SI-BONE (SIBN) 10-Q 12 Nov 19 2019 Q3 Quarterly report Financial data

Document And Entity Information

Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2019	Nov. 08, 2019
Document And Entity Information [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Entity Registrant Name	SI-BONE, Inc.
Entity Central Index Key	0001459839
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		25,005,329
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Current Reporting Status	Yes

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 12,614	$ 25,120
Short-term investments	83,609	97,103
Accounts receivable, net of allowance for doubtful accounts of $310 and $263, respectively	9,918	8,486
Inventory	4,953	3,343
Prepaid expenses and other current assets	1,619	1,990
Total current assets	112,713	136,042
Long-term investments	5,273	0
Property and equipment, net	3,025	2,154
Other non-current assets	305	325
TOTAL ASSETS	121,316	138,521
Current liabilities:
Accounts payable	2,623	2,146
Accrued liabilities and other	10,211	6,860
Total current liabilities	12,834	9,006
Long-term borrowings	39,158	38,963
Other long-term liabilities	363	360
TOTAL LIABILITIES	52,355	48,329
Commitments and contingencies
STOCKHOLDERS’ EQUITY
Preferred stock, $0.0001 par value; 5,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.0001 par value; 100,000,000 shares authorized; 24,965,512 and 24,450,757 shares issued and outstanding, respectively	3	3
Additional paid-in capital	254,965	246,927
Accumulated other comprehensive income	475	439
Accumulated deficit	(186,482)	(157,177)
TOTAL STOCKHOLDERS’ EQUITY	68,961	90,192
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 121,316	$ 138,521

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 310	$ 263
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock authorized (in shares)	5,000,000	5,000,000
Preferred stock issued (in shares)	0	0
Preferred stock outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock authorized (in shares)	100,000,000	100,000,000
Common stock issued (in shares)	24,965,512	24,450,757
Common stock outstanding (in shares)	24,965,512	24,450,757

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 16,182	$ 13,381	$ 47,490	$ 39,756
Cost of goods sold	1,630	1,221	4,744	3,451
Gross profit	14,552	12,160	42,746	36,305
Operating expenses:
Sales and marketing	16,443	10,605	48,985	31,890
Research and development	1,874	1,373	5,503	3,875
General and administrative	6,816	3,226	15,776	8,198
Total operating expenses	25,133	15,204	70,264	43,963
Loss from operations	(10,581)	(3,044)	(27,518)	(7,658)
Interest and other income (expense), net:
Interest income	612	69	2,051	199
Interest expense	(1,243)	(1,282)	(3,706)	(3,826)
Other expense, net	(94)	(535)	(132)	(855)
Net loss	(11,306)	(4,792)	(29,305)	(12,140)
Other comprehensive income (loss):
Changes in foreign currency translation	(4)	(4)	(11)	29
Unrealized gain (loss) on marketable securities	(37)	0	47	0
Comprehensive loss	$ (11,347)	$ (4,796)	$ (29,269)	$ (12,111)
Net loss per share, basic and diluted (in dollars per share)	$ (0.46)	$ (1.29)	$ (1.19)	$ (3.34)
Weighted-average number of common shares used to compute basic and diluted net loss per share (in shares)	24,803,452	3,712,876	24,596,788	3,638,905

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Temporary equity, beginning of period (in shares) at Dec. 31, 2017	11,871,578
Temporary equity, beginning of period at Dec. 31, 2017	$ 118,548
Temporary equity, end of period (in shares) at Mar. 31, 2018	11,871,578
Temporary equity, end of period at Mar. 31, 2018	$ 118,548
Stockholders' equity (deficit), beginning of period (in shares) at Dec. 31, 2017		3,603,140
Stockholders' equity (deficit), beginning of period at Dec. 31, 2017	(129,378)	$ 1	$ 9,943	$ 402	$ (139,724)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		4,207
Issuance of common stock upon exercise of stock options	18		18
Stock-based compensation	391		391
Vesting of early exercised stock options	20		20
Foreign currency translation	(21)			(21)
Net loss	(4,201)				(4,201)
Stockholders' equity (deficit), ending of period (in shares) at Mar. 31, 2018		3,607,347
Stockholders' equity (deficit), ending of period at Mar. 31, 2018	$ (133,171)	$ 1	10,372	381	(143,925)
Temporary equity, beginning of period (in shares) at Dec. 31, 2017	11,871,578
Temporary equity, beginning of period at Dec. 31, 2017	$ 118,548
Temporary equity, end of period (in shares) at Sep. 30, 2018	11,871,578
Temporary equity, end of period at Sep. 30, 2018	$ 118,548
Stockholders' equity (deficit), beginning of period (in shares) at Dec. 31, 2017		3,603,140
Stockholders' equity (deficit), beginning of period at Dec. 31, 2017	(129,378)	$ 1	9,943	402	(139,724)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Foreign currency translation	29
Unrealized gain (loss) on marketable securities	0
Net loss	(12,140)
Stockholders' equity (deficit), ending of period (in shares) at Sep. 30, 2018		3,912,907
Stockholders' equity (deficit), ending of period at Sep. 30, 2018	$ (139,429)	$ 1	12,003	431	(151,864)
Temporary equity, beginning of period (in shares) at Mar. 31, 2018	11,871,578
Temporary equity, beginning of period at Mar. 31, 2018	$ 118,548
Temporary equity, end of period (in shares) at Jun. 30, 2018	11,871,578
Temporary equity, end of period at Jun. 30, 2018	$ 118,548
Stockholders' equity (deficit), beginning of period (in shares) at Mar. 31, 2018		3,607,347
Stockholders' equity (deficit), beginning of period at Mar. 31, 2018	(133,171)	$ 1	10,372	381	(143,925)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		44,195
Issuance of common stock upon exercise of stock options	190		190
Issuance of common stock upon exercises of unvested stock options (in shares)		55,726
Issuance of common stock upon exercises of unvested stock options	0
Stock-based compensation	363		363
Vesting of early exercised stock options	8		8
Foreign currency translation	54			54
Net loss	(3,147)				(3,147)
Stockholders' equity (deficit), ending of period (in shares) at Jun. 30, 2018		3,707,268
Stockholders' equity (deficit), ending of period at Jun. 30, 2018	$ (135,703)	$ 1	10,933	435	(147,072)
Temporary equity, end of period (in shares) at Sep. 30, 2018	11,871,578
Temporary equity, end of period at Sep. 30, 2018	$ 118,548
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		205,639
Issuance of common stock upon exercise of stock options	707		707
Stock-based compensation	327		327
Vesting of early exercised stock options	36		36
Foreign currency translation	(4)			(4)
Unrealized gain (loss) on marketable securities	0
Net loss	(4,792)				(4,792)
Stockholders' equity (deficit), ending of period (in shares) at Sep. 30, 2018		3,912,907
Stockholders' equity (deficit), ending of period at Sep. 30, 2018	(139,429)	$ 1	12,003	431	(151,864)
Stockholders' equity (deficit), beginning of period (in shares) at Dec. 31, 2018		24,450,757
Stockholders' equity (deficit), beginning of period at Dec. 31, 2018	90,192	$ 3	246,927	439	(157,177)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		46,809
Issuance of common stock upon exercise of stock options	125		125
Stock-based compensation	1,871		1,871
Vesting of early exercised stock options	66		66
Additional accrual of IPO related cost	(160)		(160)
Foreign currency translation	(19)			(19)
Unrealized gain (loss) on marketable securities	25			25
Net loss	(9,345)				(9,345)
Stockholders' equity (deficit), ending of period (in shares) at Mar. 31, 2019		24,497,566
Stockholders' equity (deficit), ending of period at Mar. 31, 2019	82,755	$ 3	248,829	445	(166,522)
Stockholders' equity (deficit), beginning of period (in shares) at Dec. 31, 2018		24,450,757
Stockholders' equity (deficit), beginning of period at Dec. 31, 2018	$ 90,192	$ 3	246,927	439	(157,177)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)	359,200
Foreign currency translation	$ (11)
Unrealized gain (loss) on marketable securities	47
Net loss	(29,305)
Stockholders' equity (deficit), ending of period (in shares) at Sep. 30, 2019		24,965,512
Stockholders' equity (deficit), ending of period at Sep. 30, 2019	68,961	$ 3	254,965	475	(186,482)
Stockholders' equity (deficit), beginning of period (in shares) at Mar. 31, 2019		24,497,566
Stockholders' equity (deficit), beginning of period at Mar. 31, 2019	82,755	$ 3	248,829	445	(166,522)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		137,185
Issuance of common stock upon exercise of stock options	442		442
Issuance of common stock related to employee stock purchase plan (in shares)		99,086
Issuance of common stock related to employee stock purchase plan	1,263		1,263
Issuance of common stock upon vesting of restricted stock units (in shares)		27,320
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation	1,814		1,814
Vesting of early exercised stock options	56		56
Foreign currency translation	12			12
Unrealized gain (loss) on marketable securities	59			59
Net loss	(8,654)				(8,654)
Stockholders' equity (deficit), ending of period (in shares) at Jun. 30, 2019		24,761,157
Stockholders' equity (deficit), ending of period at Jun. 30, 2019	77,747	$ 3	252,404	516	(175,176)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options (in shares)		175,070
Issuance of common stock upon exercise of stock options	611		611
Issuance of common stock upon vesting of restricted stock units (in shares)		38,115
Issuance of common stock upon vesting of restricted stock units	0
Repurchase of unvested early exercised stock options (in shares)		(8,830)
Repurchase of unvested early exercised stock options	0
Stock-based compensation	1,911		1,911
Vesting of early exercised stock options	39		39
Foreign currency translation	(4)			(4)
Unrealized gain (loss) on marketable securities	(37)			(37)
Net loss	(11,306)				(11,306)
Stockholders' equity (deficit), ending of period (in shares) at Sep. 30, 2019		24,965,512
Stockholders' equity (deficit), ending of period at Sep. 30, 2019	$ 68,961	$ 3	$ 254,965	$ 475	$ (186,482)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities
Net loss	$ (29,305)	$ (12,140)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	5,596	1,081
Depreciation and amortization	570	536
Accretion on marketable securities	(1,288)	0
Amortization of debt issuance costs	194	194
Change in fair value of redeemable convertible preferred stock warrants	0	681
Loss on sale and disposal of property and equipment	152	95
Changes in operating assets and liabilities:
Accounts receivable	(1,383)	354
Inventory	(1,575)	(458)
Prepaid expenses and other assets	394	495
Accounts payable	526	(884)
Accrued liabilities and other	3,525	1,844
Net cash used in operating activities	(22,594)	(8,202)
Cash flows from investing activities
Maturities of marketable securities	117,100	0
Purchases of marketable securities	(107,545)	0
Purchases of property and equipment	(1,639)	(777)
Net cash provided by (used in) investing activities	7,916	(777)
Cash flows from financing activities
Proceeds from the exercise of stock options	1,178	915
Proceeds from issuance of common stock under employee stock purchase plan	1,263	0
Repurchase of unvested early exercised stock options	(38)	0
Payments of public offering costs	(167)	(288)
Net cash provided by financing activities	2,236	627
Effect of exchange rate changes on cash and cash equivalents	(64)	(52)
Net decrease in cash and cash equivalents	(12,506)	(8,404)
Cash and cash equivalents at
Beginning of period	25,120	22,408
End of period	12,614	14,004
Supplemental disclosure of non-cash information
Vesting of early exercised stock options	161	64
Purchases of property and equipment included in accounts payable and accrued liabilities	31	35
Public offering costs included in accounts payable	$ 0	$ 865

