes inter partes On April 27, 2018, Boston Scientific filed a second patent lawsuit alleging patent infringement, theft of trade secrets and tortious interference with contract. The lawsuit, filed in the U.S. 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. In relation to this lawsuit, the Company filed petitions for inter partes On August 23, 2018, the Oklahoma Police Pension and Retirement System filed a putative securities class action complaint against the Company and certain individual officers alleging violations of Sections 10(b) and 20(a) of the Exchange Act, and Rule 10b-5 of the Exchange Act. The lawsuit, filed in the U.S. District Court for the Northern District of California, seeks unspecified damages and attorneys’ fees based on alleged misleading statements or omissions by the Company and the individual officers regarding the Company’s rights in technology underlying the Senza SCS systems and the termination of the Company’s former Vice President of Worldwide Sales. On November 3, 2018, a related shareholder derivative lawsuit was filed in the United States District Court for the Northern District of California seeking unspecified damages, injunctive relief and attorneys’ fees based on alleged violations of Section 14(a) of the Securities and Exchange Act of 1934, breach of fiduciary duties, unjust enrichment and waste of corporate assets. On August 1, 2019, U.S. District Judge Vince Chhabria granted the Company’s motion to dismiss the pending securities class action complaint, with leave to file an amended complaint within 21 days of the order. The plaintiffs did not file an amended complaint, and on August 23, 2019, the securities class action was dismissed. On September 6, 2019, the related shareholder derivative lawsuit was voluntarily dismissed On February 14 2019, the Company filed a lawsuit for patent infringement against Stimwave Technologies, Inc. (Stimwave) asserting that Stimwave is infringing the Company’s patents covering inventions related to its HF10 therapy and the Senza system, as well as a claim for false advertising under the Lanham Action Section 43(a), 15 U.S.C. § 1125(a). In relation to this lawsuit, on July 24, 2019, the court granted Nevro's motion for preliminary injunction, and has issued an order barring Stimwave, and all affiliated persons and entities, from infringing patent claims covering frequencies between 3 kHz and 10 kHz by programming Stimwave's SCS systems to deliver its recently introduced high-frequency, paresthesia-free SCS therapy. Per Nevro's request, the court order does not enjoin Stimwave from providing follow-up care and programming for any patients who were already programmed with such high frequency therapy. On July 25, 2019, Stimwave filed a Notice of Appeal to the U.S. Court of Appeals for the Federal Circuit. During the appeal, the litigation in the District of Delaware will continue on the merits. As of September 30, 2019, the Company did not record a liability, as an outcome or potential loss range cannot be reasonably determined The Company is and may from time to time continue to be involved in various legal proceedings to defend its intellectual property, including several pending European patent oppositions at the European Patent Office (EPO) initiated by the Company’s competitors Medtronic and Boston Scientific and an entitlement action filed by Boston Scientific in Germany. In addition, the Company is and may from time to time also be involved in various legal proceedings of a character normally incident to the ordinary course of business, such as product liability and professional liability matters, 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	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Long-term Debt	7. 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. 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. 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 September 30 , 2019 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 December 3 1 , 2019 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 September 30 , 2019 , 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. The net carrying amount of the liability component of the 2021 Notes was as follows (in thousands): September 30, December 31, 2019 2018 Principal $ 172,500 $ 172,500 Unamortized discount (12,208 ) (17,305 ) Unamortized issuance cost (2,014 ) (2,801 ) Net carrying amount $ 158,278 $ 152,394 The net carrying amount of the equity component of the 2021 Notes was as follows (in thousands): September 30, December 31, 2019 2018 Debt discount related to value of conversion option $ 32,945 $ 32,945 Debt issuance cost (1,179 ) (1,179 ) Net carrying amount $ 31,766 $ 31,766 The following table sets forth the interest expense recognized related to the 2021 Notes (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Contractual interest expense $ 754 $ 755 $ 2,264 $ 2,265 Amortization of debt discount 1,728 1,625 5,097 4,791 Amortization of debt issuance costs 272 240 787 697 Total interest expense related to the 2021 Notes $ 2,754 $ 2,620 $ 8,148 $ 7,753 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.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Loss Per Share	8. Net Loss Per Share The following table summarizes the computation of basic and diluted net loss per share (in thousands, except share and per share data): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Net loss, basic and diluted $ (17,847 ) $ (11,265 ) $ (89,944 ) $ (39,598 ) Weighted average shares used to compute basic and diluted net loss per share 30,929,938 30,123,188 30,659,117 29,997,201 Net loss per share, basic and diluted $ (0.58 ) $ (0.37 ) $ (2.93 ) $ (1.32 ) Basic net loss per share is computed by dividing the net loss by the weighted average number of common shares outstanding for the period. Diluted net loss per share is computed by dividing the net loss by the weighted average number of common shares and dilutive common stock equivalents outstanding for the period, if inclusion of these is dilutive. 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 September 30, 2019. In connection with the issuance of the 2021 Notes, the Company entered into convertible bond hedges. The convertible bond hedges are not included for purposes of calculating the number of diluted shares outstanding, as their effect would be anti-dilutive. The convertible bond hedges are generally expected, but not guaranteed, to reduce the potential dilution and/or offset the cash payments the Company is required to make upon conversion of the 2021 Notes. 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, as the effect would be anti-dilutive: September 30, 2019 2018 Unreleased restricted stock 1,417,636 935,916 Options to purchase common stock 2,092,433 2,355,039 Convertible senior notes 1,790,033 1,790,033 Warrants related to the issuance of convertible senior notes 1,790,033 1,790,033 Total 7,090,135 6,871,021

