0001459839-21-000012 | 10-K | XBRL Viewer

Cover - USD ($) $ in Millions	12 Months Ended
Cover - USD ($) $ in Millions	Dec. 31, 2020	Mar. 05, 2021	Jun. 30, 2020
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Document Period End Date	Dec. 31, 2020
Current Fiscal Year End Date	--12-31
Document Transition Report	false
Entity File Number	001-38701
Entity Registrant Name	SI-BONE, Inc.
Entity Central Index Key	0001459839
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	FY
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 Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
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
ICFR Auditor Attestation Flag	false
Entity Shell Company	false
Entity Public Float			$ 394.1
Entity Common Stock, Shares Outstanding		32,727,666
Documents Incorporated by Reference	Portions of the Registrant’s Definitive Proxy Statement relating to the Annual Meeting of Shareholders, which will be filed with the Securities and Exchange Commission within 120 days after the end of the Registrant’s fiscal year ended December 31, 2020, are incorporated by reference into Part III of this Report.

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
CURRENT ASSETS
Cash and cash equivalents	$ 53,581	$ 10,435
Short-term investments	142,851	81,345
Accounts receivable, net of allowance for doubtful accounts of $263 and $238, respectively	13,611	11,720
Inventory	5,633	5,452
Prepaid expenses and other current assets	2,565	2,510
Total current assets	218,241	111,462
Long-term investments	0	1,278
Property and equipment, net	4,527	3,954
Other non-current assets	374	315
TOTAL ASSETS	223,142	117,009
CURRENT LIABILITIES
Accounts payable	3,271	2,811
Accrued liabilities and other	10,199	11,605
Current portion of long-term borrowings	0	4,358
Total current liabilities	13,470	18,774
Long-term borrowings	39,455	34,865
Other long-term liabilities	854	362
TOTAL LIABILITIES	53,779	54,001
Commitments and contingencies (Note 6)
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; 32,583,220 and 25,163,803 shares issued and outstanding, respectively	3	3
Additional paid-in capital	408,113	258,121
Accumulated other comprehensive income	524	464
Accumulated deficit	(239,277)	(195,580)
TOTAL STOCKHOLDERS’ EQUITY	169,363	63,008
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 223,142	$ 117,009

CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 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)	32,583,220	25,163,803
Common stock outstanding (in shares)	32,583,220	25,163,803

CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Income Statement [Abstract]
Revenue	$ 73,387	$ 67,301
Cost of goods sold	8,902	6,790
Gross profit	64,485	60,511
Operating expenses:
Sales and marketing	73,790	68,251
Research and development	9,459	7,279
General and administrative	19,803	20,984
Total operating expenses	103,052	96,514
Loss from operations	(38,567)	(36,003)
Interest and other income (expense), net:
Interest income	1,097	2,551
Interest expense	(6,101)	(4,949)
Other expense, net	(126)	(2)
Net loss	(43,697)	(38,403)
Other comprehensive income (loss):
Unrealized gain (loss) of marketable securities	(59)	44
Changes in foreign currency translation	119	(19)
Comprehensive loss	$ (43,637)	$ (38,378)
Net loss per share, basic and diluted (in dollars per share)	$ (1.50)	$ (1.55)
Weighted-average number of common shares used to compute basic and diluted net loss per share (in shares)	29,059,171	24,705,980

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 balance (in shares) at Dec. 31, 2018		24,450,757
Stockholders' equity, beginning balance at Dec. 31, 2018	$ 90,192	$ 3	$ 246,927	$ 439	$ (157,177)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)	444,924	444,788
Issuance of common stock upon exercise of stock options, net of shares withheld	$ 1,490		1,490
Issuance of common stock related to employee stock purchase plan (in shares)	168,457	168,457
Issuance of common stock related to employee stock purchase plan	$ 2,203		2,203
Issuance of common stock upon vesting of restricted stock units (in shares)		108,631
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	7,464		7,464
Vesting of early exercised stock options	197		197
Additional accrual of IPO related costs	(160)		(160)
Foreign currency translation	(19)			(19)
Net unrealized gain (loss) on marketable securities	44			44
Net loss	(38,403)				(38,403)
Stockholders' equity, ending balance (in shares) at Dec. 31, 2019		25,163,803
Stockholders' equity, ending balance at Dec. 31, 2019	63,008	$ 3	258,121	464	(195,580)
Increase (Decrease) in Stockholders' Equity
Issuance of common stock from public offerings, net of underwriting discounts, commissions and offering costs (in shares)		6,613,560
Issuance of common stock from public offerings, net of underwriting discounts, commissions and offering costs	$ 134,616	$ 0	134,616
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)	323,701	323,701
Issuance of common stock upon exercise of stock options, net of shares withheld	$ 1,463		1,463
Issuance of common stock related to employee stock purchase plan (in shares)	137,377	137,377
Issuance of common stock related to employee stock purchase plan	$ 1,915		1,915
Issuance of common stock upon vesting of restricted stock units (in shares)		344,779
Issuance of common stock upon vesting of restricted stock units	0
Stock-based compensation	11,927		11,927
Vesting of early exercised stock options	71		71
Foreign currency translation	119			119
Net unrealized gain (loss) on marketable securities	(59)			(59)
Net loss	(43,697)				(43,697)
Stockholders' equity, ending balance (in shares) at Dec. 31, 2020		32,583,220
Stockholders' equity, ending balance at Dec. 31, 2020	$ 169,363	$ 3	$ 408,113	$ 524	$ (239,277)

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Cash flows from operating activities
Net loss	$ (43,697)	$ (38,403)
Adjustments to reconcile net loss to net cash used in operating activities
Stock-based compensation	11,927	7,464
Depreciation and amortization	1,130	774
Bad debt expense	234	0
Accretion of discount on marketable securities	115	(1,413)
Realized gain on marketable securities	(46)	0
Amortization of debt issuance costs	292	259
Loss on extinguishment of debt	1,534	0
Loss on sale and disposal of property and equipment	376	171
Changes in operating assets and liabilities
Accounts receivable	(2,186)	(3,236)
Inventory	(274)	(2,105)
Prepaid expenses and other assets	(136)	(515)
Accounts payable	835	383
Accrued liabilities and other	(766)	4,994
Net cash used in operating activities	(30,662)	(31,627)
Cash flows from investing activities
Maturities of marketable securities	104,716	159,800
Sales of marketable securities	14,095	0
Purchases of marketable securities	(179,166)	(143,864)
Purchases of property and equipment	(2,561)	(2,445)
Net cash (used in) provided by investing activities	(62,916)	13,491
Cash flows from financing activities
Proceeds from follow-on public offering, net of underwriting discounts, commissions and offering costs	134,616	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 the exercise of common stock options	1,463	1,490
Proceeds from issuance of common stock under employee stock purchase plan	1,915	2,203
Repurchase of unvested early exercised stock options	0	(38)
Payments of initial public offering costs	0	(167)
Net cash provided by financing activities	136,401	3,488
Effect of exchange rate changes on cash and cash equivalents	323	(37)
Net increase (decrease) in cash and cash equivalents	43,146	(14,685)
Cash and cash equivalents at
Beginning of year	10,435	25,120
End of year	53,581	10,435
Supplemental disclosure of cash flow information
Cash paid for interest	4,276	4,949
Supplemental disclosure of non-cash information
Vesting of early exercised stock options	71	197
Unpaid purchases of property and equipment	$ 26	$ 375

The Company and Nature of Business	12 Months Ended
The Company and Nature of Business	Dec. 31, 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. Public Offerings of Common Stock 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 to the Company, net of underwriting discounts and commissions and offering costs. In January 2020, the Company received $50.0 million net proceeds, after deducting the underwriting discounts and commissions, from its 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 its 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 the 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 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 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. In addition to the shares sold by the Company in the second follow-on offering, in October 2020, 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.

Summary of Significant Accounting Policies

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation and Principles of Consolidation

The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”). The consolidated financial statements include the Company's accounts, as well as those of the Company's wholly-owned international subsidiaries. All inter-company accounts and transactions have been eliminated.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Significant accounting estimates and management judgments reflected in the consolidated financial statements primarily includes the fair value of stock options. 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

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 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) if the Company's total annual gross revenues are $1.07 billion or more; or (ii) the Company has issued more than $1.0 billion in non-convertible debt in the past three years; or (iii) the Company becomes a “large accelerated filer,” as defined in Rule 12b-2 of the Exchange Act.

Segments

Operating segments are based on components of the Company that engage in business activities that earn revenue and incur expenses and (a) whose operating results are regularly reviewed by the Company’s chief operating decision maker (“CODM”), to make decisions about resource allocation and performance and (b) for which discrete financial information is available. The CODM for the Company are the Chief Executive Officer (“CEO”) and Chief Operating Officer & Chief Financial Officer (“COO/CFO”). The CEO and the COO/CFO review financial information presented on a consolidated basis, accompanied by information about revenue by geographic region, for purposes of evaluating financial performance. The Company has one business activity and there are no segment managers who are held accountable for operations, operating results or plans for levels or components below the consolidated unit level. Accordingly, the Company has determined that it has a single reportable and operating segment structure.

The Company derives substantially all of its revenue from sales to customers in the U.S. Revenue by geography is based on billing address of the customer. International revenue accounted for less than 10% of the total revenue during the periods presented. Long-lived assets held outside the U.S. are immaterial. Following table summarizes the Company's revenue by geography:


	Year ended December 31,
	2020		2019
	(in thousands)
United States	$	68,118	$	61,843
International	5,269		5,458
	$	73,387	$	67,301

Foreign Currency

The Company’s foreign subsidiaries use local currency as their functional currency. Assets and liabilities are translated at exchange rates prevailing at the balance sheet dates. Revenue, costs and expenses are translated into U.S. dollars using average exchange rates for the period. Gains and losses from foreign currency translation are recorded as a component of accumulated other comprehensive income (loss). Gains and losses from foreign currency transactions are recognized as a component of other income (expense), net.

