Nevro (NVRO) 10-Q 5 Aug 20 2020 Q2 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	6 Months Ended
	Jun. 30, 2020	Jul. 30, 2020
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Jun. 30, 2020
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q2
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		34,312,963
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	Jun. 30, 2020	Dec. 31, 2019
Current assets
Cash and cash equivalents	$ 276,515	$ 65,373
Short-term investments	285,825	172,429
Accounts receivable, net of allowance for doubtful accounts of $2,766 and $797 at June 30, 2020 and December 31, 2019, respectively	56,660	82,833
Inventories	91,849	91,579
Prepaid expenses and other current assets	6,088	9,838
Total current assets	716,937	422,052
Property and equipment, net	11,436	11,766
Operating lease assets	19,867	21,533
Other assets	3,976	13,338
Restricted cash	956	956
Total assets	753,172	469,645
Current liabilities
Accounts payable	18,657	16,048
Accrued liabilities	33,865	50,966
Short-term debt	164,465
Other current liabilities	3,781	3,597
Total current liabilities	220,768	70,611
Long-term debt	137,345	160,300
Long-term operating lease liabilities	18,634	20,445
Other long-term liabilities	1,997	1,937
Total liabilities	378,744	253,293
Commitments and contingencies (Note 6)
Stockholders’ equity
Preferred stock, $0.001 par value, 10,000,000 shares authorized at June 30, 2020 and December 31, 2019; zero shares issued and outstanding at June 30, 2020 and December 31, 2019
Common stock, $0.001 par value, 290,000,000 shares authorized at June 30, 2020 and December 31, 2019; 34,274,490 and 31,544,361 shares issued and outstanding at June 30, 2020 and December 31, 2019, respectively	34	32
Additional paid-in capital	850,669	626,401
Accumulated other comprehensive loss	(556)	(313)
Accumulated deficit	(475,719)	(409,768)
Total stockholders’ equity	374,428	216,352
Total liabilities and stockholders’ equity	$ 753,172	$ 469,645

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Statement Of Financial Position [Abstract]
Accounts receivable, allowance for doubtful accounts	$ 2,766	$ 797
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	34,274,490	31,544,361
Common stock, shares outstanding	34,274,490	31,544,361

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Income Statement [Abstract]
Revenue	$ 56,390	$ 93,571	$ 143,857	$ 175,719
Cost of revenue	21,140	29,628	48,060	58,567
Gross profit	35,250	63,943	95,797	117,152
Operating expenses
Research and development	10,444	14,930	22,656	29,065
Sales, general and administrative	60,167	75,573	131,569	156,901
Total operating expenses	70,611	90,503	154,225	185,966
Loss from operations	(35,361)	(26,560)	(58,428)	(68,814)
Interest income	754	1,489	2,018	3,038
Interest expense	(6,122)	(2,710)	(8,948)	(5,398)
Other income (expense), net	(290)	118	(243)	(225)
Loss before income taxes	(41,019)	(27,663)	(65,601)	(71,399)
Provision for income taxes	44	358	350	698
Net loss	(41,063)	(28,021)	(65,951)	(72,097)
Other comprehensive loss:
Changes in foreign currency translation adjustment	361	(377)	(468)	(101)
Changes in unrealized gains on short-term investments, net	440	195	225	440
Net change in other comprehensive loss	801	(182)	(243)	339
Comprehensive loss	$ (40,262)	$ (28,203)	$ (66,194)	$ (71,758)
Net loss per share, basic and diluted	$ (1.21)	$ (0.91)	$ (2)	$ (2.36)
Weighted average number of common shares used to compute basic and diluted net loss per share	33,988,082	30,677,567	32,913,947	30,521,463

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, 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	(72,097)
Other comprehensive loss	339
Ending balances at Jun. 30, 2019	201,542	$ 31	580,428	(378,179)	(738)
Ending balances, shares at Jun. 30, 2019		30,870,626
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	(103,700)
Ending balances at Dec. 31, 2019	216,352	$ 32	626,401	(409,768)	(313)
Ending balances, shares at Dec. 31, 2019		31,544,361
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)
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
Shares withheld for tax obligations, shares		(6,530)
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
Beginning balances at Dec. 31, 2019	216,352	$ 32	626,401	(409,768)	(313)
Beginning balances, shares at Dec. 31, 2019		31,544,361
Exercise of common stock options	17,364		17,364
Exercise of common stock options, shares		390,476
Issuance of common stock upon release of restricted stock units		99,790
Shares withheld for tax obligations	(1,187)		(1,187)
Shares withheld for tax obligations, shares		(11,055)
Stock based compensation	8,483		8,483
Net loss	(24,888)			(24,888)
Other comprehensive loss	(1,044)				(1,044)
Ending balances at Mar. 31, 2020	215,080	$ 32	651,061	(434,656)	(1,357)
Ending balances, shares at Mar. 31, 2020		32,023,572
Beginning balances at Dec. 31, 2019	216,352	$ 32	626,401	(409,768)	(313)
Beginning balances, shares at Dec. 31, 2019		31,544,361
Net loss	(65,951)
Other comprehensive loss	(243)
Ending balances at Jun. 30, 2020	374,428	$ 34	850,669	(475,719)	(556)
Ending balances, shares at Jun. 30, 2020		34,274,490
Beginning balances at Mar. 31, 2020	215,080	$ 32	651,061	(434,656)	(1,357)
Issuance of common stock upon underwritten public offering, net of issuance costs	147,144	$ 2	147,142
Issuance of common stock upon underwritten public offering, net of issuance costs		1,868,750
Conversion feature of convertible senior notes due 2025, net of allocated costs	48,340		48,340
Purchase of bond hedges	(52,390)		(52,390)
Sale of warrants	34,933		34,933
Beginning balances, shares at Mar. 31, 2020		32,023,572
Exercise of common stock options	8,357		8,357
Exercise of common stock options, shares		196,024
Issuance of common stock upon release of restricted stock units		146,105
Shares withheld for tax obligations	(1,551)		(1,551)
Issuance of common stock under employee stock purchase plan	4,690		4,690
Issuance of common stock under employee stock purchase plan, shares		52,733
Shares withheld for tax obligations, shares		(12,694)
Stock based compensation	10,087		10,087
Net loss	(41,063)			(41,063)
Other comprehensive loss	801				801
Ending balances at Jun. 30, 2020	$ 374,428	$ 34	$ 850,669	$ (475,719)	$ (556)
Ending balances, shares at Jun. 30, 2020		34,274,490

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Cash flows from operating activities
Net loss			$ (65,951)	$ (72,097)
Adjustments to reconcile net loss to net cash used in operating activities
Depreciation and amortization	$ 1,184	$ 1,109	2,480	2,194
Amortization of operating lease assets			1,666	1,618
Stock-based compensation expense			18,572	20,123
Accretion of discount on short-term investments			(41)	(1,359)
Provision for doubtful accounts	1,500		1,967	380
Write-down of inventory			3,278	1,396
Loss on disposal of equipment			12
Non-cash interest expense			6,206	3,887
Unrealized (gains) losses on foreign currency transactions			(607)	(465)
Changes in operating assets and liabilities
Accounts receivable			23,750	13,201
Inventories			(3,553)	(458)
Prepaid expenses and other current assets			3,740	(735)
Other assets			1,863	(209)
Accounts payable			3,223	(329)
Accrued liabilities			(16,858)	733
Other long-term liabilities			(1,751)	(1,257)
Net cash used in operating activities			(22,004)	(33,377)	$ (50,200)
Cash flows from investing activities
Purchases of short-term investments			(237,017)	(136,963)
Proceeds from maturity of short-term investments			123,884	181,063
Repayment from (investment in) private company			7,500	(5,500)
Purchases of property and equipment			(1,993)	(1,378)
Net cash provided by (used in) investing activities			(107,626)	37,222
Cash flows from financing activities
Proceeds from issuance of common stock in public offering, net			147,144
Proceeds from issuance of convertible notes			189,750
Convertible notes debt issuance costs			(6,105)
Proceeds from issuance of warrants			34,933
Purchase of convertible note hedges			(52,390)
Minimum tax withholding paid on behalf of employees for net share settlement			(2,738)	(560)
Proceeds from issuance of common stock to employees			30,411	8,255
Net cash provided by financing activities			341,005	7,695
Effect of exchange rate changes on cash and cash equivalents			(233)	6
Net increase (decrease) in cash, cash equivalents and restricted cash			211,142	11,546
Cash, cash equivalents and restricted cash
Cash, cash equivalents and restricted cash at beginning of period			66,329	51,872	51,872
Cash, cash equivalents and restricted cash at end of period	$ 277,471	$ 63,418	277,471	63,418	$ 66,329
Significant non-cash transactions
Purchases of property and equipment in accounts payable			$ 453	$ 243