The Company and Nature of Busin

The Company and Nature of Business	9 Months Ended
	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
The Company and Nature of Business	The Company and Nature of Business SI-BONE, Inc. (the “Company”) was incorporated in the state of Delaware on March 18, 2008 and is headquartered in Santa Clara, California. The Company is a medical device company that has pioneered a proprietary minimally invasive surgical implant system to fuse the sacroiliac joint for treatment of the most common types of sacroiliac joint disorders that cause lower back pain. The Company introduced its primary product, the iFuse Implant System, or iFuse, in 2009 in the United States, in 2010 in certain countries in the European Union, and in 2015 in certain countries in the rest of the world. Reverse Stock Split In October 2018, the Company's board of directors and stockholders approved a 1-for-18 reverse stock split of the Company's common stock and redeemable convertible preferred stock, which was effected on October 4, 2018. The par value of the common stock and redeemable convertible preferred stock was not adjusted as a result of the reverse split. All issued and outstanding share and per share amounts of common stock, redeemable convertible preferred stock, stock options, and warrants included in the accompanying condensed consolidated financial statements have been adjusted to reflect this reverse stock split for all periods presented. Initial Public Offering On October 16, 2018, the Company’s Registration Statement on Form S-1 (File No. 333-227445) relating to the initial public offering (IPO) of its common stock was declared effective by the Securities and Exchange Commission (SEC). Pursuant to such Registration Statement, the Company sold 8,280,000 shares at an initial public offering price of $15.00 per share for net proceeds of $113.4 million to the Company, net of underwriting discounts and commissions and offering costs. Upon the closing of the IPO, the Company's outstanding shares of redeemable convertible preferred stock were automatically converted into an aggregate of 12,066,654 shares of common stock and the Company's outstanding warrants to purchase 156,550 shares of redeemable convertible preferred stock were automatically converted into warrants to purchase an aggregate of 160,657 shares of common stock, resulting in reclassification of the related redeemable convertible preferred stock warrant liability of $1.2 million in additional paid-in-capital.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Basis of Presentation and Principles of Consolidation The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP have been condensed or omitted, and accordingly the balance sheet as of December 31, 2018 has been derived from the audited consolidated financial statements at that date but does not include all of the information required by GAAP for complete financial statements. These unaudited interim condensed consolidated financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments that are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the three and nine months ended September 30, 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or for any other interim period or for any other future year. The accompanying condensed consolidated financial statements should be read in conjunction with the audited financial statements and related notes thereto for the year ended December 31, 2018 contained in the Company’s Annual Report on Form 10-K filed with the SEC on March 14, 2019. Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Significant accounting estimates and management judgments reflected in the consolidated financial statements include: fair value of assets and liabilities; analysis of the allowance for doubtful accounts; inventory valuation; valuation of deferred tax assets, including related valuation allowances; fair value of common stock and redeemable convertible preferred stock warrants; stock-based compensation; and useful lives of long lived assets. Estimates are based on historical experience, where applicable and other assumptions believed to be reasonable by the management. Actual results could differ from those estimates. Significant Accounting Policies The Company’s significant accounting policies are disclosed in the Company’s Annual Report on Form 10-K for the year ended December 31, 2018 . There have been no material changes to these accounting policies. JOBS Act Accounting Election As an emerging growth company under the Jumpstart Our Business Startups Act of 2012 (the "JOBS Act"), the Company is eligible to take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies. The Company has elected to take advantage of the extended transition period for adopting new or revised accounting standards that have different effective dates for public and private companies. Those standards apply to companies until the earlier of the date that it is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, these condensed consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. The Company continues to be an emerging growth company for five years following the completion of the IPO, unless one of the following occurs: (i) if the Company's total annual gross revenues are $1.07 billion or more; or (ii) the Company has issued more than $1.0 billion in non-convertible debt in the past three years; or (iii) the Company becomes a "large accelerated filer," as defined in Rule 12b-2 of the Exchange Act. Segments The chief operating decision makers for the Company are the Chief Executive Officer ("CEO") and Chief Operating Officer & Chief Financial Officer ("COO/CFO"). The CEO and the COO/CFO review financial information presented on a consolidated basis, accompanied by information about revenue by geographic region, for purposes of 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. Accordingly, the Company has determined that it has a single reportable and operating segment structure. The Company derives substantially all of its revenue from sales to customers in the United States. Revenue by geography is based on billing address of the customer. No single country outside the United States accounts for more than 10% of the total revenue during the periods presented. Long-lived assets held outside the United States are immaterial. The table below summarizes the Company's revenue by geography: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 (in thousands) United States $ 14,856 $ 12,216 $ 43,325 $ 35,672 International 1,326 1,165 4,165 4,084 $ 16,182 $ 13,381 $ 47,490 $ 39,756 Concentration of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents. The Company’s cash and cash equivalents are deposited with financial institutions in the United States and in Europe; the majority of the Company’s cash and cash equivalents are deposited with a single financial institution in the United States. Deposits in this institution exceed the amount of insurance provided on such deposits. The Company has not experienced any losses on its deposits of cash and cash equivalents. The Company’s revenue and accounts receivable are spread across a large number of customers, primarily in the United States, and no one customer accounts for more than 10% of total revenue or gross accounts receivable in any period presented. Other Risks and Uncertainties The Company is subject to risks common to medical device companies including, but not limited to, new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, product liability, the ability to obtain adequate coverage and reimbursement from third-party payors, uncertainty of market acceptance of products, and the need to obtain additional financing. The Company is dependent on third-party manufacturers and suppliers, in some cases single source suppliers. The Company currently has limited long term contracts with its key suppliers and is subject to risks such as manufacturing failures, non-compliance with regulatory requirements, price fluctuations, inability to properly meet demand and third-party supplier discontinuation of operations. Recently Issued Accounting Standards Not Yet Effective In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The new standard is effective for fiscal years beginning after December 15, 2017 for public companies, and for fiscal years beginning after December 15, 2018, and interim periods beginning after December 15, 2019, for private companies. Early application is permitted. The standard permits the use of either the retrospective or cumulative effect transition method. In March 2016, the FASB issued ASU 2016-08, which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10, which clarifies certain aspects of identifying performance obligations and licensing implementation guidance. In May 2016, the FASB issued ASU 2016-12, which relates to disclosures of remaining performance obligations, as well as other amendments to guidance on collectability, non-cash consideration and the presentation of sales and other similar taxes collected from customers. In November 2018, the FASB issued ASU 2018-18 , which clarifies when transactions between participants in a collaborative arrangement are within the scope of the FASB’s revenue standard, Topic 606. The Company will adopt this standard using the modified retrospective method effective for the year ending December 31, 2019, which will be first presented on the Company's Annual Report on Form 10-K for the year ended December 31, 2019. As an emerging growth company that elected to take advantage of the JOBS Act accounting election, the Company is not required to adopt the new revenue standard in the interim reporting periods for the year ending December 31, 2019, but rather for the fiscal year ending December 31, 2019 and then in the interim periods following the year of adoption. The Company also is not required, and intends not, to revise its 2019 interim periods which were and will be reported under ASC 605 in its fiscal year 2020 interim financial reporting. The Company is finalizing its assessment of the impact of adopting this new standard on its accounting policies and processes. As it relates to product sales where the Company's sales representative delivers the product at the point of implantation at hospital or other medical facilities, which represents majority of the Company's revenue, the Company expects to continue to recognize the revenue upon completion of the procedure and authorization by the customer. As it relates to sale of products through distributors and hospitals where product is ordered in advance of the procedure, the Company expects to continue to recognize the revenue upon shipments to the customers. Additionally, the new standard requires the capitalization of costs to obtain a contract, primarily sales commissions, and amortization of these costs over the contract period or estimated customer life. The Company expects to continue expensing all sales commissions as incurred. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires that lessee's recognize a right-of-use asset and a lease liability for all leases with lease terms greater than twelve months in the balance sheet. A lease liability is a lessee's obligation to make lease payments arising from a lease, measured on a discounted basis; and a right-of-use asset is an asset that represents the lessee’s right to use, or control use of, a specified asset for the lease term for all leases (with the exception of short-term leases) at the adoption date. In July 2018, the FASB issued ASU 2018-10 and ASU 2018-11, which provides clarification on the narrow aspects of the guidance and provide an additional transition method to adopt the new leases standard. The new transition method allows an entity to recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. In March 2019, the FASB issued ASU 2019-01, which provides clarification on implementation issues associated with adopting ASU 2016-02. The new guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018 for public companies and effective for fiscal years beginning after December 15, 2019 and interim periods within fiscal years beginning after December 15, 2020 for private companies. Early adoption is permitted for any interim or annual financial statements not yet issued. The new leases standard must be adopted using a modified retrospective transition method and allows for the application of the new guidance at the beginning of the earliest comparative period presented or at the adoption date. The Company is currently evaluating the impact of this standard on its consolidated financial statements and anticipates adopting the standard for the fiscal year ending December 31, 2020. In June 2018, the FASB issued ASU 2018-07, Improvements to Non-employee Share-Based Payment Accounting. ASU 2018-07 expands the scope of Topic 718, Compensation-Stock Compensation, to include share-based payments issued to non-employees for goods or services. Consequently, the accounting for share-based payments to non-employees and employees will be substantially aligned. ASU 2018-07 supersedes Subtopic 505-50, Equity-Equity-Based Payments to Non-Employees. For public business entities, the amendments are effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. For all other entities, the amendments are effective for fiscal years beginning after December 15, 2019, and interim periods within fiscal years beginning after December 15, 2020. Early adoption is permitted, but no earlier than a company’s adoption date of ASC 606. The Company is currently evaluating the impact that the adoption of this standard will have on the consolidated financial statements, and anticipates adopting the standard for the fiscal year ending December 31, 2020. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurements, which eliminates, adds or modifies certain disclosure requirements for fair value measurements. Entities will no longer be required to disclose the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, but will be required to disclose the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. This ASU is effective for fiscal years beginning after December 15, 2019, including interim periods within that fiscal year, with early adoption permitted to adopt either the entire standard or only the provisions that eliminate or modify the requirements. The Company is currently evaluating the impact that the adoption of this standard will have on the consolidated financial statements, and anticipates adopting the standard for the fiscal year ending December 31, 2020. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The new standard revises the accounting requirements related to the measurement of credit losses and will require organizations to measure all expected credit losses for financial assets based on historical experience, current conditions and reasonable and supportable forecasts about collectability. Assets must be presented in the financial statements at the net amount expected to be collected. The amendments to this update are effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years for public companies and are effective for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years for private companies. The Company is currently evaluating the impact of this standard on its consolidated financial statements, but do not expect the standard will have a material impact on our consolidated financial statements. Recently Adopted Accounting Standards In July 2019, the FASB issued ASU 2019-07, Codification Updates to SEC Sections - Amendments to SEC Paragraphs Pursuant to SEC Final Rule Releases No. 33-10532, Disclosure Update and Simplification, and Nos. 33-10231 and 33-10442, Investment Company Reporting Modernization, and Miscellaneous Updates. This update clarifies or improves the disclosure and presentation requirements of a variety of codification topics by aligning them with the SEC’s regulations, thereby eliminating redundancies and making the codification easier to apply. This update is effective upon issuance. The Company does not expect the disclosure and presentation amendments included in this update, which are to be applied prospectively, to have a material impact on its consolidated financial statements and related disclosures. In February 2018, the FASB issued ASU 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220). This update provides companies with the option to reclassify stranded tax effects caused by the 2017 Tax Cuts and Jobs Act from accumulated other comprehensive income to retained earnings. This standard is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. The Company has adopted this standard effective January 1, 2019, and the adoption did not have any material impact on the Company’s consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230), which provides guidance on the following eight specific cash flow classification issues: (1) debt prepayment or debt extinguishment costs; (2) settlement of zero-coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing; (3) contingent consideration payments made after a business combination; (4) proceeds from the settlement of insurance claims; (5) proceeds from the settlement of corporate-owned life insurance policies, including bank-owned life insurance policies; (6) distributions received from equity method investees; (7) beneficial interests in securitization transactions; and (8) separately identifiable cash flows and application of the predominance principle. This update is effective for reporting periods beginning after December 15, 2017 for public companies, and fiscal years beginning after December 15, 2018 and interim periods within fiscal years beginning after December 15, 2019 for private companies, with early adoption permitted. The Company has adopted this standard effective January 1, 2019, and the adoption did not have any material impact on the Company’s consolidated financial statements.

