SI-BONE (SIBN) 10-Q 3 Nov 20 2020 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2020	Oct. 29, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2020
Document Transition Report	false
Entity File Number	001-38701
Entity Registrant Name	SI-BONE, INC.
Entity Central Index Key	0001459839
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	26-2216351
Entity Address, Address Line One	471 El Camino Real
Entity Address, Address Line Two	Suite 101
Entity Address, City or Town	Santa Clara
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	95050
City Area Code	408
Local Phone Number	207-0700
Title of 12(b) Security	Common Stock, par value $0.0001 per share
Trading Symbol	SIBN
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		32,360,839

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 55,996	$ 10,435
Short-term investments	76,024	81,345
Accounts receivable, net of allowance for doubtful accounts of $263 and $238, respectively	11,417	11,720
Inventory	5,071	5,452
Prepaid expenses and other current assets	1,014	2,510
Total current assets	149,522	111,462
Long-term investments	0	1,278
Property and equipment, net	4,479	3,954
Other non-current assets	314	315
TOTAL ASSETS	154,315	117,009
Current liabilities:
Accounts payable	3,102	2,811
Accrued liabilities and other	8,719	11,605
Current portion of long-term borrowings	0	4,358
Total current liabilities	11,821	18,774
Long-term borrowings	39,368	34,865
Other long-term liabilities	1,095	362
TOTAL LIABILITIES	52,284	54,001
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; 28,838,577 and 25,163,803 shares issued and outstanding, respectively	3	3
Additional paid-in capital	331,896	258,121
Accumulated other comprehensive income	430	464
Accumulated deficit	(230,298)	(195,580)
TOTAL STOCKHOLDERS’ EQUITY	102,031	63,008
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 154,315	$ 117,009

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 263	$ 238
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)	28,838,577	25,163,803
Common stock outstanding (in shares)	28,838,577	25,163,803

CONDENSED CONSOLIDATED STATEMEN

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Income Statement [Abstract]
Revenue	$ 20,373	$ 16,182	$ 51,243	$ 47,490
Cost of goods sold	2,578	1,630	6,627	4,744
Gross profit	17,795	14,552	44,616	42,746
Operating expenses:
Sales and marketing	18,772	16,443	53,808	48,985
Research and development	2,778	1,874	7,033	5,503
General and administrative	4,920	6,816	14,471	15,776
Total operating expenses	26,470	25,133	75,312	70,264
Loss from operations	(8,675)	(10,581)	(30,696)	(27,518)
Interest and other income (expense), net:
Interest income	192	612	1,019	2,051
Interest expense	(1,102)	(1,243)	(5,016)	(3,706)
Other income (expense), net	111	(94)	(25)	(132)
Net loss	(9,474)	(11,306)	(34,718)	(29,305)
Other comprehensive income (loss):
Changes in foreign currency translation	(33)	(4)	(23)	(11)
Unrealized gain (loss) on marketable securities	(147)	(37)	(11)	47
Comprehensive loss	$ (9,654)	$ (11,347)	$ (34,752)	$ (29,269)
Net loss per share, basic and diluted (in dollars per share)	$ (0.33)	$ (0.46)	$ (1.23)	$ (1.19)
Weighted-average number of common shares used to compute basic and diluted net loss per share (in shares)	28,713,418	24,803,452	28,155,561	24,596,788

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Stockholders' equity, beginning of period (in shares) at Dec. 31, 2018		24,450,757
Stockholders' equity, 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, net of shares withheld (in shares)		46,809
Issuance of common stock upon exercise of stock options, net of shares withheld	125		125
Stock-based compensation	1,871		1,871
Vesting of early exercised stock options	66		66
Additional accrual of IPO related costs	(160)		(160)
Foreign currency translation	(19)			(19)
Net unrealized gain (loss) on marketable securities	25			25
Net loss	(9,345)				(9,345)
Stockholders' equity, end of period (in shares) at Mar. 31, 2019		24,497,566
Stockholders' equity, end of period at Mar. 31, 2019	82,755	$ 3	248,829	445	(166,522)
Stockholders' equity, beginning of period (in shares) at Dec. 31, 2018		24,450,757
Stockholders' equity, 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 related to employee stock purchase plan (in shares)	99,086
Issuance of common stock related to employee stock purchase plan	$ 1,300
Foreign currency translation	(11)
Net unrealized gain (loss) on marketable securities	47
Net loss	(29,305)
Stockholders' equity, end of period (in shares) at Sep. 30, 2019		24,965,512
Stockholders' equity, end of period at Sep. 30, 2019	68,961	$ 3	254,965	475	(186,482)
Stockholders' equity, beginning of period (in shares) at Mar. 31, 2019		24,497,566
Stockholders' equity, 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, net of shares withheld (in shares)		137,185
Issuance of common stock upon exercise of stock options, net of shares withheld	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
Net unrealized gain (loss) on marketable securities	59			59
Net loss	(8,654)				(8,654)
Stockholders' equity, end of period (in shares) at Jun. 30, 2019		24,761,157
Stockholders' equity, end 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, net of shares withheld (in shares)		175,070
Issuance of common stock upon exercise of stock options, net of shares withheld	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)
Net unrealized gain (loss) on marketable securities	(37)			(37)
Net loss	(11,306)				(11,306)
Stockholders' equity, end of period (in shares) at Sep. 30, 2019		24,965,512
Stockholders' equity, end of period at Sep. 30, 2019	68,961	$ 3	254,965	475	(186,482)
Stockholders' equity, beginning of period (in shares) at Dec. 31, 2019		25,163,803
Stockholders' equity, beginning of period at Dec. 31, 2019	63,008	$ 3	258,121	464	(195,580)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from public offering, net of underwriting discounts, commissions and offering costs (in shares)		3,135,053
Issuance of common stock from public offering, net of underwriting discounts, commissions and offering costs	62,978		62,978
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)		43,334
Issuance of common stock upon exercise of stock options, net of shares withheld	174		174
Issuance of common stock upon vesting of restricted stock units (in shares)		63,938
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation	2,622		2,622
Vesting of early exercised stock options	27		27
Foreign currency translation	12			12
Net unrealized gain (loss) on marketable securities	221			221
Net loss	(12,772)				(12,772)
Stockholders' equity, end of period (in shares) at Mar. 31, 2020		28,406,128
Stockholders' equity, end of period at Mar. 31, 2020	116,270	$ 3	323,922	697	(208,352)
Stockholders' equity, beginning of period (in shares) at Dec. 31, 2019		25,163,803
Stockholders' equity, beginning of period at Dec. 31, 2019	$ 63,008	$ 3	258,121	464	(195,580)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)	227,334
Issuance of common stock related to employee stock purchase plan (in shares)	74,685
Issuance of common stock related to employee stock purchase plan	$ 1,000
Foreign currency translation	(23)
Net unrealized gain (loss) on marketable securities	(11)
Net loss	(34,718)
Stockholders' equity, end of period (in shares) at Sep. 30, 2020		28,838,577
Stockholders' equity, end of period at Sep. 30, 2020	102,031	$ 3	331,896	430	(230,298)
Stockholders' equity, beginning of period (in shares) at Mar. 31, 2020		28,406,128
Stockholders' equity, beginning of period at Mar. 31, 2020	116,270	$ 3	323,922	697	(208,352)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)		46,608
Issuance of common stock upon exercise of stock options, net of shares withheld	185		185
Issuance of common stock related to employee stock purchase plan (in shares)		74,685
Issuance of common stock related to employee stock purchase plan	991		991
Issuance of common stock upon vesting of restricted stock units (in shares)		85,030
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation	2,955		2,955
Vesting of early exercised stock options	26		26
Foreign currency translation	(2)			(2)
Net unrealized gain (loss) on marketable securities	(85)			(85)
Net loss	(12,472)				(12,472)
Stockholders' equity, end of period (in shares) at Jun. 30, 2020		28,612,451
Stockholders' equity, end of period at Jun. 30, 2020	107,868	$ 3	328,079	610	(220,824)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)		137,392
Issuance of common stock upon exercise of stock options, net of shares withheld	628		628
Issuance of common stock upon vesting of restricted stock units (in shares)		88,734
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation	3,180		3,180
Vesting of early exercised stock options	9		9
Foreign currency translation	(33)			(33)
Net unrealized gain (loss) on marketable securities	(147)			(147)
Net loss	(9,474)				(9,474)
Stockholders' equity, end of period (in shares) at Sep. 30, 2020		28,838,577
Stockholders' equity, end of period at Sep. 30, 2020	$ 102,031	$ 3	$ 331,896	$ 430	$ (230,298)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019
Cash flows from operating activities
Net loss	$ (34,718)	$ (29,305)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	8,757	5,596
Depreciation and amortization	786	570
Bad debt expense	235	0
Accretion on marketable securities	(16)	(1,288)
Realized gain on marketable securities	(43)	0
Amortization of debt issuance costs	204	194
Loss on extinguishment of debt	1,534	0
Loss on sale and disposal of property and equipment	248	152
Changes in operating assets and liabilities:
Accounts receivable	63	(1,383)
Inventory	337	(1,575)
Prepaid expenses and other assets	1,489	394
Accounts payable	416	526
Accrued liabilities and other	(2,072)	3,525
Net cash used in operating activities	(22,780)	(22,594)
Cash flows from investing activities
Maturities of marketable securities	63,200	117,100
Sales of marketable securities	12,592	0
Purchases of marketable securities	(69,145)	(107,545)
Purchases of property and equipment	(1,744)	(1,639)
Net cash provided by investing activities	4,903	7,916
Cash flows from financing activities
Proceeds from follow-on public offering, net of underwriting discounts, commissions and offering costs	62,978	0
Proceeds from debt financing	45,297	0
Principal repayments of debt financing	(45,297)	0
Payments of debt issuance costs	(750)	0
Payments of prepayment penalty and lender fees	(843)	0
Proceeds from issuance of common stock under employee stock purchase plan	991	1,263
Proceeds from the exercise of stock options	987	1,178
Repurchase of Unvested Stock Options	0	(38)
Payments of additional initial public offering related costs	0	(167)
Net cash provided by financing activities	63,363	2,236
Effect of exchange rate changes on cash and cash equivalents	75	(64)
Net increase (decrease) in cash and cash equivalents	45,561	(12,506)
Cash and cash equivalents at
Beginning of period	10,435	25,120
End of period	55,996	12,614
Supplemental disclosure of non-cash information
Vesting of early exercised stock options	62	161
Unpaid purchases of property and equipment	$ 256	$ 31