Formation and Business of the C

Formation and Business of the Company	6 Months Ended
	Jun. 30, 2020
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, 2019, the Company incurred a net loss of $103.7 million and used $50.2 million of cash in operations. For the six months ended June 30, 2020, the Company incurred a net loss of $66.0 million and used $22.0 million of cash in operations. At June 30, 2020 and December 31, 2019, the Company had an accumulated deficit of $475.7 million and $409.8 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 (2021 Notes). Additionally, in April 2020, the Company issued a total of $189.8 million aggregate principal amount of convertible senior notes due 2025 (2025 Notes). The total net proceeds from this debt offering, after deducting initial purchase discounts and debt issuance costs, were approximately $183.6 million. Concurrent with this debt offering, the Company also completed an underwritten public offering for 1,868,750 shares of its common stock, from which the Company received cash proceeds of $147.1 million, net of underwriting discounts and commissions and offering costs. 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 June 30, 2020 and for the six months ended June 30, 2020 and 2019, 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 25, 2020. 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 June 30, 2020, and the results of its operations and cash flows for the six months ended June 30, 2020 and 2019. All such adjustments are of a normal and recurring nature. The interim financial data as of June 30, 2020 is not necessarily indicative of the results to be expected for the year ending December 31, 2020, 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, 2019 included in the Annual Report.

Summary of Significant Accounti

Summary of Significant Accounting Policies	6 Months Ended
	Jun. 30, 2020
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. Other Risks and Uncertainties The Company is subject to risks related to the public health crises such as the global pandemic associated with COVID-19, which has spread to most countries and all 50 states within the United States. The COVID-19 outbreak has negatively impacted, and may continue to negatively impact the Company’s operations and revenues and overall financial condition by decreasing the number of Senza systems procedures performed. The number of Senza systems procedures performed, similar to other elective surgical procedures, has decreased as health care organizations globally have prioritized the treatment of patients with COVID-19. For example, in the United States, some governmental authorities have recommended, and in certain cases required, that elective, specialty and other procedures and appointments, be suspended or canceled to avoid non-essential patient exposure to medical environments and potential infection with COVID-19 and to focus limited resources and personnel capacity toward the treatment of COVID- 19. These measures and challenges may continue for the duration of the pandemic, which is uncertain, and will reduce our revenue while the pandemic continues. In addition, the Company is also 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. 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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 United States 90 % 83 % 88 % 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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 Net unrealized foreign currency gain (loss) $ 542 $ 483 $ 757 $ 501 Net realized foreign currency gain (loss) (384 ) (316 ) (534 ) (626 ) 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 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 June 30, 2020 and December 31, 2019. The Company also held cash in foreign banks of approximately $3.1 million at June 30, 2020 and $12.1 million at December 31, 2019 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 and 2025 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 six months ended June 30, 2020 and 2019, no single customer accounted for 10% Credit Losses In June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on 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 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 $49.0 million and $52.4 million as of June 30, 2020 and December 31, 2019, respectively. At June 30, 2020 and December 31, 2019, 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 June 30, 2020 and December 31, 2019 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 and 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. The Company’s investment securities at any point in time may include agency bonds, commercial paper, corporate notes and money market funds. The Company segments its investment portfolio based on security type and the underlying risk profiles of the securities. The Company regularly reviews the securities in an unrealized loss position and evaluates the current expected credit loss by considering factors such as historical experience, market data, issuer-specific factors, current economic conditions and credit ratings. Inventories Inventories are stated at the lower of cost or net realizable value. Cost is determined using the standard cost method which approximates the first-in, first-out basis. Net realizable value is determined as the prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. The Company regularly reviews inventory quantities compared to forecasted sales to record a provision for excess and obsolete inventory when appropriate. Inventory write-downs are recorded for excess and obsolete inventory. The Company estimates forecasted sales by considering product acceptance in the marketplace, customer demand, historical sales, product obsolescence and technological innovations. The Company’s policy is to write down inventory that has become obsolete, inventory that has a cost basis in excess of its expected lower of cost or net realizable value, and inventory in excess of expected requirements. The estimate of excess quantities is judgmental and primarily dependent on the Company’s estimates of future demand for a particular product. If the estimate of future demand is inaccurate based on actual sales, the Company may increase the write-down for excess inventory for that component and record a charge to inventory impairment in the accompanying consolidated statements of operations and comprehensive loss. The Company periodically evaluates the carrying value of inventory on hand for potential excess amount over demand using the same lower of cost or net realizable value approach as that has been used to value the inventory. The Company also periodically evaluates inventory quantities in consideration of actual loss experience. As a result of these evaluations, the Company recognized total write-downs of $2.8 million and $0.3 million for the three months ended June 30, 2020 and 2019, respectively, and $3.3 million and $0.5 million for the six months ended June 30, 2020 and 2019, respectively. T 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. For the three and six months ended June 30, 2020, the Company recognized bad debt expenses of $1.5 million and $2.0 million, respectively. 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 June 30, 2020. Income Taxes During the three and six months ended June 30, 2020 and 2019, 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 six months ended June 30, 2020 and 2019 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. No interest or penalties related to income taxes have been recognized in the statements of operations and comprehensive loss for the three and six months ended June 30 , 2020 and 2019 . 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 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 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 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. In March 2020, the Company granted PSUs to certain members of the management team. The number of shares to be issued upon vesting is based on the total shareholder return of the Company’s common stock compared to the Index, as well as certain performance criteria related to a specific financial target over a two-year performance period. These PSUs may become eligible for vesting before the end of the two-year performance period. The Company has and will assess the achievement status of these PSUs on a quarterly basis and records the related stock-based compensation expenses based on the estimated achievement payout. For the three months ended March 31, 2020, the Company determined that the achievement status for these PSUs was not possible, and therefore did not record stock-based compensation expenses related to these grants. During the three months ended June 30, 2020, the Company modified the performance criteria for these PSUs to reflect the changed market conditions as a result of the COVID-19 pandemic, and granted the Company’s CEO PSUs, incorporating the same modified performance criteria. Stock-based compensation expenses for these PSUs were recorded in the three months ended June 30, 2020. All granted PSUs are subject to the grantees’ continued service to the Company through the applicable vesting date. 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 December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This ASU eliminates certain exceptions related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences related to changes in ownership of equity method investments and foreign subsidiaries. ASU 2019-12 also simplifies aspects of accounting for franchise taxes and enacted changes in tax laws or rates, and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. ASU 2019-12 is effective for public entities for annual periods beginning after December 15, 2020, with early adoption permitted. The Company has not determined the potential effects of the guidance on its consolidated financial statements.

Lease Accounting

Lease Accounting	6 Months Ended
	Jun. 30, 2020
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 non-lease components (such as common area expenses). As of June 30, 2020, the Company has leases with remaining terms of less than 2 years 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: June 30, 2020 December 31, 2019 Operating Lease Term and Discount Rate Weighted-average remaining lease term 4.82 years 5.31 years Weighted-average discount rate 7.0% 7.0% As of June 30, 2020, t he maturity of lease liabilities are as follows (in thousands): Operating Leases 2020, remaining months $ 2,495 2021 5,073 2022 5,258 2023 5,522 2024 5,688 Thereafter 2,399 Total lease payments 26,435 Less: Interest (4,118 ) Present value of lease liabilities $ 22,317 Supplemental lease cost information are as follows (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Operating lease cost $ 1,234 $ 1,239 $ 2,468 $ 2,514 Supplemental balance sheet information are as follows (in thousands): June 30, 2020 December 31, 2019 Operating Leases: Operating lease assets $ 19,867 $ 21,533 Other current liabilities $ 3,683 $ 3,498 Long term operating lease liabilities 18,634 20,445 Total operating lease liabilities $ 22,317 $ 23,943 Supplemental cash flow information are as follows (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flow from operating leases $ 1,218 $ 884 $ 2,429 $ 1,780 See Note 6 for further details of the Company’s lease commitments.