Employee Benefit Plans

Employee Benefit Plans	9 Months Ended
	Sep. 30, 2019
Postemployment Benefits [Abstract]
Employee Benefit Plans	9. Employee Benefit Plans 401(k) 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. 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. The Company recorded an expense for matching contributions of and $0.3 million and $2.9 million for the three and nine months ended September 30, 2019, respectively, and $0.3 million and $2.4 million for the three and nine months ended September 30, 2018, respectively. Employee Stock Purchase Plan The Company’s 2014 Employee Stock Purchase Plan (ESPP) allows eligible employees to purchase shares of the Company’s Class A common stock at a discount through payroll deductions of up to 15% of their eligible compensation, subject to any plan limitations. The ESPP generally provides for six-month offering periods, and at the end of each offering period, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s Class A common stock on the first trading day of the offering period or on the last trading day of the offering period. There were zero and 119,393 shares of common stock issued under the ESPP for the three and nine months ended September 30, 2019. There were zero and 53,824 shares of common stock issued under the ESPP for the three and nine months ended September 30, 2018. Shares available for future purchase under the ESPP were 1,207,212 at September 30, 2019.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation These condensed consolidated financial statements have been prepared in accordance with U.S. GAAP. The condensed consolidated financial statements include the Company’s accounts and those of its 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 by information about revenue by geographic region, for purposes of allocating resources and evaluating financial performance. 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. Revenue by geography is based on the billing address of the customer. The United States was the only country with revenue accounting for more than 10% of the total revenue in any of the periods presented, as follows: Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 United States 84 % 83 % 83 % 82 % Long-lived assets and operating income located outside the United States 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) on 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. Additionally, realized gains and losses resulting from transactions denominated in currencies other than the local currency are recorded in other income (expense), net in the condensed consolidated statements of operations and comprehensive loss. The Company recorded net unrealized and net realized foreign currency transaction gains (losses) during the periods presented as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Net unrealized foreign currency gain (loss) $ 190 $ (6 ) $ 690 $ (892 ) Net realized foreign currency gain (loss) (459 ) (75 ) (1,086 ) 217 As the Company’s international operations grow, its risks associated with 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 USD 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 U.S. GAAP requires management to make estimates and assumptions that affect the amounts reported in the condensed consolidated financial statements and accompanying notes. Significant accounting estimates and management judgments reflected in the condensed consolidated financial statements include items such as allowances for doubtful accounts; warranty obligations; clinical accruals; stock-based compensation; depreciation and amortization periods; inventory valuation; valuation of investments; and accounting for income taxes. 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 and is in excess of federally insured limits. The Company maintained investments in money market funds that were not federally insured during the periods ended September 30, 2019 and December 31, 2018. The Company also held cash in foreign banks of approximately $8.9 million at September 30, 2019 and $4.1 million at December 31, 2018 that was not federally insured. The Company has not experienced any losses on its deposits of cash and cash equivalents. The Company’s convertible note hedge transactions, entered into in connection with the 2021 Notes, subject the Company to credit risk such that the counterparties may be unable to fulfill the terms of the transactions. The associated risk is mitigated by limiting the counterparties to major financial institutions. In the international markets in which the Company participates, the Company uses a combination of a direct sales force , sales agents and independent 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. During the three and nine months ended September 30, 2019 and 2018, no single customer accounted for 10% 10% 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, manufacturing quality and scaling, continued reimbursement from third-party payors, There can be no assurance that the Company’s products or services will continue to be accepted in its existing marketplaces, 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 may choose to raise additional funds to further enhance its research and development efforts, for product expansion opportunities or to acquire a new business or products that are complementary to its business. 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 The 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 $17.3 million and $15.6 million as of September 30, 2019 and December 31, 2018, respectively. At September 30, 2019 and December 31, 2018, the Company’s cash equivalents were held at institutions in the United States and include deposits in a money market fund which was unrestricted as to withdrawal or use.
Restricted Cash	Restricted Cash Restricted cash as of September 30, 2019 and December 31, 2018 consists of a letter of credit of $0.6 million representing collateral for the Company’s Redwood City, California building lease pursuant to an agreement dated March 5, 2015. Restricted cash as of September 30, 2019 additionally includes certificates of deposit of $0.4 million, representing collateral for charges related to certain of the Company’s credit cards.
Investment Securities	Investment Securities The Company classifies its investment securities as available-for-sale. 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 at the date of purchase are also classified as short-term investments as management considers them to be available for current operations if needed. The Company’s investment securities classified as available-for-sale are recorded at fair value. Unrealized gains and losses, deemed temporary in nature, are reported as a separate component of accumulated 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 net realizable value of such inventory. Cost is determined using the standard cost method which approximates the first-in, first-out basis. Net realizable value is determined as the estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. 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 writes down inventory that has become obsolete, inventory that has a cost basis in excess of its expected net realizable value, and inventory that is 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 amounts over demand using the same lower of cost or net realizable value approach that has been used to value inventory. The Company also periodically evaluates inventory quantities in consideration of actual loss experience. In addition, the Company determines at times that there may be certain inventory that does not meet its product requirements. As a result of these evaluations, the Company recognized total write-downs of $0.4 million and $0.5 million for the three months ended September 30, 2019 and 2018, respectively, and $4.5 million and $0.9 million for the nine months ended September 30, 2019 and 2018, respectively. The total write-down for the nine months ended September 30, 2019 included $3.6 million related to an excess raw material charge. The Company’s estimation of the future demand for any given particular component of the Senza product may vary and may result in changes in estimates of inventory values in any particular period.
Shipping and Handling Costs	Shipping and Handling Costs The Company has made the accounting policy election under ASC 606 to account for shipping and handling costs as a fulfillment activity. These costs are accrued when the related revenue is recognized.
