0001459839-21-000045 | 10-Q | XBRL Viewer

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Cover - shares	3 Months Ended
Cover - shares	Mar. 31, 2021	Apr. 30, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2021
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	2021
Document Fiscal Period Focus	Q1
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	Non-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		32,831,631

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 37,364	$ 53,581
Short-term investments	147,687	142,851
Accounts receivable, net of allowance for doubtful accounts of $263	13,088	13,611
Inventory	7,408	5,633
Prepaid expenses and other current assets	2,563	2,565
Total current assets	208,110	218,241
Property and equipment, net	7,285	4,527
Other non-current assets	366	374
TOTAL ASSETS	215,761	223,142
Current liabilities:
Accounts payable	5,183	3,271
Accrued liabilities and other	8,525	10,199
Total current liabilities	13,708	13,470
Long-term borrowings	39,543	39,455
Other long-term liabilities	843	854
TOTAL LIABILITIES	54,094	53,779
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; 32,808,534 and 32,583,220 shares issued and outstanding, respectively	3	3
Additional paid-in capital	412,753	408,113
Accumulated other comprehensive income	430	524
Accumulated deficit	(251,519)	(239,277)
TOTAL STOCKHOLDERS’ EQUITY	161,667	169,363
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 215,761	$ 223,142

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 263	$ 263
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock authorized (in shares)	5,000,000	5,000,000
Preferred stock issued (in shares)	0	0
Preferred stock outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock authorized (in shares)	100,000,000	100,000,000
Common stock issued (in shares)	32,808,534	32,583,220
Common stock outstanding (in shares)	32,808,534	32,583,220

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Income Statement [Abstract]
Revenue	$ 20,442	$ 16,821
Cost of goods sold	2,200	1,932
Gross profit	18,242	14,889
Operating expenses:
Sales and marketing	20,922	19,281
Research and development	2,955	2,090
General and administrative	5,940	5,400
Total operating expenses	29,817	26,771
Loss from operations	(11,575)	(11,882)
Interest and other income (expense), net:
Interest income	61	498
Interest expense	(1,064)	(1,231)
Other income (expense), net	336	(157)
Net loss	(12,242)	(12,772)
Other comprehensive income (loss):
Changes in foreign currency translation	(115)	12
Unrealized gain on marketable securities	21	221
Comprehensive loss	$ (12,336)	$ (12,539)
Net loss per share, basic and diluted (in dollars per share)	$ (0.37)	$ (0.47)
Weighted-average shares used to compute basic and diluted net loss per share	32,691,578	27,252,409

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, 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 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, 2020		32,583,220
Stockholders' equity, beginning of period at Dec. 31, 2020	$ 169,363	$ 3	408,113	524	(239,277)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)	93,975	93,975
Issuance of common stock upon exercise of stock options, net of shares withheld	$ 601		601
Issuance of common stock upon vesting of restricted stock units (in shares)		131,339
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation	4,030		4,030
Vesting of early exercised stock options	9		9
Foreign currency translation	(115)			(115)
Net unrealized gain on marketable securities	21			21
Net loss	(12,242)				(12,242)
Stockholders' equity, end of period (in shares) at Mar. 31, 2021		32,808,534
Stockholders' equity, end of period at Mar. 31, 2021	$ 161,667	$ 3	$ 412,753	$ 430	$ (251,519)

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Cash flows from operating activities
Net loss	$ (12,242)	$ (12,772)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	4,030	2,622
Depreciation and amortization	340	249
Bad debt expense	0	192
Accretion on marketable securities	331	(25)
Amortization of debt issuance costs	88	65
Loss on sale and disposal of property and equipment	104	0
Changes in operating assets and liabilities:
Accounts receivable	581	2,207
Inventory	(1,725)	(256)
Prepaid expenses and other assets	20	581
Accounts payable	1,059	76
Accrued liabilities and other	(1,945)	(2,294)
Net cash used in operating activities	(9,359)	(9,355)
Cash flows from investing activities
Maturities of marketable securities	33,200	21,000
Purchases of marketable securities	(38,346)	(16,777)
Purchases of property and equipment	(1,976)	(884)
Net cash (used in) provided by investing activities	(7,122)	3,339
Cash flows from financing activities
Proceeds from follow-on public offering, net of underwriting discounts, commissions and offering costs	0	62,978
Proceeds from the exercise of stock options	601	174
Net cash provided by financing activities	601	63,152
Effect of exchange rate changes on cash and cash equivalents	(337)	(3)
Net (decrease) increase in cash and cash equivalents	(16,217)	57,133
Cash and cash equivalents at
Beginning of period	53,581	10,435
End of period	37,364	67,568
Supplemental disclosure of non-cash information
Vesting of early exercised stock options	9	27
Unpaid purchases of property and equipment	$ 1,195	$ 52