Fair Value Measurements

Fair Value Measurements	6 Months Ended
	Jun. 30, 2020
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 June 30, 2020 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 48,993 $ — $ — $ 48,993 Agency bonds (iii) — 121,363 — 121,363 Commercial paper (ii) — 310,727 — 310,727 Corporate notes (ii) — 64,936 — 64,936 Treasury bonds (iii) 5,047 — — 5,047 Total assets $ 54,040 $ 497,026 $ — $ 551,066 Balance as of December 31, 2019 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 52,359 $ — $ — $ 52,359 Agency bonds (iii) — $ 17,246 — 17,246 Commercial paper (iii) — 12,449 — 12,449 Corporate notes (iii) — 142,734 — 142,734 Total assets $ 52,359 $ 172,429 $ — $ 224,788 (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 June 30, 2020 and December 31, 2019, the fair value of the 1.75% convertible senior notes due 2021 was $234.9 million and $232.6 million, respectively. As of June 30, 2020, the fair value of the 2.75% convertible senior notes due 2025 was $259.7 million. The fair value was determined on the basis of market prices observable for similar instruments and is considered Level 2 in the fair value hierarchy (See Note 7).

Balance Sheet Components

Balance Sheet Components	6 Months Ended
	Jun. 30, 2020
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): June 30, 2020 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Agency bonds $ 121,281 $ 94 $ (12 ) $ 121,363 Commercial paper (i) 310,681 52 (6 ) 310,727 Corporate notes (i) 64,631 305 — 64,936 Treasury bonds 5,047 — — 5,047 Total securities $ 501,640 $ 451 $ (18 ) $ 502,073 December 31, 2019 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Agency bonds $ 17,209 $ 37 $ — $ 17,246 Commercial paper $ 12,425 $ 24 $ — 12,449 Corporate notes 142,588 150 (4 ) 142,734 Total securities $ 172,222 $ 211 $ (4 ) $ 172,429 (i) Includes $202.0 million of commercial paper and $14.3 million of corporate notes that is 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 June 30, 2020 were as follows (in thousands): Amortized Cost Fair Value Amounts maturing within one year $ 440,660 $ 441,086 Amounts maturing after one year through five years 60,980 60,987 Total investment securities $ 501,640 $ 502,073 Inventories (in thousands) June 30, December 31, 2020 2019 Raw materials $ 28,593 $ 26,354 Finished goods 63,256 65,225 Total inventories $ 91,849 $ 91,579 Property and Equipment, Net (in thousands) June 30, December 31, 2020 2019 Laboratory equipment $ 6,456 $ 5,733 Computer equipment and software 10,500 9,909 Furniture and fixtures 3,918 3,898 Leasehold improvements 4,226 4,226 Construction in process 1,793 1,006 Total 26,893 24,772 Less: Accumulated depreciation and amortization (15,457 ) (13,006 ) Property and equipment, net $ 11,436 $ 11,766 The Company recognized depreciation and amortization expense on property and equipment as follows (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Depreciation and amortization expense $ 1,184 $ 1,109 $ 2,480 $ 2,194 Accrued Liabilities (in thousands) June 30, December 31, 2020 2019 Accrued payroll and related expenses $ 23,288 $ 36,056 Accrued professional fees 1,193 1,633 Accrued taxes 1,055 2,353 Accrued clinical and research expenses 906 2,157 Accrued interest 1,475 243 Accrued warranty 933 1,178 Accrued other 5,015 7,346 Total accrued liabilities $ 33,865 $ 50,966

Commitments and Contingencies

Commitments and Contingencies	6 Months Ended
	Jun. 30, 2020
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 commence d on June 1, 2018 , and it will expire on May 31, 2025 . The first amendment also extends the lease term for the original premises to terminate on the same date as the Expansion Premises , which is May 31, 2025 . In April 2017, the Company entered into a second amendment to the lease for a temporary space for a period beginning in May 2017 and which ended on June 1, 2018 , the Commencement Date of the Expansion Premises. 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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 Beginning balance $ 1,192 $ 1,307 $ 1,178 $ 1,236 Provision for warranty 291 471 723 936 Utilization (550 ) (487 ) (968 ) (881 ) Ending balance $ 933 $ 1,291 $ 933 $ 1,291 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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 Royalty expense $ 483 $ 773 $ 1,227 $ 1,430 Contingent Consideration In February 2019, the Company entered into an agreement with a privately-held company to, among other things, provide the privately-held company financing in the form of a secured convertible note. Through March 31, 2020, the Company had provided financing totaling $8.5 million in the form of two secured convertible notes. The agreement additionally provided the Company with the exclusive right, but not the obligation, to acquire the privately-held company. The value of the secured convertible notes, measured at amortized cost, and the value of certain rights in relation to the agreement, measured at cost and monitored for impairment on an ongoing basis, were reported in Other Assets on the Condensed Consolidated Balance Sheet. The accretion of amortized cost was recorded in Interest Income, while any changes in value from impairment assessment were recorded in Other Income (Expense) in the Consolidated Statements of Operations and Comprehensive Income. The Company concluded that the privately-held company was a variable interest entity, however the Company was not the primary beneficiary as it did not retain power to direct the activities that most significantly impact its economic performance. In April 2020, the Company elected not to exercise its option to make a further investment in the privately-held company pursuant to the agreement. In connection with this decision, the Company no longer has the exclusive right to acquire the privately-held company. In June 2020, the privately-held company paid off the outstanding principal and accrued interest of its secured convertible notes in full. As a result of these two events, the Company recorded a net expense of $0.4 million in Other Income (Expense) in the Consolidated Statements of Operations and Comprehensive Income in the three months ended June 30, 2020. 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 June 30, 2020 and December 31, 2019. Indemnification The Company enters into standard indemnification arrangements in the ordinary course of business. Pursuant to these arrangements, the Company indemnifies, holds harmless and agrees to reimburse the indemnified parties for losses suffered or incurred by the indemnified party, in connection with any trade secret, copyright, patent or other intellectual property infringement claim by any third-party with respect to the Company’s technology. The term of these indemnification agreements is generally perpetual. The maximum potential amount of future payments the Company could be required to make under these agreements is not determinable because it involves claims that may be made against the Company in the future, but have not yet been made. The Company has entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers, other than liabilities arising from willful misconduct of the individual. The maximum potential amount of future payments the Company could be required to make under these indemnification agreements is unlimited; however, the Company has director and officer insurance coverage that reduces the Company’s exposure and enables the Company to recover a portion of any future amounts paid. The Company believes the estimated fair value of these indemnification agreements in excess of applicable insurance coverage is minimal. 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 California 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 California Court issued an order on claim construction and summary judgment. In the order, the California Court ruled that six asserted method claims in three of the Company’s asserted patents were patent eligible and not invalid as indefinite. Collectively, the asserted claims cover methods for delivering SCS therapy at frequencies between 1.5 kHz and 100 kHz. The California Court, however, found that Boston Scientific is not currently infringing the six upheld method claims. Specifically, the California 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 Boston Scientific modified the Spectra WaveWriter systems to prevent them from being 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 California Court found such use to fall within the safe harbor provision of 35 U.S.C. § 271(e). The California 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 California Court also found that the asserted system claims in four of the Company 's asserted patents were invalid as indefinite. As discussed below, the California Court’s finding of invalidity was overturned by the U.S. Court of Appeals for the Federal Circuit (the Federal Circuit) . On July 27, 2018, the parties submitted a joint statement to the California Court wherein Boston Scientific asserted 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 was 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 the Company’s declaratory judgment claims without prejudice, each side to bear its own fees and costs as to these claims, and jointly requested that the California Court enter such a dismissal. The dismissal was thereafter entered as a court order on July 31, 2018. The Company and Boston Scientific each appealed portions of the California 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 Delaware I 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, trade secret misappropriation and tortious interference with contract (the Delaware II Delaware II inter partes inter partes Delaware II Delaware I Delaware II Delaware II inter partes Delaware II On February 14, 2019, the Company filed a lawsuit for patent infringement against Stimwave Technologies, Inc. (Stimwave) in the Delaware Court asserting that Stimwave was 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 Delaware Court granted Nevro's motion for preliminary injunction, and issued an order barring Stimwave, and all affiliated persons and entities, from infringing patent claims covering frequencies between 3 kHz and 10 kHz. On February 27, 2020, the Company and Stimwave entered into a Settlement Agreement, in which Stimwave agreed to cease commercialization of all high frequency spinal cord stimulation systems worldwide. Stimwave also agreed to entry of a permanent injunction in the Delaware Court, under which Stimwave’s products will not deliver spinal cord stimulation therapy that includes pulse frequencies between 1,500 Hz and 100,000 Hz. The permanent injunction was filed with the Delaware Court and entered on March 2, 2020. After the Delaware Court entered the permanent injunction, the case (including Stimwave’s appeal of the preliminary injunction order) were dismissed. As part of the permanent injunction filing, Stimwave acknowledged the validity of the patents Nevro asserted in the litigation. Per Nevro's request, the permanent injunction order does not enjoin Stimwave from providing follow-up care and programming for any patients who were already programmed with high frequency therapy in the United States prior to March 6, 2020, and in the rest of the world prior to April 30, 2020. On February 28, 2020, the Company filed a lawsuit in the Delaware Court for patent infringement against Nalu Medical, Inc. (Nalu) asserting that Nalu is infringing the Company’s patents covering inventions related to its HF10 therapy and the Senza system. As of June 30, 2020, 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.