Concentration of Credit Risk

Financial instruments that potentially subject the Company to a concentration of credit risk consist of cash and marketable securities. The Company’s cash and marketable securities are deposited with financial institutions in the U.S. and in Europe. The majority of the Company’s cash and marketable securities are deposited with a single financial institution in the U.S. Deposits in this institution exceed the amount of insurance provided on such deposits. The Company has not experienced any net losses on its deposits of cash and marketable securities.

The Company’s revenue and accounts receivable are spread across a large number of customers, primarily in the U.S., and no customer accounts for more than 10% of total revenue or gross accounts receivable in any period presented.

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.

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.

Liquidity

As of December 31, 2020, the Company had cash and marketable securities of $196.4 million compared to $93.1 million as of December 31, 2019. The Company has financed its operations through our public offerings, debt financing arrangements, and the sale of its products. As of December 31, 2020 and 2019 the Company had $39.5 million and $39.2 million outstanding debt, respectively. As of December 31, 2020, the Company's accumulated deficit was $239.3 million. During the years ended December 31, 2020 and 2019, the Company incurred a net loss of $43.7 million and $38.4 million, respectively. The Company has not achieved positive cash flow from operations to date.

Based upon the Company's current operating plan, the Company believes that its existing cash and marketable securities will enable the Company to fund its operating expenses and capital expenditure requirements through at least the next 12 months. However, the economic impact of the duration and severity of the COVID-19 pandemic, and the Company's responses thereto (including such actions that the Company had taken or may take in the future as disclosed elsewhere in this Report) poses risk and uncertainties in its future available capital resources. Further, the Company may face challenges and uncertainties and, as a result, its available capital resources may be consumed more rapidly than currently expected due to, but not limited to, the following as a result of the COVID-19 pandemic or otherwise: (a) decreases in sales of its products and the uncertainty of future revenues from new products; (b) changes that the Company may make to the business that affect ongoing operating expenses; (c) changes that the Company may make in its business strategy; (d) regulatory developments affecting its existing products; (e) changes the Company may make in its research and development spending plans; and (f) other items affecting the Company's forecasted level of expenditures and use of cash resources.

Fair Value of Financial Instruments

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 Company's marketable securities are classified as Level 1 or Level 2 of the fair value hierarchy as defined below. 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.

The Company discloses and recognizes the fair value of its assets and liabilities using a hierarchy that prioritizes the inputs to valuation techniques used to measure fair value. Fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based on assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, a three-tier value hierarchy has been established, which prioritizes the inputs used in measuring fair value as follows:

Level 1: Quoted prices (unadjusted) in active market that are accessible at measurement date for assets or liabilities. The fair value hierarchy gives the highest priority to Level 1 inputs.

Level 2: Observable prices that are based on inputs not quoted on active markets, but corroborated by market data.

Level 3: Unobservable inputs are used when little or no market data is available. The fair value hierarchy gives the lowest priority to Level 3 inputs.

Assets and liabilities measured at fair value are classified in their entirety based on the lowest level of input that is significant to the fair value measurement. The Company’s assessment of the significance of a particular input to the fair value measurement in its entirety requires management to make judgments and considers factors specific to the asset or liability.

Cash and Cash Equivalents

The Company considers all highly liquid investments with remaining maturities at the date of purchase of three months or less to be cash equivalents.

Marketable Securities

The Company's marketable securities primarily consist of investments in money market funds, U.S. treasury securities, corporate bonds and commercial paper. All of the Company's marketable securities are available-for-sale and are 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 or remaining maturity is greater than three months and not more than twelve months. Long-term investments are securities that original or remaining maturity is more than twelve months. All marketable securities are recorded at their estimated fair value. Unrealized gains and losses on available-for-sale securities are recorded in accumulated other comprehensive income (loss) (“OCI”) on the 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 they are related to deterioration in credit risk or if it is likely the Company will sell the securities before the recovery of their cost basis. Realized gains and losses and declines in value judged to be other-than-temporary are determined based on the specific identification method and are reported in other income (expense), net in the consolidated statements of operations.

Accounts Receivable and Allowance for Doubtful Accounts

Accounts receivable are recorded at the invoiced amount and do not bear interest. The Company generally does not require collateral or other security in support of accounts receivable. Allowances are provided for individual accounts receivable when the Company becomes aware of a customer’s inability to meet its financial obligations, such as in the case of bankruptcy, deterioration in the customer’s operating results or change in financial position. If circumstances related to such customers change, estimates of the recoverability of receivables would be further adjusted. The Company also considers broad factors in evaluating the sufficiency of its allowance for doubtful accounts, including the length of time receivables are past due, significant one-time events, creditworthiness of customers and historical experience. Account balances are charged off against the allowance after all means of collection have been exhausted and the potential for recovery is considered remote.

Inventory

Inventory is stated at lower of cost or net realizable value. The Company establishes the inventory basis by determining the cost based on standard costs approximating the purchase costs on a first-in, first-out basis. The excess and obsolete inventory is estimated based on future demand and market conditions. Inventory write-downs are charged to cost of goods sold.

Property and Equipment

Property and equipment are stated at cost less accumulated depreciation and amortization. All property and equipment is depreciated on a straight-line basis over the estimated useful lives of the assets, which are as follows:


Computer and office equipment			3 – 5 years
Machinery and equipment			3 – 5 years
Furniture and fixtures			7 years

Leasehold improvements are amortized over the lesser of their useful lives or the life of the lease. Upon sale or retirement of the assets, the cost and related accumulated depreciation are removed from the consolidated balance sheet and the resulting gain or loss is recognized in the consolidated statement of operations. Maintenance and repairs are charged to operations as incurred.

Impairment of Long-Lived Assets

The Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets (or asset group) may not be fully recoverable. Whenever events or changes in circumstances suggest that the carrying amount of long-lived assets may not be recoverable, the Company estimates the future cash flows expected to be generated by the assets (or asset group) from its use or eventual disposition. If the sum of the expected future cash flows is less than the carrying amount of those assets, the Company recognizes an impairment loss based on the excess of the carrying amount over the fair value of the assets. Significant management judgment is required in the grouping of long-lived assets and forecasts of future operating results that are used in the discounted cash flow method of valuation. Through December 31, 2020 and 2019, the Company has not experienced impairment losses on its long-lived assets.

Revenue Recognition

The Company’s revenue is derived from the sale of its products to medical groups and hospitals through its direct sales force and distributors throughout the U.S. and Europe.

The Company adopted the new revenue standard in accordance with ASC Topic 606, Revenue from Contracts with Customers (“ASC 606”) effective for the fiscal year ended December 31, 2019. Revenue is recognized when control is transferred to the customer, in an amount that reflects the consideration the Company expects to be entitled to in exchange for the goods or services. Under the new revenue recognition standard, the Company applies the following five step approach: (1) identify the contract with a customer, (2) identify the performance obligations in the contract, (3) determine the transaction price, (4) allocate the transaction price to the performance obligations in the contract, and (5) recognize revenue when a performance obligation is satisfied. As it relates to product sales where the Company's sales representative delivers the product at the point of implantation at the hospital or medical facilities, the Company continues to recognize the revenue upon completion of the procedure and authorization by the customer, net of rebates and price discounts. This represents the majority of the Company's consolidated revenue. The Company also generates a small portion of revenue from the sale of products through distributors and to certain hospital or medical facilities where the products are ordered in advance of a procedure. The performance obligation is the delivery of the products and therefore, revenue is recognized upon shipment to the customers, net of rebates and price discounts. The Company accounts for rebates and price discounts as a reduction to revenue, calculated based on the terms agreed to with the customer. Historically, there had been no significant price discounts. Sales prices are specified in either the customer contract, agreed price list, or purchase order, which is executed prior to the transfer of control to the customer. For certain hospitals and medical facilities, the Company has agreements in place consists of either a master services agreement or an agreed price list, which defines the terms and conditions of the arrangement, including the pricing information, payment terms and pertinent aspects of the relationship between the parties. The Company also has agreements in place with its distributors, which include standard terms that do not allow for payment contingent on resale of the product, obtaining financing, or other terms that could impact the distributor’s payment obligation. The Company's standard payment terms are generally net 30 to 90 days.

Shipping and Handling Costs

Shipping and handling costs are treated as fulfillment costs, which are expensed as incurred and are included in cost of goods sold.

Costs to Obtain Customer Contracts

Sales commissions and related expenses are considered incremental and recoverable costs of acquiring customer contracts. The Company’s sales commissions paid to its sales representatives are 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. The period of benefit is concurrent with when the Company recognizes its revenue and as such, the Company recognizes sales commission as expense when incurred.

Warranty

The Company has a warranty program that provides a purchaser a one-time replacement of any iFuse implant at no additional cost for a revision procedure within a one-year period following the original procedure and is accounted for as a warranty accrual. The Company also provides a purchaser with a one-time credit equal to the purchase price paid for use on future purchases for any revision procedure within the one-year period following an original procedure where an implant is not required. The warranty is not priced or sold separately and is intended to safeguard the customer against defects and it does not provide incremental service to the customer. As such, it is considered an assurance type warranty and is not accounted as a service type warranty, which could represent a separate performance obligation. The Company accounts for these one-time credits as sales reserves and is included in accrued liabilities and other in the consolidated balance sheets. Sales and warranty reserves from the warranty program were immaterial as of December 31, 2020 and 2019.

Medical Device Excise Tax

In accordance with the Patient Protection and Affordable Care Act, effective January 1, 2013, the Company began to incur an excise tax on sales of medical devices in the U.S. The Company recorded the medical device excise tax within the cost of goods sold in the consolidated statements of operations and comprehensive loss when incurred. Effective January 1, 2016, the Consolidated Appropriations Act of 2016, which was signed into law in December 2015, included a two-year suspension on the medical device excise tax. In January 2018, the suspension on the tax on medical devices was further extended through January 1, 2020. In December 2019, the U.S. Senate passed a bipartisan legislation to permanently repeal the medical device excise tax.