The Company and Nature of Business	3 Months Ended
The Company and Nature of Business	Mar. 31, 2021
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 the first quarter of 2020, the Company received $63.0 million of net proceeds from its first follow-on public offering of 4,300,000 shares of the Company's common stock, of which 2,490,053 shares were offered and sold by the Company, and the exercise of underwriter's option to purchase from the Company an additional 645,000 shares of the Company's common stock, at a public offering price of $21.50 per share. 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 consolidated statements of operations in the year ended December 31, 2020. In October 2020, the Company received $71.6 million of net proceeds from its second follow-on public offering of shares of the Company's common stock, of which 3,000,000 shares were offered and sold by the Company, 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. In addition to the shares sold by the Company in this second follow-on offering, the selling stockholder sold 190,053 shares of the Company's common stock previously held by the selling stockholder at a price to the public of $22.00 per share. The Company did not receive any proceeds from the sale by the selling stockholder. 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 uncertain and difficult to predict. 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, the extent and severity of the impact on the Company's customers, approval and dissemination of COVID-19 vaccines, and the lifting of pandemic-related restrictions, many 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. The Company is also subject to risks common to medical device companies including, but not limited to, new technological innovations, dependence on key personnel, protection of proprietary technology, compliance with government regulations, product liability, the ability to obtain adequate coverage and reimbursement from third-party payors and uncertainty of market acceptance of products. The Company is dependent on third-party manufacturers and suppliers, in some cases single source suppliers. The Company currently has limited long term contracts with its key suppliers and is subject to risks such as manufacturing failures, non-compliance with regulatory requirements, price fluctuations, inability to properly meet demand and third-party supplier discontinuation of operations.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2021

Accounting Policies [Abstract]

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, 2020 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 months ended March 31, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 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, 2020 contained in the Company’s Annual Report on Form 10-K filed with the SEC on March 10, 2021.

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, 2020. 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 March 31,
	2021		2020
	(in thousands)
United States	$	18,770	$	15,297
International	1,672		1,524
	$	20,442	$	16,821

Recently Adopted Accounting Pronouncement

In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. ASU 2019-12 simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating incomes taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. ASU 2019-12 is effective in 2021 and interim periods within that year and permits for an early adoption. The Company adopted ASU 2019-12 effective January 1, 2021. The adoption of the guidance did not have a material impact on its financials statements and related disclosures.

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, ASU 2019-08 and ASU 2019-11 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.

Marketable Securities

3 Months Ended

Mar. 31, 2021

Investments, Debt and Equity Securities [Abstract]

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:


	March 31, 2021
	Amortized Cost		Unrealized Gains		Unrealized Losses		Aggregate Fair Value
	(in thousands)
Money market funds	$	29,402	$	—	$	—	$	29,402

Cash equivalents	29,402		—		—		29,402

U.S. treasury securities	84,758		21		—		84,779
Corporate bonds	12,946		—		(4)		12,942
Commercial paper	49,966		—		—		49,966
Short-term investments	147,670		21		(4)		147,687



Total marketable securities	$	177,072	$	21	$	(4)	$	177,089


	December 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses		Aggregate Fair Value
	(in thousands)
Money market funds	$	45,948	$	—	$	—	$	45,948
Commercial paper	1,400		—		—		1,400
Cash equivalents	47,348		—		—		47,348

U.S. treasury securities	74,779		4		(7)		74,776
Corporate bonds	8,940		4		(6)		8,938
Commercial paper	59,137		—		—		59,137
Short-term investments	142,856		8		(13)		142,851



Total marketable securities	$	190,204	$	8	$	(13)	$	190,199

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 March 31, 2021 or December 31, 2020.

Fair Value Measurement

3 Months Ended

Mar. 31, 2021

Fair Value Disclosures [Abstract]

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:


	March 31, 2021
	Level 1		Level 2		Level 3		Total
	(in thousands)
Marketable securities
Money market funds	$	29,402	$	—	$	—	$	29,402
U.S. treasury securities	84,779		—		—		84,779
Corporate bonds	—		12,942		—		12,942
Commercial paper	—		49,966		—		49,966
Total marketable securities	$	114,181	$	62,908	$	—	$	177,089

	December 31, 2020
	Level 1		Level 2		Level 3		Total
	(in thousands)
Marketable securities
Money market funds	$	45,948	$	—	$	—	$	45,948
U.S. treasury securities	74,776		—		—		74,776
Corporate bonds	—		8,938		—		8,938
Commercial paper	—		60,537		—		60,537
Total marketable securities	$	120,724	$	69,475	$	—	$	190,199

- Definition

The entire disclosure for the fair value of financial instruments (as defined), including financial assets and financial liabilities (collectively, as defined), and the measurements of those instruments as well as disclosures related to the fair value of non-financial assets and liabilities. Such disclosures about the financial instruments, assets, and liabilities would include: (1) the fair value of the required items together with their carrying amounts (as appropriate); (2) for items for which it is not practicable to estimate fair value, disclosure would include: (a) information pertinent to estimating fair value (including, carrying amount, effective interest rate, and maturity, and (b) the reasons why it is not practicable to estimate fair value; (3) significant concentrations of credit risk including: (a) information about the activity, region, or economic characteristics identifying a concentration, (b) the maximum amount of loss the entity is exposed to based on the gross fair value of the related item, (c) policy for requiring collateral or other security and information as to accessing such collateral or security, and (d) the nature and brief description of such collateral or security; (4) quantitative information about market risks and how such risks are managed; (5) for items measured on both a recurring and nonrecurring basis information regarding the inputs used to develop the fair value measurement; and (6) for items presented in the financial statement for which fair value measurement is elected: (a) information necessary to understand the reasons for the election, (b) discussion of the effect of fair value changes on earnings, (c) a description of [similar groups] items for which the election is made and the relation thereof to the balance sheet, the aggregate carrying value of items included in the balance sheet that are not eligible for the election; (7) all other required (as defined) and desired information.