Debt

Debt	6 Months Ended
	Jun. 30, 2020
Debt Disclosure [Abstract]
Debt	7. Debt 2021 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 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. 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. 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 the same proportion as the accounting for the proceeds from the issuance of the 2021 Notes. 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): June 30, December 31, 2020 2019 Principal $ 172,500 $ 172,500 Unamortized discount (6,878 ) (10,462 ) Unamortized issuance cost (1,157 ) (1,738 ) Net carrying amount $ 164,465 $ 160,300 The net carrying amount of the equity component of the 2021 Notes was as follows (in thousands): June 30, December 31, 2020 2019 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 2025 Notes and Convertible Note Hedge and Warrant Transactions In April 2020, the Company issued $165.0 million aggregate principal amount of 2.75% convertible senior notes due 2025 in a registered underwritten public offering and an additional $24.8 million aggregate principal amount of such notes pursuant to underwriters exercise in full of their option to purchase additional 2025 Notes. The interest rates are fixed at 2.75% per annum and are payable semi-annually in arrears on April 1 and October 1 of each year, commencing on October 1, 2020. The total net proceeds from the debt offering, after deducting initial purchase discounts and debt issuance costs, were approximately $183.6 million. Each $1,000 principal amount of the 2025 Notes will initially be convertible into 9.5238 shares of the Company’s common stock, which is equivalent to an initial conversion price of approximately $105.00 per share, subject to adjustment upon the occurrence of specified events. The 2025 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 October 1, 2024, only under the following circumstances: (1) during any calendar quarter commencing after the calendar quarter ending on June 30, 2020 (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 2025 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 October 1, 2024 until the close of business on the second scheduled trading day immediately preceding the maturity date, holders may convert their 2025 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. addition, if specific corporate events occur prior to the applicable maturity date, the Company will increase the conversion rate for a holder who elects to convert their notes in connection with such a corporate event in certain circumstances. During the three months ended June 30, 2020 the conditions allowing holders of the 2025 Notes to convert have not been met. The 2025 Notes are therefore not convertible during the three months ended September 30, 2020 and are classified as long-term debt. Should the sale price condition be met in a future quarter, the 2025 Notes will be convertible at the holders’ option during the immediately following quarter. As of June 30, 2020, the if-converted value of the 2025 Notes exceeded the principal value of those notes by $ 26.2 million. In connection with the offering of the 2025 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 $105.00 per share. The total cost of the convertible note hedge transactions was $52.4 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 $147.00 per share. The Company received $34.9 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 $105.00 to $147.00 per share. As these transactions meet certain accounting criteria, the convertible note hedges and warrants are recorded in stockholders’ equity and will not be subsequently remeasured as long as they continue to meet the conditions for equity classification. The net cost of $17.5 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. In accounting for the issuance of the convertible senior notes, the Company separated the 2025 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 $49.9 million and was determined by deducting the fair value of the liability component from the par value of the 2025 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 2025 Notes expense at an effective interest rate of 10.2% over the contractual terms of the notes. In accounting for the debt issuance costs of $6.1 million related to the 2025 Notes, the Company allocated the total amount incurred to the liability and equity components of the 2025 Notes based on the same proportion as the accounting for the proceeds from the issuance of the 2025 Notes. Issuance costs attributable to the liability component were $4.5 million and will be amortized to interest expense using the effective interest method over the contractual terms of the 2025 Notes. The net carrying amount of the liability component of the 2025 Notes was as follows (in thousands): June 30, 2020 Principal $ 189,750 Unamortized discount (48,043 ) Unamortized issuance cost (4,362 ) Net carrying amount $ 137,345 The net carrying amount of the equity component of the 2025 Notes was as follows (in thousands): June 30, 2020 Debt discount related to value of conversion option $ 49,947 Debt issuance cost (1,607 ) Net carrying amount $ 48,340 The following table sets forth the interest expense recognized related to the 2021 Notes and the 2025 Notes (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Contractual interest expense $ 1,987 $ 755 $ 2,742 $ 1,510 Amortization of debt discount 3,704 1,693 5,487 3,369 Amortization of debt issuance costs 429 260 716 515 Total interest expense $ 6,120 $ 2,708 $ 8,945 $ 5,394

Net Loss Per Share

Net Loss Per Share	6 Months Ended
	Jun. 30, 2020
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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 Net loss, basic and diluted $ (41,063 ) $ (28,021 ) $ (65,951 ) $ (72,097 ) Weighted average shares used to compute basic and diluted net loss per share 33,988,082 30,677,567 32,913,947 30,521,463 Net loss per share, basic and diluted $ (1.21 ) $ (0.91 ) $ (2.00 ) $ (2.36 ) 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. The conversion spread for the Company’s outstanding convertible senior notes 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 and $105.00 for the 2025 Notes. Although this condition was met in the three months ended June 30, 2020, the Company excluded the potential shares issuable upon conversion of the 2021 Notes and the 2025 Notes in the calculation of diluted earnings per share, as their inclusion would have been anti-dilutive due to the net loss position of the Company during this period. In connection with the issuance of the 2021 Notes and 2025 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 and 2025 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: June 30, 2020 2019 Unreleased restricted stock 1,268,703 1,405,998 Options to purchase common stock 1,036,244 2,095,461 Convertible senior notes 3,597,174 1,790,033 Warrants related to the issuance of convertible senior notes 3,597,174 1,790,033 Total 9,499,295 7,081,525