Research and Development

Research and development costs are charged to operations as incurred and consist of costs incurred by the Company for the development of the Company’s product which primarily include: (1) employee-related expenses, including salaries, benefits, travel and non-cash stock-based compensation expense; (2) external research and development expenses; and (3) other expenses, which include direct and allocated expenses for facilities and other costs.

Advertising Expenditures

The cost of advertising is expensed as incurred and is included under sales and marketing expense in the consolidated statements of operations. Advertising expenses were $0.3 million and $0.4 million for the year ended December 31, 2020 and 2019, respectively.

Loss Contingency

The Company is subject to various potential loss contingencies arising in the ordinary course of business. From time to time, the Company may be involved in certain proceedings, legal actions and claims. Such matters are subject to many uncertainties, and the outcomes of these matters are not within the Company's control and may not be known for prolonged periods of time. In some actions, the claimants may seek damages, as well as other relief, including injunctions which may prohibit the Company to engage in certain activities, which, if granted, could require significant expenditures and/or result in lost revenues. The Company records a liability in the consolidated financial statements when a loss is known or considered probable and the amount can be reasonably estimated. If the reasonable estimate of a known or probable loss is a range, and no amount within the range is a better estimate than any other, the minimum amount of the range is accrued. If a loss is reasonably possible but not known or probable, and can be reasonably estimated, the estimated loss or range of loss is disclosed. In most cases, significant judgment is required to estimate the amount and timing of a loss to be recorded.

Stock-Based Compensation

The Company applies the fair value recognition provisions of stock-based compensation. Stock-based compensation expense is recognized over the requisite service period using the straight-line method and is based on the value of the portion of stock-based payment awards that is ultimately expected to vest. As such, the Company’s stock-based compensation is reduced for the estimated forfeitures at the date of grant and revised, if necessary, in subsequent periods if actual forfeitures differ from those estimates. The Company uses historical data to estimate pre-vesting forfeitures and record stock-based compensation expense only for those awards that are expected to vest. To the extent actual forfeitures differ from the estimates, the difference will be recorded as a cumulative adjustment in the period that the estimates are revised.

The Company estimates the grant date fair value of stock options using the Black-Scholes option valuation model. The model requires management to make a number of assumptions including expected volatility, expected term, risk-free interest rate and expected dividends. A number of these assumptions are subjective, and their determination generally require judgment.

•Expected Term - The expected term represents the period that the share-based awards are expected to be outstanding. The Company uses the simplified method to determine the expected term as permitted by the guidance since the Company has no sufficient historical exercise patterns to estimate the expected life. The simplified method is calculated as the average of the time to vesting and the contractual life of the options.

•Expected Volatility - Since the Company became public in October 2018 and has no sufficient trading history, the Company uses stock price volatility using the average historical volatilities of publicly traded companies within its industry that the Company considers to be comparable to its business over a period approximately equal to the expected term for its stock options.

•Risk-Free Interest Rate - The risk-free interest rate is based on the U.S. Treasury zero coupon issued in effect at the time of grant for periods corresponding with the expected term of the option.

•Dividend Yield - The Company has not paid any dividends and has no current plans to pay dividends on its common stock. As such, the Company uses expected dividend yield of zero.

The fair value of the restricted stock unit (“RSU”) grant is based on the market price of the Company’s common stock on the date of grant.

Prior to IPO, the fair value of the shares of the Company's common stock has historically been determined by its Board of Directors since there were no public market information available for the Company's common stock. The estimated fair value of the Company's common stock was determined at each valuation date in accordance with the guidelines outlined in the American Institute of Certified Public Accountants Practice Aid, Valuation of Privately-Held-Company Equity Securities Issued as Compensation. Subsequent to its IPO, the Company uses the market closing price for its common stock as reported on the Nasdaq Global Market on the date of grant.

Equity instruments issued to non-employees are recorded at their fair value on the measurement date and are subject to periodic adjustments as the underlying equity instruments vest. The Company believes that the estimated fair value of the stock options is more readily measurable than the fair value of the services received. Stock-based compensation related to stock options granted to non-employees is recognized as the stock options are earned.

In the event the underlying terms of stock options are modified on which stock-based compensation was granted, additional expense is recognized for any modification that increases the total fair value of the share-based payment arrangement at the modification date.

Income Taxes

The Company accounts for income taxes under the asset and liability method, whereby deferred tax assets and liabilities are determined based on the difference between the financial statement and tax bases of assets and liabilities using the enacted tax rates in effect for the year in which the differences are expected to affect taxable income. A valuation allowance is established when necessary to reduce deferred tax assets to the amounts expected to be realized.

The Company recognizes uncertain tax positions when it meets a more-likely-than-not threshold. The Company recognizes potential accrued interest and penalties related to unrecognized tax benefits as income tax expense.

Net Loss per Share of Common Stock

The Company calculates basic and diluted net loss per common share attributable to shareholders in conformity with the two-class method required for companies with participating securities. The Company considers all early exercised stock options to be participating securities as the holders are entitled to receive dividends on a pari passu basis in the event that a dividend is paid on common stock. Under the two-class method, the net loss attributable to common stock is not allocated to the early exercised stock options as the holders do not have a contractual obligation to share in losses.

Basic net loss per common share is calculated by dividing the net loss by the weighted-average number of common shares outstanding during the period, without consideration for potentially dilutive securities. Diluted net loss per share is computed by dividing the net loss by the weighted-average number of common shares and potentially dilutive securities outstanding for the period. For purposes of the diluted net loss per share calculation, common stock options and warrants are considered to be potentially dilutive securities. Because the Company has reported a net loss in all periods presented, common stock options and warrants are anti-dilutive and therefore diluted net loss per common share is the same as basic net loss per common share for those periods.

Comprehensive Loss

Comprehensive loss represents all changes in the stockholders’ equity except those resulting from distributions to stockholders. The Company’s unrealized foreign currency translation income (losses) and unrealized gains (losses) on marketable securities represent the two components of other comprehensive income that are excluded from the reported net loss for each of the reporting periods and has been presented in the consolidated statements of operations and comprehensive loss.

Warrants

The Company accounts for warrants for shares of common stock as equity in accordance with the accounting guidance for derivatives. The accounting guidance provides a scope exception from classifying and measuring as a financial liability a contract that would otherwise meet the definition of a derivative if the contract is both (i) indexed to the entity’s own stock and (ii) classified in the stockholders’ equity section of the consolidated balance sheet. The Company determined that the warrants for shares of common stock issued in connection with its prior debt arrangements are required to be classified in equity. Warrants classified as equity are recorded as additional paid-in capital on the consolidated balance sheet and no further adjustments to their valuation are made. In connection with the IPO, all of the Company's redeemable convertible preferred stock warrants were automatically converted into common stock warrants.

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 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 revenue by geography, refer to Segments in “Note 2 - Summary of Significant Accounting Policies” in the accompanying Notes to Consolidated Financial Statements.

Other Recently Adopted Accounting Standards

In June 2018, the Financial Accounting Standards Board ("FASB") issued Accounting Standards Update (“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. The Company adopted this standard effective for the year ended December 31, 2020, and the adoption did not have any material impact on the Company’s 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 has adopted this standard effective for the year ended December 31, 2020, and the adoption did not have any material impact on the Company’s consolidated financial statements.

Recently Issued Accounting Standards Not Yet Effective

In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842), which requires that lessee's recognize a right-of-use asset and a lease liability for all leases with lease terms greater than twelve months in the balance sheet. A lease liability is a lessee's obligation to make lease payments arising from a lease, measured on a discounted basis; and a right-of-use asset is an asset that represents the lessee’s right to use, or control use of, a specified asset for the lease term for all leases (with the exception of short-term leases) at the adoption date. In July 2018, the FASB issued ASU 2018-10 and ASU 2018-11, which provides clarification on the narrow aspects of the guidance and provide an additional transition method to adopt the new leases standard. The new transition method allows an entity to recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. In March 2019, the FASB issued ASU 2019-01, which provides clarification on implementation issues associated with adopting ASU 2016-02. The new 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 now 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 on 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 adoption of the standard will have a material impact on the Company's consolidated financial statements.

Marketable Securities

12 Months Ended

Dec. 31, 2020

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

The table below summarizes the marketable securities:


	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


	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 matured in April 2020. The Company did not identify any of its marketable securities as other-than-temporarily impaired as of December 31, 2020 and 2019.

Fair Value Measurement

12 Months Ended

Dec. 31, 2020

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 and liabilities that requires 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:


	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

	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

- 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

12 Months Ended

Dec. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Balance Sheet Components

Inventory

As of December 31, 2020 and 2019, inventory consisted entirely of finished goods.

Property and Equipment, net:


	December 31, 2020		December 31, 2019
	(in thousands)
Machinery and equipment	$	6,342	$	4,613
Construction in progress	1,692		1,854
Computer and office equipment	714		598
Leasehold improvements	503		497
Furniture and fixtures	233		187
	9,484		7,749
Less: Accumulated depreciation and amortization	(4,957)		(3,795)
	$	4,527	$	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 $1.1 million and $0.8 million for the years ended December 31, 2020 and 2019, respectively.

Accrued Liabilities and Other:


	December 31, 2020		December 31, 2019
	(in thousands)
Accrued compensation and related expenses	$	9,175	$	7,274
Accrued litigation expense	—		3,200

Accrued professional services	511		392


Others	513		739
	$	10,199	$	11,605

Commitments and Contingencies

12 Months Ended

Dec. 31, 2020

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 expense charged to operations under operating leases totaled approximately $1.2 million and $1.2 million for the years ended December 31, 2020 and 2019, respectively.