+ References + Details

Balance Sheet Components

3 Months Ended

Mar. 31, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Balance Sheet Components

Inventory

As of March 31, 2021 and December 31, 2020, inventory consisted entirely of finished goods.

Property and Equipment, net:


	March 31, 2021		December 31, 2020
	(in thousands)
Machinery and equipment	$	7,371	$	6,342
Construction in progress	3,707		1,692
Computer and office equipment	730		714
Leasehold improvements	503		503
Furniture and fixtures	231		233
	12,542		9,484
Less: Accumulated depreciation and amortization	(5,257)		(4,957)
	$	7,285	$	4,527

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 March 31, 2021 and 2020, respectively.

Accrued Liabilities and Other:


	March 31, 2021		December 31, 2020
	(in thousands)
Accrued compensation and related expenses	$	7,049	$	9,175

Accrued professional services	392		511
Others	1,084		513
	$	8,525	$	10,199

Commitments and Contingencies

3 Months Ended

Mar. 31, 2021

Commitments and Contingencies Disclosure [Abstract]

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 expenses charged to operations under operating leases were $0.3 million for both the three months ended March 31, 2021 and 2020.

The table below summarizes aggregate future minimum lease payments under all leases as of March 31, 2021:


Year ending December 31,	(in thousands)
Remainder of 2021	$	801
2022	1,019
2023	933
2024	917
2025	412
Thereafter	23
	$	4,105

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 $0.5 million and $0.3 million as of March 31, 2021 and December 31, 2020, respectively.

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

3 Months Ended

Mar. 31, 2021

Debt Disclosure [Abstract]

Borrowings

Term Loan

The following table summarizes the outstanding borrowings from the term loan described below, as of the dates presented:


	March 31, 2021		December 31, 2020
	(in thousands)
Principal outstanding and final fee	$	41,000	$	41,000
Less: Unamortized debt issuance costs	(624)		(661)
Unaccreted value of final fee	(833)		(884)
Outstanding debt, net of debt issuance costs and unaccreted value of final fee	$	39,543	$	39,455
Classified as:

Long-term borrowings	$	39,543	$	39,455

In October 2017, the Company entered into a term loan with Biopharma Credit Investments IV Sub LP (“Pharmakon”) in 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. The effective interest rate related to the Pharmakon Term Loan for the three months ended March 31, 2020 was 12.3%. The Company paid in full and terminated the Pharmakon Term Loan in May 2020.

The outstanding debt as of March 31, 2021 and December 31, 2020 is related to a term loan pursuant to the Loan and Security Agreement dated May 29, 2020, entered into by the Company with Solar Capital Partners (“Solar”). Pursuant to the Loan and Security Agreement, Solar provided an aggregate principal amount of $40.0 million term loan (the “Solar Term Loan”). 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. 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 consolidated statement of operations for the year ended December 31, 2020.

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 effective interest rate related to the Solar Term Loan for the three months ended March 31, 2021 was 10.6%.

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 table below summarizes the future principal and final fee payments under the Solar Term Loan as of March 31, 2021:


Year ending December 31,	(in thousands)
2021 (remaining nine months)	$	—
2022	—
2023	11,667
2024	20,000
2025	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 March 31, 2021, 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.

CARES Act

On March 27, 2020, the U.S. federal government enacted the “Coronavirus Aid, Relief and Economic Security (CARES) Act,” which, among other things, allowed employers to defer the deposit and payment of an employer's share of social security taxes through December 31, 2020. The Company recorded a total liability of $1.0 million related to the deferral of the social security taxes of which $0.5 million is included in each accrued liabilities and other and other long-term liabilities in the condensed consolidated balance sheets as of March 31, 2021 and December 31, 2020

Stock-Based Incentive Compensation Plans

3 Months Ended

Mar. 31, 2021

Share-based Payment Arrangement [Abstract]

Stock-Based Incentive Compensation Plans

Stock Options

The table below summarizes the stock option activity for the three months ended March 31, 2021:


	Number of Shares	Weighted- Average Exercise Price
Outstanding as of December 31, 2020	2,405,957	$8.54

Exercised	(93,975)	6.39
Canceled and forfeited	(50)	4.68
Outstanding as of March 31, 2021	2,311,932	8.62

As of March 31, 2021, the unrecognized compensation cost related to stock options was $2.7 million, which is expected to be recognized over a period of approximately 1.7 years.