Revenue Recognition	Revenue Recognition Revenue is recognized when obligations under the terms of a contract with customers are satisfied, which occurs with the transfer of control of the Company’s goods to its customers. Revenue is measured as the amount of consideration the Company expects to receive in exchange for transferring the goods. 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 the point in time when control transfers to the customers. 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, the transfer of control occurs at the time of shipment of the product. These 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. Sales, value add, and other taxes the Company collects concurrent with revenue-producing activities are excluded from revenue. The expected costs associated with warranty obligations continue to be recognized as expense when the products are sold (see Note 6). The Company periodically provides incentive offers, in the form of rebates, to customers based on their aggregate levels of purchases. 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 provides a limited one- to five-year warranty 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 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 September 30, 2019.
Income Taxes	Income Taxes During the three and nine months ended September 30, 2019 and 2018, the Company calculated its interim tax provision to record taxes incurred on a discrete basis due to the variability of taxable income in the jurisdictions in which it operates. The provision for income taxes for the three and nine months ended September 30, 2019 and 2018 is primarily comprised of foreign and state taxes based upon income earned during the period with no tax benefit recorded for the loss jurisdiction. 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. A nominal amount of interest and penalties have been recognized for the three and nine months ended September 30, 2019. No interest or penalties related to income taxes have been recognized in the statements of operations and comprehensive loss for the three and nine months ended September 30, 2018.
Other Comprehensive Income (Loss)	Other Comprehensive Income (Loss) Other comprehensive income (loss) represents all changes in the stockholders’ equity except those resulting from distributions to stockholders. The Company’s changes in unrealized gains and losses on 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 have been presented in the consolidated statements of operations and comprehensive loss.
Research and Development	Research and Development Research and development costs, 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, 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. In March 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-09, Stock Compensation (Topic 718): Improvements to Employee Shared-Based Payment Accounting , which the Company adopted on January 1, 2017. Under ASU 2016-09, entities are permitted to make an accounting policy election to either estim ate forfeitures on share-based payment awards, as previously required, or to recognize forfeitures as they occur. The Company has elected to continue to estimate forfeitures expected to occur to determine the amount of compensation cost recognized in each period. ASU 2016-09 also requires that entities recognize, on a prospective basis, all excess tax benefits and tax deficiencies as income tax expense or benefit in the income statement as discrete items in the reporting period in which they occur. The adoption did not result in a cumulative-effect adjustment to accumulated deficit as of January 1, 2017 using the modified retrospective method. Additionally, under ASU 2016-09, excess tax benefits are classified as an operating activity in the statement of cash flows. The Company has elected the presentation of excess tax benefits in the statement of cash flows using the prospective transition method. 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. Changes in the assumptions can materially affect the fair value and ultimately how much stock-based compensation expense is recognized. 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. 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 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 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 also issues stock options and restricted stock units with vesting based upon completion of performance goals. The fair value for these performance-based awards is recognized over the period during which the goals are to be achieved. Stock-based compensation expense recognized at fair value includes the impact of estimated probability that the goals would be achieved, which is assessed prior to the requisite service period for the specific goals. In March 2019, the Company granted performance stock units (PSUs) to the Company’s Chief Executive Officer. The PSUs are subject to continued service to the Company through the vesting date. The number of shares to be issued upon vesting are based on the total shareholder return of the Company’s common stock compared to the S&P Healthcare Equipment Select Industry Index (the Index), subject to an upward adjustment based on the Company’s absolute stock price performance over the specified measurement period. If the performance metrics are not met within the specified time limits, the PSUs will be canceled. The fair value of the PSUs is determined on the date of grant using a Monte Carlo simulation model, which is based on a larger number of possible stock price outcomes for the Company’s stock and the Index. The use of the Monte Carlo simulation model requires the input of certain assumptions, including the expected stock price volatility of the Company and members of the Index, correlation between changes in the stock price of the Company and members of the Index, risk-free interest rate and expected dividends, as applicable. The fair value of the PSUs is recognized over the specified measurement period on a straight-line basis. Upon adoption of ASU 2016-09 as described above, excess tax benefits or deficiencies from share-based award activity are reflected in the consolidated statements of operations as a component of the provision for income taxes, whereas they were previously recognized as additional paid-in capital.
Net Loss per Share of Common Stock	Net Loss per Share of Common Stock Basic net loss per common share is calculated by dividing net loss 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 net loss 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, the Company’s restricted stock units and options to purchase shares of common stock 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 June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments The FASB has also issued several updates to ASU No. 2016-13. The Company has not determined the potential effects of the guidance on its consolidated financial statements
Adoption of ASC 842	Adoption of ASC 842 On January 1, 2019, the Company adopted the new accounting standard ASC 842, Leases The Company adopted the new lease standard using the transition method that allowed entities to initially apply ASC 842 at the adoption date and recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption (the optional transition method). The Company elected the package of transitional practical expedients, such that, for leases existing prior to the adoption of ASC 842, the Company will not need to reassess whether contracts are leases, will retain historical lease classification and historical initial direct costs classification. The Company also elected the hindsight practical expedient to determine the lease term for existing leases. Operating lease assets and operating lease liabilities are recognized based on the present value of minimum lease payments over the remaining lease term. The Company uses its incremental borrowing rate based on information available when determining the lease liabilities. Lease cost is recognized on a straight-line basis over the expected lease term.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Schedule of Revenue by Major Customers by Geographic Area	The United States was the only country with revenue accounting for more than 10% of the total revenue in any of the periods presented, as follows: Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 United States 84 % 83 % 83 % 82 %
Net Unrealized and Net Realized Foreign Currency Transaction Gains (Losses)	The Company recorded net unrealized and net realized foreign currency transaction gains (losses) during the periods presented as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Net unrealized foreign currency gain (loss) $ 190 $ (6 ) $ 690 $ (892 ) Net realized foreign currency gain (loss) (459 ) (75 ) (1,086 ) 217