The aggregate future minimum lease payments under all leases as of December 31, 2020 are as follows:


Year Ending December 31,	(in thousands)
2021	$	1,081
2022	1,001
2023	908
2024	893
2025	381
Thereafter	24
	$	4,288

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 $0.3 million and $0.4 million as of December 31, 2020 and 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 $3.2 million during the year ended December 31, 2019 within general and administrative expenses in the consolidated financial statements, which was the Company's estimated cost to resolve the matter pursuant to the Settlement Agreement and based on 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 year ended December 31, 2020 within general and administrative expenses in the 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

12 Months Ended

Dec. 31, 2020

Debt Disclosure [Abstract]

Borrowings

Term Loan

The following table summarizes the outstanding borrowings from the term loan as of the periods presented:


	December 31, 2020		December 31, 2019
	(in thousands)
Principal outstanding and final fee	$	41,000	$	40,000
Less: Unamortized debt issuance costs	(661)		(777)
Unaccreted value of final fee	(884)		—
Outstanding debt, net of debt issuance costs and unaccreted value of final fee	$	39,455	$	39,223
Classified as:
Current portion of long-term borrowings	$	—	$	4,358
Long-term borrowings	$	39,455	$	34,865

The outstanding debt as of December 31, 2019 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 consolidated statement of operations for the year ended December 31, 2020. The total debt issuance costs of $0.8 million associated with the Solar Term Loan were recorded in the 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 the greater 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 3.00% 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 Pharmakon Term Loan was 12.4% and 12.3% for the term loan's outstanding periods for the years ended December 31, 2020 and 2019, respectively. The effective interest rate related to the Solar Term Loan was 10.6% for the term loan's outstanding period for year ended December 31, 2020.

The table below summarizes the future principal and final fee payments under the Solar Term Loan as of December 31, 2020:


Year ending December 31,	(in thousands)
2021	$	—
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 5.00% above the rate effective immediately before the event of default and may be declared immediately due and payable by Solar. As of December 31, 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 our 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,” 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.

The CARES Act allows 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 consolidated balance sheets as of December 31, 2020.

Warrants

12 Months Ended

Dec. 31, 2020

Other Liabilities Disclosure [Abstract]

Warrants

The table below summarizes common stock warrants issued and outstanding at both December 31, 2020 and 2019:


Date			Number of Shares Underlying Warrants	Price per Share	Fair Value (in thousands)
Issuance	Expiration
3/1/2017	3/1/2027	[a]	1,388	$5.94	$	5	[b]
7/22/2013	7/22/2023	[a]	32,983	$9.10	122		[b]
11/26/2014	11/26/2024	[a]	6,680	$16.47	49		[b]
10/20/2015	10/20/2025	[a]	41,650	$16.47	396		[c]
11/9/2015	11/9/2025	[a]	25,709	$16.47	244		[c]
12/22/2016	12/22/2026	[a]	9,712	$10.03	45		[c]
			118,122		$	861

[a] Common stock warrants will remain outstanding until the earlier of the expiration date or the date exercised by the holder.

[b] Fair value at the date of issuance.

[c] Fair value at the date of conversion from redeemable convertible preferred stock to common stock warrants in conjunction with the IPO on October 16, 2018.

Common and Preferred Stock	12 Months Ended
Common and Preferred Stock	Dec. 31, 2020
Equity [Abstract]
Common and Preferred Stock	Common and Preferred Stock The Company's certificate of incorporate as amended and restated in October 2018, authorizes the Company to issue 100,000,000 shares of common stock and 5,000,000 shares of preferred stock, each having a par value of $0.0001. Common stock issued and outstanding as of December 31, 2020 and 2019 were 32,583,220 shares and 25,163,803 shares, respectively. As of December 31, 2020 and 2019, there was no preferred stock issued and outstanding. The holders of common stock are entitled to receive dividends whenever funds are legally available, as, when, and if declared by the Board of Directors. There have been no dividends declared to date.

Stock-Based Compensation

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Stock-Based Compensation

2008 Stock Option Plan and 2018 Equity Incentive Plan

In April 2008, the Company adopted the 2008 Stock Option Plan (the “2008 SOP”), as amended, under which the Board of Directors may issue incentive and non-qualified stock options to employees, directors and consultants. In October 2018, the Company adopted the 2018 Equity Incentive Plan (the “2018 EIP”), which serves as the successor to the 2008 SOP, under which the Board of Directors may issue incentive and non-qualified stock options and RSUs to employees, directors and consultants. No new options have been granted under the 2008 SOP since August 2018. Outstanding options under the 2008 SOP continue to be subject to the terms and conditions of that plan.

The number of shares of common stock reserved for issuance under the 2018 EIP will automatically increase on January 1 of each year, beginning January 1, 2019, and continuing through and including January 1, 2028, by 5% of the total number of shares of the Company's capital stock outstanding on December 31 of the preceding calendar year, or a lesser number of shares determined by the Company's Board of Directors. On January 1, 2019 and 2020, the total number of shares of common stock reserved for issuance increased by 1,222,538 and 1,258,190 shares respectively. As of December 31, 2020, a total of 2,843,814 shares of common stock are available for future grants under the 2018 EIP. On January 1, 2021, the total number of shares of common stock reserved for issuance under the 2018 EIP automatically increased by 1,629,161 shares.

The Board of Directors has the authority to determine to whom options will be granted, the number of shares, the term and the exercise price. If an individual owns stock representing more than 10% of the outstanding shares, the price of each share shall be at least 110% of the fair market value, as determined by the Board of Directors. The exercise price of an incentive stock option and a non-qualified stock option shall not be less than 100% and 85%, respectively, of the fair market value on the date of grant.

Options granted have a term of 10 years, except, options granted to individuals holding more than 10% of the outstanding shares have a term of five years. Options generally vest over a four-year period. Certain stock options are exercisable immediately, but are subject to a right of repurchase by the Company for any unvested shares. RSUs granted under the 2018 EIP generally vest over two to four years based upon continued services and are settled at vesting in shares of the Company's common stock.

Stock Options

The following table summarizes stock option activity for the years ended December 31, 2020 and 2019:


	Options Outstanding
	Number of Shares	Weighted-Average Exercise Price	Weighted-Average Contractual Remaining Life (Years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2018	2,641,198	$4.27
Granted	638,983	$20.89
Exercised	(444,924)	$3.36
Canceled and forfeited	(116,286)	$11.30
Outstanding as of December 31, 2019	2,718,971	$8.02
Granted	26,236	$17.31
Exercised	(323,701)	$4.52
Canceled and forfeited	(15,549)	$17.07
Outstanding as of December 31, 2020	2,405,957	$8.54	5.80	$	51,402
Options vested and exercisable as of December 31, 2020	2,069,020	$6.85	5.40	$	47,689
Options vested and expected to vest as of December 31, 2020	2,390,755	$8.36	6.00	$	51,493

The aggregate intrinsic value of options exercised during the years ended December 31, 2020 and 2019 amounted to $5.6 million and $6.8 million, respectively, representing the difference between the fair value of the Company's common stock at the date of exercise and the exercise price paid. The aggregate intrinsic values of options outstanding, options vested and exercisable, and options vested and expected to vest as of December 31, 2020 represents the difference between the weighted average exercise price and the closing price of the Company’s common stock on the last trading day of the year.

Outstanding options and exercisable options information by range of exercise prices as of December 31, 2020 was as follows:


Exercise Price			Options Outstanding			Options Vested and Exercisable
			Number of Shares	Average Remaining Contractual Life (Years)	Weighted- Average Exercise Price	Number of Shares	Weighted- Average Exercise Price
$0.84	-	$3.69	465,071	3.40	$3.31	465,071	$3.31
$3.70	-	$4.41	689,903	4.80	$4.29	689,903	$4.29
$4.42	-	$5.31	458,812	6.40	$4.67	422,974	$4.67
$5.32	-	$20.51	356,271	7.50	$12.08	282,203	$11.00
$20.52	-	$22.00	435,900	8.00	$22.00	208,869	$22.00
			2,405,957	5.80	$8.54	2,069,020	$6.85

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:


	Year ended December 31,
	2020			2019
Weighted average grant date fair value per share	$8.16			$9.78
Expected term (years)	5.5	to	7.0	5.0	to	7.0
Expected volatility	46.7%	to	47.2%	41.7%	to	47.3%
Risk-free interest rate	1.6%	to	1.6%	1.3%	to	2.6%
Dividend yield	—%			—%

As of December 31, 2020, there was $3.2 million of unrecognized compensation cost related to stock options granted. These costs are expected to be recognized over a period of approximately 1.9 years.

Early Exercise of Unvested Stock Options

Early exercises of stock options under the Company's 2008 SOP 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 December 31, 2020 and 2019, the Company had a total of 5,836 and 21,404 shares of common stock, respectively, subject to repurchase under the 2008 SOP.

Restricted Stock Units

The following table summarizes restricted stock units activity for the years ended December 31, 2020 and 2019:


	Number of Shares	Weighted- Average Grant Date Fair Value
Outstanding as of December 31, 2018	53,436	$11.69
Granted	639,726	$20.14
Vested	(108,631)	$19.10
Canceled and forfeited	(41,490)	$18.48
Outstanding as of December 31, 2019	543,041	$19.72
Granted	1,016,432	$20.17
Vested	(344,779)	$19.87
Canceled and forfeited	(49,399)	$19.73
Outstanding as of December 31, 2020	1,165,295	$20.07

As of December 31, 2020, there was a total unrecognized compensation cost of $19.3 million. These costs are expected to be recognized over a period of approximately 2.9 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 offering 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. There were 515,307 shares of common stock originally reserved for issuance under the ESPP. Under the ESPP, the number of shares reserved for issuance under the ESPP automatically increases on January 1st of each year, starting on January 1, 2019, and continuing through January 1, 2029, by an amount equal to (i) the lesser of 1% of the total number of shares of the Registrant’s common stock outstanding on December 31st of the preceding calendar year, and (ii) 555,555 shares of common stock. As of December 31, 2020, a total of 705,618 shares of common stock are available for future grants under the 2018 EIP. On January 1, 2021, the total number of shares of common stock reserved for issuance under the ESPP Plan increased by 325,832 shares.