The Company and Nature of Busin

The Company and Nature of Business	9 Months Ended
	Sep. 30, 2020
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 U.S., in 2010 in certain countries in the European Union, and in 2015 in certain countries in the rest of the world. In October 2018, the Company completed its initial public offering (“IPO”), by issuing 8,280,000 shares of common stock, at an offering price of $15.00 per share, for net proceeds of $113.4 million after deducting underwriting discounts and commissions and offering costs. In January 2020, the Company received $50.3 million of net proceeds, after deducting the underwriting discounts and commissions, from its first follow-on public offering of 4,300,000 shares of the Company's common stock at a public offering price of $21.50 per share, of which 2,490,053 shares were offered and sold by the Company. Further, in February 2020, the underwriters fully exercised their option to purchase 645,000 shares of the Company's common stock at a public offering price of $21.50 per share for an additional net proceeds of $13.0 million to the Company, after deducting underwriting discounts and commissions. The total public offering costs incurred in connection with the follow-on offering were allocated based on the gross proceeds received by the Company and the other selling shareholders on a pro-rated basis. Public offering cost of $0.4 million allocated to selling of shares by the Company was charged against the gross proceeds received from the follow-on offering. Public offering costs of $0.2 million allocated to selling of shares by the selling shareholders was recognized as transaction costs within general and administrative expenses on the unaudited condensed consolidated statements of operations in the first quarter of 2020. In October 2020, the Company received $71.9 million of net proceeds, after deducting the underwriting discounts and commissions, from its second follow-on public offering. See Note 12 - Subsequent Events of Notes to Condensed Consolidated Financial Statements for related discussions.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2020
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, 2019 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, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 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, 2019 contained in the Company’s Annual Report on Form 10-K filed with the SEC on March 11, 2020. Risks and Uncertainties The Company is subject to risks and uncertainties as a result of the COVID-19 pandemic. The extent of the impact of the COVID-19 pandemic on the Company's business is highly uncertain and difficult to predict, as the response to the pandemic and the information surrounding the pandemic is rapidly evolving. The severity of the impact of the COVID-19 pandemic on the Company's business will depend on a number of factors, including, but not limited to, the duration and severity of the pandemic and the extent and severity of the impact on the Company's customers, all of which are uncertain and cannot be predicted. The Company's future results of operations and liquidity could be adversely impacted by delays in payments of outstanding receivable amounts beyond normal payment terms, supply chain disruptions and uncertain demand, excess and obsolete inventory, and the impact of any initiatives and programs that the Company may undertake to address financial and operations challenges faced by its customers. 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. 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, 2019. 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 until December 31, 2023, unless one of the following occurs: (i) the Company's total annual gross revenues are $1.07 billion or more; (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 Company manages and operates as one reportable segment. The Company derives substantially all of its revenue from sales to customers in the U.S. Revenue by geography is based on billing address of the customer. No single country outside the U.S. accounts for more than 10% of the total revenue during the periods presented. Long-lived assets held outside the U.S. are immaterial. The table below summarizes the Company's revenue by geography: Three Months Ended September 30, Nine months ended September 30, 2020 2019 2020 2019 (in thousands) United States $ 18,924 $ 14,856 $ 47,442 $ 43,325 International 1,449 1,326 3,801 4,165 $ 20,373 $ 16,182 $ 51,243 $ 47,490 Adoption of New Revenue Recognition Standard The Company adopted the new revenue recognition standards (“ASC 606”) using the modified retrospective method effective for the year ended December 31, 2019. This approach was applied to all contracts that were not completed as of January 1, 2019. As an emerging growth company that elected to take advantage of the JOBS Act accounting election, the Company was not required to adopt the new revenue standard in the interim reporting periods on the year of adoption and is not required, and intends not, to revise its 2019 interim periods which were reported under previous revenue recognition standards (“ASC 605”). The adoption of ASC 606 did not result in a material impact on the Company’s condensed consolidated financial statements and no adjustment was made to the opening balance of accumulated deficit at January 1, 2019. ASC 606's core principle is that a reporting entity will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. As it relates to product sales where the Company's sales representative delivers the product at the point of implantation at hospital or medical facilities, which represents majority of the Company's revenue, the Company continues to recognize the revenue upon completion of the procedure and authorization by the customer, net of rebates and price discounts. As it relates to sale of products through distributors and hospitals where product is ordered in advance of the procedure, the Company continues to recognize the revenue upon shipments to the customers, net of rebates and price discounts. Additionally, ASC 606 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’s sales commissions paid to its sales representatives is generally based on the surgeries performed. The Company applied the practical expedient that permits an entity to expense the cost to obtain a contract as incurred when the expected amortization is one year or less. As such, the Company recognize sales commission as expense when incurred. The Company disaggregates revenues from contracts with customers into geographical regions. The Company determined that disaggregating revenue into these categories depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by regional economic factors. For information regarding revenue by geography, refer to Segments in “Note 2 - Summary of Significant Accounting Policies” in the accompanying Notes to Condensed Consolidated Financial Statements. Recently Issued Accounting Standards Not Yet Effective In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“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 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. In November 2019, the FASB issued ASU 2019-10, which revised the mandatory effective dates of the new leases standard. Further, due to the impact of the COVID-19, in June 2020, the FASB issued ASU 2020-05 to further defer the effective date for one year for entities in the “all other” categories. For public companies, the new guidance became effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018. For all other entities, the new guidance is now effective for fiscal years beginning after December 15, 2021 and interim periods within fiscal years beginning after December 15, 2022. Early adoption is still permitted for any interim or annual financial statements not yet issued. As an emerging growth company, the new leases standard is effective for the Company for the fiscal year ending December 31, 2022 and interim periods within fiscal year ending December 31, 2023. The Company is currently evaluating the impact of this standard on its consolidated financial statements including the timing of its adoption. The Company anticipates electing several practical expedients that permit the Company not to reassess (1) whether a contract is or contains a lease, (2) the classification of existing leases, and (3) whether previously capitalized initial direct costs would qualify for capitalization under ASC 842. The Company expects that the adoption of this new standard will have a material impact on its balance sheet. The most significant impact would be the recognition of operating lease right-of-use assets and liability. The standard is not expected to have a material impact to the Company's consolidated statements of income and cash flows. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. FASB issued ASU 2019-05 in May 2019 and ASU 2019-08 in November 2019 for codification improvements of Topic 326. 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. In November 2019, the FASB issued ASU 2019-10, which defers the effective date of ASU 2016-13 for public companies that are eligible to be smaller reporting companies and all other companies, to fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. In February 2020, the FASB issued ASU 2020-02, which provides guidance regarding methodologies, documentation, and internal controls related to expected credit losses. The Company is currently evaluating the impact of this standard on its consolidated financial statements but does not expect the standard will have a material impact on the Company's consolidated financial statements. 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-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 will adopt this new guidance for the year ending December 31, 2020 and does not expect it to have a material impact on its consolidated financial statements. 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 update 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 will adopt this new guidance for the year ending December 31, 2020 and does not expect it to have a material impact on its consolidated financial statements.