Lease Accounting (Tables)

Lease Accounting (Tables)	9 Months Ended
	Sep. 30, 2019
Schedule of Weighted Average Lease Terms and Discounts Rates	The weighted average lease terms and discounts rates are as follows: September 30, 2019 Operating Lease Term and Discount Rate Weighted-average remaining lease term 5.56 years Weighted-average discount rate 7.0%
Schedule of Maturity of Lease Liabilities	As of September 30, 2019, t he maturity of lease liabilities are as follows (in thousands): Operating Leases 2019, remaining months $ 1,213 2020 4,924 2021 5,073 2022 5,258 2023 5,522 Thereafter 8,086 Total lease payments 30,076 Less: Interest (5,342 ) Present value of lease liabilities $ 24,734
Supplemental Lease Cost Information	Supplemental lease cost information are as follows (in thousands): Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Operating lease cost $ 1,239 $ 3,807
Schedule Of Operating Lease Assets and Liabilities	Supplemental balance sheet information are as follows (in thousands): September 30, 2019 Operating Leases: Operating lease assets $ 22,348 Other current liabilities $ 3,410 Long term operating lease liabilities 21,324 Total operating lease liabilities $ 24,734
Schedule of Supplemental Cash Flow Information Related to Lease	Supplemental cash flow information are as follows (in thousands): Three Months Ended Nine Months Ended September 30, 2019 September 30, 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flow from operating leases $ 1,010 $ 2,809
ASC 842 [Member]
Schedule of Impact of Changes Made to the Consolidated Balance Sheet from the Adoption of ASC 842	Adoption of the new lease standard resulted in the recording of operating lease assets of $24.8 million and operating lease liabilities of $26.2 million. The impact of the changes made to the consolidated balance sheet as of January 1, 2019 from the adoption of ASC 842 were as follows (in thousands): Balance at Adjustments Due Balance at December 31, 2018 to ASC 842 January 1, 2019 Balance Sheet: Operating lease assets $ — $ 24,771 $ 24,771 Other current liabilities 119 2,389 2,508 Long-term operating lease liabilities — 23,805 23,805 Other long-term liabilities 2,825 (1,423 ) 1,402

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2019
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 September 30, 2019 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 17,279 $ — $ — $ 17,279 Agency bonds (iii) — 12,964 — 12,964 Commercial paper (ii) — 54,047 — 54,047 Corporate notes (iii) — 129,653 — 129,653 Total assets $ 17,279 $ 196,664 $ — $ 213,943 Balance as of December 31, 2018 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 15,572 $ — $ — $ 15,572 Commercial paper (ii) — 119,602 — 119,602 Corporate notes (ii) — 111,532 — 111,532 Total assets $ 15,572 $ 231,134 $ — $ 246,706 (i) Included in cash and cash equivalents on the condensed consolidated balance sheets. (i i ) Included in cash and cash equivalents or short-term investments on the condensed consolidated balance sheets. (iii) Included in short-term investments on the condensed consolidated balance sheets.

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2019
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, excluding investments in money market funds (in thousands): September 30, 2019 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Agency bonds $ 12,952 $ 12 $ — $ 12,964 Commercial paper (i) 53,996 51 — 54,047 Corporate notes 129,342 311 — 129,653 Total securities $ 196,290 $ 374 $ — $ 196,664 December 31, 2018 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Commercial paper (ii) $ 119,692 $ — $ (90 ) $ 119,602 Corporate notes (ii) 111,652 — (120 ) 111,532 Total securities $ 231,344 $ — $ (210 ) $ 231,134 (i) Includes $13.2 million of commercial paper that is classified as cash and cash equivalents on the condensed consolidated balance sheets. (ii) Includes $15.8 million of commercial paper and $2.0 million of corporate notes that are classified as cash and cash equivalents on the condensed consolidated balance sheets.
Summary of Contractual Maturities of Investment Securities	The contractual maturities of the Company’s investment securities as of September 30, 2019 were as follows (in thousands): Amortized Cost Fair Value Amounts maturing within one year $ 163,797 $ 164,135 Amounts maturing after one year through five years 32,493 32,529 Total investment securities $ 196,290 $ 196,664
Components of Inventories	Inventories (in thousands) September 30, December 31, 2019 2018 Raw materials $ 32,442 $ 37,453 Finished goods 58,288 54,582 Total inventories $ 90,730 $ 92,035
Schedule of Property and Equipment, Net and Depreciation and Amortization Expense	Property and Equipment, Net (in thousands) September 30, December 31, 2019 2018 Laboratory equipment $ 3,587 $ 2,874 Computer equipment and software 9,691 8,751 Furniture and fixtures 3,978 3,903 Leasehold improvements 4,218 4,218 Construction in process 2,309 1,811 Total 23,783 21,557 Less: Accumulated depreciation and amortization (12,062 ) (8,756 ) Property and equipment, net $ 11,721 $ 12,801 The Company recognized depreciation and amortization expense on property and equipment as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Depreciation and amortization expense $ 1,112 $ 1,078 $ 3,306 $ 2,845
Summary of Accrued Liabilities	Accrued Liabilities (in thousands) September 30, December 31, 2019 2018 Accrued payroll and related expenses $ 28,521 $ 26,792 Accrued professional fees 1,677 1,595 Accrued taxes 2,257 2,506 Accrued clinical and research expenses 1,958 1,105 Accrued interest 998 243 Accrued warranty 1,216 1,236 Inventory related liabilities 1,732 790 Accrued other 6,689 4,523 Total accrued liabilities $ 45,048 $ 38,790