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 issued 137,377 shares and 168,457 shares under the ESPP during the years ended December 31, 2020 and 2019, respectively, representing approximately $1.9 million and $2.2 million in employee contributions. As of December 31, 2020 and 2019, total accumulated ESPP related employee payroll deductions amounted to $0.4 million and $0.2 million, respectively, which were included within accrued compensation and related expenses in the consolidated balance sheets. For the years ended December 31, 2020 and 2019, the Company recognized $1.2 million and $0.8 million, respectively, of stock-based compensation expense related to ESPP. As of December 31, 2020, the unrecognized compensation cost for the ESPP was $0.2 million.

The Company estimated the fair value of ESPP purchase rights during the offering period using a Black-Scholes option pricing model with the following assumptions:


	Year ended December 31,
	2020			2019
Expected term (years)	0.5	to	1.0	0.5
Expected volatility	38.3%	to	79.4%	38.3%	to	58.4%
Risk-free interest rate	0.1%	to	1.6%	1.6%	to	2.4%
Dividend yield	—%			—%

Stock-Based Compensation

The following table sets forth stock-based compensation expense recognized for the periods presented:


	Year ended December 31,
	2020		2019
	(in thousands)
Cost of goods sold	$	331	$	185
Sales and marketing	5,527		3,335
Research and development	1,139		516
General and administrative	4,930		3,428
	$	11,927	$	7,464

Employee Benefit Plan	12 Months Ended
Employee Benefit Plan	Dec. 31, 2020
Retirement Benefits [Abstract]
Employee Benefit Plan	Employee Benefit PlanThe Company sponsors a 401(k) plan covering all employees. Contributions made by the Company are discretionary and are determined annually by the Board of Directors. Effective January 1, 2019, the Company made a discretionary matching contribution equal to dollar for dollar employee contribution, up to 3% eligible compensation of the employee, with a maximum annual contribution from the Company of one thousand dollars per employee. Further, in order for an employee to receive the matching contribution, the employee must be at least 21 years old, work at least 1,000 hours per year, and must be employed by the Company at the beginning through the end of the year. For the years ended December 31, 2020 and 2019, the Company made $0.2 million and $0.1 million, respectively, contributions to the 401(k) plan.

- Definition

The entire disclosure for retirement benefits.

+ References

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+ Details

Net Loss Per Share of Common Stock

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Net Loss Per Share of Common Stock

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


	Year ended December 31,
	2020		2019
	(in thousands, except share and per share data)
Net loss	$	(43,697)	$	(38,403)

Weighted-average shares used to compute basic and diluted net loss per share	29,059,171		24,705,980

Net loss per share, basic and diluted	$	(1.50)	$	(1.55)

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:


	Year ended December 31,
	2020	2019
Stock options	2,405,957	2,718,971
Restricted stock units	1,165,295	543,041
Shares subject to repurchase	5,836	21,404
ESPP purchase rights	83,040	65,442
Common stock warrants	118,122	118,122
	3,778,250	3,466,980

Income Taxes

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Income Taxes

The components of the Company’s loss before income taxes are as follows:


	Year ended December 31,
	2020		2019
	(in thousands)
Domestic	$	(41,708)	$	(37,709)
Foreign	(1,989)		(694)
Loss before income taxes	$	(43,697)	$	(38,403)

There was no provision for income taxes recorded for the years ended December 31, 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 periodically evaluates the realizability of its net deferred tax assets based on the expected realization and is dependent on the Company's ability to generate sufficient future taxable income during periods prior to the expiration of tax attributes to fully utilize these assets.

The components of deferred income taxes are as follows:


	Year ended December 31,
	2020		2019
	(in thousands)
Federal	$	9,855	$	8,523
State	2,711		1,569
Foreign	583		(200)
Total deferred income taxes	13,149		9,892
Change in deferred tax valuation allowance	(13,149)		(9,892)
Net deferred income tax	$	—	$	—

Income tax expense differs from the amount computed by applying the statutory federal income tax rate due to the following:


	Year ended December 31,
	2020		2019
Tax at statutory federal rate	(21.0)	%	(21.0)	%
State tax, net of federal benefit	(6.2)	%	(4.1)	%
Tax credits	(0.7)	%	(0.7)	%
Change in deferred tax valuation allowance	30.1	%	25.8	%
Stock compensation	(1.2)	%	(1.5)	%
Foreign rate differences	(1.3)	%	0.5	%
Other	0.3	%	1.0	%
Total income tax expense	—	%	—	%

The tax effects of temporary differences and carryforwards that give rise to significant portions of the deferred tax assets are presented below:


	Year ended December 31,
	2020		2019
	(in thousands)
Net operating loss carryforwards	$	52,331	$	42,032
Research and development credits	3,160		2,428
Accruals and reserves	5,450		4,222
Stock compensation	2,395		1,512
Depreciation and amortization	117		110
Total deferred tax assets	63,453		50,304
Less: Valuation allowance	(63,453)		(50,304)
Total deferred tax asset, net of valuation allowance	$	—	$	—

The following table summarizes changes in the valuation allowance for the years ended December 31, 2020 and 2019:


	Year ended December 31,
	2020		2019
	(in thousands)
Beginning balance	$	50,304	$	40,412
Additions during the period	13,149		9,892
Ending balance	$	63,453	$	50,304

As of December 31, 2020, the Company had net operating loss (“NOL”) carryforwards of approximately $200.5 million and $165.0 million available to reduce future taxable income, if any, for federal and state income tax purposes, respectively. If not utilized, the Company’s federal NOL carryforward begins to expire in 2028, and the state NOL carryforward begins to expire in 2021.

As of December 31, 2020, the Company had credit carryforwards of approximately $2.5 million and $2.5 million available to reduce future taxable income, if any, for both federal and state income tax purposes, respectively. The federal credits begin to expire in 2029, and the state credits have no expiration date.

The Company updated its Section 382 ownership change analysis through December 31, 2020 and determined that the last ownership change was in February 2020 due to the follow-offering. The analysis concluded that no additional NOL carryforwards will expire due to the Section 382 limitation from the ownership change for both federal and state tax purposes. The Company maintains the reduction of $1.4 million of its NOL carryforwards from the previous ownership change. The Company will continually assess the need to update its Section 382 ownership change analysis, as the Company may experience ownership changes in the future that could materially limit its ability to use its NOL carryforwards.

The CARES Act includes provisions relating to refundable payroll tax credits, deferment of employer's 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 deferred the payment of an employer's share of social security taxes through December 31, 2020 of $1.0 million.

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 loss position for the year ended December 31, 2020, the new legislation did not impact the current year provision. The Company will continue to monitor the possible California net operating loss and credit limitations in future periods.

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. The changes in the Company’s uncertain income tax positions for the years ended December 31, 2020 and 2019 consisted of the following:


	Year ended December 31,
	2020		2019
	(in thousands)
Balance at beginning of the year	$	1,287	$	1,084
Increases related to current year's tax positions	226		203
Balance at end of the year	$	1,513	$	1,287

The Company has elected to recognize interest and penalties related to uncertain tax positions as a component of income tax expense. The Company has no accrued interest related to unrecognized tax benefits as of December 31, 2020 and 2019. None of the Company’s unrecognized tax benefits that, if recognized, would affect its effective tax rates for the years ended December 31, 2020 and 2019. The Company does not anticipate the total amounts of unrecognized tax benefits will significantly increase or decrease in the next 12 months.

The Company currently has no federal, state or foreign tax examinations in progress nor has it had any federal or state examinations since inception. As a result of the Company’s net operating loss carry forwards, all of its tax years are subject to federal and state tax examinations.

- 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

Related Party Transactions	12 Months Ended
Related Party Transactions	Dec. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transactions 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 year ended December 31, 2020, the Company expensed $118,000 of the reimbursement charges from SeaSpine, which was recorded within research and development expense in the consolidated statement of operations. There was no outstanding liabilities to SeaSpine as of 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.

Summary of Significant Accounting Policies (Policies)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Basis of Presentation

The accompanying consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”).

Principles of Consolidation

The consolidated financial statements include the Company's accounts, as well as those of the Company's wholly-owned international subsidiaries. All inter-company accounts and transactions have been eliminated.

Use of Estimates

Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Significant accounting estimates and management judgments reflected in the consolidated financial statements primarily includes the fair value of stock options. 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

Segments

Foreign Currency

Concentration of Credit Risk

Fair Value of Financial Instruments

Level 1: Quoted prices (unadjusted) in active market that are accessible at measurement date for assets or liabilities. The fair value hierarchy gives the highest priority to Level 1 inputs.

Level 2: Observable prices that are based on inputs not quoted on active markets, but corroborated by market data.

Level 3: Unobservable inputs are used when little or no market data is available. The fair value hierarchy gives the lowest priority to Level 3 inputs.

Cash and Cash Equivalents

The Company considers all highly liquid investments with remaining maturities at the date of purchase of three months or less to be cash equivalents.

Marketable Securities

Accounts Receivable and Allowance for Doubtful Accounts

Accounts Receivable and Allowance for Doubtful AccountsAccounts receivable are recorded at the invoiced amount and do not bear interest. The Company generally does not require collateral or other security in support of accounts receivable. Allowances are provided for individual accounts receivable when the Company becomes aware of a customer’s inability to meet its financial obligations, such as in the case of bankruptcy, deterioration in the customer’s operating results or change in financial position. If circumstances related to such customers change, estimates of the recoverability of receivables would be further adjusted. The Company also considers broad factors in evaluating the sufficiency of its allowance for doubtful accounts, including the length of time receivables are past due, significant one-time events, creditworthiness of customers and historical experience. Account balances are charged off against the allowance after all means of collection have been exhausted and the potential for recovery is considered remote.