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Marketable Securities	Marketable Securities All of the Company's marketable securities were available-for-sale and were classified based on their maturities. Marketable securities with remaining maturities at the date of purchase of three months or less are classified as cash equivalents. Short term investments are securities that original maturity or remaining maturity is greater than three months and not more than twelve months. Long-term investments are securities that original maturity or remaining maturity is greater than twelve months. The table below summarizes the marketable securities as of September 30, 2019 and December 31, 2018 : September 30, 2019 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) Money market funds $ 8,956 $ — $ — $ 8,956 Cash equivalents 8,956 — — 8,956 U.S. treasury securities 74,881 41 (12 ) 74,910 Corporate bonds 8,693 6 — 8,699 Short-term investments 83,574 47 (12 ) 83,609 Corporate bonds 5,251 22 — 5,273 Long-term investments 5,251 22 — 5,273 Total marketable securities $ 97,781 $ 69 $ (12 ) $ 97,838 December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) U.S. treasury securities $ 1,000 $ — $ — $ 1,000 Commercial paper 6,635 — — 6,635 Money market funds 15,223 — — 15,223 Cash equivalents 22,858 — — 22,858 U.S. treasury securities 65,491 2 (4 ) 65,489 Corporate bonds 19,708 15 (3 ) 19,720 Commercial paper 11,894 — — 11,894 Short-term investments 97,093 17 (7 ) 97,103 Total marketable securities $ 119,951 $ 17 $ (7 ) $ 119,961 The maturities of the long-term investments outstanding as of September 30, 2019 range from 13 to 14 months. Unrealized gains and losses on marketable securities are recorded in accumulated other comprehensive loss.

Fair Value Measurement

Fair Value Measurement	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Fair Value Measurement	Fair Value Measurement Carrying amounts of certain of the Company’s financial instruments, including cash equivalents, accounts receivable, accounts payable and accrued liabilities, approximate fair value due to their relatively short maturities and market interest rates, if applicable. The carrying value of the Company’s long-term debt also approximates fair value based on management’s estimation that a current interest rate would not differ materially from the stated rate. There were no other financial assets or liabilities that required fair value hierarchy measurements and disclosures for the periods presented. The table below summarizes the fair value of the Company’s marketable securities measured at fair value on a recurring basis based on the three-tier fair value hierarchy: September 30, 2019 Level 1 Level 2 Level 3 Total (in thousands) Marketable securities Money market funds [1] $ 8,956 $ — $ — $ 8,956 U.S. treasury securities 74,910 — — 74,910 Corporate bonds — 13,972 — 13,972 Total marketable securities $ 83,866 $ 13,972 $ — $ 97,838 December 31, 2018 Level 1 Level 2 Level 3 Total (in thousands) Marketable securities Money market funds [1] $ 15,223 $ — $ — $ 15,223 U.S. treasury securities 66,489 — — 66,489 Corporate bonds — 19,720 — 19,720 Commercial paper — 18,529 — 18,529 Total marketable securities $ 81,712 $ 38,249 $ — $ 119,961 [1] Included in cash and cash equivalents on the condensed consolidated balance sheets.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Components	Balance Sheet Components Inventory As of September 30, 2019 and December 31, 2018 , inventory consisted entirely of finished goods. Property and Equipment, net : September 30, 2019 December 31, 2018 (in thousands) Machinery and equipment $ 4,175 $ 3,785 Construction in progress 1,297 730 Computer and office equipment 561 407 Leasehold improvements 497 448 Furniture and fixtures 154 148 6,684 5,518 Less: Accumulated depreciation and amortization (3,659 ) (3,364 ) $ 3,025 $ 2,154 Depreciation expense was $0.2 million and $0.2 million for the three months ended September 30, 2019 and 2018 , respectively and $0.6 million and $0.5 million for the nine months ended September 30, 2019 and 2018 , respectively. Accrued Liabilities and Other : September 30, 2019 December 31, 2018 (in thousands) Accrued compensation and related expenses $ 6,097 $ 5,425 Accrued litigation expense 2,500 — Accrued professional services 730 583 Sales tax payable 346 388 Liability for early exercise of unvested stock options 133 331 Others 405 133 $ 10,211 $ 6,860