Employee Benefit Plans

Employee Benefit Plans	6 Months Ended
	Jun. 30, 2020
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 millio n and $ 2.4 million for the three and six months ended June 30, 2020, respectively, and $ million and $ 2.6 million for the three and six months ended June 30, 2019 , 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 There were 52,733 shares of common stock issued under the ESPP for the three and six months ended June 30, 2020 and 119,393 shares of common stock issued under the ESPP for the three and six months ended June 30, 2019. Shares available for future purchase under the ESPP were 1,424,355 at June 30, 2020.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	6 Months Ended
	Jun. 30, 2020
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.
Other Risks and uncertainties	Other Risks and Uncertainties The Company is subject to risks related to the public health crises such as the global pandemic associated with COVID-19, which has spread to most countries and all 50 states within the United States. The COVID-19 outbreak has negatively impacted, and may continue to negatively impact the Company’s operations and revenues and overall financial condition by decreasing the number of Senza systems procedures performed. The number of Senza systems procedures performed, similar to other elective surgical procedures, has decreased as health care organizations globally have prioritized the treatment of patients with COVID-19. For example, in the United States, some governmental authorities have recommended, and in certain cases required, that elective, specialty and other procedures and appointments, be suspended or canceled to avoid non-essential patient exposure to medical environments and potential infection with COVID-19 and to focus limited resources and personnel capacity toward the treatment of COVID- 19. These measures and challenges may continue for the duration of the pandemic, which is uncertain, and will reduce our revenue while the pandemic continues. In addition, the Company is also 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.
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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 United States 90 % 83 % 88 % 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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 Net unrealized foreign currency gain (loss) $ 542 $ 483 $ 757 $ 501 Net realized foreign currency gain (loss) (384 ) (316 ) (534 ) (626 ) 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	Concentration of Credit Risk 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 June 30, 2020 and December 31, 2019. The Company also held cash in foreign banks of approximately $3.1 million at June 30, 2020 and $12.1 million at December 31, 2019 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 and 2025 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 six months ended June 30, 2020 and 2019, no single customer accounted for 10%
Credit Losses	Credit Losses In June 2016, the Financial Accounting Standards Board (FASB) issued Accounting Standards Update (ASU) No. 2016-13, Financial Instruments – Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments
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 $49.0 million and $52.4 million as of June 30, 2020 and December 31, 2019, respectively. At June 30, 2020 and December 31, 2019, 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 June 30, 2020 and December 31, 2019 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 and 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. The Company’s investment securities at any point in time may include agency bonds, commercial paper, corporate notes and money market funds. The Company segments its investment portfolio based on security type and the underlying risk profiles of the securities. The Company regularly reviews the securities in an unrealized loss position and evaluates the current expected credit loss by considering factors such as historical experience, market data, issuer-specific factors, current economic conditions and credit ratings.
Inventories	Inventories Inventories are stated at the lower of cost or net realizable value. Cost is determined using the standard cost method which approximates the first-in, first-out basis. Net realizable value is determined as the prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. The Company regularly reviews inventory quantities compared to forecasted sales to record a provision for excess and obsolete inventory when appropriate. Inventory write-downs are recorded for excess and obsolete inventory. The Company estimates forecasted sales by considering product acceptance in the marketplace, customer demand, historical sales, product obsolescence and technological innovations. The Company’s policy is to write down inventory that has become obsolete, inventory that has a cost basis in excess of its expected lower of cost or net realizable value, and inventory in excess of expected requirements. The estimate of excess quantities is judgmental and primarily dependent on the Company’s estimates of future demand for a particular product. If the estimate of future demand is inaccurate based on actual sales, the Company may increase the write-down for excess inventory for that component and record a charge to inventory impairment in the accompanying consolidated statements of operations and comprehensive loss. The Company periodically evaluates the carrying value of inventory on hand for potential excess amount over demand using the same lower of cost or net realizable value approach as that has been used to value the inventory. The Company also periodically evaluates inventory quantities in consideration of actual loss experience. As a result of these evaluations, the Company recognized total write-downs of $2.8 million and $0.3 million for the three months ended June 30, 2020 and 2019, respectively, and $3.3 million and $0.5 million for the six months ended June 30, 2020 and 2019, respectively. T
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. For the three and six months ended June 30, 2020, the Company recognized bad debt expenses of $1.5 million and $2.0 million, respectively.
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 June 30, 2020.
Income Taxes	Income Taxes During the three and six months ended June 30, 2020 and 2019, 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 six months ended June 30, 2020 and 2019 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. No interest or penalties related to income taxes have been recognized in the statements of operations and comprehensive loss for the three and six months ended June 30 , 2020 and 2019 .
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 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 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 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. In March 2020, the Company granted PSUs to certain members of the management team. The number of shares to be issued upon vesting is based on the total shareholder return of the Company’s common stock compared to the Index, as well as certain performance criteria related to a specific financial target over a two-year performance period. These PSUs may become eligible for vesting before the end of the two-year performance period. The Company has and will assess the achievement status of these PSUs on a quarterly basis and records the related stock-based compensation expenses based on the estimated achievement payout. For the three months ended March 31, 2020, the Company determined that the achievement status for these PSUs was not possible, and therefore did not record stock-based compensation expenses related to these grants. During the three months ended June 30, 2020, the Company modified the performance criteria for these PSUs to reflect the changed market conditions as a result of the COVID-19 pandemic, and granted the Company’s CEO PSUs, incorporating the same modified performance criteria. Stock-based compensation expenses for these PSUs were recorded in the three months ended June 30, 2020. All granted PSUs are subject to the grantees’ continued service to the Company through the applicable vesting date. 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 December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. This ASU eliminates certain exceptions related to the approach for intraperiod tax allocation, the methodology for calculating income taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences related to changes in ownership of equity method investments and foreign subsidiaries. ASU 2019-12 also simplifies aspects of accounting for franchise taxes and enacted changes in tax laws or rates, and clarifies the accounting for transactions that result in a step-up in the tax basis of goodwill. ASU 2019-12 is effective for public entities for annual periods beginning after December 15, 2020, with early adoption permitted. 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)	6 Months Ended
	Jun. 30, 2020
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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 United States 90 % 83 % 88 % 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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 Net unrealized foreign currency gain (loss) $ 542 $ 483 $ 757 $ 501 Net realized foreign currency gain (loss) (384 ) (316 ) (534 ) (626 )

Lease Accounting (Tables)

Lease Accounting (Tables)	6 Months Ended
	Jun. 30, 2020
Schedule of Weighted Average Lease Terms and Discounts Rates	The weighted average lease terms and discounts rates are as follows: June 30, 2020 December 31, 2019 Operating Lease Term and Discount Rate Weighted-average remaining lease term 4.82 years 5.31 years Weighted-average discount rate 7.0% 7.0%
Schedule of Maturity of Lease Liabilities	As of June 30, 2020, t he maturity of lease liabilities are as follows (in thousands): Operating Leases 2020, remaining months $ 2,495 2021 5,073 2022 5,258 2023 5,522 2024 5,688 Thereafter 2,399 Total lease payments 26,435 Less: Interest (4,118 ) Present value of lease liabilities $ 22,317
Supplemental Lease Cost Information	Supplemental lease cost information are as follows (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Operating lease cost $ 1,234 $ 1,239 $ 2,468 $ 2,514
Schedule Of Operating Lease Assets and Liabilities	Supplemental balance sheet information are as follows (in thousands): June 30, 2020 December 31, 2019 Operating Leases: Operating lease assets $ 19,867 $ 21,533 Other current liabilities $ 3,683 $ 3,498 Long term operating lease liabilities 18,634 20,445 Total operating lease liabilities $ 22,317 $ 23,943
Schedule of Supplemental Cash Flow Information Related to Lease	Supplemental cash flow information are as follows (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flow from operating leases $ 1,218 $ 884 $ 2,429 $ 1,780
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)	6 Months Ended
	Jun. 30, 2020
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 June 30, 2020 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 48,993 $ — $ — $ 48,993 Agency bonds (iii) — 121,363 — 121,363 Commercial paper (ii) — 310,727 — 310,727 Corporate notes (ii) — 64,936 — 64,936 Treasury bonds (iii) 5,047 — — 5,047 Total assets $ 54,040 $ 497,026 $ — $ 551,066 Balance as of December 31, 2019 Level 1 Level 2 Level 3 Total Assets: Money market funds (i) $ 52,359 $ — $ — $ 52,359 Agency bonds (iii) — $ 17,246 — 17,246 Commercial paper (iii) — 12,449 — 12,449 Corporate notes (iii) — 142,734 — 142,734 Total assets $ 52,359 $ 172,429 $ — $ 224,788 (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)	6 Months Ended
	Jun. 30, 2020
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): June 30, 2020 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Agency bonds $ 121,281 $ 94 $ (12 ) $ 121,363 Commercial paper (i) 310,681 52 (6 ) 310,727 Corporate notes (i) 64,631 305 — 64,936 Treasury bonds 5,047 — — 5,047 Total securities $ 501,640 $ 451 $ (18 ) $ 502,073 December 31, 2019 Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Aggregate Fair Value Investment Securities Agency bonds $ 17,209 $ 37 $ — $ 17,246 Commercial paper $ 12,425 $ 24 $ — 12,449 Corporate notes 142,588 150 (4 ) 142,734 Total securities $ 172,222 $ 211 $ (4 ) $ 172,429 (i) Includes $202.0 million of commercial paper and $14.3 million of corporate notes that is 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 June 30, 2020 were as follows (in thousands): Amortized Cost Fair Value Amounts maturing within one year $ 440,660 $ 441,086 Amounts maturing after one year through five years 60,980 60,987 Total investment securities $ 501,640 $ 502,073
Components of Inventories	Inventories (in thousands) June 30, December 31, 2020 2019 Raw materials $ 28,593 $ 26,354 Finished goods 63,256 65,225 Total inventories $ 91,849 $ 91,579
Schedule of Property and Equipment, Net and Depreciation and Amortization Expense	Property and Equipment, Net (in thousands) June 30, December 31, 2020 2019 Laboratory equipment $ 6,456 $ 5,733 Computer equipment and software 10,500 9,909 Furniture and fixtures 3,918 3,898 Leasehold improvements 4,226 4,226 Construction in process 1,793 1,006 Total 26,893 24,772 Less: Accumulated depreciation and amortization (15,457 ) (13,006 ) Property and equipment, net $ 11,436 $ 11,766 The Company recognized depreciation and amortization expense on property and equipment as follows (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Depreciation and amortization expense $ 1,184 $ 1,109 $ 2,480 $ 2,194
Summary of Accrued Liabilities	Accrued Liabilities (in thousands) June 30, December 31, 2020 2019 Accrued payroll and related expenses $ 23,288 $ 36,056 Accrued professional fees 1,193 1,633 Accrued taxes 1,055 2,353 Accrued clinical and research expenses 906 2,157 Accrued interest 1,475 243 Accrued warranty 933 1,178 Accrued other 5,015 7,346 Total accrued liabilities $ 33,865 $ 50,966