Marketable Securities

Marketable Securities	9 Months Ended
	Sep. 30, 2020
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 for which the original maturity or remaining maturity is greater than twelve months. The table below summarizes the marketable securities: September 30, 2020 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) Money market funds $ 52,290 $ — $ — $ 52,290 Cash equivalents 52,290 — — 52,290 U.S. treasury securities 56,994 24 — 57,018 Corporate bonds 8,595 19 — 8,614 Commercial paper 10,392 — — 10,392 Short-term investments 75,981 43 — 76,024 Total marketable securities $ 128,271 $ 43 $ — $ 128,314 December 31, 2019 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) Money market funds $ 3,068 $ — $ — $ 3,068 Commercial paper 2,495 — — 2,495 Cash equivalents 5,563 — — 5,563 U.S. treasury securities 67,051 34 (2) 67,083 Corporate bonds 9,075 24 (2) 9,097 Commercial paper 5,165 — — 5,165 Short-term investments 81,291 58 (4) 81,345 Corporate bonds 1,278 — — 1,278 Long-term investments 1,278 — — 1,278 Total marketable securities $ 88,132 $ 58 $ (4) $ 88,186 The long-term investments outstanding as of December 31, 2019 mature in April 2021. Unrealized gains and losses on available-for-sale securities are recorded in accumulated other comprehensive income (loss) on the condensed consolidated balance sheets. The Company evaluates its investments to assess whether those in unrealized loss positions are other-than-temporarily impaired. The Company considers impairments to be other-than-temporary if it is related to deterioration in credit risk or if it is likely the Company will sell the securities before the recovery of their cost basis. The Company did not identify any of its marketable securities as other-than-temporarily impaired as of September 30, 2020 and December 31, 2019.

Fair Value Measurement

Fair Value Measurement	9 Months Ended
	Sep. 30, 2020
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, 2020 Level 1 Level 2 Level 3 Total (in thousands) Marketable securities Money market funds $ 52,290 $ — $ — $ 52,290 U.S. treasury securities 57,018 — — 57,018 Corporate bonds — 8,614 — 8,614 Commercial paper — 10,392 — 10,392 Total marketable securities $ 109,308 $ 19,006 $ — $ 128,314 December 31, 2019 Level 1 Level 2 Level 3 Total (in thousands) Marketable securities Money market funds $ 3,068 $ — $ — $ 3,068 U.S. treasury securities 67,083 — — 67,083 Corporate bonds — 10,375 — 10,375 Commercial paper — 7,660 — 7,660 Total marketable securities $ 70,151 $ 18,035 $ — $ 88,186

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Components	Balance Sheet Components Inventory As of September 30, 2020 and December 31, 2019, inventory consisted entirely of finished goods. Property and Equipment, net : September 30, 2020 December 31, 2019 (in thousands) Machinery and equipment $ 5,927 $ 4,613 Construction in progress 1,731 1,854 Computer and office equipment 670 598 Leasehold improvements 503 497 Furniture and fixtures 229 187 9,060 7,749 Less: Accumulated depreciation and amortization (4,581) (3,795) $ 4,479 $ 3,954 Construction in progress pertains to cost of individual components of a custom instrument set used for surgical placement of iFuse implants that have not yet been placed into service. Depreciation expense was $0.3 million and $0.2 million for the three months ended September 30, 2020 and 2019, respectively, and $0.8 million and $0.6 million for the nine months ended September 30, 2020 and 2019, respectively. Accrued Liabilities and Other : September 30, 2020 December 31, 2019 (in thousands) Accrued compensation and related expenses $ 7,754 $ 7,274 Accrued litigation expense — 3,200 Accrued professional services 377 392 Others 588 739 $ 8,719 $ 11,605