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Operating Leases The Company has an existing seven -year non-cancelable operating lease for an office building space in Santa Clara, California which commenced in April 2018. Also, the Company has non-cancelable operating leases for its office building space in Gallarate, Italy and Mannheim, Germany which both expire in November 2024. Further, the Company also leases vehicles under operating lease arrangements for certain of its sales personnel in Europe which expire various times in 2019 to 2022. Rent expense is recorded over the lease terms on a straight-line basis. Rent expense charged to operations under operating leases was $0.3 million and $0.3 million for three months ended September 30, 2019 and 2018 , respectively, and $0.9 million and $0.9 million for the nine months ended September 30, 2019 and 2018 , respectively. The table below summarizes aggregate future minimum lease payments under all leases as of September 30, 2019 : Year ending December 31, (in thousands) 2019 (remaining three months) $ 295 2020 1,071 2021 958 2022 884 2023 831 Thereafter 1,178 $ 5,217 Purchase Commitments and Obligations The Company has certain purchase commitments related to inventory used in normal course of business. These commitments amounted to $0.3 million and $0.2 million as of September 30, 2019 and December 31, 2018 , respectively. The amounts paid under these arrangements may be less in the event that the arrangement is renegotiated or canceled. Contingencies From time to time, the Company may have certain contingent liabilities that arise in the ordinary course of business activities. The Company records a liability in the consolidated financial statements when a loss is known or considered probable and the amount can be reasonably estimated. If the reasonable estimate of a known or probable loss is a range, and no amount within the range is a better estimate than any other, the minimum amount of the range is accrued. If a loss is reasonably possible but not known or probable, and can be reasonably estimated, the estimated loss or range of loss is disclosed. In most cases, significant judgment is required to estimate the amount and timing of a loss to be recorded. Legal Proceedings On February 6, 2019, a putative class action captioned Eric B. Fromer Chiropractic, Inc. v. SI-BONE, Inc. (Civil Action No. 5:19-cv-633-SVK), was filed in the United States District Court, Northern District of California. The complaint alleges violations of the Telephone Consumer Protection Act (the “TCPA”) on behalf of an individual and putative classes of persons alleged to be similarly situated. The complaint alleges that the Company sent invitations to an educational dinner event to health care providers by way of facsimile transmission. The TCPA prohibits using a fax machine to send unsolicited advertisements not including proper opt-out instructions or to send unsolicited advertisements to persons with whom the sender did not have an established business relationship. On August 5, 2019, the District Court denied the Company’s motion to dismiss the case. The Company believes that it has meritorious defenses and intends to continue to defend itself in the action. Litigation of this kind is often resolved through mediation and settlement. If this lawsuit is resolved through a negotiated settlement, the Company believes that a loss associated with resolution of the pending claim is probable. The Company has accrued litigation expense of $2.5 million during the three months ended September 30, 2019 within general and administrative expenses in the condensed consolidated financial statements. The accrual reflects the estimable and probable costs that the Company may incur concerning the mediation activities and settlement negotiations between the Company and the named plaintiff. The Company continues to evaluate its defenses based on its internal review and investigation, new information and future circumstances. Final disposition of the lawsuit, whether through settlement or through trial, may result in a loss in excess of the aggregate recorded amount. However, a range of reasonably possible excess losses is not estimable at this time. 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 Company has not incurred costs to defend lawsuits or settle claims related to these indemnification agreements. No liability associated with such indemnifications has been recorded to date.

Borrowings

Borrowings	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Borrowings	Borrowings The Company had $39.2 million and $39.0 million of outstanding debt, net of debt issuance costs, as of September 30, 2019 and December 31, 2018 , respectively. The outstanding debt is related to a term loan entered by the Company with Biopharma Credit Investments IV Sub LP, or Pharmakon, in October 2017 for total loan proceeds of $40.0 million . The total debt issuance costs of $1.3 million were recorded as a direct deduction from the carrying amount of the term loan on the consolidated balance sheet, and are being amortized over the period of the term loan using the effective interest method to interest expense in the consolidated statement of operations. The term loan includes an interest-only period for 35 months through September 2020 and is then repaid in equal quarterly principal payments plus interest through December 2022, and is classified as long-term borrowings on the consolidated balance sheet. The term loan carries a fixed interest rate of 11.5% and a closing fee of 1.5% of the funded amount, or $0.6 million . The term loan includes a pre-payment fee equal to the remaining interest due for the first 30 months of the agreement if it is prepaid within the first 30 months, a 2% prepayment penalty for months 31-48, and a 1% penalty for months 49-60. The term loan requires the Company to maintain a minimum cash balance of $5.0 million and beginning with the three months ended March 31, 2019, the Company is required to meet either minimum net sales or trailing 12-month consolidated earnings before interest, taxes, depreciation, and amortization ("EBITDA") targets as discussed in detail in Note 7 of Notes to Consolidated Financial Statements in the Annual Report on Form 10-K filed with the SEC on March 14, 2019. The loan is a senior obligation secured with a blanket first lien on the assets of the Company. The effective interest rate for the three months ended September 30, 2019 and 2018 was 12.4% and for the nine months ended September 30, 2019 and 2018 was 12.3% . The Company was in compliance with all debt covenants as of September 30, 2019 . The table below summarizes annual future minimum principal payments under the loan agreement as of September 30, 2019 : Year ending December 31, (in thousands) 2019 (remaining three months) $ — 2020 4,444 2021 17,778 2022 17,778 Total future minimum payments 40,000 Less: Amount representing debt issuance costs (842 ) Long-term borrowings $ 39,158

Warrants

Warrants	9 Months Ended
	Sep. 30, 2019
Other Liabilities Disclosure [Abstract]
Warrants	Warrants The table below summarizes common stock warrants issued and outstanding at both September 30, 2019 and December 31, 2018 : Date Number of Price per Fair Value (in thousands) Issuance Expiration 3/1/2017 3/1/2027 [a] 1,388 $ 5.94 $ 5 [b] 7/19/2013 7/22/2023 [a] 32,983 9.10 122 [b] 11/26/2014 11/26/2024 [a] 6,680 16.47 49 [b] 10/20/2015 10/20/2025 [a] 41,650 16.47 396 [c] 11/9/2015 11/9/2025 [a] 25,709 16.47 244 [c] 12/22/2016 12/22/2026 [a] 9,712 10.03 45 [c] 118,122 $ 861 [a] Common stock warrants will remain outstanding until the earlier of the expiration date or the date exercised by the holder. [b] Fair value at the date of issuance. [c] Fair value at the date of conversion from redeemable convertible preferred stock to common stock warrants in conjunction with the IPO on October 16, 2018.

Stock-Based Incentive Compensat

Stock-Based Incentive Compensation Plans	9 Months Ended
	Sep. 30, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Stock-Based Incentive Compensation Plans	Stock-Based Incentive Compensation Plans 2018 Equity Incentive Plan In October 2018, the Company adopted the 2018 Equity Incentive Plan (the "2018 EIP"). The number of shares of common stock reserved for issuance under the 2018 EIP will automatically increase on January 1 of each year, beginning January 1, 2019, and continuing through and including January 1, 2028, by 5% of the total number of shares of the Company's capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company's Board of Directors. On January 1, 2019, the total number of shares of common stock reserved for issuance increased by 1,222,538 shares. The Company filed a Registration Statement on Form S-8 on March 22, 2019 to register these additional shares reserved for issuance under the 2018 EIP. As of September 30, 2019 , a total of 2,569,444 shares of common stock are available for future grants under the 2018 EIP. Stock Options The table below summarizes the stock option activity for the nine months ended September 30, 2019 : Number of Weighted- Outstanding as of December 31, 2018 2,641,198 $4.27 Granted 638,983 20.89 Exercised (359,200 ) 3.29 Canceled and forfeited (96,496 ) 9.36 Outstanding as of September 30, 2019 2,824,485 7.98 As of September 30, 2019 , there was $6.3 million of unrecognized compensation cost related to stock options granted. These costs are expected to be recognized over a period of approximately 2.7 years . The table below summarizes the weighted average grant date fair value per share and the assumptions used to estimate the grant date fair value of the stock options granted during the respective periods using the Black-Scholes option-pricing model: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Weighted average grant date fair value per share $5.43 $3.48 $9.78 $2.47 Expected term (years) 5.0 to 7.0 5.3 to 7.0 5.0 to 7.0 5.0 to 7.0 Expected volatility 46.62% to 47.25% 41.00% to 44.00% 41.68% to 47.25% 41.00% to 46.00% Risk-free interest rate 1.32% to 1.39% 2.74% to 2.80% 1.32% to 2.59% 2.35% to 2.93% Dividend yield —% —% —% —% Early Exercise of Unvested Stock Options Early exercises of stock options are subject to a right of repurchase by the Company of any unvested shares. The repurchase rights lapse over the original vesting period of the options. The Company accounts for the cash received in consideration for the early exercised options as a liability included in accrued liabilities, which is then reclassified to stockholders’ equity as the options vest. As of September 30, 2019 and December 31, 2018 , the Company had a total of 29,268 and 74,019 shares of common stock, respectively, subject to repurchase under the 2008 Stock Option Plan and $0.1 million and $0.3 million , respectively, of associated liabilities for the repurchase. Restricted Stock Units The table below summarizes restricted stock units activity for the nine months ended September 30, 2019 : Number of Shares Weighted Average Grant Date Fair Value Outstanding as of December 31, 2018 53,436 $11.69 Granted 607,585 20.30 Vested (65,435 ) 20.74 Canceled and forfeited (30,156) 19.45 Outstanding as of September 30, 2019 565,430 19.48 As of September 30, 2019 , there was a total unrecognized compensation cost of $8.9 million related to the restricted stock units granted. These costs are expected to be recognized over a period of approximately 3.3 years . Employee Stock Purchase Plan Under the Company's 2018 Employee Stock Purchase Plan (the "ESPP") adopted in October 2018, the Company allows eligible employees to purchase shares of the Company's common stock through payroll deductions at the price equal to 85% of the lesser of the fair market value of the stock as of the first date or the ending date of each six month offering period. There were 515,307 shares of common stock originally reserved for issuance under the ESPP. On March 22, 2019, the Company filed a Registration Statement on Form S-8 to register 244,507 additional shares of common stock for issuance under the ESPP. As of September 30, 2019 and December 31, 2018 , total accumulated ESPP related employee payroll deductions amounted to $0.7 million and $0.4 million , respectively, which were included within accrued compensation and related expenses in the consolidated balance sheets. For the three and nine months ended September 30, 2019 , the Company recognized $0.2 million and $0.6 million , respectively, of stock-based compensation expense related to ESPP. As of September 30, 2019 , the unrecognized compensation cost for the ESPP was $0.1 million . The Company estimated the fair value of ESPP purchase rights during the offer period which commenced in May 2019 and ends in November 2019, using a Black-Scholes option pricing model with the following assumptions: Nine Months Ended September 30, 2019 Expected term (years) 0.50 Expected volatility 58.35% Risk-free interest rate 2.49% Dividend yield —% Stock-Based Compensation The table below presents the detail of stock-based compensation expense amounts included in the condensed consolidated statements of operations: Three Months Ended Nine Months Ended 2019 2018 2019 2018 (in thousands) Cost of goods sold $ 57 $ 5 $ 163 $ 17 Sales and marketing 807 110 2,481 350 Research and development 144 30 364 101 General and administrative 903 183 2,588 613 $ 1,911 $ 328 $ 5,596 $ 1,081