Inventory

InventoryInventory is stated at lower of cost or net realizable value. The Company establishes the inventory basis by determining the cost based on standard costs approximating the purchase costs on a first-in, first-out basis. The excess and obsolete inventory is estimated based on future demand and market conditions. Inventory write-downs are charged to cost of goods sold.

Property and Equipment


Computer and office equipment			3 – 5 years
Machinery and equipment			3 – 5 years
Furniture and fixtures			7 years

Impairment of Long-Lived Assets

Impairment of Long-Lived AssetsThe Company reviews long-lived assets for impairment whenever events or changes in circumstances indicate that the carrying amount of the assets (or asset group) may not be fully recoverable. Whenever events or changes in circumstances suggest that the carrying amount of long-lived assets may not be recoverable, the Company estimates the future cash flows expected to be generated by the assets (or asset group) from its use or eventual disposition. If the sum of the expected future cash flows is less than the carrying amount of those assets, the Company recognizes an impairment loss based on the excess of the carrying amount over the fair value of the assets. Significant management judgment is required in the grouping of long-lived assets and forecasts of future operating results that are used in the discounted cash flow method of valuation.

Revenue Recognition

The Company’s revenue is derived from the sale of its products to medical groups and hospitals through its direct sales force and distributors throughout the U.S. and Europe.

Shipping and Handling Costs

Shipping and handling costs are treated as fulfillment costs, which are expensed as incurred and are included in cost of goods sold.

Costs to Obtain Customer Contracts

Warranty Program

Warranty The Company has a warranty program that provides a purchaser a one-time replacement of any iFuse implant at no additional cost for a revision procedure within a one-year period following the original procedure and is accounted for as a warranty accrual. The Company also provides a purchaser with a one-time credit equal to the purchase price paid for use on future purchases for any revision procedure within the one-year period following an original procedure where an implant is not required. The warranty is not priced or sold separately and is intended to safeguard the customer against defects and it does not provide incremental service to the customer. As such, it is considered an assurance type warranty and is not accounted as a service type warranty, which could represent a separate performance obligation. The Company accounts for these one-time credits as sales reserves and is included in accrued liabilities and other in the consolidated balance sheets.

Medical Device Excise Tax

Medical Device Excise TaxIn accordance with the Patient Protection and Affordable Care Act, effective January 1, 2013, the Company began to incur an excise tax on sales of medical devices in the U.S. The Company recorded the medical device excise tax within the cost of goods sold in the consolidated statements of operations and comprehensive loss when incurred. Effective January 1, 2016, the Consolidated Appropriations Act of 2016, which was signed into law in December 2015, included a two-year suspension on the medical device excise tax. In January 2018, the suspension on the tax on medical devices was further extended through January 1, 2020.

Research and Development

Advertising Expenditures

Advertising ExpendituresThe cost of advertising is expensed as incurred and is included under sales and marketing expense in the consolidated statements of operations.

Loss Contingency

Loss ContingencyThe Company is subject to various potential loss contingencies arising in the ordinary course of business. From time to time, the Company may be involved in certain proceedings, legal actions and claims. Such matters are subject to many uncertainties, and the outcomes of these matters are not within the Company's control and may not be known for prolonged periods of time. In some actions, the claimants may seek damages, as well as other relief, including injunctions which may prohibit the Company to engage in certain activities, which, if granted, could require significant expenditures and/or result in lost revenues. The Company records a liability in the consolidated financial statements when a loss is known or considered probable and the amount can be reasonably estimated. If the reasonable estimate of a known or probable loss is a range, and no amount within the range is a better estimate than any other, the minimum amount of the range is accrued. If a loss is reasonably possible but not known or probable, and can be reasonably estimated, the estimated loss or range of loss is disclosed. In most cases, significant judgment is required to estimate the amount and timing of a loss to be recorded.

Stock-Based Compensation

•Dividend Yield - The Company has not paid any dividends and has no current plans to pay dividends on its common stock. As such, the Company uses expected dividend yield of zero.

The fair value of the restricted stock unit (“RSU”) grant is based on the market price of the Company’s common stock on the date of grant.

Income Taxes

Net Loss per Share of Common Stock

Comprehensive Loss

Warrants

WarrantsThe Company accounts for warrants for shares of common stock as equity in accordance with the accounting guidance for derivatives. The accounting guidance provides a scope exception from classifying and measuring as a financial liability a contract that would otherwise meet the definition of a derivative if the contract is both (i) indexed to the entity’s own stock and (ii) classified in the stockholders’ equity section of the consolidated balance sheet. The Company determined that the warrants for shares of common stock issued in connection with its prior debt arrangements are required to be classified in equity. Warrants classified as equity are recorded as additional paid-in capital on the consolidated balance sheet and no further adjustments to their valuation are made. In connection with the IPO, all of the Company's redeemable convertible preferred stock warrants were automatically converted into common stock warrants.

Recent Accounting Pronouncements

Adoption of New Revenue Recognition Standard

Other Recently Adopted Accounting Standards

Recently Issued Accounting Standards Not Yet Effective

Summary of Significant Accounting Policies (Tables)

12 Months Ended

Dec. 31, 2020

Accounting Policies [Abstract]

Schedule of Revenue by Geography

Following table summarizes the Company's revenue by geography:


	Year ended December 31,
	2020		2019
	(in thousands)
United States	$	68,118	$	61,843
International	5,269		5,458
	$	73,387	$	67,301

Schedule of Property and Equipment

All property and equipment is depreciated on a straight-line basis over the estimated useful lives of the assets, which are as follows:


Computer and office equipment			3 – 5 years
Machinery and equipment			3 – 5 years
Furniture and fixtures			7 years

Property and Equipment, net:


	December 31, 2020		December 31, 2019
	(in thousands)
Machinery and equipment	$	6,342	$	4,613
Construction in progress	1,692		1,854
Computer and office equipment	714		598
Leasehold improvements	503		497
Furniture and fixtures	233		187
	9,484		7,749
Less: Accumulated depreciation and amortization	(4,957)		(3,795)
	$	4,527	$	3,954

Marketable Securities (Tables)

12 Months Ended

Dec. 31, 2020

Investments, Debt and Equity Securities [Abstract]

Schedule of Marketable Securities

The table below summarizes the marketable securities:


	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


	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)

12 Months Ended

Dec. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of Assets and Liabilities 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:


	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

	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 (Tables)

12 Months Ended

Dec. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Property and Equipment, Net

All property and equipment is depreciated on a straight-line basis over the estimated useful lives of the assets, which are as follows:


Computer and office equipment			3 – 5 years
Machinery and equipment			3 – 5 years
Furniture and fixtures			7 years

Property and Equipment, net:


	December 31, 2020		December 31, 2019
	(in thousands)
Machinery and equipment	$	6,342	$	4,613
Construction in progress	1,692		1,854
Computer and office equipment	714		598
Leasehold improvements	503		497
Furniture and fixtures	233		187
	9,484		7,749
Less: Accumulated depreciation and amortization	(4,957)		(3,795)
	$	4,527	$	3,954

Schedule of Accrued Liabilities and Other

Accrued Liabilities and Other:


	December 31, 2020		December 31, 2019
	(in thousands)
Accrued compensation and related expenses	$	9,175	$	7,274
Accrued litigation expense	—		3,200

Accrued professional services	511		392


Others	513		739
	$	10,199	$	11,605

Commitments and Contingencies (Tables)

12 Months Ended

Dec. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Schedule of Aggregate Future Minimum Lease Payments

The aggregate future minimum lease payments under all leases as of December 31, 2020 are as follows:


Year Ending December 31,	(in thousands)
2021	$	1,081
2022	1,001
2023	908
2024	893
2025	381
Thereafter	24
	$	4,288

Borrowings (Tables)

12 Months Ended

Dec. 31, 2020

Debt Disclosure [Abstract]

Schedule of Outstanding Borrowings

The following table summarizes the outstanding borrowings from the term loan as of the periods presented:


	December 31, 2020		December 31, 2019
	(in thousands)
Principal outstanding and final fee	$	41,000	$	40,000
Less: Unamortized debt issuance costs	(661)		(777)
Unaccreted value of final fee	(884)		—
Outstanding debt, net of debt issuance costs and unaccreted value of final fee	$	39,455	$	39,223
Classified as:
Current portion of long-term borrowings	$	—	$	4,358
Long-term borrowings	$	39,455	$	34,865

Schedule of Annual Future Minimum Principal Payments Under Loan Agreements


Year ending December 31,	(in thousands)
2021	$	—
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
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-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
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-Name Accounting Standards Codification
-Topic 835
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-URI http://asc.fasb.org/extlink&oid=119993939&loc=d3e28541-108399

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 235
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-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=120395691&loc=d3e23780-122690

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Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 942
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-URI http://asc.fasb.org/extlink&oid=75038535&loc=d3e64711-112823

Reference 9: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 835
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-URI http://asc.fasb.org/extlink&oid=114775985&loc=d3e28878-108400

Reference 10: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
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-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

Warrants (Tables)

12 Months Ended

Dec. 31, 2020

Other Liabilities Disclosure [Abstract]

Schedule of Warrants Issued and Outstanding

The table below summarizes common stock warrants issued and outstanding at both December 31, 2020 and 2019:


Date			Number of Shares Underlying Warrants	Price per Share	Fair Value (in thousands)
Issuance	Expiration
3/1/2017	3/1/2027	[a]	1,388	$5.94	$	5	[b]
7/22/2013	7/22/2023	[a]	32,983	$9.10	122		[b]
11/26/2014	11/26/2024	[a]	6,680	$16.47	49		[b]
10/20/2015	10/20/2025	[a]	41,650	$16.47	396		[c]
11/9/2015	11/9/2025	[a]	25,709	$16.47	244		[c]
12/22/2016	12/22/2026	[a]	9,712	$10.03	45		[c]
			118,122		$	861

[a] Common stock warrants will remain outstanding until the earlier of the expiration date or the date exercised by the holder.