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2020
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Operating Leases The Company has a non-cancelable operating lease for an office building space, located in Santa Clara, California which expires in May 2025. The Company also has non-cancelable operating leases for its office building spaces in Gallarate, Italy and Mannheim, Germany which both expire in November 2024, and in Knaresborough, United Kingdom, which expires in December 2025. Further, the Company also leases vehicles under operating lease arrangements for certain of its sales personnel in Europe which expire various times in 2021 to 2023. 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, 2020 and 2019, respectively, and $0.9 million and $0.9 million for the nine months ended September 30, 2020 and 2019, respectively. The table below summarizes aggregate future minimum lease payments under all leases as of September 30, 2020: Year ending December 31, (in thousands) 2020 (remaining three months) $ 282 2021 1,042 2022 963 2023 875 2024 875 Thereafter 364 $ 4,401 Purchase Commitments and Obligations The Company has certain purchase commitments related to its inventory management with certain manufacturing suppliers wherein the Company is required to purchase the amounts forecasted in a blanket purchase order. The contractual obligations represent future cash commitments and liabilities under agreements with third parties and exclude orders for goods and services entered into in the normal course of business that are not enforceable or legally binding. These outstanding commitments amounted to $0.4 million and $0.4 million as of September 30, 2020 and December 31, 2019, respectively. Legal Proceedings On February 6, 2019, a putative class action captioned Eric B. Fromer Chiropractic, Inc. (“Plaintiff”) v. SI-BONE, Inc. (Civil Action No. 5:19-cv-633-SVK), was filed in the U.S. District Court, Northern District of California (the “California Action”). The complaint alleges violations of the Telephone Consumer Protection Act (the “TCPA”) on behalf of an individual and a putative class 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. The plaintiff sought various forms of relief, including statutory damages of $500 for each violation of the TCPA or, in the alternative, treble damages of up to $1,500 for each knowing and willful violation of the TCPA and a permanent injunction prohibiting the Company from sending or having sent advertisements by way of facsimile transmission. Subsequently on December 20, 2019, Plaintiff the filed a putative class action captioned Eric B. Fromer Chiropractic, Inc. v. SI-BONE, Inc. (Case No. 1922-CC12323), in the Circuit Court of the City of St. Louis, State of Missouri (the “Missouri Action”). The Missouri Action alleges the same TCPA violations as the California Action. On December 23, 2019 the parties filed a joint stipulation of dismissal of the California Action and on January 14, 2020, the parties executed a definitive settlement agreement (the “Settlement Agreement”) pursuant to which, the Company agreed to settle all disputes regarding the advertising faxes to the settlement class. The Company accrued litigation expense of $2.5 million during the three months ended September 30, 2019 and accrued additional $0.7 million during the three months ended December 31, 2019, within general and administrative expenses in the condensed consolidated financial statements, for a total of $3.2 million accrued litigation expense as of December 31, 2019. The initial accrued litigation expense reflected the estimable and probable costs that the Company may incur concerning the mediation activities and settlement negotiations between the Company and the named plaintiff, and was subsequently adjusted based on the cost to resolve the matter pursuant to the Settlement Agreement and the estimated class members' claim submission rate. Following the notice and claims submission process, on June 22, 2020, the Circuit Court of the City of St. Louis, State of Missouri, approved a final order to pay the approved claims submitted by class members, fees, expenses and incentive awards totaling $2.6 million as final settlement. Accordingly, the Company recorded a reversal of accrued litigation expense of $0.6 million in the second quarter of 2020 within general and administrative expenses in the condensed consolidated financial statements. The Company made the final settlement payment on July 1, 2020. 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, 2020
Debt Disclosure [Abstract]
Borrowings	Borrowings Term Loan The following table summarizes the outstanding borrowings from the term loan described below, as of the dates presented: September 30, 2020 December 31, 2019 (in thousands) Principal and final fee payments $ 41,000 $ 40,000 Less: Unamortized debt issuance costs (699) (777) Unaccreted value of final fee (933) — Outstanding debt, net of debt issuance costs and unaccreted value of final fee $ 39,368 $ 39,223 Classified as: Current portion of long-term borrowings $ — $ 4,358 Long-term borrowings $ 39,368 $ 34,865 The outstanding debt as of December 31, 2019 was related to a term loan entered by the Company with Biopharma Credit Investments IV Sub LP (“Pharmakon”) in October 2017 for total loan proceeds of $40.0 million (the “Pharmakon Term Loan”). The Pharmakon Term Loan included an interest-only period for 35 months through September 2020 and then equal quarterly principal payments plus interest through December 2022. The Pharmakon Term Loan carried a fixed interest rate of 11.5% and allowed for early prepayment. The prepayment penalty fee was equal to the remaining interest due if prepaid within the first 30 months, a 2% penalty for months 31-48, and a 1% penalty for months 49-60. On May 29, 2020, the Company entered into a Loan and Security Agreement with Solar Capital Partners (“Solar”) providing for a term loan of an aggregate principal amount of $40.0 million to the Company (the “Solar Term Loan”). In accordance with the Loan and Security Agreement, the Company paid in full and terminated the Pharmakon Term Loan, which was accounted for as debt extinguishment in accordance with the accounting standards. The Company recognized the unamortized debt issuance costs of $0.7 million and the prepayment penalty and lender fees of $0.8 million related to Pharmakon Term Loan as a loss on debt extinguishment. The costs and fees are reflected as interest expense in the condensed consolidated statement of operations for the three and nine months ended September 30, 2020. The total debt issuance costs of $0.8 million associated with the Solar Term Loan were recorded in the condensed consolidated balance sheet as a direct deduction from the carrying amount of the loan, and are amortized as a component of interest expense using straight-line method over the life of the term loan. The Solar Term Loan bears interest at a rate per annum equal to 9.40% plus London Interbank Offered Rate (“LIBOR”), payable monthly in arrears. LIBOR means the greater of (i) 0.33% or (ii) one-month LIBOR (or a comparable replacement rate to be determined by the collateral agent if the LIBOR is no longer available), which rate shall reset monthly. The Solar Term Loan matures in 60 months on June 1, 2025 (“Maturity Date”), with an interest-only period of 36 months through June 2023, and then repaid in equal monthly principal payments plus interest through maturity date. Pursuant to the Loan and Security Agreement, the Company may voluntarily prepay the Solar Term Loan, in full or in part, but only in increments of $10.0 million, for a prepayment premium in an amount equal to 3.0% of the principal if prepaid in year one, 1.25% of the principal if prepaid in year two, and 0.50% of the principal if prepaid in year three or later. The prepayment premium will be waived if the Company voluntarily prepays and refinances the outstanding balance with Solar. The Solar Term Loan is secured by substantially all of the Company’s assets. The Company is also obligated to pay a final fee equal to $1.0 million or 2.5% of the aggregate principal amount of the Solar Term Loan, which was fully earned by Solar on the effective date of the Loan and Security Agreement. With respect to the Solar Term Loan, this final fee shall be due and payable on the earliest of (i) the maturity date, (ii) the acceleration of the loan balance or (iii) its full prepayment, refinancing, substitution or replacement. The final fee was included within the long-term borrowings and is accreted to interest expense using straight-line method over the life of the term loan. The effective interest rate related to the Solar Term Loan and Pharmakon Term Loan (excluding the write-down of unamortized debt issuance costs and prepayment penalty related to the Pharmakon Term Loan) was 10.8% and 12.4% for the three months ended September 30, 2020 and 2019, respectively, and 11.6% and 12.3% for the nine months ended September 30, 2020 and 2019, respectively. The table below summarizes the future principal and final fee payments under the Solar Term Loan as of September 30, 2020: Year ending December 31, (in thousands) 2020 (remaining three months) $ — 2021 — 2022 — 2023 11,667 2024 20,000 Thereafter 9,333 Total principal and final fee payments $ 41,000 Subject to other customary covenants set forth in the Loan and Security Agreement with Solar, the Company is required to maintain unrestricted cash and cash equivalents based on the trailing 12-month net products revenues tested on a monthly basis as follows: (a) $15.0 million if net product revenue is less than $75.0 million; or (b) $7.5 million if net product revenue is greater than or equal to $75.0 million, but less than $100.0 million (the “minimum liquidity requirement”). The Company is not subject to minimum liquidity requirement when trailing twelve-month net product revenues exceeds $100.0 million. Upon the occurrence of an event of default of certain customary covenants, including the minimum liquidity requirements, as specified in the Loan and Security Agreement, subject to specified cure periods, all amounts owed by the Company would begin to bear interest at a rate that is 5.0% above the rate effective immediately before the event of default and may be declared immediately due and payable by Solar. As of September 30, 2020, the Company was in compliance with all debt covenants. Though there are uncertainties surrounding the impact of the COVID-19 pandemic that may impact its future revenue, the Company believes that it has sufficient cash and cash equivalents to meet the minimum liquidity requirements in the foreseeable succeeding periods. PPP Loan On March 27, 2020, the U.S. federal government enacted the “Coronavirus Aid, Relief and Economic Security (CARES) Act,” and among other things, established the Paycheck Protection Program (“PPP”), administered by the Small Business Administration (“SBA”), whereby certain small businesses were eligible for a loan to fund payroll expenses, rent, and related costs. The loan may be forgiven if the funds are used for payroll and other qualified expenses. The Company met the requirements to apply for the PPP loan given that the Company has less than 500 employees and the business was negatively impacted by COVID-19. The Company submitted its application and was approved for the SBA program and received the proceeds from the PPP loan amounting to $5.3 million on April 21, 2020, pursuant to a Promissory Note with Silicon Valley Bank (“SVB”). In light of the subsequent clarifications from the U.S. government on the eligibility criteria, the Company determined it was appropriate to repay the entire amount of the PPP loan. Accordingly, on April 29, 2020, the Company repaid in full the PPP loan and correspondingly terminated the Promissory Note.

Stock-Based Incentive Compensat

Stock-Based Incentive Compensation Plans	9 Months Ended
	Sep. 30, 2020
Share-based Payment Arrangement [Abstract]
Stock-Based Incentive Compensation Plans	Stock-Based Incentive Compensation Plans Stock Options The table below summarizes the stock option activity for the nine months ended September 30, 2020: Number of Weighted- Outstanding as of December 31, 2019 2,718,971 $8.02 Granted 26,236 17.31 Exercised (227,334) 4.34 Canceled and forfeited (13,524) 17.21 Outstanding as of September 30, 2020 2,504,349 8.40 As of September 30, 2020, the unrecognized compensation cost related to stock options was $3.7 million, which is expected to be recognized over a period of approximately 2.1 years. There were no stock options granted during the three months ended September 30, 2020. The table below summarizes the weighted average grant date fair value per share and the assumptions used to estimate the grant date fair value using the Black-Scholes option-pricing model of the stock options granted during the periods presented: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Weighted average grant date fair value per share — $5.43 $8.37 $9.78 Expected term (years) — 5.0 to 7.0 5.5 to 7.0 5.0 to 7.0 Expected volatility — 46.6% to 47.3% 46.7% to 47.2% 41.7% to 47.3% Risk-free interest rate — 1.32% to 1.39% 1.56% to 1.64% 1.32% to 2.59% Dividend yield — —% —% —% Early Exercise of Unvested Stock Options Early exercises of stock options under the Company's 2008 Stock Option Plan 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, 2020 and December 31, 2019, the Company had a total of 7,784 shares and 21,404 shares of common stock, respectively, subject to repurchase under the Company's 2008 Stock Option Plan. Restricted Stock Units The table below summarizes restricted stock units activity for the nine months ended September 30, 2020: Number of Shares Weighted Average Grant Date Fair Value Outstanding as of December 31, 2019 543,041 $19.72 Granted 979,082 20.08 Vested (237,702) 20.67 Canceled and forfeited (34,248) 19.55 Outstanding as of September 30, 2020 1,250,173 19.83 As of September 30, 2020, the unrecognized compensation cost related to the restricted stock units was $20.9 million, which is expected to be recognized over a period of approximately 3.0 years. Employee Stock Purchase Plan The Company's 2018 Employee Stock Purchase Plan (the “ESPP”) 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 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 2020 2019 2020 2019 (in thousands) Cost of goods sold $ 87 $ 57 $ 243 $ 163 Sales and marketing 1,488 807 3,976 2,481 Research and development 299 144 827 364 General and administrative 1,306 903 3,711 2,588 $ 3,180 $ 1,911 $ 8,757 $ 5,596