Net Loss Per Share of Common St

Net Loss Per Share of Common Stock	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Net Loss Per Share of Common Stock	Net Loss Per Share of Common Stock Basic and Diluted Net Loss per Share The table below summarizes the computation of basic and diluted net loss per share: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 (in thousands, except share and per share data) Net loss $ (11,306 ) $ (4,792 ) $ (29,305 ) $ (12,140 ) Weighted-average shares used to compute basic and diluted net loss per share 24,803,452 3,712,876 * 24,596,788 3,638,905 * Net loss per share, basic and diluted $ (0.46 ) $ (1.29 ) * $ (1.19 ) $ (3.34 ) * * Calculated based on the 1-for-18 reverse stock split effected October 4, 2018. Because the Company has reported a net loss in all periods presented, outstanding stock options, restricted stock units, shares subject to repurchase, ESPP purchase rights, common stock warrants, shares of redeemable convertible preferred stock and redeemable convertible preferred stock warrants are anti-dilutive and therefore diluted net loss per common share is the same as basic net loss per common share for the periods presented. The following anti-dilutive common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Stock options 2,824,485 2,711,667 2,824,485 2,711,667 Restricted stock units 565,430 — 565,430 — Shares subject to repurchase 29,268 78,757 29,268 78,757 ESPP purchase rights 72,679 — 72,679 — Redeemable convertible preferred stock — 12,066,654 — 12,066,654 Redeemable convertible preferred stock warrants — 160,657 — 160,657 Common stock warrants 118,122 124,326 118,122 124,326 3,609,984 15,142,061 3,609,984 15,142,061

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2019
Income Tax Disclosure [Abstract]
Income Taxes	Income Taxes In determining quarterly provisions for income taxes, the Company uses the annual estimated effective tax rate applied to the actual year-to-date profit or loss, adjusted for discrete items arising in that quarter. The Company updates its estimate of its annual effective tax rate at the end of each quarterly period. The estimate takes into account annual forecasted income (loss) before income taxes, the geographic mix of income (loss) before income taxes and any significant permanent tax items. The Company did not have provision for income taxes for the three and nine months ended September 30, 2019 and 2018 . The Company continues to maintain a full valuation allowance against its net deferred tax assets due to the uncertainty surrounding realization of such assets. The Company accounts for the uncertainty in income taxes by utilizing a comprehensive model for the recognition, measurement, presentation and disclosure in financial statements of any uncertain tax positions that have been taken or are expected to be taken on an income tax return. There had been no changes in the estimated uncertain tax benefits recorded as of December 31, 2018 .

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Basis of Presentation	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP have been condensed or omitted, and accordingly the balance sheet as of December 31, 2018 has been derived from the audited consolidated financial statements at that date but does not include all of the information required by GAAP for complete financial statements.
Principles of Consolidation	These unaudited interim condensed consolidated financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments that are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the three and nine months ended September 30, 2019 are not necessarily indicative of the results to be expected for the year ending December 31, 2019 or for any other interim period or for any other future year.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Significant accounting estimates and management judgments reflected in the consolidated financial statements include: fair value of assets and liabilities; analysis of the allowance for doubtful accounts; inventory valuation; valuation of deferred tax assets, including related valuation allowances; fair value of common stock and redeemable convertible preferred stock warrants; stock-based compensation; and useful lives of long lived assets. Estimates are based on historical experience, where applicable and other assumptions believed to be reasonable by the management. Actual results could differ from those estimates.
JOBS Act Accounting Election	JOBS Act Accounting Election As an emerging growth company under the Jumpstart Our Business Startups Act of 2012 (the "JOBS Act"), the Company is eligible to take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies. The Company has elected to take advantage of the extended transition period for adopting new or revised accounting standards that have different effective dates for public and private companies. Those standards apply to companies until the earlier of the date that it is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, these condensed consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. The Company continues to be an emerging growth company for five years following the completion of the IPO, unless one of the following occurs: (i) if the Company's total annual gross revenues are $1.07 billion or more; or (ii) the Company has issued more than $1.0 billion in non-convertible debt in the past three years; or (iii) the Company becomes a "large accelerated filer," as defined in Rule 12b-2 of the Exchange Act.
Segments	Segments The chief operating decision makers for the Company are the Chief Executive Officer ("CEO") and Chief Operating Officer & Chief Financial Officer ("COO/CFO"). The CEO and the COO/CFO review financial information presented on a consolidated basis, accompanied by information about revenue by geographic region, for purposes of 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. Accordingly, the Company has determined that it has a single reportable and operating segment structure.
Concentration of Credit Risk	Concentration of Credit Risk Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and cash equivalents. The Company’s cash and cash equivalents are deposited with financial institutions in the United States and in Europe; the majority of the Company’s cash and cash equivalents are deposited with a single financial institution in the United States. Deposits in this institution exceed the amount of insurance provided on such deposits. The Company has not experienced any losses on its deposits of cash and cash equivalents. The Company’s revenue and accounts receivable are spread across a large number of customers, primarily in the United States, and no one customer accounts for more than 10% of total revenue or gross accounts receivable in any period presented.
Recent Accounting Standards	Recently Issued Accounting Standards Not Yet Effective In May 2014, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“ASU”) 2014-09, Revenue from Contracts with Customers, which requires an entity to recognize the amount of revenue to which it expects to be entitled for the transfer of promised goods or services to customers. The new standard is effective for fiscal years beginning after December 15, 2017 for public companies, and for fiscal years beginning after December 15, 2018, and interim periods beginning after December 15, 2019, for private companies. Early application is permitted. The standard permits the use of either the retrospective or cumulative effect transition method. In March 2016, the FASB issued ASU 2016-08, which clarifies the implementation guidance on principal versus agent considerations. In April 2016, the FASB issued ASU 2016-10, which clarifies certain aspects of identifying performance obligations and licensing implementation guidance. In May 2016, the FASB issued ASU 2016-12, which relates to disclosures of remaining performance obligations, as well as other amendments to guidance on collectability, non-cash consideration and the presentation of sales and other similar taxes collected from customers. In November 2018, the FASB issued ASU 2018-18 , which clarifies when transactions between participants in a collaborative arrangement are within the scope of the FASB’s revenue standard, Topic 606. The Company will adopt this standard using the modified retrospective method effective for the year ending December 31, 2019, which will be first presented on the Company's Annual Report on Form 10-K for the year ended December 31, 2019. As an emerging growth company that elected to take advantage of the JOBS Act accounting election, the Company is not required to adopt the new revenue standard in the interim reporting periods for the year ending December 31, 2019, but rather for the fiscal year ending December 31, 2019 and then in the interim periods following the year of adoption. The Company also is not required, and intends not, to revise its 2019 interim periods which were and will be reported under ASC 605 in its fiscal year 2020 interim financial reporting. The Company is finalizing its assessment of the impact of adopting this new standard on its accounting policies and processes. As it relates to product sales where the Company's sales representative delivers the product at the point of implantation at hospital or other medical facilities, which represents majority of the Company's revenue, the Company expects to continue to recognize the revenue upon completion of the procedure and authorization by the customer. As it relates to sale of products through distributors and hospitals where product is ordered in advance of the procedure, the Company expects to continue to recognize the revenue upon shipments to the customers. Additionally, the new standard requires the capitalization of costs to obtain a contract, primarily sales commissions, and amortization of these costs over the contract period or estimated customer life. The Company expects to continue expensing all sales commissions as incurred. In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires that lessee's recognize a right-of-use asset and a lease liability for all leases with lease terms greater than twelve months in the balance sheet. A lease liability is a lessee's obligation to make lease payments arising from a lease, measured on a discounted basis; and a right-of-use asset is an asset that represents the lessee’s right to use, or control use of, a specified asset for the lease term for all leases (with the exception of short-term leases) at the adoption date. In July 2018, the FASB issued ASU 2018-10 and ASU 2018-11, which provides clarification on the narrow aspects of the guidance and provide an additional transition method to adopt the new leases standard. The new transition method allows an entity to recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. In March 2019, the FASB issued ASU 2019-01, which provides clarification on implementation issues associated with adopting ASU 2016-02. The new guidance is effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018 for public companies and effective for fiscal years beginning after December 15, 2019 and interim periods within fiscal years beginning after December 15, 2020 for private companies. Early adoption is permitted for any interim or annual financial statements not yet issued. The new leases standard must be adopted using a modified retrospective transition method and allows for the application of the new guidance at the beginning of the earliest comparative period presented or at the adoption date. The Company is currently evaluating the impact of this standard on its consolidated financial statements and anticipates adopting the standard for the fiscal year ending December 31, 2020. In June 2018, the FASB issued ASU 2018-07, Improvements to Non-employee Share-Based Payment Accounting. ASU 2018-07 expands the scope of Topic 718, Compensation-Stock Compensation, to include share-based payments issued to non-employees for goods or services. Consequently, the accounting for share-based payments to non-employees and employees will be substantially aligned. ASU 2018-07 supersedes Subtopic 505-50, Equity-Equity-Based Payments to Non-Employees. For public business entities, the amendments are effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. For all other entities, the amendments are effective for fiscal years beginning after December 15, 2019, and interim periods within fiscal years beginning after December 15, 2020. Early adoption is permitted, but no earlier than a company’s adoption date of ASC 606. The Company is currently evaluating the impact that the adoption of this standard will have on the consolidated financial statements, and anticipates adopting the standard for the fiscal year ending December 31, 2020. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurements, which eliminates, adds or modifies certain disclosure requirements for fair value measurements. Entities will no longer be required to disclose the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, but will be required to disclose the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. This ASU is effective for fiscal years beginning after December 15, 2019, including interim periods within that fiscal year, with early adoption permitted to adopt either the entire standard or only the provisions that eliminate or modify the requirements. The Company is currently evaluating the impact that the adoption of this standard will have on the consolidated financial statements, and anticipates adopting the standard for the fiscal year ending December 31, 2020. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. The new standard revises the accounting requirements related to the measurement of credit losses and will require organizations to measure all expected credit losses for financial assets based on historical experience, current conditions and reasonable and supportable forecasts about collectability. Assets must be presented in the financial statements at the net amount expected to be collected. The amendments to this update are effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years for public companies and are effective for fiscal years beginning after December 15, 2020, including interim periods within those fiscal years for private companies. The Company is currently evaluating the impact of this standard on its consolidated financial statements, but do not expect the standard will have a material impact on our consolidated financial statements. Recently Adopted Accounting Standards In July 2019, the FASB issued ASU 2019-07, Codification Updates to SEC Sections - Amendments to SEC Paragraphs Pursuant to SEC Final Rule Releases No. 33-10532, Disclosure Update and Simplification, and Nos. 33-10231 and 33-10442, Investment Company Reporting Modernization, and Miscellaneous Updates. This update clarifies or improves the disclosure and presentation requirements of a variety of codification topics by aligning them with the SEC’s regulations, thereby eliminating redundancies and making the codification easier to apply. This update is effective upon issuance. The Company does not expect the disclosure and presentation amendments included in this update, which are to be applied prospectively, to have a material impact on its consolidated financial statements and related disclosures. In February 2018, the FASB issued ASU 2018-02, Income Statement-Reporting Comprehensive Income (Topic 220). This update provides companies with the option to reclassify stranded tax effects caused by the 2017 Tax Cuts and Jobs Act from accumulated other comprehensive income to retained earnings. This standard is effective for all entities for fiscal years, and interim periods within those fiscal years, beginning after December 15, 2018. Early adoption is permitted. The Company has adopted this standard effective January 1, 2019, and the adoption did not have any material impact on the Company’s consolidated financial statements. In August 2016, the FASB issued ASU 2016-15, Statement of Cash Flows (Topic 230), which provides guidance on the following eight specific cash flow classification issues: (1) debt prepayment or debt extinguishment costs; (2) settlement of zero-coupon debt instruments or other debt instruments with coupon interest rates that are insignificant in relation to the effective interest rate of the borrowing; (3) contingent consideration payments made after a business combination; (4) proceeds from the settlement of insurance claims; (5) proceeds from the settlement of corporate-owned life insurance policies, including bank-owned life insurance policies; (6) distributions received from equity method investees; (7) beneficial interests in securitization transactions; and (8) separately identifiable cash flows and application of the predominance principle. This update is effective for reporting periods beginning after December 15, 2017 for public companies, and fiscal years beginning after December 15, 2018 and interim periods within fiscal years beginning after December 15, 2019 for private companies, with early adoption permitted. The Company has adopted this standard effective January 1, 2019, and the adoption did not have any material impact on the Company’s consolidated financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2019
Accounting Policies [Abstract]
Schedule of Revenue by Geography	The table below summarizes the Company's revenue by geography: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 (in thousands) United States $ 14,856 $ 12,216 $ 43,325 $ 35,672 International 1,326 1,165 4,165 4,084 $ 16,182 $ 13,381 $ 47,490 $ 39,756