There were no stock options granted during the three months ended March 31, 2021. 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 in 2020:


			Three Months Ended March 31,
	2020
Weighted average grant date fair value per share	$8.37
Expected term (years)	5.5	to	7.0
Expected volatility	46.74 %	to	47.20 %
Risk-free interest rate	1.56 %	to	1.64 %
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 March 31, 2021 and December 31, 2020, the Company had a total of 3,889 shares and 5,836 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 three months ended March 31, 2021:


	Number of Shares	Weighted Average Grant Date Fair Value
Outstanding as of December 31, 2020	1,165,295	$20.07
Granted	816,928	28.91
Vested	(131,339)	19.36
Canceled and forfeited	(6,759)	24.82
Outstanding as of March 31, 2021	1,844,125	24.02

As of March 31, 2021, the unrecognized compensation cost related to the restricted stock units was $37.8 million, which is expected to be recognized over a period of approximately 3.2 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 month offering period. The offer period generally commences in May and November. On March 26, 2020, the Company's Compensation Committee approved the amendment of the terms of future offerings under the ESPP which, among other things, increased the maximum number of shares that may be purchased on any single purchase date, provided for automatic enrollment in a new offering, and provided that the offering which commenced in May 2020 be twelve months in duration and consist of two purchase periods.

The fair value of the ESPP shares is estimated using the Black-Scholes option pricing model, which is being amortized over the requisite service period. The Company did not issue any shares under the ESPP during the three months ended March 31, 2021 and March 31, 2020. As of March 31, 2021 and December 31, 2020, total accumulated ESPP related employee payroll deductions amounted to $1.3 million and $0.4 million, respectively, which were included within accrued compensation and related expenses in the condensed consolidated balance sheets.

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 March 31,
	2021		2020
	(in thousands)
Cost of goods sold	$	174	$	71
Sales and marketing	1,899		1,141
Research and development	419		240
General and administrative	1,538		1,170
	$	4,030	$	2,622

Net Loss Per Share of Common Stock

3 Months Ended

Mar. 31, 2021

Earnings Per Share [Abstract]

Net Loss Per Share of Common Stock

The table below summarizes the computation of basic and diluted net loss per share:


	Three Months Ended March 31,
	2021		2020
	(in thousands, except share and per share data)
Net loss	$	(12,242)	$	(12,772)

Weighted-average shares used to compute basic and diluted net loss per share	32,691,578		27,252,409

Net loss per share, basic and diluted	$	(0.37)	$	(0.47)

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 March 31,
	2021	2020
Stock options	2,311,932	2,700,554
Restricted stock units	1,844,125	1,342,211
Shares subject to repurchase	3,889	15,567
ESPP purchase rights	101,282	65,442
Common stock warrants	118,122	118,122
	4,379,350	4,241,896

Related Party Transaction	3 Months Ended
Related Party Transaction	Mar. 31, 2021
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 months ended March 31, 2021 and 2020, the Company expensed $10,000 and $22,000, respectively, of the reimbursement charges from SeaSpine, which were recorded within research and development expense in the condensed consolidated statements of operations. There were no outstanding liabilities to SeaSpine as of March 31, 2021 and December 31, 2020. Certain intellectual property developed pursuant to the project plan will be owned by the Company, certain intellectual property developed pursuant to the project plan will be owned by SeaSpine, and other intellectual property developed pursuant to the project plan will be jointly owned by SeaSpine and the Company. The Company also agreed to provide SeaSpine a royalty-free, worldwide, perpetual, non-exclusive license of certain of the Company's intellectual property incorporated into the product to be developed. The Company also agreed to pay SeaSpine a product royalty, in an amount specified in the Development Agreement, for each resulting product sold for a period of 10 years beginning on the initial market launch. The term of the Development Agreement shall continue until the expiration of all royalty terms, unless earlier terminated by either party, as provided for by the Development Agreement.

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2021
Income Tax Disclosure [Abstract]
Income Taxes	Income TaxesIn 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 months ended March 31, 2021 and 2020. 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, 2020.

- Definition

The entire disclosure for income taxes. Disclosures may include net deferred tax liability or asset recognized in an enterprise's statement of financial position, net change during the year in the total valuation allowance, approximate tax effect of each type of temporary difference and carryforward that gives rise to a significant portion of deferred tax liabilities and deferred tax assets, utilization of a tax carryback, and tax uncertainties information.

+ References + Details

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2021
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, 2020 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 months ended March 31, 2021 are not necessarily indicative of the results to be expected for the year ending December 31, 2021 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.
Recently Adopted Accounting Pronouncement and Recently Issued Accounting Standards	Recently Adopted Accounting Pronouncement In December 2019, the FASB issued ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes. ASU 2019-12 simplifies the accounting for income taxes by eliminating certain exceptions to the guidance in ASC 740 related to the approach for intraperiod tax allocation, the methodology for calculating incomes taxes in an interim period and the recognition of deferred tax liabilities for outside basis differences. ASU 2019-12 is effective in 2021 and interim periods within that year and permits for an early adoption. The Company adopted ASU 2019-12 effective January 1, 2021. The adoption of the guidance did not have a material impact on its financials statements and related disclosures. 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, ASU 2019-08 and ASU 2019-11 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.

- Definition

Disclosure of accounting policy for segment reporting.