Commitments and Contingencies (

Commitments and Contingencies (Tables)	6 Months Ended
	Jun. 30, 2020
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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 Beginning balance $ 1,192 $ 1,307 $ 1,178 $ 1,236 Provision for warranty 291 471 723 936 Utilization (550 ) (487 ) (968 ) (881 ) Ending balance $ 933 $ 1,291 $ 933 $ 1,291
Summary of Royalty Expense	The Company recognized royalty expense during the periods indicated as follows (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Royalty expense $ 483 $ 773 $ 1,227 $ 1,430

Debt (Tables)

Debt (Tables)	6 Months Ended
	Jun. 30, 2020
Debt Instrument [Line Items]
Interest Expense Recognized Related to Convertible Notes Table Text Block	The following table sets forth the interest expense recognized related to the 2021 Notes and the 2025 Notes (in thousands): Three Months Ended Six Months Ended June 30, June 30, 2020 2019 2020 2019 Contractual interest expense $ 1,987 $ 755 $ 2,742 $ 1,510 Amortization of debt discount 3,704 1,693 5,487 3,369 Amortization of debt issuance costs 429 260 716 515 Total interest expense $ 6,120 $ 2,708 $ 8,945 $ 5,394
2021 Notes and Convertible Notes [Member] | 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): June 30, December 31, 2020 2019 Principal $ 172,500 $ 172,500 Unamortized discount (6,878 ) (10,462 ) Unamortized issuance cost (1,157 ) (1,738 ) Net carrying amount $ 164,465 $ 160,300
2021 Notes and Convertible Notes [Member] | 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): June 30, December 31, 2020 2019 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
2025 Notes and Convertible Notes [Member] | Debt, Liability Component [Member]
Debt Instrument [Line Items]
Net Carrying Amount of Convertible Debt	The net carrying amount of the liability component of the 2025 Notes was as follows (in thousands): June 30, 2020 Principal $ 189,750 Unamortized discount (48,043 ) Unamortized issuance cost (4,362 ) Net carrying amount $ 137,345
2025 Notes and Convertible Notes [Member] | Debt, Equity Component [Member]
Debt Instrument [Line Items]
Net Carrying Amount of Convertible Debt	The net carrying amount of the equity component of the 2025 Notes was as follows (in thousands): June 30, 2020 Debt discount related to value of conversion option $ 49,947 Debt issuance cost (1,607 ) Net carrying amount $ 48,340

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	6 Months Ended
	Jun. 30, 2020
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 Six Months Ended June 30, June 30, 2020 2019 2020 2019 Net loss, basic and diluted $ (41,063 ) $ (28,021 ) $ (65,951 ) $ (72,097 ) Weighted average shares used to compute basic and diluted net loss per share 33,988,082 30,677,567 32,913,947 30,521,463 Net loss per share, basic and diluted $ (1.21 ) $ (0.91 ) $ (2.00 ) $ (2.36 )
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: June 30, 2020 2019 Unreleased restricted stock 1,268,703 1,405,998 Options to purchase common stock 1,036,244 2,095,461 Convertible senior notes 3,597,174 1,790,033 Warrants related to the issuance of convertible senior notes 3,597,174 1,790,033 Total 9,499,295 7,081,525

Formation and Business of the_2

Formation and Business of the Company - Additional Information (Detail) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended				6 Months Ended		12 Months Ended
	Apr. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Formation and Business of the Company [Line Items]
Net loss		$ 41,063	$ 24,888	$ 28,021	$ 44,076	$ 65,951	$ 72,097	$ 103,700
Cash used in operations						22,004	$ 33,377	50,200
Accumulated deficit		$ 475,719				475,719		$ 409,768
Common stock in underwriting public offering	1,868,750
Net proceeds from common stock	$ 147,100					$ 147,144
1.75% Convertible Senior Notes due 2021 [Member]
Formation and Business of the Company [Line Items]
Debt instrument due year						2021		2021
2.75% Convertible senior notes due 2025 [Member]
Formation and Business of the Company [Line Items]
Debt instrument due year						2025
Aggregate principal amount of convertible senior notes	189,800
Net proceeds from the debt offering after deducting transaction costs	$ 183,600

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Additional Information (Detail)	3 Months Ended		6 Months Ended		12 Months Ended
	Jun. 30, 2020USD ($)Customer	Jun. 30, 2019USD ($)Customer	Jun. 30, 2020USD ($)BusinessCustomer	Jun. 30, 2019USD ($)Customer	Dec. 31, 2019USD ($)Customer
Summary Of Significant Accounting Policies [Line Items]
Number of business activities | Business			1
Cash held in foreign banks	$ 3,100,000		$ 3,100,000		$ 12,100,000
Money market funds	49,000,000		49,000,000		52,400,000
Restricted cash	956,000		956,000		956,000
Write down of inventory	2,800,000	$ 300,000	3,300,000	$ 500,000
Bad debt expense	1,500,000		$ 1,967,000	380,000
Standard product warranty, description			limited one- to five-year warranty
Impairment charges			$ 0
Interest or penalties recognized	0	$ 0	$ 0	$ 0
Employee stock purchase plan offering period			6 months	6 months
RSU's [Member]
Summary Of Significant Accounting Policies [Line Items]
Vesting term				4 years
Certificates of Deposit [Member]
Summary Of Significant Accounting Policies [Line Items]
Restricted cash	400,000		$ 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
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
1.75% Convertible Senior Notes due 2021 [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt instrument due year			2021		2021
1.75% Convertible Senior Notes due 2021 [Member] | Minimum [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt instrument due year			2021
2.75% Convertible Senior Notes due 2025 [Member] | Maximum [Member]
Summary Of Significant Accounting Policies [Line Items]
Debt instrument due year			2025

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Revenue by Major Customers by Geographic Area (Detail)	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Revenue [Member] | Geographic Concentration Risk [Member] | United States [Member]
Concentration Risk [Line Items]
Revenue	90.00%	83.00%	88.00%	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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Accounting Policies [Abstract]
Net unrealized foreign currency gain (loss)	$ 542	$ 483	$ 757	$ 501
Net realized foreign currency gain (loss)	$ (384)	$ (316)	$ (534)	$ (626)