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Schedule of Activities Related to Warranty Obligations	Activities related to warranty obligations were as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Beginning balance $ 1,291 $ 943 $ 1,236 $ 708 Provision for warranty 490 597 1,426 1,681 Utilization (565 ) (447 ) (1,446 ) (1,296 ) Ending balance $ 1,216 $ 1,093 $ 1,216 $ 1,093
Summary of Royalty Expense	The Company recognized royalty expense during the periods indicated as follows (in thousands): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Royalty expense $ 829 $ 795 $ 2,259 $ 2,280

Long-term Debt (Tables)

Long-term Debt (Tables)	9 Months Ended
	Sep. 30, 2019
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): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Contractual interest expense $ 754 $ 755 $ 2,264 $ 2,265 Amortization of debt discount 1,728 1,625 5,097 4,791 Amortization of debt issuance costs 272 240 787 697 Total interest expense related to the 2021 Notes $ 2,754 $ 2,620 $ 8,148 $ 7,753
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): September 30, December 31, 2019 2018 Principal $ 172,500 $ 172,500 Unamortized discount (12,208 ) (17,305 ) Unamortized issuance cost (2,014 ) (2,801 ) Net carrying amount $ 158,278 $ 152,394
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): September 30, December 31, 2019 2018 Debt discount related to value of conversion option $ 32,945 $ 32,945 Debt issuance cost (1,179 ) (1,179 ) Net carrying amount $ 31,766 $ 31,766

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss per Share	The following table summarizes the computation of basic and diluted net loss per share (in thousands, except share and per share data): Three Months Ended Nine Months Ended September 30, September 30, 2019 2018 2019 2018 Net loss, basic and diluted $ (17,847 ) $ (11,265 ) $ (89,944 ) $ (39,598 ) Weighted average shares used to compute basic and diluted net loss per share 30,929,938 30,123,188 30,659,117 29,997,201 Net loss per share, basic and diluted $ (0.58 ) $ (0.37 ) $ (2.93 ) $ (1.32 )
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, as the effect would be anti-dilutive: September 30, 2019 2018 Unreleased restricted stock 1,417,636 935,916 Options to purchase common stock 2,092,433 2,355,039 Convertible senior notes 1,790,033 1,790,033 Warrants related to the issuance of convertible senior notes 1,790,033 1,790,033 Total 7,090,135 6,871,021

Formation and Business of the_2

Formation and Business of the Company - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended						9 Months Ended		12 Months Ended
	Jun. 30, 2016	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Formation and Business of the Company [Line Items]
Net loss		$ 17,847	$ 28,021	$ 44,076	$ 11,265	$ 10,620	$ 17,713	$ 89,944	$ 39,598	$ 49,200
Cash used in operations								36,750	$ 10,708	5,700
Accumulated deficit		$ 396,026						$ 396,026		$ 306,082
1.75% Convertible Senior Notes due 2021 [Member]
Formation and Business of the Company [Line Items]
Debt instrument due year	2021							2021		2021

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jun. 30, 2016	Sep. 30, 2019USD ($)Customer	Sep. 30, 2018USD ($)Customer	Sep. 30, 2019USD ($)BusinessCustomer	Sep. 30, 2018USD ($)Customer	Dec. 31, 2018USD ($)Customer
Summary Of Significant Accounting Policies [Line Items]
Number of business activities | Business				1
Cash held in foreign banks		$ 8,900,000		$ 8,900,000		$ 4,100,000
Money market funds		17,300,000		17,300,000		15,600,000
Restricted cash		956,000		956,000		606,000
Write down of inventory		400,000	$ 500,000	4,500,000	$ 900,000
Excess raw material charge				$ 3,600,000
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
Certificates of Deposit [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash		400,000		$ 400,000
Letter of Credit [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash		$ 600,000		$ 600,000		$ 600,000
Customer Concentration Risk [Member] | Revenue [Member]
Summary Of Significant Accounting Policies [Line Items]
Concentration risk, percentage		10.00%	10.00%	10.00%	10.00%
Number of customers accounted 10% or more concentration risk | Customer		0	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 10% or more concentration risk | Customer				0		0
1.75% Convertible Senior Notes due 2021 [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt instrument due year	2021			2021		2021