[b] Fair value at the date of issuance.

[c] Fair value at the date of conversion from redeemable convertible preferred stock to common stock warrants in conjunction with the IPO on October 16, 2018.

Stock-Based Compensation (Tables)

12 Months Ended

Dec. 31, 2020

Share-based Payment Arrangement [Abstract]

Schedule of Stock Option Activity

The following table summarizes stock option activity for the years ended December 31, 2020 and 2019:


	Options Outstanding
	Number of Shares	Weighted-Average Exercise Price	Weighted-Average Contractual Remaining Life (Years)	Aggregate Intrinsic Value (in thousands)
Outstanding as of December 31, 2018	2,641,198	$4.27
Granted	638,983	$20.89
Exercised	(444,924)	$3.36
Canceled and forfeited	(116,286)	$11.30
Outstanding as of December 31, 2019	2,718,971	$8.02
Granted	26,236	$17.31
Exercised	(323,701)	$4.52
Canceled and forfeited	(15,549)	$17.07
Outstanding as of December 31, 2020	2,405,957	$8.54	5.80	$	51,402
Options vested and exercisable as of December 31, 2020	2,069,020	$6.85	5.40	$	47,689
Options vested and expected to vest as of December 31, 2020	2,390,755	$8.36	6.00	$	51,493

Schedule of Options by Range of Exercise Price

Outstanding options and exercisable options information by range of exercise prices as of December 31, 2020 was as follows:


Exercise Price			Options Outstanding			Options Vested and Exercisable
			Number of Shares	Average Remaining Contractual Life (Years)	Weighted- Average Exercise Price	Number of Shares	Weighted- Average Exercise Price
$0.84	-	$3.69	465,071	3.40	$3.31	465,071	$3.31
$3.70	-	$4.41	689,903	4.80	$4.29	689,903	$4.29
$4.42	-	$5.31	458,812	6.40	$4.67	422,974	$4.67
$5.32	-	$20.51	356,271	7.50	$12.08	282,203	$11.00
$20.52	-	$22.00	435,900	8.00	$22.00	208,869	$22.00
			2,405,957	5.80	$8.54	2,069,020	$6.85

Schedule of Valuation Assumptions Related to Stock Option Awards


	Year ended December 31,
	2020			2019
Weighted average grant date fair value per share	$8.16			$9.78
Expected term (years)	5.5	to	7.0	5.0	to	7.0
Expected volatility	46.7%	to	47.2%	41.7%	to	47.3%
Risk-free interest rate	1.6%	to	1.6%	1.3%	to	2.6%
Dividend yield	—%			—%

Schedule of Restricted Stock Unit Activity

The following table summarizes restricted stock units activity for the years ended December 31, 2020 and 2019:


	Number of Shares	Weighted- Average Grant Date Fair Value
Outstanding as of December 31, 2018	53,436	$11.69
Granted	639,726	$20.14
Vested	(108,631)	$19.10
Canceled and forfeited	(41,490)	$18.48
Outstanding as of December 31, 2019	543,041	$19.72
Granted	1,016,432	$20.17
Vested	(344,779)	$19.87
Canceled and forfeited	(49,399)	$19.73
Outstanding as of December 31, 2020	1,165,295	$20.07

Schedule of Valuation Assumptions Related to ESPP Purchase Rights

The Company estimated the fair value of ESPP purchase rights during the offering period using a Black-Scholes option pricing model with the following assumptions:


	Year ended December 31,
	2020			2019
Expected term (years)	0.5	to	1.0	0.5
Expected volatility	38.3%	to	79.4%	38.3%	to	58.4%
Risk-free interest rate	0.1%	to	1.6%	1.6%	to	2.4%
Dividend yield	—%			—%

Schedule of Stock-Based Compensation Expense

Stock-Based Compensation

The following table sets forth stock-based compensation expense recognized for the periods presented:


	Year ended December 31,
	2020		2019
	(in thousands)
Cost of goods sold	$	331	$	185
Sales and marketing	5,527		3,335
Research and development	1,139		516
General and administrative	4,930		3,428
	$	11,927	$	7,464

Net Loss Per Share of Common Stock (Tables)

12 Months Ended

Dec. 31, 2020

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Net Loss per Share

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


	Year ended December 31,
	2020		2019
	(in thousands, except share and per share data)
Net loss	$	(43,697)	$	(38,403)

Weighted-average shares used to compute basic and diluted net loss per share	29,059,171		24,705,980

Net loss per share, basic and diluted	$	(1.50)	$	(1.55)

Schedule of Antidilutive Securities Excluded from Computation of Diluted Net Loss per Share


	Year ended December 31,
	2020	2019
Stock options	2,405,957	2,718,971
Restricted stock units	1,165,295	543,041
Shares subject to repurchase	5,836	21,404
ESPP purchase rights	83,040	65,442
Common stock warrants	118,122	118,122
	3,778,250	3,466,980

Income Taxes (Tables)

12 Months Ended

Dec. 31, 2020

Income Tax Disclosure [Abstract]

Schedule of Components of Loss Before Income Taxes

The components of the Company’s loss before income taxes are as follows:


	Year ended December 31,
	2020		2019
	(in thousands)
Domestic	$	(41,708)	$	(37,709)
Foreign	(1,989)		(694)
Loss before income taxes	$	(43,697)	$	(38,403)

Schedule of Components of Income Tax Expense

The components of deferred income taxes are as follows:


	Year ended December 31,
	2020		2019
	(in thousands)
Federal	$	9,855	$	8,523
State	2,711		1,569
Foreign	583		(200)
Total deferred income taxes	13,149		9,892
Change in deferred tax valuation allowance	(13,149)		(9,892)
Net deferred income tax	$	—	$	—

Schedule of Effective Income Tax Rate Reconciliation

Income tax expense differs from the amount computed by applying the statutory federal income tax rate due to the following:


	Year ended December 31,
	2020		2019
Tax at statutory federal rate	(21.0)	%	(21.0)	%
State tax, net of federal benefit	(6.2)	%	(4.1)	%
Tax credits	(0.7)	%	(0.7)	%
Change in deferred tax valuation allowance	30.1	%	25.8	%
Stock compensation	(1.2)	%	(1.5)	%
Foreign rate differences	(1.3)	%	0.5	%
Other	0.3	%	1.0	%
Total income tax expense	—	%	—	%

Schedule of Deferred Tax Assets

The tax effects of temporary differences and carryforwards that give rise to significant portions of the deferred tax assets are presented below:


	Year ended December 31,
	2020		2019
	(in thousands)
Net operating loss carryforwards	$	52,331	$	42,032
Research and development credits	3,160		2,428
Accruals and reserves	5,450		4,222
Stock compensation	2,395		1,512
Depreciation and amortization	117		110
Total deferred tax assets	63,453		50,304
Less: Valuation allowance	(63,453)		(50,304)
Total deferred tax asset, net of valuation allowance	$	—	$	—

Summary of Changes in Valuation Allowance

The following table summarizes changes in the valuation allowance for the years ended December 31, 2020 and 2019:


	Year ended December 31,
	2020		2019
	(in thousands)
Beginning balance	$	50,304	$	40,412
Additions during the period	13,149		9,892
Ending balance	$	63,453	$	50,304

Schedule of Uncertain Income Tax Positions

The changes in the Company’s uncertain income tax positions for the years ended December 31, 2020 and 2019 consisted of the following:


	Year ended December 31,
	2020		2019
	(in thousands)
Balance at beginning of the year	$	1,287	$	1,084
Increases related to current year's tax positions	226		203
Balance at end of the year	$	1,513	$	1,287

The Company and Nature of Business (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended				12 Months Ended
	Oct. 31, 2020	Feb. 29, 2020	Jan. 31, 2020	Oct. 31, 2018	Dec. 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)				$ 15.00
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			$ 50.0
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
Public offering price (in dollars per share)		$ 21.50
Net proceeds from sale of stock		$ 13.0
Second follow-on public offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)	3,000,000
Public offering price (in dollars per share)	$ 22.00
Net proceeds from sale of stock	$ 71.6
Secondary offering by selling shareholders
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)	190,053
Public offering price (in dollars per share)	$ 22.00
Allocated public offering costs					$ 0.2

Summary of Significant Accounting Policies - Segments (Details) $ in Thousands	12 Months Ended
	Dec. 31, 2020 USD ($) segment	Dec. 31, 2019 USD ($)
Accounting Policies [Abstract]
Number of reportable segments \| segment	1
Number of operating segments \| segment	1
Disaggregation of Revenue [Line Items]
Revenue	$ 73,387	$ 67,301
Revenue		67,301
United States
Disaggregation of Revenue [Line Items]
Revenue	68,118
Revenue		61,843
International
Disaggregation of Revenue [Line Items]
Revenue	$ 5,269
Revenue		$ 5,458

- 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.