+ References + Details

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2021

Accounting Policies [Abstract]

Schedule of Revenue by Geography

The table below summarizes the Company's revenue by geography:


	Three Months Ended March 31,
	2021		2020
	(in thousands)
United States	$	18,770	$	15,297
International	1,672		1,524
	$	20,442	$	16,821

Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2021

Investments, Debt and Equity Securities [Abstract]

Schedule of Marketable Securities

The table below summarizes the marketable securities:


	March 31, 2021
	Amortized Cost		Unrealized Gains		Unrealized Losses		Aggregate Fair Value
	(in thousands)
Money market funds	$	29,402	$	—	$	—	$	29,402

Cash equivalents	29,402		—		—		29,402

U.S. treasury securities	84,758		21		—		84,779
Corporate bonds	12,946		—		(4)		12,942
Commercial paper	49,966		—		—		49,966
Short-term investments	147,670		21		(4)		147,687



Total marketable securities	$	177,072	$	21	$	(4)	$	177,089


	December 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses		Aggregate Fair Value
	(in thousands)
Money market funds	$	45,948	$	—	$	—	$	45,948
Commercial paper	1,400		—		—		1,400
Cash equivalents	47,348		—		—		47,348

U.S. treasury securities	74,779		4		(7)		74,776
Corporate bonds	8,940		4		(6)		8,938
Commercial paper	59,137		—		—		59,137
Short-term investments	142,856		8		(13)		142,851



Total marketable securities	$	190,204	$	8	$	(13)	$	190,199

Fair Value Measurement (Tables)

3 Months Ended

Mar. 31, 2021

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:


	March 31, 2021
	Level 1		Level 2		Level 3		Total
	(in thousands)
Marketable securities
Money market funds	$	29,402	$	—	$	—	$	29,402
U.S. treasury securities	84,779		—		—		84,779
Corporate bonds	—		12,942		—		12,942
Commercial paper	—		49,966		—		49,966
Total marketable securities	$	114,181	$	62,908	$	—	$	177,089

	December 31, 2020
	Level 1		Level 2		Level 3		Total
	(in thousands)
Marketable securities
Money market funds	$	45,948	$	—	$	—	$	45,948
U.S. treasury securities	74,776		—		—		74,776
Corporate bonds	—		8,938		—		8,938
Commercial paper	—		60,537		—		60,537
Total marketable securities	$	120,724	$	69,475	$	—	$	190,199

Balance Sheet Components (Tables)

3 Months Ended

Mar. 31, 2021

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Property and Equipment, Net

Property and Equipment, net:


	March 31, 2021		December 31, 2020
	(in thousands)
Machinery and equipment	$	7,371	$	6,342
Construction in progress	3,707		1,692
Computer and office equipment	730		714
Leasehold improvements	503		503
Furniture and fixtures	231		233
	12,542		9,484
Less: Accumulated depreciation and amortization	(5,257)		(4,957)
	$	7,285	$	4,527

Schedule of Accrued Liabilities and Other

Accrued Liabilities and Other:


	March 31, 2021		December 31, 2020
	(in thousands)
Accrued compensation and related expenses	$	7,049	$	9,175

Accrued professional services	392		511
Others	1,084		513
	$	8,525	$	10,199

Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2021

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 March 31, 2021:


Year ending December 31,	(in thousands)
Remainder of 2021	$	801
2022	1,019
2023	933
2024	917
2025	412
Thereafter	23
	$	4,105

Borrowings (Tables)

3 Months Ended

Mar. 31, 2021

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:


	March 31, 2021		December 31, 2020
	(in thousands)
Principal outstanding and final fee	$	41,000	$	41,000
Less: Unamortized debt issuance costs	(624)		(661)
Unaccreted value of final fee	(833)		(884)
Outstanding debt, net of debt issuance costs and unaccreted value of final fee	$	39,543	$	39,455
Classified as:

Long-term borrowings	$	39,543	$	39,455

Schedule of Future Principal and Final Fee Payments

The table below summarizes the future principal and final fee payments under the Solar Term Loan as of March 31, 2021:


Year ending December 31,	(in thousands)
2021 (remaining nine months)	$	—
2022	—
2023	11,667
2024	20,000
2025	9,333

Total principal and final fee payments	$	41,000

- Definition

Tabular disclosure of long-debt instruments or arrangements, including identification, terms, features, collateral requirements and other information necessary to a fair presentation. These are debt arrangements that originally required repayment more than twelve months after issuance or greater than the normal operating cycle of the entity, if longer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28541-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 6
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21506-112644

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28551-108399

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21521-112644

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21538-112644

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 470
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
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Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
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+ Details

Stock-Based Incentive Compensation Plans (Tables)

3 Months Ended

Mar. 31, 2021

Share-based Payment Arrangement [Abstract]

Schedule of Stock Option Activity

The table below summarizes the stock option activity for the three months ended March 31, 2021:


	Number of Shares	Weighted- Average Exercise Price
Outstanding as of December 31, 2020	2,405,957	$8.54

Exercised	(93,975)	6.39
Canceled and forfeited	(50)	4.68
Outstanding as of March 31, 2021	2,311,932	8.62

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 in 2020:


			Three Months Ended March 31,
	2020
Weighted average grant date fair value per share	$8.37
Expected term (years)	5.5	to	7.0
Expected volatility	46.74 %	to	47.20 %
Risk-free interest rate	1.56 %	to	1.64 %
Dividend yield	—%

Schedule of Restricted Stock Unit Activity

The table below summarizes restricted stock units activity for the three months ended March 31, 2021:


	Number of Shares	Weighted Average Grant Date Fair Value
Outstanding as of December 31, 2020	1,165,295	$20.07
Granted	816,928	28.91
Vested	(131,339)	19.36
Canceled and forfeited	(6,759)	24.82
Outstanding as of March 31, 2021	1,844,125	24.02

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 March 31,
	2021		2020
	(in thousands)
Cost of goods sold	$	174	$	71
Sales and marketing	1,899		1,141
Research and development	419		240
General and administrative	1,538		1,170
	$	4,030	$	2,622

Net Loss Per Share of Common Stock (Tables)

3 Months Ended

Mar. 31, 2021

Earnings Per Share [Abstract]

Schedule of Computation 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 March 31,
	2021		2020
	(in thousands, except share and per share data)
Net loss	$	(12,242)	$	(12,772)

Weighted-average shares used to compute basic and diluted net loss per share	32,691,578		27,252,409

Net loss per share, basic and diluted	$	(0.37)	$	(0.47)

Schedule of Anti-dilutive Common Stock Equivalents 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 March 31,
	2021	2020
Stock options	2,311,932	2,700,554
Restricted stock units	1,844,125	1,342,211
Shares subject to repurchase	3,889	15,567
ESPP purchase rights	101,282	65,442
Common stock warrants	118,122	118,122
	4,379,350	4,241,896

The Company and Nature of Business (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended	3 Months Ended	12 Months Ended
	Oct. 31, 2020	Mar. 31, 2020	Dec. 31, 2020
First follow-on public offering
Subsidiary, Sale of Stock [Line Items]
Net proceeds from sale of stock		$ 63.0
Public offering price (in dollars per share)		$ 21.50
Number of shares issued (in shares)		2,490,053
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)	478,507	645,000
Second follow-on public offering
Subsidiary, Sale of Stock [Line Items]
Net proceeds from sale of stock	$ 71.6
Public offering price (in dollars per share)	$ 22.00
Number of shares issued (in shares)	3,000,000
Secondary offering by selling shareholders
Subsidiary, Sale of Stock [Line Items]
Public offering price (in dollars per share)	$ 22.00
Number of shares issued (in shares)	190,053
Allocated public offering costs			$ 0.2

Summary of Significant Accounting Policies - Narrative (Details)	3 Months Ended
	Mar. 31, 2021 segment
Accounting Policies [Abstract]
Number of reportable segments	1
Number of operating segments	1

Summary of Significant Accounting Policies - Revenue by Geography (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Disaggregation of Revenue [Line Items]
Revenue	$ 20,442	$ 16,821
United States
Disaggregation of Revenue [Line Items]
Revenue	18,770	15,297
International
Disaggregation of Revenue [Line Items]
Revenue	$ 1,672	$ 1,524

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
-SubTopic 10
-Section 50
-Paragraph 30
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e8906-108599

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 280
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Reference 3: http://www.xbrl.org/2003/role/disclosureRef
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Reference 4: http://www.xbrl.org/2003/role/disclosureRef
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Reference 5: http://www.xbrl.org/2003/role/disclosureRef
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-Name Accounting Standards Codification
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Reference 6: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 7: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 8: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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Reference 9: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
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-URI http://asc.fasb.org/extlink&oid=120311839&loc=d3e9054-108599

Reference 10: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
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-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=121604090&loc=SL49130545-203045

Reference 11: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 924
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-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 11.L)
-URI http://asc.fasb.org/extlink&oid=6472922&loc=d3e499488-122856

+ Details

Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Cash equivalents
Carrying Value	$ 29,402	$ 47,348
Short-term investments
Amortized Cost	147,670	142,856
Unrealized Gains	21	8
Unrealized Losses	(4)	(13)
Aggregate Fair Value	147,687	142,851
Total marketable securities, Amortized Cost	177,072	190,204
Total marketable securities, Unrealized Gains	21	8
Total marketable securities, Unrealized Losses	(4)	(13)
Total marketable securities, Aggregate Fair Value	177,089	190,199
Money market funds
Cash equivalents
Carrying Value	29,402	45,948
U.S. treasury securities
Short-term investments
Amortized Cost	84,758	74,779
Unrealized Gains	21	4
Unrealized Losses	0	(7)
Aggregate Fair Value	84,779	74,776
Corporate bonds
Short-term investments
Amortized Cost	12,946	8,940
Unrealized Gains	0	4
Unrealized Losses	(4)	(6)
Aggregate Fair Value	12,942	8,938
Commercial paper
Cash equivalents
Carrying Value		1,400
Short-term investments
Amortized Cost	49,966	59,137
Unrealized Gains	0	0
Unrealized Losses	0	0
Aggregate Fair Value	$ 49,966	$ 59,137