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Revenue by Major Customers by Geographic Area (Detail)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Revenue [Member] | Geographic Concentration Risk [Member] | United States [Member]
Concentration Risk [Line Items]
Revenue	84.00%	83.00%	83.00%	82.00%

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Net Unrealized and Net Realized Foreign Currency Transaction Gains (Losses) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Accounting Policies [Abstract]
Net unrealized foreign currency gain (loss)	$ 190	$ (6)	$ 690	$ (892)
Net realized foreign currency gain (loss)	$ (459)	$ (75)	$ (1,086)	$ 217

Lease Accounting - Additional I

Lease Accounting - Additional Information (Detail) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Jan. 01, 2019
Lessee Lease Description [Line Items]
Operating lease assets	$ 22,348
Operating lease liabilities	24,734
ASC 842 [Member]
Lessee Lease Description [Line Items]
Operating lease assets	24,800	$ 24,771
Operating lease liabilities	$ 26,200
Existence of option to extend the lease	true
Option to extend the lease term, description	As of September 30, 2019, the Company has leases with remaining terms of less than 1 year to 6 years, some of which may include options to extend the lease term for up to 5 years.
ASC 842 [Member] | Minimum [Member]
Lessee Lease Description [Line Items]
Lease term	12 months
Operating lease, remaining term	1 year
ASC 842 [Member] | Maximum [Member]
Lessee Lease Description [Line Items]
Operating lease, remaining term	6 years
Options to extend the lease term	5 years

Lease Accounting - Schedule of

Lease Accounting - Schedule of Impact of Changes Made to the Consolidated Balance Sheet from the Adoption of ASC 842 (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jan. 01, 2019	Dec. 31, 2018
Lessee Lease Description [Line Items]
Operating lease assets	$ 22,348
Other current liabilities	3,509		$ 119
Long-term operating lease liabilities	21,324
Other long-term liabilities	1,712		$ 2,825
ASC 842 [Member]
Lessee Lease Description [Line Items]
Operating lease assets	$ 24,800	$ 24,771
Other current liabilities		2,508
Long-term operating lease liabilities		23,805
Other long-term liabilities		1,402
ASC 842 [Member] | Adjustments due to ASC 842 [Member]
Lessee Lease Description [Line Items]
Operating lease assets		24,771
Other current liabilities		2,389
Long-term operating lease liabilities		23,805
Other long-term liabilities		$ (1,423)

Lease Accounting - Schedule o_2

Lease Accounting - Schedule of Weighted Average Lease Terms and Discounts Rates (Detail)	Sep. 30, 2019
Leases [Abstract]
Weighted-average remaining lease term	5 years 6 months 21 days
Weighted-average discount rate	7.00%

Lease Accounting - Schedule o_3

Lease Accounting - Schedule of Maturity of Lease Liabilities (Detail) $ in Thousands	Sep. 30, 2019USD ($)
Leases [Abstract]
2019, remaining months	$ 1,213
2020	4,924
2021	5,073
2022	5,258
2023	5,522
Thereafter	8,086
Total lease payments	30,076
Less: Interest	(5,342)
Present value of lease liabilities	$ 24,734

Lease Accounting - Supplemental

Lease Accounting - Supplemental Lease Cost Information (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Leases [Abstract]
Operating lease cost	$ 1,239	$ 3,807

Lease Accounting - Summary of O

Lease Accounting - Summary of Operating Lease Assets and Liabilities (Detail) $ in Thousands	Sep. 30, 2019USD ($)
Operating Leases:
Operating lease assets	$ 22,348
Other current liabilities	3,410
Long term operating lease liabilities	21,324
Total operating lease liabilities	$ 24,734

Lease Accounting - Schedule o_4

Lease Accounting - Schedule of Supplemental Cash Flow Information Related to Lease (Detail) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flow from operating leases	$ 1,010	$ 2,809

Fair Value Measurements - Finan

Fair Value Measurements - Financial Instruments Measured at Fair Value on Recurring Basis (Detail) - Fair Value Measurements Recurring [Member] - USD ($) $ in Thousands		Sep. 30, 2019		Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		$ 213,943		$ 246,706
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		17,279		15,572
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		196,664		231,134
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[1]	17,279		15,572
Money Market Funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[1]	17,279		15,572
Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[2]	12,964
Agency Bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[2]	12,964
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[3]	54,047		119,602
Commercial Paper [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[3]	54,047		119,602
Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		129,653	[2]	111,532	[3]
Corporate Notes [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		$ 129,653	[2]	$ 111,532	[3]
[1]	Included in cash and cash equivalents on the condensed consolidated balance sheets.
[2]	Included in short-term investments on the condensed consolidated balance sheets.
[3]	Included in cash and cash equivalents or short-term investments on the condensed consolidated balance sheets.

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Detail) - 1.75% Convertible Senior Notes due 2021 [Member] - USD ($) $ in Millions	1 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2016	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate	1.75%	1.75%	1.75%
Debt instrument due year	2021	2021	2021
Fair value of notes		$ 197.5	$ 160.5

Balance Sheet Components - Summ

Balance Sheet Components - Summary of Gross Unrealized Gains and Unrealized Losses of Investment Securities Excluding Investments in Money Market Funds (Detail) - USD ($) $ in Thousands		Sep. 30, 2019		Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 196,290		$ 231,344
Gross Unrealized Holding Gains		374
Gross Unrealized Holding Losses				(210)
Aggregate Fair Value		196,664		231,134
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		12,952
Gross Unrealized Holding Gains		12
Aggregate Fair Value		12,964
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		53,996	[1]	119,692	[2]
Gross Unrealized Holding Gains	[1]	51
Gross Unrealized Holding Losses	[2]			(90)
Aggregate Fair Value		54,047	[1]	119,602	[2]
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		129,342		111,652	[2]
Gross Unrealized Holding Gains		311
Gross Unrealized Holding Losses	[2]			(120)
Aggregate Fair Value		$ 129,653		$ 111,532	[2]
[1]	Includes $13.2 million of commercial paper that is classified as cash and cash equivalents on the condensed consolidated balance sheets.
[2]	Includes $15.8 million of commercial paper and $2.0 million of corporate notes that are classified as cash and cash equivalents on the condensed consolidated balance sheets.