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2019
Investments, Debt and Equity Securities [Abstract]
Schedule of Marketable Securities	The table below summarizes the marketable securities as of September 30, 2019 and December 31, 2018 : September 30, 2019 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) Money market funds $ 8,956 $ — $ — $ 8,956 Cash equivalents 8,956 — — 8,956 U.S. treasury securities 74,881 41 (12 ) 74,910 Corporate bonds 8,693 6 — 8,699 Short-term investments 83,574 47 (12 ) 83,609 Corporate bonds 5,251 22 — 5,273 Long-term investments 5,251 22 — 5,273 Total marketable securities $ 97,781 $ 69 $ (12 ) $ 97,838 December 31, 2018 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) U.S. treasury securities $ 1,000 $ — $ — $ 1,000 Commercial paper 6,635 — — 6,635 Money market funds 15,223 — — 15,223 Cash equivalents 22,858 — — 22,858 U.S. treasury securities 65,491 2 (4 ) 65,489 Corporate bonds 19,708 15 (3 ) 19,720 Commercial paper 11,894 — — 11,894 Short-term investments 97,093 17 (7 ) 97,103 Total marketable securities $ 119,951 $ 17 $ (7 ) $ 119,961

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	9 Months Ended
	Sep. 30, 2019
Fair Value Disclosures [Abstract]
Schedule of Marketable Securities Measured at Fair Value on Recurring Basis	The table below summarizes the fair value of the Company’s marketable securities measured at fair value on a recurring basis based on the three-tier fair value hierarchy: September 30, 2019 Level 1 Level 2 Level 3 Total (in thousands) Marketable securities Money market funds [1] $ 8,956 $ — $ — $ 8,956 U.S. treasury securities 74,910 — — 74,910 Corporate bonds — 13,972 — 13,972 Total marketable securities $ 83,866 $ 13,972 $ — $ 97,838 December 31, 2018 Level 1 Level 2 Level 3 Total (in thousands) Marketable securities Money market funds [1] $ 15,223 $ — $ — $ 15,223 U.S. treasury securities 66,489 — — 66,489 Corporate bonds — 19,720 — 19,720 Commercial paper — 18,529 — 18,529 Total marketable securities $ 81,712 $ 38,249 $ — $ 119,961 [1] Included in cash and cash equivalents on the condensed consolidated balance sheets.

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Property and Equipment, Net	Property and Equipment, net : September 30, 2019 December 31, 2018 (in thousands) Machinery and equipment $ 4,175 $ 3,785 Construction in progress 1,297 730 Computer and office equipment 561 407 Leasehold improvements 497 448 Furniture and fixtures 154 148 6,684 5,518 Less: Accumulated depreciation and amortization (3,659 ) (3,364 ) $ 3,025 $ 2,154
Schedule of Accrued Liabilities and Other	Accrued Liabilities and Other : September 30, 2019 December 31, 2018 (in thousands) Accrued compensation and related expenses $ 6,097 $ 5,425 Accrued litigation expense 2,500 — Accrued professional services 730 583 Sales tax payable 346 388 Liability for early exercise of unvested stock options 133 331 Others 405 133 $ 10,211 $ 6,860

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Schedule of Aggregate Future Minimum Lease Payments	The table below summarizes aggregate future minimum lease payments under all leases as of September 30, 2019 : Year ending December 31, (in thousands) 2019 (remaining three months) $ 295 2020 1,071 2021 958 2022 884 2023 831 Thereafter 1,178 $ 5,217

Borrowings (Tables)

Borrowings (Tables)	9 Months Ended
	Sep. 30, 2019
Debt Disclosure [Abstract]
Schedule of Annual Future Minimum Principal Payments Under Loan Agreements	The table below summarizes annual future minimum principal payments under the loan agreement as of September 30, 2019 : Year ending December 31, (in thousands) 2019 (remaining three months) $ — 2020 4,444 2021 17,778 2022 17,778 Total future minimum payments 40,000 Less: Amount representing debt issuance costs (842 ) Long-term borrowings $ 39,158

Warrants (Tables)

Warrants (Tables)	9 Months Ended
	Sep. 30, 2019
Other Liabilities Disclosure [Abstract]
Schedule of Warrants Issued and Outstanding	The table below summarizes common stock warrants issued and outstanding at both September 30, 2019 and December 31, 2018 : Date Number of Price per Fair Value (in thousands) Issuance Expiration 3/1/2017 3/1/2027 [a] 1,388 $ 5.94 $ 5 [b] 7/19/2013 7/22/2023 [a] 32,983 9.10 122 [b] 11/26/2014 11/26/2024 [a] 6,680 16.47 49 [b] 10/20/2015 10/20/2025 [a] 41,650 16.47 396 [c] 11/9/2015 11/9/2025 [a] 25,709 16.47 244 [c] 12/22/2016 12/22/2026 [a] 9,712 10.03 45 [c] 118,122 $ 861 [a] Common stock warrants will remain outstanding until the earlier of the expiration date or the date exercised by the holder. [b] Fair value at the date of issuance. [c] Fair value at the date of conversion from redeemable convertible preferred stock to common stock warrants in conjunction with the IPO on October 16, 2018.