Net Loss Per Share of Common St

Net Loss Per Share of Common Stock	9 Months Ended
	Sep. 30, 2020
Earnings Per Share [Abstract]
Net Loss Per Share of Common Stock	Net Loss Per Share of Common Stock The table below summarizes the computation of basic and diluted net loss per share: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 (in thousands, except share and per share data) Net loss $ (9,474) $ (11,306) $ (34,718) $ (29,305) Weighted-average shares used to compute basic and diluted net loss per share 28,713,418 24,803,452 28,155,561 24,596,788 Net loss per share, basic and diluted $ (0.33) $ (0.46) $ (1.23) $ (1.19) 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 and common 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, 2020 2019 2020 2019 Stock options 2,504,349 2,824,485 2,504,349 2,824,485 Restricted stock units 1,250,173 565,430 1,250,173 565,430 Shares subject to repurchase 7,784 29,268 7,784 29,268 ESPP purchase rights 138,950 72,679 138,950 72,679 Common stock warrants 118,122 118,122 118,122 118,122 4,019,378 3,609,984 4,019,378 3,609,984

Related Party Transaction

Related Party Transaction	9 Months Ended
	Sep. 30, 2020
Related Party Transactions [Abstract]
Related Party Transaction	Related Party Transaction On February 24, 2020, the Company entered into a joint development agreement (the “Development Agreement”) with SeaSpine Orthopedics Corporation (“SeaSpine”) to develop a next generation device for sacropelvic fixation. Mr. Keith Valentine, who serves as the President, Chief Executive Officer and a member of the board of directors of SeaSpine, also serves as a member of the Company's Board of Directors since August 2015. Pursuant to the development plan, SeaSpine shall use reasonable efforts to assist in the development of the potential product offering, including licensing certain existing intellectual property to be incorporated into such product. Under the terms of the Development Agreement, the Company agreed to make monthly payments to SeaSpine to reimburse for full time resources employed by SeaSpine responsible to conduct the development activities. For the three and nine months ended September 30, 2020, the Company expensed $40,000 and $86,000, respectively, of the reimbursement charges from SeaSpine, which was recorded within research and development expense in the condensed consolidated statement of operations. The outstanding liability to SeaSpine as of September 30, 2020 amounted to $10,000, recorded within accrued liabilities and other in the condensed consolidated balance sheet.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2020
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, 2020 and 2019. 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, 2019. The CARES Act includes provisions relating to refundable payroll tax credits, deferment of employer side social security payments, net operating loss carryback periods, alternative minimum tax credit refunds, modifications to the net interest deduction limitations and technical corrections to tax depreciation methods for qualified improvement property. The Company evaluated its impact of the CARES Act as part of ASC 740 consideration and does not expect the provisions of the CARES Act would result in a material impact to the consolidated financial statements. The Company continues to monitor the impact this CARES Act may have on its business. On June 29, 2020, Governor Gavin Newsom signed California Assembly Bill 85 (AB 85) into law. The legislation suspends the California net operating loss deductions for 2020, 2021, and 2022 for certain taxpayers and imposes a limitation of certain California Tax Credits for 2020, 2021, and 2022. The legislation disallows the use of California net operating loss deductions if the taxpayer recognizes business income and its adjusted gross income is greater than $1.0 million. The carryover periods for net operating loss deductions disallowed by this provision will be extended. Additionally, any business credit will only offset a maximum of $5.0 million of California tax. Given the Company’s expected loss position in the current year, the new legislation will not impact the current year provision. The Company will continue to monitor the possible California net operating loss and credit limitations in future periods.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Second Follow-On Offering On October 19, 2020, the Company received $71.9 million of net proceeds, after deducting the underwriting discounts and commissions but before offering expenses, from its second follow-on public offering of 3,000,000 shares of the Company's common stock, and the exercise of underwriter's option to purchase from the Company an additional 478,507 shares of the Company's common stock, at a public offering price of $22.00 per share. The estimated total offering cost of approximately $0.4 million will be charged against the gross proceeds received from this second follow-on offering. The Company currently intends to use the net proceeds from this offering to support the continued commercial expansion of its products, including the increase of its sales force, additional medical affairs and educational efforts, research and development and clinical studies, direct to patient marketing, as well as for working capital and general corporate purposes. The Company may also use a portion of the net proceeds to acquire or invest in complementary products, technologies, or businesses; however, the Company currently has no agreements or commitments to complete any such transactions.

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2020
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, 2019 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, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 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. 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 until December 31, 2023, unless one of the following occurs: (i) the Company's total annual gross revenues are $1.07 billion or more; (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	SegmentsThe Company manages and operates as one reportable segment.
Adoption of New Revenue Recognition Standard	Adoption of New Revenue Recognition Standard The Company adopted the new revenue recognition standards (“ASC 606”) using the modified retrospective method effective for the year ended December 31, 2019. This approach was applied to all contracts that were not completed as of January 1, 2019. As an emerging growth company that elected to take advantage of the JOBS Act accounting election, the Company was not required to adopt the new revenue standard in the interim reporting periods on the year of adoption and is not required, and intends not, to revise its 2019 interim periods which were reported under previous revenue recognition standards (“ASC 605”). The adoption of ASC 606 did not result in a material impact on the Company’s condensed consolidated financial statements and no adjustment was made to the opening balance of accumulated deficit at January 1, 2019. ASC 606's core principle is that a reporting entity will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. As it relates to product sales where the Company's sales representative delivers the product at the point of implantation at hospital or medical facilities, which represents majority of the Company's revenue, the Company continues to recognize the revenue upon completion of the procedure and authorization by the customer, net of rebates and price discounts. As it relates to sale of products through distributors and hospitals where product is ordered in advance of the procedure, the Company continues to recognize the revenue upon shipments to the customers, net of rebates and price discounts. Additionally, ASC 606 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’s sales commissions paid to its sales representatives is generally based on the surgeries performed. The Company applied the practical expedient that permits an entity to expense the cost to obtain a contract as incurred when the expected amortization is one year or less. As such, the Company recognize sales commission as expense when incurred. The Company disaggregates revenues from contracts with customers into geographical regions. The Company determined that disaggregating revenue into these categories depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by regional economic factors. For information regarding revenue by geography, refer to Segments in “Note 2 - Summary of Significant Accounting Policies” in the accompanying Notes to Condensed Consolidated Financial Statements.
Recent Accounting Standards	Recently Issued Accounting Standards Not Yet Effective In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update (“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 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. In November 2019, the FASB issued ASU 2019-10, which revised the mandatory effective dates of the new leases standard. Further, due to the impact of the COVID-19, in June 2020, the FASB issued ASU 2020-05 to further defer the effective date for one year for entities in the “all other” categories. For public companies, the new guidance became effective for fiscal years, and for interim periods within those fiscal years, beginning after December 15, 2018. For all other entities, the new guidance is now effective for fiscal years beginning after December 15, 2021 and interim periods within fiscal years beginning after December 15, 2022. Early adoption is still permitted for any interim or annual financial statements not yet issued. As an emerging growth company, the new leases standard is effective for the Company for the fiscal year ending December 31, 2022 and interim periods within fiscal year ending December 31, 2023. The Company is currently evaluating the impact of this standard on its consolidated financial statements including the timing of its adoption. The Company anticipates electing several practical expedients that permit the Company not to reassess (1) whether a contract is or contains a lease, (2) the classification of existing leases, and (3) whether previously capitalized initial direct costs would qualify for capitalization under ASC 842. The Company expects that the adoption of this new standard will have a material impact on its balance sheet. The most significant impact would be the recognition of operating lease right-of-use assets and liability. The standard is not expected to have a material impact to the Company's consolidated statements of income and cash flows. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. FASB issued ASU 2019-05 in May 2019 and ASU 2019-08 in November 2019 for codification improvements of Topic 326. 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. In November 2019, the FASB issued ASU 2019-10, which defers the effective date of ASU 2016-13 for public companies that are eligible to be smaller reporting companies and all other companies, to fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. In February 2020, the FASB issued ASU 2020-02, which provides guidance regarding methodologies, documentation, and internal controls related to expected credit losses. The Company is currently evaluating the impact of this standard on its consolidated financial statements but does not expect the standard will have a material impact on the Company's consolidated financial statements. 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-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 will adopt this new guidance for the year ending December 31, 2020 and does not expect it to have a material impact on its consolidated financial statements. 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 update 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 will adopt this new guidance for the year ending December 31, 2020 and does not expect it to have a material impact on its consolidated financial statements.