Balance Sheet Components - Su_2

Balance Sheet Components - Summary of Gross Unrealized Gains and Unrealized Losses of Investment Securities Excluding Investments in Money Market Funds (Parenthetical) (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	$ 49,338	$ 51,266
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	$ 13,200	15,800
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents		$ 2,000

Balance Sheet Components - Su_3

Balance Sheet Components - Summary of Contractual Maturities of Investment Securities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Investments Debt And Equity Securities [Abstract]
Amortized Cost, Amounts maturing within one year	$ 163,797
Amortized Cost, Amounts maturing after one year through five years	32,493
Amortized Cost	196,290	$ 231,344
Fair Value, Amounts maturing within one year	164,135
Fair Value, Amounts maturing after one year through five years	32,529
Fair Value, Total investment securities	$ 196,664	$ 231,134

Balance Sheet Components - Comp

Balance Sheet Components - Components of Inventories (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Inventory Disclosure [Abstract]
Raw materials	$ 32,442	$ 37,453
Finished goods	58,288	54,582
Total inventories	$ 90,730	$ 92,035

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 23,783	$ 21,557
Less: Accumulated depreciation and amortization	(12,062)	(8,756)
Property and equipment, net	11,721	12,801
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,587	2,874
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	9,691	8,751
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,978	3,903
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,218	4,218
Construction in Process [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,309	$ 1,811

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Property and Equipment, Depreciation and Amortization Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 1,112	$ 1,078	$ 3,306	$ 2,845

Balance Sheet Components - Su_4

Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Dec. 31, 2017
Payables And Accruals [Abstract]
Accrued payroll and related expenses	$ 28,521		$ 26,792
Accrued professional fees	1,677		1,595
Accrued taxes	2,257		2,506
Accrued clinical and research expenses	1,958		1,105
Accrued interest	998		243
Accrued warranty	1,216	$ 1,291	1,236	$ 1,093	$ 943	$ 708
Inventory related liabilities	1,732		790
Accrued other	6,689		4,523
Total accrued liabilities	$ 45,048		$ 38,790

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)

Aug. 01, 2019

Feb. 28, 2019USD ($)ConvertibleNote

Apr. 30, 2017

Dec. 31, 2016USD ($)ft²

Mar. 31, 2015USD ($)ft²

Sep. 30, 2019USD ($)

Sep. 30, 2018USD ($)

Sep. 30, 2019USD ($)

Sep. 30, 2018USD ($)

Mar. 31, 2019Patent

Dec. 31, 2018USD ($)

Dec. 09, 2016Patent

Other Commitments [Line Items]

Standard product warranty, description

limited one- to five-year warranty

Retainer fees

$ 13,019,000

$ 12,478,000

$ 42,084,000

$ 34,979,000

Expectation period for first obligation

12 months

Secured convertible note, measured at amortized cost

5,700,000

$ 5,700,000

Value of certain rights measured at cost

1,000,000

1,000,000

Contingent liabilities

0

0

$ 0

Litigation amendment period

21 days

Patent Infringement [Member]

Other Commitments [Line Items]

Contingent liabilities

0

0

Boston Scientific Corporation [Member]

Other Commitments [Line Items]

Patent infringement lawsuit allegation against number of patents | Patent

8

10

First Obligation [Member]

Other Commitments [Line Items]

Additional contingent consideration payment secured by convertible notes

$ 2,000,000

Number of additional secured convertible notes | ConvertibleNote

2

Second Obligation [Member]

Other Commitments [Line Items]

Additional contingent consideration payment secured by convertible notes

$ 3,000,000

Licensing Agreement [Member]

Other Commitments [Line Items]

Annual royalty payment

$ 829,000

$ 795,000

$ 2,259,000

$ 2,280,000

Mayo And VGL [Member] | Licensing Agreement [Member]

Other Commitments [Line Items]

License agreement, terms

The agreement will terminate upon the expiration of (1) the last to expire of the licensed patents or (2) the Company’s obligations to pay royalties, whichever is later, unless terminated earlier. The agreement can be terminated by the Company, Mayo or VGL upon 60 days’ notice of a party’s material breach if such breach remains uncured after such 60-day period.