Stock-Based Incentive Compens_2

Stock-Based Incentive Compensation Plans (Tables)	9 Months Ended
	Sep. 30, 2019
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]
Schedule of Stock Option Activity Under Stock Option Plan	The table below summarizes the stock option activity for the nine months ended September 30, 2019 : Number of Weighted- Outstanding as of December 31, 2018 2,641,198 $4.27 Granted 638,983 20.89 Exercised (359,200 ) 3.29 Canceled and forfeited (96,496 ) 9.36 Outstanding as of September 30, 2019 2,824,485 7.98
Schedule of Valuation Assumptions Related to Stock Option Awards	The Company estimated the fair value of ESPP purchase rights during the offer period which commenced in May 2019 and ends in November 2019, using a Black-Scholes option pricing model with the following assumptions: Nine Months Ended September 30, 2019 Expected term (years) 0.50 Expected volatility 58.35% Risk-free interest rate 2.49% Dividend yield —% The table below summarizes the weighted average grant date fair value per share and the assumptions used to estimate the grant date fair value of the stock options granted during the respective periods using the Black-Scholes option-pricing model: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Weighted average grant date fair value per share $5.43 $3.48 $9.78 $2.47 Expected term (years) 5.0 to 7.0 5.3 to 7.0 5.0 to 7.0 5.0 to 7.0 Expected volatility 46.62% to 47.25% 41.00% to 44.00% 41.68% to 47.25% 41.00% to 46.00% Risk-free interest rate 1.32% to 1.39% 2.74% to 2.80% 1.32% to 2.59% 2.35% to 2.93% Dividend yield —% —% —% —%
Schedule of Restricted Stock Unit Activity	The table below summarizes restricted stock units activity for the nine months ended September 30, 2019 : Number of Shares Weighted Average Grant Date Fair Value Outstanding as of December 31, 2018 53,436 $11.69 Granted 607,585 20.30 Vested (65,435 ) 20.74 Canceled and forfeited (30,156) 19.45 Outstanding as of September 30, 2019 565,430 19.48
Schedule of Stock-Based Compensation	The table below presents the detail of stock-based compensation expense amounts included in the condensed consolidated statements of operations: Three Months Ended Nine Months Ended 2019 2018 2019 2018 (in thousands) Cost of goods sold $ 57 $ 5 $ 163 $ 17 Sales and marketing 807 110 2,481 350 Research and development 144 30 364 101 General and administrative 903 183 2,588 613 $ 1,911 $ 328 $ 5,596 $ 1,081

Net Loss Per Share of Common _2

Net Loss Per Share of Common Stock (Tables)	9 Months Ended
	Sep. 30, 2019
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss per Share	The table below summarizes the computation of basic and diluted net loss per share: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 (in thousands, except share and per share data) Net loss $ (11,306 ) $ (4,792 ) $ (29,305 ) $ (12,140 ) Weighted-average shares used to compute basic and diluted net loss per share 24,803,452 3,712,876 * 24,596,788 3,638,905 * Net loss per share, basic and diluted $ (0.46 ) $ (1.29 ) * $ (1.19 ) $ (3.34 ) * * Calculated based on the 1-for-18 reverse stock split effected October 4, 2018.
Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss per Share	The following anti-dilutive common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented: Three Months Ended September 30, Nine Months Ended September 30, 2019 2018 2019 2018 Stock options 2,824,485 2,711,667 2,824,485 2,711,667 Restricted stock units 565,430 — 565,430 — Shares subject to repurchase 29,268 78,757 29,268 78,757 ESPP purchase rights 72,679 — 72,679 — Redeemable convertible preferred stock — 12,066,654 — 12,066,654 Redeemable convertible preferred stock warrants — 160,657 — 160,657 Common stock warrants 118,122 124,326 118,122 124,326 3,609,984 15,142,061 3,609,984 15,142,061

The Company and Nature of Bus_2

The Company and Nature of Business (Details) $ / shares in Units, $ in Millions	Oct. 16, 2018USD ($)$ / sharesshares	Oct. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Reverse stock split ratio		0.0556
Common stock issued upon conversion of redeemable convertible preferred stock (in shares)	12,066,654
Adjustments to additional paid-in capital related to warrants | $	$ 1.2
IPO
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in IPO (in shares)	8,280,000
IPO share price (in dollars per share) | $ / shares	$ 15
Net proceeds from IPO | $	$ 113.4
Common Stock
Subsidiary, Sale of Stock [Line Items]
Warrants to purchase shares of stock (in shares)	160,657
Preferred Stock Warrants | Redeemable Convertible Preferred Stock
Subsidiary, Sale of Stock [Line Items]
Number of warrants converted (in shares)	156,550

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Segments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019USD ($)	Sep. 30, 2018USD ($)	Sep. 30, 2019USD ($)segment	Sep. 30, 2018USD ($)
Accounting Policies [Abstract]
Number of reportable segments | segment			1
Number of operating segments | segment			1
Disaggregation of Revenue [Line Items]
Revenue	$ 16,182	$ 13,381	$ 47,490	$ 39,756
United States
Disaggregation of Revenue [Line Items]
Revenue	14,856	12,216	43,325	35,672
International
Disaggregation of Revenue [Line Items]
Revenue	$ 1,326	$ 1,165	$ 4,165	$ 4,084

Marketable Securities (Details)

Marketable Securities (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Cash equivalents
Carrying Value	$ 8,956	$ 22,858
Short-term investments
Amortized Cost	83,574	97,093
Unrealized Gains	47	17
Unrealized Losses	(12)	(7)
Aggregate Fair Value	83,609	97,103
Long-term investments
Amortized Cost	5,251
Unrealized Gains	22
Unrealized Losses	0
Aggregate Fair Value	5,273	0
Total marketable securities, Amortized Cost	97,781	119,951
Total marketable securities, Unrealized Gains	69	17
Total marketable securities, Unrealized Losses	(12)	(7)
Total marketable securities, Aggregate Fair Value	97,838	119,961
Money market funds
Cash equivalents
Carrying Value	8,956	15,223
U.S. treasury securities
Cash equivalents
Carrying Value		1,000
Short-term investments
Amortized Cost	74,881	65,491
Unrealized Gains	41	2
Unrealized Losses	(12)	(4)
Aggregate Fair Value	74,910	65,489
Corporate bonds
Short-term investments
Amortized Cost	8,693	19,708
Unrealized Gains	6	15
Unrealized Losses	0	(3)
Aggregate Fair Value	8,699	19,720
Long-term investments
Amortized Cost	5,251
Unrealized Gains	22
Unrealized Losses	0
Aggregate Fair Value	$ 5,273
Commercial paper
Cash equivalents
Carrying Value		6,635
Short-term investments
Amortized Cost		11,894
Unrealized Gains		0
Unrealized Losses		0
Aggregate Fair Value		$ 11,894
Minimum
Marketable Securities [Line Items]
Long-term investments, maturity (in months)	13 months
Maximum
Marketable Securities [Line Items]
Long-term investments, maturity (in months)	14 months

Fair Value Measurement - Market

Fair Value Measurement - Marketable Securities Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Marketable securities
Marketable securities	$ 97,838	$ 119,961
Money market funds
Marketable securities
Marketable securities	8,956	15,223
U.S. treasury securities
Marketable securities
Marketable securities	74,910	66,489
Corporate bonds
Marketable securities
Marketable securities	13,972	19,720
Commercial paper
Marketable securities
Marketable securities		18,529
Level 1
Marketable securities
Marketable securities	83,866	81,712
Level 1 | Money market funds
Marketable securities
Marketable securities	8,956	15,223
Level 1 | U.S. treasury securities
Marketable securities
Marketable securities	74,910	66,489
Level 1 | Corporate bonds
Marketable securities
Marketable securities	0	0
Level 1 | Commercial paper
Marketable securities
Marketable securities		0
Level 2
Marketable securities
Marketable securities	13,972	38,249
Level 2 | Money market funds
Marketable securities
Marketable securities	0	0
Level 2 | U.S. treasury securities
Marketable securities
Marketable securities	0	0
Level 2 | Corporate bonds
Marketable securities
Marketable securities	13,972	19,720
Level 2 | Commercial paper
Marketable securities
Marketable securities		18,529
Level 3
Marketable securities
Marketable securities	0	0
Level 3 | Money market funds
Marketable securities
Marketable securities	0	0
Level 3 | U.S. treasury securities
Marketable securities
Marketable securities	0	0
Level 3 | Corporate bonds
Marketable securities
Marketable securities	$ 0	0
Level 3 | Commercial paper
Marketable securities
Marketable securities		$ 0

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Property and Equipment, Net
Property and equipment, gross	$ 6,684		$ 6,684		$ 5,518
Less: Accumulated depreciation and amortization	(3,659)		(3,659)		(3,364)
Property and equipment, net	3,025		3,025		2,154
Depreciation expense	200	$ 200	600	$ 500
Machinery and equipment
Property and Equipment, Net
Property and equipment, gross	4,175		4,175		3,785
Construction in progress
Property and Equipment, Net
Property and equipment, gross	1,297		1,297		730
Computer and office equipment
Property and Equipment, Net
Property and equipment, gross	561		561		407
Leasehold improvements
Property and Equipment, Net
Property and equipment, gross	497		497		448
Furniture and fixtures
Property and Equipment, Net
Property and equipment, gross	$ 154		$ 154		$ 148

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities and Other (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Accrued Liabilities and Other
Accrued compensation and related expenses	$ 6,097	$ 5,425
Accrued litigation expense	2,500	0
Accrued professional services	730	583
Sales tax payable	346	388
Liability for early exercise of unvested stock options	133	331
Others	405	133
Accrued liabilities and other	$ 10,211	$ 6,860