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020 2019 2020 2019 (in thousands) United States $ 18,924 $ 14,856 $ 47,442 $ 43,325 International 1,449 1,326 3,801 4,165 $ 20,373 $ 16,182 $ 51,243 $ 47,490

Marketable Securities (Tables)

Marketable Securities (Tables)	9 Months Ended
	Sep. 30, 2020
Investments, Debt and Equity Securities [Abstract]
Schedule of Marketable Securities	The table below summarizes the marketable securities: September 30, 2020 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) Money market funds $ 52,290 $ — $ — $ 52,290 Cash equivalents 52,290 — — 52,290 U.S. treasury securities 56,994 24 — 57,018 Corporate bonds 8,595 19 — 8,614 Commercial paper 10,392 — — 10,392 Short-term investments 75,981 43 — 76,024 Total marketable securities $ 128,271 $ 43 $ — $ 128,314 December 31, 2019 Amortized Cost Unrealized Gains Unrealized Losses Aggregate Fair Value (in thousands) Money market funds $ 3,068 $ — $ — $ 3,068 Commercial paper 2,495 — — 2,495 Cash equivalents 5,563 — — 5,563 U.S. treasury securities 67,051 34 (2) 67,083 Corporate bonds 9,075 24 (2) 9,097 Commercial paper 5,165 — — 5,165 Short-term investments 81,291 58 (4) 81,345 Corporate bonds 1,278 — — 1,278 Long-term investments 1,278 — — 1,278 Total marketable securities $ 88,132 $ 58 $ (4) $ 88,186

Fair Value Measurement (Tables)

Fair Value Measurement (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020 Level 1 Level 2 Level 3 Total (in thousands) Marketable securities Money market funds $ 52,290 $ — $ — $ 52,290 U.S. treasury securities 57,018 — — 57,018 Corporate bonds — 8,614 — 8,614 Commercial paper — 10,392 — 10,392 Total marketable securities $ 109,308 $ 19,006 $ — $ 128,314 December 31, 2019 Level 1 Level 2 Level 3 Total (in thousands) Marketable securities Money market funds $ 3,068 $ — $ — $ 3,068 U.S. treasury securities 67,083 — — 67,083 Corporate bonds — 10,375 — 10,375 Commercial paper — 7,660 — 7,660 Total marketable securities $ 70,151 $ 18,035 $ — $ 88,186

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Schedule of Property and Equipment, Net	Property and Equipment, net : September 30, 2020 December 31, 2019 (in thousands) Machinery and equipment $ 5,927 $ 4,613 Construction in progress 1,731 1,854 Computer and office equipment 670 598 Leasehold improvements 503 497 Furniture and fixtures 229 187 9,060 7,749 Less: Accumulated depreciation and amortization (4,581) (3,795) $ 4,479 $ 3,954
Schedule of Accrued Liabilities and Other	Accrued Liabilities and Other : September 30, 2020 December 31, 2019 (in thousands) Accrued compensation and related expenses $ 7,754 $ 7,274 Accrued litigation expense — 3,200 Accrued professional services 377 392 Others 588 739 $ 8,719 $ 11,605

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020: Year ending December 31, (in thousands) 2020 (remaining three months) $ 282 2021 1,042 2022 963 2023 875 2024 875 Thereafter 364 $ 4,401

Borrowings (Tables)

Borrowings (Tables)	9 Months Ended
	Sep. 30, 2020
Debt Disclosure [Abstract]
Schedule of Outstanding Borrowings	The following table summarizes the outstanding borrowings from the term loan described below, as of the dates presented: September 30, 2020 December 31, 2019 (in thousands) Principal and final fee payments $ 41,000 $ 40,000 Less: Unamortized debt issuance costs (699) (777) Unaccreted value of final fee (933) — Outstanding debt, net of debt issuance costs and unaccreted value of final fee $ 39,368 $ 39,223 Classified as: Current portion of long-term borrowings $ — $ 4,358 Long-term borrowings $ 39,368 $ 34,865
Schedule of Annual Future Minimum Principal Payments Under Loan Agreements	The table below summarizes the future principal and final fee payments under the Solar Term Loan as of September 30, 2020: Year ending December 31, (in thousands) 2020 (remaining three months) $ — 2021 — 2022 — 2023 11,667 2024 20,000 Thereafter 9,333 Total principal and final fee payments $ 41,000

Stock-Based Incentive Compens_2

Stock-Based Incentive Compensation Plans (Tables)	9 Months Ended
	Sep. 30, 2020
Share-based Payment Arrangement [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, 2020: Number of Weighted- Outstanding as of December 31, 2019 2,718,971 $8.02 Granted 26,236 17.31 Exercised (227,334) 4.34 Canceled and forfeited (13,524) 17.21 Outstanding as of September 30, 2020 2,504,349 8.40
Schedule of Valuation Assumptions Related to Stock Option Awards	The table below summarizes the weighted average grant date fair value per share and the assumptions used to estimate the grant date fair value using the Black-Scholes option-pricing model of the stock options granted during the periods presented: Three Months Ended September 30, Nine Months Ended September 30, 2020 2019 2020 2019 Weighted average grant date fair value per share — $5.43 $8.37 $9.78 Expected term (years) — 5.0 to 7.0 5.5 to 7.0 5.0 to 7.0 Expected volatility — 46.6% to 47.3% 46.7% to 47.2% 41.7% to 47.3% Risk-free interest rate — 1.32% to 1.39% 1.56% to 1.64% 1.32% to 2.59% Dividend yield — —% —% —%
Schedule of Restricted Stock Unit Activity	The table below summarizes restricted stock units activity for the nine months ended September 30, 2020: Number of Shares Weighted Average Grant Date Fair Value Outstanding as of December 31, 2019 543,041 $19.72 Granted 979,082 20.08 Vested (237,702) 20.67 Canceled and forfeited (34,248) 19.55 Outstanding as of September 30, 2020 1,250,173 19.83
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 2020 2019 2020 2019 (in thousands) Cost of goods sold $ 87 $ 57 $ 243 $ 163 Sales and marketing 1,488 807 3,976 2,481 Research and development 299 144 827 364 General and administrative 1,306 903 3,711 2,588 $ 3,180 $ 1,911 $ 8,757 $ 5,596

Net Loss Per Share of Common _2

Net Loss Per Share of Common Stock (Tables)	9 Months Ended
	Sep. 30, 2020
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, 2020 2019 2020 2019 (in thousands, except share and per share data) Net loss $ (9,474) $ (11,306) $ (34,718) $ (29,305) Weighted-average shares used to compute basic and diluted net loss per share 28,713,418 24,803,452 28,155,561 24,596,788 Net loss per share, basic and diluted $ (0.33) $ (0.46) $ (1.23) $ (1.19)
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, 2020 2019 2020 2019 Stock options 2,504,349 2,824,485 2,504,349 2,824,485 Restricted stock units 1,250,173 565,430 1,250,173 565,430 Shares subject to repurchase 7,784 29,268 7,784 29,268 ESPP purchase rights 138,950 72,679 138,950 72,679 Common stock warrants 118,122 118,122 118,122 118,122 4,019,378 3,609,984 4,019,378 3,609,984

The Company and Nature of Bus_2

The Company and Nature of Business (Details) - USD ($) $ / shares in Units, $ in Millions	Oct. 19, 2020	Oct. 31, 2020	Feb. 29, 2020	Jan. 31, 2020	Oct. 31, 2018	Mar. 31, 2020
IPO
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)					8,280,000
Public offering price (in dollars per share)					$ 15
Net proceeds from sale of stock					$ 113.4
First follow-on public offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)				2,490,053
Public offering price (in dollars per share)				$ 21.50
Net proceeds from sale of stock				$ 50.3
Allocated public offering costs						$ 0.4
First follow-on public offering and secondary offering
Subsidiary, Sale of Stock [Line Items]
Number of shares in transaction, including shares in secondary offering (in shares)				4,300,000
Underwriters option
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)			645,000
Public offering price (in dollars per share)			$ 21.50
Net proceeds from sale of stock			$ 13
Secondary offering by selling shareholders
Subsidiary, Sale of Stock [Line Items]
Allocated public offering costs						$ 0.2
Secondary offering by selling shareholders | Subsequent event
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)	190,053
Public offering price (in dollars per share)	$ 22
Second follow-on public offering | Subsequent event
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)		3,000,000
Public offering price (in dollars per share)		$ 22
Net proceeds from sale of stock		$ 71.9