Fair Value Measurement (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Marketable securities
Marketable securities	$ 177,089	$ 190,199
Money market funds
Marketable securities
Marketable securities	29,402	45,948
U.S. treasury securities
Marketable securities
Marketable securities	84,779	74,776
Corporate bonds
Marketable securities
Marketable securities	12,942	8,938
Commercial paper
Marketable securities
Marketable securities	49,966	60,537
Level 1
Marketable securities
Marketable securities	114,181	120,724
Level 1 \| Money market funds
Marketable securities
Marketable securities	29,402	45,948
Level 1 \| U.S. treasury securities
Marketable securities
Marketable securities	84,779	74,776
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	62,908	69,475
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	12,942	8,938
Level 2 \| Commercial paper
Marketable securities
Marketable securities	49,966	60,537
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 - Property and Equipment, Net (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Property and Equipment, Net
Property and equipment, gross	$ 12,542		$ 9,484
Less: Accumulated depreciation and amortization	(5,257)		(4,957)
Property and equipment, net	7,285		4,527
Depreciation expense	300	$ 200
Machinery and equipment
Property and Equipment, Net
Property and equipment, gross	7,371		6,342
Construction in progress
Property and Equipment, Net
Property and equipment, gross	3,707		1,692
Computer and office equipment
Property and Equipment, Net
Property and equipment, gross	730		714
Leasehold improvements
Property and Equipment, Net
Property and equipment, gross	503		503
Furniture and fixtures
Property and Equipment, Net
Property and equipment, gross	$ 231		$ 233

Balance Sheet Components - Accrued Liabilities and Other (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Accrued Liabilities and Other
Accrued compensation and related expenses	$ 7,049	$ 9,175
Accrued professional services	392	511
Others	1,084	513
Accrued liabilities and other	$ 8,525	$ 10,199

Commitments and Contingencies - Narrative (Details) - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Other Commitments [Line Items]
Rent expense	$ 300,000	$ 300,000
Purchase commitments related to inventory	500,000		$ 300,000
Indemnification Agreement
Other Commitments [Line Items]
Costs to defend lawsuits or settle claims	0
Liability associated with indemnifications	$ 0

Commitments and Contingencies - Aggregate Future Minimum Lease Payments (Details) $ in Thousands	Mar. 31, 2021 USD ($)
Aggregate Future Minimum Lease Payments
Remainder of 2021	$ 801
2022	1,019
2023	933
2024	917
2025	412
Thereafter	23
Total	$ 4,105

Borrowings - Summary of Borrowings (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Debt Disclosure [Abstract]
Principal outstanding and final fee	$ 41,000	$ 41,000
Less: Unamortized debt issuance costs	(624)	(661)
Less: Unaccreted value of final fee	(833)	(884)
Outstanding debt, net of debt issuance costs and unaccreted value of final fee	39,543	39,455
Long-term borrowings	$ 39,543	$ 39,455

Borrowings - Narrative (Details) - USD ($)		1 Months Ended	3 Months Ended		12 Months Ended
Borrowings - Narrative (Details) - USD ($)	May 29, 2020	Oct. 31, 2017	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Debt Instrument [Line Items]
Recognition of unamortized debt discount and issuance costs on debt extinguishment					$ 700,000
Prepayment penalty and lender fees on debt extinguishment					800,000
Final fee			$ 833,000		884,000
Deferred liability for social security taxes, CARES Act					1,000,000.0
Accrued liabilities
Debt Instrument [Line Items]
Deferred liability for social security taxes, CARES Act					500,000
Other long-term liabilities
Debt Instrument [Line Items]
Deferred liability for social security taxes, CARES Act					$ 500,000
Term loan \| Solar Term Loan
Debt Instrument [Line Items]
Debt period payment, interest only period	36 months
Fixed interest rate (percent)	9.40%
Effective interest rate during the period (percent)			10.60%
Aggregate principal amount	$ 40,000,000.0
Unamortized debt discount and issuance cost	$ 800,000
Debt maturity term (in months)	60 months
Allowable prepayment increments per agreement	$ 10,000,000.0
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	$ 1,000,000.0
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 Term Loan \| Basis spread option
Debt Instrument [Line Items]
Basis spread on variable rate	0.33%
Term loan \| Solar Term Loan \| Net product revenue less than $75 million
Debt Instrument [Line Items]
Debt covenant minimum cash balance	$ 15,000,000.0
Term loan \| Solar Term Loan \| Net product revenue less than $75 million \| Maximum
Debt Instrument [Line Items]
Product revenue threshold for minimum liquidity covenant	75,000,000.0
Term loan \| Solar Term Loan \| 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 Term Loan \| Net product revenue more than $75 million and less than $100 million \| Maximum
Debt Instrument [Line Items]
Product revenue threshold for minimum liquidity covenant	100,000,000.0
Term loan \| Solar Term Loan \| Net product revenue more than $75 million and less than $100 million \| Minimum
Debt Instrument [Line Items]
Product revenue threshold for minimum liquidity covenant	75,000,000.0
Term loan \| Solar Term Loan \| Net product revenue more than $100 million
Debt Instrument [Line Items]
Debt covenant minimum cash balance	0
Term loan \| Solar Term Loan \| Net product revenue more than $100 million \| Minimum
Debt Instrument [Line Items]
Product revenue threshold for minimum liquidity covenant	$ 100,000,000.0
Term loan \| Pharmakon Term Loan
Debt Instrument [Line Items]
Proceeds from debt financing		$ 40,000,000.0
Debt period payment, interest only period		35 months
Fixed interest rate (percent)		11.50%
Effective interest rate during the period (percent)				12.30%
Term loan \| Pharmakon Term Loan \| Prepayment Penalty, 31-48 Months
Debt Instrument [Line Items]
Debt prepayment penalty percentage (percent)		2.00%
Term loan \| Pharmakon Term Loan \| Prepayment Penalty, 49-60 Months
Debt Instrument [Line Items]
Debt prepayment penalty percentage (percent)		1.00%