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Other Commitments [Line Items]
Rent expense	$ 300,000	$ 300,000	$ 900,000	$ 900,000
Purchase commitments related to inventory	300,000		300,000		$ 200,000
Accrued litigation expense	2,500,000		2,500,000		$ 0
Indemnification Agreement
Other Commitments [Line Items]
Costs to defend lawsuits or settle claims			0
Costs accrued to defend lawsuits	$ 0		$ 0
Santa Clara, California
Other Commitments [Line Items]
Non-cancelable operating lease term	7 years		7 years

Commitments and Contingencies_2

Commitments and Contingencies - Aggregate Future Minimum Lease Payments (Details) $ in Thousands	Sep. 30, 2019USD ($)
Aggregate Future Minimum Lease Payments
2019 (remaining three months)	$ 295
2020	1,071
2021	958
2022	884
2023	831
Thereafter	1,178
Total	$ 5,217

Borrowings - Narrative (Details

Borrowings - Narrative (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Oct. 31, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Debt Instrument [Line Items]
Long-term borrowings		$ 39,158		$ 39,158		$ 38,963
Term Loan | Pharmakon Term Loan
Debt Instrument [Line Items]
Total loan proceeds	$ 40,000
Debt issuance costs	$ 1,300
Debt period payment, interest only period	35 months
Debt interest stated percentage (percent)	11.50%
Debt closing fee percentage (percent)	1.50%
Debt instrument fee amount	$ 600
Debt covenant minimum cash balance	$ 5,000
Effective interest rate during the period (percent)		12.40%	12.40%	12.30%	12.30%
Term Loan | Pharmakon Term Loan | Prepayment Penalty, 31-48 Months
Debt Instrument [Line Items]
Debt prepayment penalty percentage (percent)	2.00%
Term Loan | Pharmakon Term Loan | Prepayment Penalty, 49-60 Months
Debt Instrument [Line Items]
Debt prepayment penalty percentage (percent)	1.00%

Borrowings - Debt Maturity (Det

Borrowings - Debt Maturity (Details) $ in Thousands	Sep. 30, 2019USD ($)
Maturities of Long-term Debt [Abstract]
2019 (remaining three months)	$ 0
2020	4,444
2021	17,778
2022	17,778
Total future minimum payments	40,000
Less: Amount representing debt issuance costs	(842)
Long-term borrowings	$ 39,158

Warrants - Issued and Outstandi

Warrants - Issued and Outstanding (Details) - Common Stock - USD ($) $ / shares in Units, $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Oct. 16, 2018
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)			160,657
Warrants Issued 3/1/2017
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	1,388	1,388
Price per Share (in dollars per share)	$ 5.94	$ 5.94
Fair Value	$ 5	$ 5
Warrants Issued 7/19/2013
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	32,983	32,983
Price per Share (in dollars per share)	$ 9.1	$ 9.1
Fair Value	$ 122	$ 122
Warrants Issued 11/26/2014
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	6,680	6,680
Price per Share (in dollars per share)	$ 16.47	$ 16.47
Fair Value	$ 49	$ 49
Warrants Issued 10/20/2015
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	41,650	41,650
Price per Share (in dollars per share)	$ 16.47	$ 16.47
Fair Value	$ 396	$ 396
Warrants Issued 11/9/2015
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	25,709	25,709
Price per Share (in dollars per share)	$ 16.47	$ 16.47
Fair Value	$ 244	$ 244
Warrants Issued 12/22/2016
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	9,712	9,712
Price per Share (in dollars per share)	$ 10.03	$ 10.03
Fair Value	$ 45	$ 45
Common Stock Warrants
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	118,122	118,122
Fair Value	$ 861	$ 861

Stock-Based Incentive Compens_3

Stock-Based Incentive Compensation Plans - Narrative (Details) - USD ($) $ in Thousands	Mar. 22, 2019	Jan. 01, 2019	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Oct. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost			$ 6,300		$ 6,300
Early exercise of stock options, share subject to repurchase (in shares)			29,268		29,268		74,019
Liability for early exercise of unvested stock options			$ 133		$ 133		$ 331
Stock-based compensation expense			1,911	$ 328	$ 5,596	$ 1,081
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, expected period for recognition (in years)					2 years 8 months 12 days
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, expected period for recognition (in years)					3 years 3 months 19 days
Unrecognized compensation cost			$ 8,900		$ 8,900
2018 EIP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual increase in shares reserved as percentage of prior year-end shares outstanding (percent)			5.00%		5.00%
Increase in number of shares of common stock reserved for issuance (in shares)		1,222,538
Number of shares of common stock available for future grants (in shares)			2,569,444		2,569,444
2018 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in number of shares of common stock reserved for issuance (in shares)	244,507
Unrecognized compensation cost			$ 100		$ 100
Number of shares reserved for issuance (in shares)								515,307
Accrued compensation and related expenses for employee payroll deductions			700		700		$ 400
Stock-based compensation expense			$ 200		$ 600

Stock-Based Incentive Compens_4

Stock-Based Incentive Compensation Plans - Stock Option Activity Under the Stock Option Plan (Details)	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Number of Shares
Outstanding, beginning of period (in shares) | shares	2,641,198
Granted (in shares) | shares	638,983
Exercised (in shares) | shares	(359,200)
Canceled and forfeited (in shares) | shares	(96,496)
Outstanding, end of period (in shares) | shares	2,824,485
Weighted-Average Exercise Price
Outstanding, beginning of period (in dollars per share) | $ / shares	$ 4.27
Granted (in dollars per share) | $ / shares	20.89
Exercised (in dollars per share) | $ / shares	3.29
Canceled and forfeited (in dollars per share) | $ / shares	9.36
Outstanding, end of period (in dollars per share) | $ / shares	$ 7.98

Stock-Based Incentive Compens_5

Stock-Based Incentive Compensation Plans - Weighted Average Grant Date Fair Value and Assumptions (Details) - $ / shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Weighted average grant date fair value per share and fair value assumptions for estimate fair value
Weighted average grant date fair value per share (in dollars per share)	$ 5.43	$ 3.48	$ 9.78	$ 2.47
Stock Options
Weighted average grant date fair value per share and fair value assumptions for estimate fair value
Expected volatility, minimum (percent)	46.62%	41.00%	41.68%	41.00%
Expected volatility, maximum (percent)	47.25%	44.00%	47.25%	46.00%
Risk-free interest rate, minimum (percent)	1.32%	2.74%	1.32%	2.35%
Risk-free interest rate, maximum (percent)	1.39%	2.80%	2.59%	2.93%
Dividend yield (percent)	0.00%	0.00%	0.00%	0.00%
Minimum | Stock Options
Weighted average grant date fair value per share and fair value assumptions for estimate fair value
Expected term (years)	5 years 8 days	5 years 3 months 17 days	5 years 8 days	5 years
Maximum | Stock Options
Weighted average grant date fair value per share and fair value assumptions for estimate fair value
Expected term (years)	6 years 11 months 23 days	7 years	7 years	7 years

Stock-Based Incentive Compens_6

Stock-Based Incentive Compensation Plans - Restricted Stock Units Activity (Details) - Restricted Stock Units	9 Months Ended
	Sep. 30, 2019$ / sharesshares
Number of Shares
Outstanding, beginning of period (in shares) | shares	53,436
Granted (in shares) | shares	607,585
Vested (in shares) | shares	(65,435)
Canceled and forfeited (in shares) | shares	(30,156)
Outstanding, end of period (in shares) | shares	565,430
Weighted Average Grant Date Fair Value
Outstanding, beginning of period (in dollars per share) | $ / shares	$ 11.69
Granted (in dollars per share) | $ / shares	20.30
Vested (in dollars per share) | $ / shares	20.74
Canceled and forfeited (in dollars per share) | $ / shares	19.45
Outstanding, end of period (in dollars per share) | $ / shares	$ 19.48

Stock-Based Incentive Compens_7

Stock-Based Incentive Compensation Plans - Employee Stock Purchase Plan (Details) - ESPP Purchase Rights	3 Months Ended
	Sep. 30, 2019
Assumptions for estimation of fair value of ESPP purchase rights
Expected term (years)	6 months
Expected volatility (percent)	58.35%
Risk-free interest rate (percent)	2.49%
Dividend yield (percent)	0.00%

Stock-Based Incentive Compens_8

Stock-Based Incentive Compensation Plans - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,911	$ 328	$ 5,596	$ 1,081
Cost of goods sold
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	57	5	163	17
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	807	110	2,481	350
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	144	30	364	101
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 903	$ 183	$ 2,588	$ 613

Net Loss Per Share of Common _3

Net Loss Per Share of Common Stock - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018
Earnings Per Share [Abstract]
Net loss	$ (11,306)	$ (8,654)	$ (9,345)	$ (4,792)	$ (3,147)	$ (4,201)	$ (29,305)	$ (12,140)
Weighted-average number of common shares used to compute basic and diluted net loss per share (in shares)	24,803,452			3,712,876			24,596,788	3,638,905
Net loss per share, basic and diluted (in dollars per share)	$ (0.46)			$ (1.29)			$ (1.19)	$ (3.34)

Net Loss Per Share of Common _4

Net Loss Per Share of Common Stock - Antidilutive Securities Excluding from Computation of Earnings Per Share (Details) - shares	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	3,609,984	15,142,061	3,609,984	15,142,061
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	2,824,485	2,711,667	2,824,485	2,711,667
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	565,430	0	565,430	0
Shares subject to repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	29,268	78,757	29,268	78,757
ESPP purchase rights
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	72,679	0	72,679	0
Redeemable convertible preferred stock
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	0	12,066,654	0	12,066,654
Redeemable convertible preferred stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	0	160,657	0	160,657
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	118,122	124,326	118,122	124,326