Lease Accounting - Additional I

Lease Accounting - Additional Information (Detail) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2020	Dec. 31, 2019	Jan. 01, 2019
Lessee Lease Description [Line Items]
Operating lease assets	$ 19,867	$ 21,533
Operating lease liabilities	$ 22,317	$ 23,943
ASC 842 [Member]
Lessee Lease Description [Line Items]
Operating lease assets			$ 24,771
Operating lease liabilities			$ 26,200
Existence of option to extend the lease	true
Option to extend the lease term, description	As of June 30, 2020, the Company has leases with remaining terms of less than 2 years 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	2 years
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	Jun. 30, 2020	Dec. 31, 2019	Jan. 01, 2019	Dec. 31, 2018
Lessee Lease Description [Line Items]
Operating lease assets	$ 19,867	$ 21,533
Other current liabilities	3,781	3,597		$ 119
Long-term operating lease liabilities	18,634	20,445
Other long-term liabilities	$ 1,997	$ 1,937		$ 2,825
ASC 842 [Member]
Lessee Lease Description [Line Items]
Operating lease assets			$ 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)	Jun. 30, 2020	Dec. 31, 2019
Leases [Abstract]
Weighted-average remaining lease term	4 years 9 months 25 days	5 years 3 months 21 days
Weighted-average discount rate	7.00%	7.00%

Lease Accounting - Schedule o_3

Lease Accounting - Schedule of Maturity of Lease Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Leases [Abstract]
2020, remaining months	$ 2,495
2021	5,073
2022	5,258
2023	5,522
2024	5,688
Thereafter	2,399
Total lease payments	26,435
Less: Interest	(4,118)
Present value of lease liabilities	$ 22,317	$ 23,943

Lease Accounting - Supplemental

Lease Accounting - Supplemental Lease Cost Information (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Leases [Abstract]
Operating lease cost	$ 1,234	$ 1,239	$ 2,468	$ 2,514

Lease Accounting - Summary of O

Lease Accounting - Summary of Operating Lease Assets and Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Operating Leases:
Operating lease assets	$ 19,867	$ 21,533
Other current liabilities	3,683	3,498
Long term operating lease liabilities	18,634	20,445
Total operating lease liabilities	$ 22,317	$ 23,943

Lease Accounting - Schedule o_4

Lease Accounting - Schedule of Supplemental Cash Flow Information Related to Lease (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flow from operating leases	$ 1,218	$ 884	$ 2,429	$ 1,780

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		Jun. 30, 2020		Dec. 31, 2019
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		$ 551,066		$ 224,788
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		54,040		52,359
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		497,026		172,429
Money Market Funds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[1]	48,993		52,359
Money Market Funds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[1]	48,993		52,359
Agency Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[2]	121,363		17,246
Agency Bonds [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[2]	121,363		17,246
Commercial Paper [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		310,727	[3]	12,449	[2]
Commercial Paper [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		310,727	[3]	12,449	[2]
Corporate Notes [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		64,936	[3]	142,734	[2]
Corporate Notes [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets		64,936	[3]	$ 142,734	[2]
Treasury Bonds [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[2]	5,047
Treasury Bonds [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Total assets	[2]	$ 5,047
[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) - USD ($) $ in Millions	6 Months Ended	12 Months Ended
	Jun. 30, 2020	Dec. 31, 2019
1.75% Convertible Senior Notes due 2021 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate	1.75%	1.75%
Debt instrument due year	2021	2021
Fair value of notes	$ 234.9	$ 232.6
2.75% Convertible senior notes due 2025 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Debt instrument interest rate	2.75%
Debt instrument due year	2025
Fair value of notes	$ 259.7

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		Jun. 30, 2020		Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		$ 501,640		$ 172,222
Gross Unrealized Holding Gains		451		211
Gross Unrealized Holding Losses		(18)		(4)
Aggregate Fair Value		502,073		172,429
Agency Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		121,281		17,209
Gross Unrealized Holding Gains		94		37
Gross Unrealized Holding Losses		(12)
Aggregate Fair Value		121,363		17,246
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		310,681	[1]	12,425
Gross Unrealized Holding Gains		52	[1]	24
Gross Unrealized Holding Losses	[1]	(6)
Aggregate Fair Value		310,727	[1]	12,449
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		64,631	[1]	142,588
Gross Unrealized Holding Gains		305	[1]	150
Gross Unrealized Holding Losses				(4)
Aggregate Fair Value		64,936	[1]	$ 142,734
Treasury Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost		5,047
Aggregate Fair Value		$ 5,047
[1]	Includes $202.0 million of commercial paper and $14.3 million of corporate notes that is 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	Jun. 30, 2020	Dec. 31, 2019
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	$ 276,515	$ 65,373
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	202,000
Corporate Notes [Member]
Schedule of Available-for-sale Securities [Line Items]
Cash and cash equivalents	$ 14,300

Balance Sheet Components - Su_3

Balance Sheet Components - Summary of Contractual Maturities of Investment Securities (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Investments Debt And Equity Securities [Abstract]
Amortized Cost, Amounts maturing within one year	$ 440,660
Amortized Cost, Amounts maturing after one year through five years	60,980
Amortized Cost	501,640	$ 172,222
Fair Value, Amounts maturing within one year	441,086
Fair Value, Amounts maturing after one year through five years	60,987
Fair Value, Total investment securities	$ 502,073	$ 172,429

Balance Sheet Components - Comp

Balance Sheet Components - Components of Inventories (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Inventory Disclosure [Abstract]
Raw materials	$ 28,593	$ 26,354
Finished goods	63,256	65,225
Total inventories	$ 91,849	$ 91,579

Balance Sheet Components - Sche

Balance Sheet Components - Schedule of Property and Equipment, Net (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Dec. 31, 2019
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 26,893	$ 24,772
Less: Accumulated depreciation and amortization	(15,457)	(13,006)
Property and equipment, net	11,436	11,766
Laboratory Equipment [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	6,456	5,733
Computer Equipment and Software [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	10,500	9,909
Furniture and Fixtures [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	3,918	3,898
Leasehold Improvements [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,226	4,226
Construction in Process [Member]
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 1,793	$ 1,006

Balance Sheet Components - Sc_2

Balance Sheet Components - Schedule of Property and Equipment, Depreciation and Amortization Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Property Plant And Equipment [Abstract]
Depreciation and amortization expense	$ 1,184	$ 1,109	$ 2,480	$ 2,194

Balance Sheet Components - Su_4

Balance Sheet Components - Summary of Accrued Liabilities (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018
Payables And Accruals [Abstract]
Accrued payroll and related expenses	$ 23,288		$ 36,056
Accrued professional fees	1,193		1,633
Accrued taxes	1,055		2,353
Accrued clinical and research expenses	906		2,157
Accrued interest	1,475		243
Accrued warranty	933	$ 1,192	1,178	$ 1,291	$ 1,307	$ 1,236
Accrued other	5,015		7,346
Total accrued liabilities	$ 33,865		$ 50,966

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Detail)

1 Months Ended

3 Months Ended

6 Months Ended

Apr. 30, 2017

Dec. 31, 2016USD ($)ft²

Mar. 31, 2015USD ($)ft²

Jun. 30, 2020USD ($)

Mar. 31, 2020USD ($)

Jun. 30, 2019USD ($)

Jun. 30, 2020USD ($)

Jun. 30, 2019USD ($)

Dec. 31, 2019USD ($)

Mar. 31, 2019Patent

Feb. 28, 2019ConvertibleNote

Dec. 09, 2016Patent

Other Commitments [Line Items]

Standard product warranty, description

limited one- to five-year warranty

Retainer fees

$ 10,444,000

$ 14,930,000

$ 22,656,000

$ 29,065,000

Contingent consideration payment secured by convertible notes

$ 8,500,000

Other income (expense), net

(290,000)

118,000

(243,000)

(225,000)

Contingent liabilities

0

0

$ 0

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

Comprehensive Income [Member]

Other Commitments [Line Items]

Other income (expense), net

400,000

First Obligation [Member]

Other Commitments [Line Items]

Number of additional secured convertible notes | ConvertibleNote

2

Licensing Agreements [Member]

Other Commitments [Line Items]

Annual royalty payment

$ 483,000

$ 773,000

$ 1,227,000

$ 1,430,000

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

Other Commitments [Line Items]