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Segments (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2019USD ($)	Sep. 30, 2020USD ($)segment	Sep. 30, 2019USD ($)
Accounting Policies [Abstract]
Number of reportable segments | segment			1
Number of operating segments | segment			1
Disaggregation of Revenue [Line Items]
Revenue	$ 20,373	$ 16,182	$ 51,243	$ 47,490
United States
Disaggregation of Revenue [Line Items]
Revenue	18,924	14,856	47,442	43,325
International
Disaggregation of Revenue [Line Items]
Revenue	$ 1,449	$ 1,326	$ 3,801	$ 4,165

Marketable Securities (Details)

Marketable Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Cash equivalents
Carrying Value	$ 52,290	$ 5,563
Short-term investments
Amortized Cost	75,981	81,291
Unrealized Gains	43	58
Unrealized Losses	0	(4)
Aggregate Fair Value	76,024	81,345
Long-term investments
Amortized Cost		1,278
Unrealized Gains		0
Unrealized Losses		0
Aggregate Fair Value	0	1,278
Total marketable securities, Amortized Cost	128,271	88,132
Total marketable securities, Unrealized Gains	43	58
Total marketable securities, Unrealized Losses	0	(4)
Total marketable securities, Aggregate Fair Value	128,314	88,186
Money market funds
Cash equivalents
Carrying Value	52,290	3,068
U.S. treasury securities
Short-term investments
Amortized Cost	56,994	67,051
Unrealized Gains	24	34
Unrealized Losses	0	(2)
Aggregate Fair Value	57,018	67,083
Corporate bonds
Short-term investments
Amortized Cost	8,595	9,075
Unrealized Gains	19	24
Unrealized Losses	0	(2)
Aggregate Fair Value	8,614	9,097
Long-term investments
Amortized Cost		1,278
Unrealized Gains		0
Unrealized Losses		0
Aggregate Fair Value		1,278
Commercial paper
Cash equivalents
Carrying Value		2,495
Short-term investments
Amortized Cost	10,392	5,165
Unrealized Gains	0	0
Unrealized Losses	0	0
Aggregate Fair Value	$ 10,392	$ 5,165

Fair Value Measurement - Market

Fair Value Measurement - Marketable Securities Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Marketable securities
Marketable securities	$ 128,314	$ 88,186
Money market funds
Marketable securities
Marketable securities	52,290	3,068
U.S. treasury securities
Marketable securities
Marketable securities	57,018	67,083
Corporate bonds
Marketable securities
Marketable securities	8,614	10,375
Commercial paper
Marketable securities
Marketable securities	10,392	7,660
Level 1
Marketable securities
Marketable securities	109,308	70,151
Level 1 | Money market funds
Marketable securities
Marketable securities	52,290	3,068
Level 1 | U.S. treasury securities
Marketable securities
Marketable securities	57,018	67,083
Level 1 | Corporate bonds
Marketable securities
Marketable securities	0	0
Level 1 | Commercial paper
Marketable securities
Marketable securities	0	0
Level 2
Marketable securities
Marketable securities	19,006	18,035
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	8,614	10,375
Level 2 | Commercial paper
Marketable securities
Marketable securities	10,392	7,660
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	$ 0

Balance Sheet Components - Prop

Balance Sheet Components - Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Property and Equipment, Net
Property and equipment, gross	$ 9,060		$ 9,060		$ 7,749
Less: Accumulated depreciation and amortization	(4,581)		(4,581)		(3,795)
Property and equipment, net	4,479		4,479		3,954
Depreciation expense	300	$ 200	800	$ 600
Machinery and equipment
Property and Equipment, Net
Property and equipment, gross	5,927		5,927		4,613
Construction in progress
Property and Equipment, Net
Property and equipment, gross	1,731		1,731		1,854
Computer and office equipment
Property and Equipment, Net
Property and equipment, gross	670		670		598
Leasehold improvements
Property and Equipment, Net
Property and equipment, gross	503		503		497
Furniture and fixtures
Property and Equipment, Net
Property and equipment, gross	$ 229		$ 229		$ 187

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities and Other (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Accrued Liabilities and Other
Accrued compensation and related expenses	$ 7,754	$ 7,274
Accrued litigation expense	0	3,200
Accrued professional services	377	392
Others	588	739
Accrued liabilities and other	$ 8,719	$ 11,605

Commitments and Contingencies -

Commitments and Contingencies - Narrative (Details) - USD ($)	Jun. 22, 2020	Feb. 06, 2019	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Other Commitments [Line Items]
Rent expense			$ 300,000			$ 300,000	$ 900,000	$ 900,000
Purchase commitments related to inventory			400,000		$ 400,000		400,000
Accrued litigation expense			0		3,200,000		0
Eric B Fromer Chiropractic Inc, class action
Other Commitments [Line Items]
Litigation expense					700,000	$ 2,500,000
Accrued litigation expense					$ 3,200,000
Settlement of approved claims by class members, fees, expenses and incentive awards	$ 2,600,000
Reversal of accrued litigation expense				$ 600,000
Statutory damages sought per violation of TCPA | Eric B Fromer Chiropractic Inc, class action
Other Commitments [Line Items]
Damages sought per violation		$ 500
Treble damages sought per violation of TCPA | Eric B Fromer Chiropractic Inc, class action
Other Commitments [Line Items]
Damages sought per violation		$ 1,500
Indemnification Agreement
Other Commitments [Line Items]
Costs to defend lawsuits or settle claims							0
Costs accrued to defend lawsuits			$ 0				$ 0

Commitments and Contingencies_2

Commitments and Contingencies - Aggregate Future Minimum Lease Payments (Details) $ in Thousands	Sep. 30, 2020USD ($)
Aggregate Future Minimum Lease Payments
2020 (remaining three months)	$ 282
2021	1,042
2022	963
2023	875
2024	875
Thereafter	364
Total	$ 4,401

Borrowings - Summary of Borrowi

Borrowings - Summary of Borrowings (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Debt Disclosure [Abstract]
Principal and final fee payments	$ 41,000	$ 40,000
Less: Unamortized debt issuance costs	(699)	(777)
Debt Instrument, Fee Amount	(933)	0
Outstanding debt, net of debt issuance costs and unaccreted value of final fee	39,368	39,223
Current portion of long-term borrowings	0	4,358
Long-term borrowings	$ 39,368	$ 34,865