Mayo Foundation [Member] | Licensing Agreement [Member]

Other Commitments [Line Items]

Retainer fees

$ 40,000

Mayo Foundation [Member] | Licensing Agreement [Member] | Minimum [Member]

Other Commitments [Line Items]

Annual royalty payment

$ 200,000

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 final year of lease term

$ 2,400,000

Redwood Office Agreement Additional Expansion Premises [Member] | Amendment 1 [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 commenced on June 1, 2018

Lease commencement date

Jun. 1, 2018

Lease agreement, expiration date

May 31, 2025

Redwood Office Agreement Additional Expansion Premises [Member] | Amendment 2 [Member]

Other Commitments [Line Items]

Lease agreement, effective date

May 31, 2017

Lease agreement, expiration date

Jun. 1, 2018

Non-cancellable Facility Lease [Member]

Other Commitments [Line Items]

Lease agreement, effective date

Mar. 1, 2017

Lease agreement, expiration date

Feb. 28, 2022

Lease agreement, lease expense

$ 400,000

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Activities Related to Warranty Obligations (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Commitments And Contingencies Disclosure [Abstract]
Beginning balance	$ 1,291	$ 943	$ 1,236	$ 708
Provision for warranty	490	597	1,426	1,681
Utilization	(565)	(447)	(1,446)	(1,296)
Ending balance	$ 1,216	$ 1,093	$ 1,216	$ 1,093

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Royalty Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Licensing Agreement [Member]
Other Commitments [Line Items]
Royalty expense	$ 829	$ 795	$ 2,259	$ 2,280

Long-term Debt - Additional Inf

Long-term Debt - Additional Information (Detail) - 1.75% Convertible Senior Notes due 2021 [Member]	1 Months Ended	9 Months Ended	12 Months Ended
	Jun. 30, 2016USD ($)d$ / sharesshares	Sep. 30, 2019	Dec. 31, 2018
Debt Instrument [Line Items]
Aggregate principal amount of convertible senior notes	$ 150,000,000
Debt instrument interest rate	1.75%	1.75%	1.75%
Debt instrument due year	2021	2021	2021
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
Warrant [Member]
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
130% for Applicable Conversion Price [Member]
Debt Instrument [Line Items]
Debt instrument convertible trading days | d	20
Debt instrument convertible consecutive trading days | d	30
98% Applicable Conversion Price [Member]
Debt Instrument [Line Items]
Debt instrument convertible trading days | d	5
Debt instrument convertible consecutive trading days | d	10
Maximum [Member]
Debt Instrument [Line Items]
Percentage of closing sale price of common stock	98.00%
Maximum [Member] | Warrant [Member]
Debt Instrument [Line Items]
Overall conversion price | $ / shares	$ 127.28
Minimum [Member] | Warrant [Member]
Debt Instrument [Line Items]
Overall conversion price | $ / shares	$ 96.37

Long-term Debt - Net Carrying A

Long-term Debt - Net Carrying Amount of Liability Component of Convertible Debt (Detail) - 1.75% Convertible Senior Notes due 2021 [Member] - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Jun. 30, 2016
Debt Instrument [Line Items]
Unamortized issuance cost			$ (5,000)
Debt, Liability Component [Member]
Debt Instrument [Line Items]
Principal	$ 172,500	$ 172,500
Unamortized discount	(12,208)	(17,305)
Unamortized issuance cost	(2,014)	(2,801)
Net carrying amount	$ 158,278	$ 152,394

Long-term Debt - Net Carrying_2

Long-term Debt - Net Carrying Amount of Equity Component of Convertible Debt (Detail) - 1.75% Convertible Senior Notes due 2021 [Member] - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	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	$ 32,945
Debt issuance cost	(1,179)	(1,179)
Net carrying amount	$ 31,766	$ 31,766

Long-term Debt - Interest Expen

Long-term Debt - Interest Expense Recognized Related to Convertible Notes (Detail) - 1.75% Convertible Senior Notes due 2021 [Member] - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Debt Instrument [Line Items]
Contractual interest expense	$ 754	$ 755	$ 2,264	$ 2,265
Amortization of debt discount	1,728	1,625	5,097	4,791
Amortization of debt issuance costs	272	240	787	697
Total interest expense related to the 2021 Notes	$ 2,754	$ 2,620	$ 8,148	$ 7,753

Net Loss Per Share - Computatio

Net Loss Per Share - Computation of Basic and Diluted Net Loss per Share (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Earnings Per Share [Abstract]
Net loss, basic and diluted	$ (17,847)	$ (28,021)	$ (44,076)	$ (11,265)	$ (10,620)	$ (17,713)	$ (89,944)	$ (39,598)	$ (49,200)
Weighted average shares used to compute basic and diluted net loss per share	30,929,938			30,123,188			30,659,117	29,997,201
Net loss per share, basic and diluted	$ (0.58)			$ (0.37)			$ (2.93)	$ (1.32)

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Detail)	Sep. 30, 2019$ / shares
1.75% Convertible Senior Notes due 2021 [Member]
Earnings Per Share Diluted [Line Items]
Convertible notes, conversion price	$ 96.37

Net Loss Per Share - Computat_2

Net Loss Per Share - Computation of Potentially Dilutive Securities Outstanding Excluded from Computation of Diluted Shares (Detail) - shares	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted shares outstanding	7,090,135	6,871,021
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	1,417,636	935,916
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	2,092,433	2,355,039
Convertible Senior Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted shares outstanding	1,790,033	1,790,033
Warrants Related to the Issuance of Convertible Senior Notes [Member]
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted shares outstanding	1,790,033	1,790,033

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense for matching contributions	$ 0.3	$ 0.3	$ 2.9	$ 2.4
ESPP offering period			6 months
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum employee subscription rate	15.00%		15.00%
Purchase price of common stock shares, lower of fair market value, percentage			85.00%
Shares of common stock issued	0	0	119,393	53,824
Shares available for future purchase	1,207,212		1,207,212