Retainer fees

$ 40,000

Mayo Foundation [Member] | Licensing Agreements [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		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Commitments And Contingencies Disclosure [Abstract]
Beginning balance	$ 1,192	$ 1,307	$ 1,178	$ 1,236
Provision for warranty	291	471	723	936
Utilization	(550)	(487)	(968)	(881)
Ending balance	$ 933	$ 1,291	$ 933	$ 1,291

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Royalty Expense (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Licensing Agreements [Member]
Other Commitments [Line Items]
Royalty expense	$ 483	$ 773	$ 1,227	$ 1,430

Debt - Additional Information (

Debt - Additional Information (Detail)	1 Months Ended		6 Months Ended
	Apr. 30, 2020USD ($)d$ / sharesshares	Jun. 30, 2016USD ($)d$ / sharesshares	Jun. 30, 2020USD ($)
Debt Instrument [Line Items]
Proceeds from issuance of warrants			$ 34,933,000
2021 Notes and Convertible Notes [Member]
Debt Instrument [Line Items]
Aggregate principal amount of convertible senior notes		$ 150,000,000
Debt instrument interest rate		1.75%
Debt instrument due year		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%
Converted Value in Excess of Principal			$ 41,400,000
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
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
Debt issuance costs attributable to the liability component		$ 5,000,000
2021 Notes and Convertible Notes [Member] | 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
2021 Notes and Convertible Notes [Member] | 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
2021 Notes and Convertible Notes [Member] | 98% Applicable Conversion Price [Member]
Debt Instrument [Line Items]
Debt instrument convertible trading days | d		5
Debt instrument convertible consecutive trading days | d		10
2021 Notes and Convertible Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of closing sale price of common stock		98.00%
2021 Notes and Convertible Notes [Member] | Maximum [Member] | Warrant [Member]
Debt Instrument [Line Items]
Overall conversion price | $ / shares		$ 127.28
2021 Notes and Convertible Notes [Member] | Minimum [Member] | Warrant [Member]
Debt Instrument [Line Items]
Overall conversion price | $ / shares		$ 96.37
2025 Notes and Convertible Notes [Member]
Debt Instrument [Line Items]
Aggregate principal amount of convertible senior notes	$ 165,000,000
Debt instrument interest rate	2.75%
Debt instrument due year	2025
Additional aggregate principal amount of convertible senior notes	$ 24,800,000
Debt instrument frequency of payment			semi-annually in arrears on April 1 and October 1 of each year, commencing on October 1, 2020.
Net proceeds from the debt offering after deducting transaction costs	183,600,000
Convertible notes principal amount	$ 1,000
Convertible notes, shares issued | shares	9.5238
Convertible notes, type of equity security issued			common stock
Convertible notes, conversion price | $ / shares	$ 105
Debt instrument convertible, percentage of conversion price	130.00%
Percentage of repurchase price, which is equal to principal amount of convertible notes	100.00%
Converted Value in Excess of Principal			$ 26,200,000
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	$ 105
Total cost of the convertible note hedge transactions	$ 52,400,000
Proceeds from issuance of warrants	34,900,000
Net cost of reduction to additional paid-in capital	17,500,000
Debt conversion, converted instrument amount	$ 49,900,000
Debt instrument, effective interest rate	10.20%
Debt issuance costs attributable to the liability and equity component, total amount	$ 6,100,000
Debt issuance costs attributable to the liability component	4,500,000
Debt issuance costs attributable to the liability component	$ 4,500,000
2025 Notes and Convertible Notes [Member] | 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	$ 147
2025 Notes and Convertible Notes [Member] | 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
2025 Notes and Convertible Notes [Member] | 98% Applicable Conversion Price [Member]
Debt Instrument [Line Items]
Debt instrument convertible trading days | d	5
Debt instrument convertible consecutive trading days | d	10
2025 Notes and Convertible Notes [Member] | Maximum [Member]
Debt Instrument [Line Items]
Percentage of closing sale price of common stock	98.00%
2025 Notes and Convertible Notes [Member] | Maximum [Member] | Warrant [Member]
Debt Instrument [Line Items]
Overall conversion price | $ / shares	$ 147
2025 Notes and Convertible Notes [Member] | Minimum [Member] | Warrant [Member]
Debt Instrument [Line Items]
Overall conversion price | $ / shares	$ 105

Debt - Net Carrying Amount of L

Debt - Net Carrying Amount of Liability Component of Convertible Debt (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Apr. 30, 2020	Dec. 31, 2019	Jun. 30, 2016
2021 Notes and Convertible Notes [Member]
Debt Instrument [Line Items]
Unamortized issuance cost				$ (5,000)
2021 Notes and Convertible Notes [Member] | Debt, Liability Component [Member]
Debt Instrument [Line Items]
Principal	$ 172,500		$ 172,500
Unamortized discount	(6,878)		(10,462)
Unamortized issuance cost	(1,157)		(1,738)
Net carrying amount	164,465		$ 160,300
2025 Notes and Convertible Notes [Member]
Debt Instrument [Line Items]
Unamortized issuance cost		$ (4,500)
2025 Notes and Convertible Notes [Member] | Debt, Liability Component [Member]
Debt Instrument [Line Items]
Principal	189,750
Unamortized discount	(48,043)
Unamortized issuance cost	(4,362)
Net carrying amount	$ 137,345

Debt - Net Carrying Amount of E

Debt - Net Carrying Amount of Equity Component of Convertible Debt (Detail) - USD ($) $ in Thousands	Jun. 30, 2020	Apr. 30, 2020	Dec. 31, 2019
1.75% Convertible Senior Notes due 2021 [Member] | 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
2025 Notes and Convertible Notes [Member]
Debt Instrument [Line Items]
Net carrying amount		$ 49,900
2025 Notes and Convertible Notes [Member] | Debt, Equity Component [Member]
Debt Instrument [Line Items]
Debt discount related to value of conversion option	49,947
Debt issuance cost	(1,607)
Net carrying amount	$ 48,340

Debt - Interest Expense Recogni

Debt - Interest Expense Recognized Related to Convertible Notes (Detail) - 2021 Notes and 2025 Notes [Member] - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Debt Instrument [Line Items]
Contractual interest expense	$ 1,987	$ 755	$ 2,742	$ 1,510
Amortization of debt discount	3,704	1,693	5,487	3,369
Amortization of debt issuance costs	429	260	716	515
Total interest expense	$ 6,120	$ 2,708	$ 8,945	$ 5,394

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				6 Months Ended		12 Months Ended
	Jun. 30, 2020	Mar. 31, 2020	Jun. 30, 2019	Mar. 31, 2019	Jun. 30, 2020	Jun. 30, 2019	Dec. 31, 2019
Earnings Per Share [Abstract]
Net loss, basic and diluted	$ (41,063)	$ (24,888)	$ (28,021)	$ (44,076)	$ (65,951)	$ (72,097)	$ (103,700)
Weighted average shares used to compute basic and diluted net loss per share	33,988,082		30,677,567		32,913,947	30,521,463
Net loss per share, basic and diluted	$ (1.21)		$ (0.91)		$ (2)	$ (2.36)

Net Loss Per Share - Additional

Net Loss Per Share - Additional Information (Detail)	Jun. 30, 2020$ / shares
2021 Notes and Convertible Notes [Member]
Earnings Per Share Diluted [Line Items]
Convertible notes, conversion price	$ 96.37
2025 Notes and Convertible Notes [Member]
Earnings Per Share Diluted [Line Items]
Convertible notes, conversion price	$ 105

Net Loss Per Share - Computat_2

Net Loss Per Share - Computation of Potentially Dilutive Securities Outstanding Excluded from Computation of Diluted Shares (Detail) - shares	6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities excluded from computation of diluted shares outstanding	9,499,295	7,081,525
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	1,268,703	1,405,998
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	1,036,244	2,095,461
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	3,597,174	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	3,597,174	1,790,033

Employee Benefit Plans - Additi

Employee Benefit Plans - Additional Information (Detail) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expense for matching contributions	$ 0.3	$ 0.7	$ 2.4	$ 2.6
ESPP offering period			6 months	6 months
Employee Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Maximum employee subscription rate					15.00%
Purchase price of common stock shares, lower of fair market value, percentage			85.00%
Shares of common stock issued	52,733	119,393	52,733	119,393
Shares available for future purchase	1,424,355		1,424,355