Borrowings - Narrative (Details

Borrowings - Narrative (Details) - USD ($)	May 29, 2020	Apr. 29, 2020	Apr. 21, 2020	Oct. 31, 2017	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019	Dec. 31, 2019
Debt Instrument [Line Items]
Total loan proceeds							$ 45,297,000	$ 0
Recognition of unamortized debt discount and issuance costs on debt extinguishment					$ 700,000		700,000
Prepayment penalty and lender fees on debt extinguishment					800,000		800,000
Final fee					$ 933,000		$ 933,000		$ 0
PPP Loan, CARES Act
Debt Instrument [Line Items]
Proceeds from PPP loan			$ 5,300,000
Repayment of PPP loan		$ 5,300,000
Term Loan | Pharmakon Term Loan
Debt Instrument [Line Items]
Total loan proceeds				$ 40,000,000
Debt period payment, interest only period				35 months
Debt interest stated percentage (percent)				11.50%
Effective interest rate during the period (percent)						12.40%		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%
Term Loan | Solar Loan and Security Agreement
Debt Instrument [Line Items]
Debt period payment, interest only period	36 months
Debt interest stated percentage (percent)	9.40%
Aggregate principal amount	$ 40,000,000
Unamortized debt discount and issuance cost	$ 800,000
Debt maturity term (in months)	60 months
Allowable prepayment increments per agreement	$ 10,000,000
Prepayment premium in year one (percent)	3.00%
Prepayment premium in year two (percent)	1.25%
Prepayment premium in year three or later (percent)	0.50%
Final fee	$ 1,000,000
Final fee as percentage of aggregate principal amount (percent)	2.50%
Incremental interest rate increase upon default of minimum liquidity covenant (percent)	5.00%
Term Loan | Solar Loan and Security Agreement | Net product revenue less than $75 million
Debt Instrument [Line Items]
Debt covenant minimum cash balance	$ 15,000,000
Term Loan | Solar Loan and Security Agreement | Net product revenue more than $75 million and less than $100 million
Debt Instrument [Line Items]
Debt covenant minimum cash balance	7,500,000
Term Loan | Solar Loan and Security Agreement | Net product revenue more than $100 million
Debt Instrument [Line Items]
Debt covenant minimum cash balance	$ 0
Term Loan | Solar Loan and Security Agreement | Basis spread option
Debt Instrument [Line Items]
Basis spread on variable rate	0.33%
Term Loan | Solar Loan and Security Agreement | Maximum | Net product revenue less than $75 million
Debt Instrument [Line Items]
Product revenue threshold for minimum liquidity covenant	$ 75,000,000
Term Loan | Solar Loan and Security Agreement | Maximum | Net product revenue more than $75 million and less than $100 million
Debt Instrument [Line Items]
Product revenue threshold for minimum liquidity covenant	100,000,000
Term Loan | Solar Loan and Security Agreement | Minimum | Net product revenue more than $75 million and less than $100 million
Debt Instrument [Line Items]
Product revenue threshold for minimum liquidity covenant	75,000,000
Term Loan | Solar Loan and Security Agreement | Minimum | Net product revenue more than $100 million
Debt Instrument [Line Items]
Product revenue threshold for minimum liquidity covenant	$ 100,000,000
Term Loan | Pharmakon and Solar Term Loans
Debt Instrument [Line Items]
Effective interest rate during the period (percent)					10.80%		11.60%

Borrowings - Debt Maturity (Det

Borrowings - Debt Maturity (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Future principal and final fee payments
2020 (remaining three months)	$ 0
2021	0
2022	0
2023	11,667
2024	20,000
Thereafter	9,333
Total principal and final fee payments	$ 41,000	$ 40,000

Stock-Based Incentive Compens_3

Stock-Based Incentive Compensation Plans - Narrative (Details) $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended
	Sep. 30, 2020USD ($)shares	Jun. 30, 2020USD ($)	Mar. 25, 2020	Jun. 30, 2019USD ($)	Sep. 30, 2020USD ($)purchase_periodshares	Sep. 30, 2020USD ($)shares	Sep. 30, 2019USD ($)shares	Dec. 31, 2019USD ($)shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, stock options	$ 3,700				$ 3,700	$ 3,700
Stock options granted (in shares) | shares	0					26,236
Early exercise of stock options, share subject to repurchase (in shares) | shares	7,784				7,784	7,784		21,404
Issuance of common stock related to employee stock purchase plan (in shares) | shares						74,685	99,086
Issuance of common stock related to employee stock purchase plan		$ 991		$ 1,263		$ 1,000	$ 1,300
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, expected period for recognition (in years)						2 years 1 month 6 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
Unrecognized compensation cost, RSUs	$ 20,900				$ 20,900	$ 20,900
2018 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price of common stock as a percent of fair market value (percent)						85.00%
Employee stock purchase program offering period interval (in months)			6 months
Accrued compensation and related expenses for employee payroll deductions	$ 700				$ 700	$ 700		$ 200
2018 Amended ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock purchase program offering period interval (in months)					12 months
Number of purchase periods in offering interval | purchase_period					2

Stock-Based Incentive Compens_4

Stock-Based Incentive Compensation Plans - Stock Option Activity Under the Stock Option Plan (Details) - $ / shares	3 Months Ended	9 Months Ended
	Sep. 30, 2020	Sep. 30, 2020
Number of Shares
Outstanding, beginning of period (in shares)		2,718,971
Granted (in shares)	0	26,236
Exercised (in shares)		(227,334)
Canceled and forfeited (in shares)		(13,524)
Outstanding, end of period (in shares)	2,504,349	2,504,349
Weighted-Average Exercise Price
Outstanding, beginning of period (in dollars per share)		$ 8.02
Granted (in dollars per share)		17.31
Exercised (in dollars per share)		4.34
Canceled and forfeited (in dollars per share)		17.21
Outstanding, end of period (in dollars per share)	$ 8.40	$ 8.40

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, 2020	Sep. 30, 2019
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	$ 8.37	$ 9.78
Stock Options
Weighted average grant date fair value per share and fair value assumptions for estimate fair value
Expected volatility, minimum (percent)	46.60%	46.70%	41.70%
Expected volatility, maximum (percent)	47.30%	47.20%	47.30%
Risk-free interest rate, minimum (percent)	1.32%	1.56%	1.32%
Risk-free interest rate, maximum (percent)	1.39%	1.64%	2.59%
Dividend yield (percent)	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	5 years 6 months	5 years
Maximum | Stock Options
Weighted average grant date fair value per share and fair value assumptions for estimate fair value
Expected term (years)	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, 2020$ / sharesshares
Number of Shares
Outstanding, beginning of period (in shares) | shares	543,041
Granted (in shares) | shares	979,082
Vested (in shares) | shares	(237,702)
Canceled and forfeited (in shares) | shares	(34,248)
Outstanding, end of period (in shares) | shares	1,250,173
Weighted Average Grant Date Fair Value
Outstanding, beginning of period (in dollars per share) | $ / shares	$ 19.72
Granted (in dollars per share) | $ / shares	20.08
Vested (in dollars per share) | $ / shares	20.67
Canceled and forfeited (in dollars per share) | $ / shares	19.55
Outstanding, end of period (in dollars per share) | $ / shares	$ 19.83

Stock-Based Incentive Compens_7

Stock-Based Incentive Compensation Plans - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 3,180	$ 1,911	$ 8,757	$ 5,596
Cost of goods sold
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	87	57	243	163
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,488	807	3,976	2,481
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	299	144	827	364
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,306	$ 903	$ 3,711	$ 2,588

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, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2020	Sep. 30, 2019
Earnings Per Share [Abstract]
Net loss	$ (9,474)	$ (12,472)	$ (12,772)	$ (11,306)	$ (8,654)	$ (9,345)	$ (34,718)	$ (29,305)
Weighted-average number of common shares used to compute basic and diluted net loss per share (in shares)	28,713,418			24,803,452			28,155,561	24,596,788
Net loss per share, basic and diluted (in dollars per share)	$ (0.33)			$ (0.46)			$ (1.23)	$ (1.19)

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, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from the computation of diluted net loss per share	4,019,378	3,609,984	4,019,378	3,609,984
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	2,504,349	2,824,485	2,504,349	2,824,485
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	1,250,173	565,430	1,250,173	565,430
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	7,784	29,268	7,784	29,268
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	138,950	72,679	138,950	72,679
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	118,122	118,122	118,122

Related Party Transaction (Deta

Related Party Transaction (Details) - SeaSpine - Joint development agreement $ in Thousands	3 Months Ended	9 Months Ended
	Sep. 30, 2020USD ($)	Sep. 30, 2020USD ($)
Related Party Transaction [Line Items]
Reimbursement charges expensed	$ 40	$ 86
Outstanding liability to SeaSpine	$ 10	$ 10
Term of product royalty sales period (in years)		10 years

Subsequent Events (Details)

Subsequent Events (Details) - USD ($) $ / shares in Units, $ in Thousands	Oct. 19, 2020	Oct. 31, 2020	Feb. 29, 2020	Sep. 30, 2020	Sep. 30, 2019
Subsequent Event [Line Items]
Offering costs				$ 0	$ 167
Underwriters option
Subsequent Event [Line Items]
Net proceeds from sale of stock			$ 13,000
Number of shares issued (in shares)			645,000
Public offering price (in dollars per share)			$ 21.50
Subsequent event | Second follow-on public offering
Subsequent Event [Line Items]
Net proceeds from sale of stock		$ 71,900
Number of shares issued (in shares)		3,000,000
Public offering price (in dollars per share)		$ 22
Offering costs		$ 400
Subsequent event | Underwriters option
Subsequent Event [Line Items]
Number of shares available for underwriter option		478,507
Subsequent event | Secondary offering by selling shareholders
Subsequent Event [Line Items]
Number of shares issued (in shares)	190,053
Public offering price (in dollars per share)	$ 22