Borrowings - Debt Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Future principal and final fee payments
2021 (remaining nine months)	$ 0
2022	0
2023	11,667
2024	20,000
2025	9,333
Total principal and final fee payments	$ 41,000	$ 41,000

Stock-Based Incentive Compensation Plans - Narrative (Details) $ in Millions	3 Months Ended	4 Months Ended	8 Months Ended	12 Months Ended
	Mar. 31, 2021 USD ($) shares	Apr. 30, 2020	Dec. 31, 2020 USD ($) purchase_period shares	Dec. 31, 2020 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, stock options	$ 2.7
Stock options granted (in shares) \| shares	0
Early exercise of stock options, share subject to repurchase (in shares) \| shares	3,889		5,836	5,836
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, expected period for recognition (in years)	1 year 8 months 12 days
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, expected period for recognition (in years)	3 years 2 months 12 days
Unrecognized compensation cost, RSUs	$ 37.8
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	12 months
Number of purchase periods in offering interval \| purchase_period			2
Accrued compensation and related expenses for employee payroll deductions	$ 1.3		$ 0.4	$ 0.4

Stock-Based Incentive Compensation Plans - Stock Option Activity (Details)	3 Months Ended
	Mar. 31, 2021 $ / shares shares
Number of Shares
Outstanding, beginning of period (in shares) \| shares	2,405,957
Exercised (in shares) \| shares	(93,975)
Canceled and forfeited (in shares) \| shares	(50)
Outstanding, end of period (in shares) \| shares	2,311,932
Weighted-Average Exercise Price
Outstanding, beginning of period (in dollars per share) \| $ / shares	$ 8.54
Exercised (in dollars per share) \| $ / shares	6.39
Canceled and forfeited (in dollars per share) \| $ / shares	4.68
Outstanding, end of period (in dollars per share) \| $ / shares	$ 8.62

Stock-Based Incentive Compensation Plans - Valuation Assumptions for Stock Options (Details)	3 Months Ended
	Mar. 31, 2020 $ / shares
Black-Scholes option-pricing model assumptions
Weighted average grant date fair value per share (in dollars per share)	$ 8.37
Stock Options
Black-Scholes option-pricing model assumptions
Expected volatility, minimum (percent)	46.74%
Expected volatility, maximum (percent)	47.20%
Risk-free interest rate, minimum (percent)	1.56%
Risk-free interest rate, maximum (percent)	1.64%
Dividend yield (percent)	0.00%
Stock Options \| Minimum
Black-Scholes option-pricing model assumptions
Expected term (years)	5 years 6 months
Stock Options \| Maximum
Black-Scholes option-pricing model assumptions
Expected term (years)	7 years

Stock-Based Incentive Compensation Plans - Restricted Stock Units Activity (Details) - Restricted Stock Units	3 Months Ended
	Mar. 31, 2021 $ / shares shares
Number of Shares
Outstanding, beginning of period (in shares) \| shares	1,165,295
Granted (in shares) \| shares	816,928
Vested (in shares) \| shares	(6,759)
Canceled and forfeited (in shares) \| shares	(131,339)
Outstanding, end of period (in shares) \| shares	1,844,125
Weighted Average Grant Date Fair Value
Outstanding, beginning of period (in dollars per share) \| $ / shares	$ 20.07
Granted (in dollars per share) \| $ / shares	28.91
Vested (in dollars per share) \| $ / shares	24.82
Canceled and forfeited (in dollars per share) \| $ / shares	19.36
Outstanding, end of period (in dollars per share) \| $ / shares	$ 24.02

Stock-Based Incentive Compensation Plans - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,622	$ 4,030
Cost of goods sold
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	71	174
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,141	1,899
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	240	419
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,170	$ 1,538

Net Loss Per Share of Common Stock - Computation of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Earnings Per Share [Abstract]
Net loss	$ (12,242)	$ (12,772)
Weighted-average shares used to compute basic and diluted net loss per share	32,691,578	27,252,409
Net loss per share, basic and diluted (in dollars per share)	$ (0.37)	$ (0.47)

- Definition

The portion of profit or loss for the period, net of income taxes, which is attributable to the parent.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 220
-SubTopic 10
-Section 45
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Reference 2: http://www.xbrl.org/2003/role/exampleRef
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+ Details

Net Loss Per Share of Common Stock - Antidilutive Common Stock Equivalents Excluded from Computation of Earnings Per Share (Details) - shares	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	4,379,350	4,241,896
Stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	2,311,932	2,700,554
Restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	1,844,125	1,342,211
Shares subject to repurchase
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	3,889	15,567
ESPP purchase rights
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	101,282	65,442
Common stock warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common stock equivalents excluded from computation of diluted net loss per share	118,122	118,122

Related Party Transaction (Details) - SeaSpine - Joint development agreement - USD ($)	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Reimbursement charges expensed	$ 10,000	$ 22,000
Outstanding liability to SeaSpine	$ 0		$ 0
Term of product royalty sales period (in years)	10 years