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+ Details

- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

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+ Details

Summary of Significant Accounting Policies - Liquidity (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Cash and marketable securities	$ 196,400	$ 93,100
Long-term debt	39,455	39,223
Accumulated deficit	239,277	195,580
Net loss	$ (43,697)	$ (38,403)

- Definition

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

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+ Details

Summary of Significant Accounting Policies - Property and Equipment (Details)	12 Months Ended
	Dec. 31, 2020
Computer and office equipment \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Computer and office equipment \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Machinery and equipment \| Minimum
Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Machinery and equipment \| Maximum
Property, Plant and Equipment [Line Items]
Estimated useful life	5 years
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Estimated useful life	7 years

Summary of Significant Accounting Policies - Impairment of Long-Lived Assets (Details) - USD ($)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Impairment losses on long-lived assets	$ 0	$ 0

Summary of Significant Accounting Policies - Revenue Recognition (Details)	12 Months Ended
	Dec. 31, 2020
Minimum
Disaggregation of Revenue [Line Items]
Standard payment terms per agreements (in days)	30 days
Maximum
Disaggregation of Revenue [Line Items]
Standard payment terms per agreements (in days)	90 days

Summary of Significant Accounting Policies - Warranty Program (Details)	12 Months Ended
	Dec. 31, 2020
Accounting Policies [Abstract]
Warranty term (in years)	1 year
Sales credit reserve term (in years)	1 year

Summary of Significant Accounting Policies - Advertising Expenditures (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Accounting Policies [Abstract]
Advertising expenses	$ 0.3	$ 0.4

Marketable Securities (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Cash equivalents
Carrying Value	$ 47,348	$ 5,563
Short-term investments
Amortized Cost	142,856	81,291
Unrealized Gains	8	58
Unrealized Losses	(13)	(4)
Aggregate Fair Value	142,851	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	190,204	88,132
Total marketable securities, Unrealized Gains	8	58
Total marketable securities, Unrealized Losses	(13)	(4)
Total marketable securities, Aggregate Fair Value	190,199	88,186
Money market funds
Cash equivalents
Carrying Value	45,948	3,068
U.S. treasury securities
Short-term investments
Amortized Cost	74,779	67,051
Unrealized Gains	4	34
Unrealized Losses	(7)	(2)
Aggregate Fair Value	74,776	67,083
Corporate bonds
Short-term investments
Amortized Cost	8,940	9,075
Unrealized Gains	4	24
Unrealized Losses	(6)	(2)
Aggregate Fair Value	8,938	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	1,400	2,495
Short-term investments
Amortized Cost	59,137	5,165
Unrealized Gains	0	0
Unrealized Losses	0	0
Aggregate Fair Value	$ 59,137	$ 5,165

Fair Value Measurement - Marketable Securities Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Marketable securities
Marketable securities	$ 190,199	$ 88,186
Money market funds
Marketable securities
Marketable securities	45,948	3,068
U.S. treasury securities
Marketable securities
Marketable securities	74,776	67,083
Corporate bonds
Marketable securities
Marketable securities	8,938	10,375
Commercial paper
Marketable securities
Marketable securities	60,537	7,660
Level 1
Marketable securities
Marketable securities	120,724	70,151
Level 1 \| Money market funds
Marketable securities
Marketable securities	45,948	3,068
Level 1 \| U.S. treasury securities
Marketable securities
Marketable securities	74,776	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	69,475	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	8,938	10,375
Level 2 \| Commercial paper
Marketable securities
Marketable securities	60,537	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 - Property and Equipment, Net (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Property and Equipment, Net
Property and equipment, gross	$ 9,484	$ 7,749
Less: Accumulated depreciation and amortization	(4,957)	(3,795)
Property and equipment, net	4,527	3,954
Depreciation expense	1,100	800
Machinery and equipment
Property and Equipment, Net
Property and equipment, gross	6,342	4,613
Construction in progress
Property and Equipment, Net
Property and equipment, gross	1,692	1,854
Computer and office equipment
Property and Equipment, Net
Property and equipment, gross	714	598
Leasehold improvements
Property and Equipment, Net
Property and equipment, gross	503	497
Furniture and fixtures
Property and Equipment, Net
Property and equipment, gross	$ 233	$ 187

Balance Sheet Components - Accrued Liabilities and Other (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Accrued Liabilities and Other
Accrued compensation and related expenses	$ 9,175	$ 7,274
Accrued litigation expense	0	3,200
Accrued professional services	511	392
Others	513	739
Accrued liabilities and other	$ 10,199	$ 11,605

Commitments and Contingencies - Narrative (Details) - USD ($)			12 Months Ended
	Jun. 22, 2020	Feb. 06, 2019	Dec. 31, 2020	Dec. 31, 2019
Operating Leased Assets [Line Items]
Rent expense			$ 1,200,000	$ 1,200,000
Purchase commitments related to inventory			300,000	400,000
Accrued litigation expense			0	3,200,000
Class action Eric B. Fromer Chiropractic Inc.
Operating Leased Assets [Line Items]
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 \| Class action Eric B. Fromer Chiropractic Inc.
Operating Leased Assets [Line Items]
Damages sought		$ 500
Treble damages sought per violation of TCPA \| Class action Eric B. Fromer Chiropractic Inc.
Operating Leased Assets [Line Items]
Damages sought		$ 1,500
Indemnification Agreement
Operating Leased Assets [Line Items]
Costs to defend lawsuits or settle claims			0
Costs accrued to defend lawsuits			$ 0

Commitments and Contingencies - Aggregate Future Minimum Lease Payments (Details) $ in Thousands	Dec. 31, 2020 USD ($)
Aggregate Future Minimum Lease Payments
2021	$ 1,081
2022	1,001
2023	908
2024	893
2025	381
Thereafter	24
Total	$ 4,288

Borrowings - Summary of Borrowings (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Debt Disclosure [Abstract]
Principal outstanding and final fee	$ 41,000	$ 40,000
Less: Unamortized debt issuance costs	(661)	(777)
Less: Unaccreted value of final fee	(884)	0
Outstanding debt, net of debt issuance costs and unaccreted value of final fee	39,455	39,223
Current portion of long-term borrowings	0	4,358
Long-term borrowings	$ 39,455	$ 34,865

Borrowings - Narrative (Details) - USD ($)				1 Months Ended	12 Months Ended
Borrowings - Narrative (Details) - USD ($)	May 29, 2020	Apr. 29, 2020	Apr. 21, 2020	Oct. 31, 2017	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Proceeds from debt financing					$ 45,297,000	$ 0
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					884,000	$ 0
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
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]
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)					12.40%	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
Fixed interest rate (percent)	9.40%
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%
Effective interest rate during the period (percent)					10.60%
Incremental interest rate increase upon default of minimum liquidity covenant (percent)	5.00%
Term Loan \| Solar Loan And Security Agreement \| Variable Option One
Debt Instrument [Line Items]
Basis spread on variable rate (percent)	0.33%
Term Loan \| Solar Loan And Security Agreement \| Debt Covenant Tranche One
Debt Instrument [Line Items]
Debt covenant minimum cash balance	$ 15,000,000.0
Product revenue threshold for minimum liquidity covenant	75,000,000.0
Term Loan \| Solar Loan And Security Agreement \| Debt Covenant Tranche One \| Minimum
Debt Instrument [Line Items]
Product revenue threshold for minimum liquidity covenant	75,000,000.0
Term Loan \| Solar Loan And Security Agreement \| Debt Covenant Tranche One \| Maximum
Debt Instrument [Line Items]
Product revenue threshold for minimum liquidity covenant	100,000,000.0
Term Loan \| Solar Loan And Security Agreement \| Debt Covenant Tranche Two
Debt Instrument [Line Items]
Debt covenant minimum cash balance	7,500,000
Term Loan \| Solar Loan And Security Agreement \| Debt Covenant Tranche Three
Debt Instrument [Line Items]
Debt covenant minimum cash balance	0
Term Loan \| Solar Loan And Security Agreement \| Debt Covenant Tranche Three \| Minimum
Debt Instrument [Line Items]
Product revenue threshold for minimum liquidity covenant	$ 100,000,000.0

Borrowings - Annual Future Minimum Principal Payments (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Maturities of Long-term Debt [Abstract]
2021	$ 0
2022	0
2023	11,667
2024	20,000
2025	9,333
Total principal and final fee payments	$ 41,000	$ 40,000

Warrants - Issued and Outstanding (Details) - Common Stock - USD ($) $ / shares in Units, $ in Thousands	Dec. 31, 2020	Dec. 31, 2019
Warrants Issued 3/1/2017
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	1,388	1,388
Price per Share (in dollars per share)	$ 5.94	$ 5.94
Fair Value	$ 5	$ 5
Warrants Issued 7/22/2013
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	32,983	32,983
Price per Share (in dollars per share)	$ 9.10	$ 9.10
Fair Value	$ 122	$ 122
Warrants Issued 11/26/2014
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	6,680	6,680
Price per Share (in dollars per share)	$ 16.47	$ 16.47
Fair Value	$ 49	$ 49
Warrants Issued 10/20/2015
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	41,650	41,650
Price per Share (in dollars per share)	$ 16.47	$ 16.47
Fair Value	$ 396	$ 396
Warrants Issued 11/9/2015
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	25,709	25,709
Price per Share (in dollars per share)	$ 16.47	$ 16.47
Fair Value	$ 244	$ 244
Warrants Issued 12/22/2016
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	9,712	9,712
Price per Share (in dollars per share)	$ 10.03	$ 10.03
Fair Value	$ 45	$ 45
Common Stock Warrants
Class of Warrant or Right [Line Items]
Number of Shares Underlying Warrants (in shares)	118,122	118,122
Fair Value	$ 861	$ 861

Common and Preferred Stock - Narrative (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Equity [Abstract]
Common stock authorized (in shares)	100,000,000	100,000,000
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock issued (in shares)	32,583,220	25,163,803
Common stock outstanding (in shares)	32,583,220	25,163,803
Preferred stock authorized (in shares)	5,000,000	5,000,000
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock issued (in shares)	0	0
Preferred stock outstanding (in shares)	0	0
Common stock, dividends declared (in dollars per share)	$ 0

Stock-Based Compensation - Narrative (Details) $ in Thousands				4 Months Ended	8 Months Ended	12 Months Ended
	Jan. 01, 2021 shares	Jan. 01, 2020 shares	Jan. 01, 2019 shares	Apr. 30, 2020	Dec. 31, 2020 USD ($) purchase_period shares	Dec. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares	Oct. 31, 2018 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Aggregate intrinsic value of options exercised \| $						$ 5,600	$ 6,800
Unrecognized compensation costs \| $					$ 3,200	$ 3,200
Early exercise of stock options, share subject to repurchase (in shares) \| shares					5,836	5,836	21,404
Issuance of common stock related to employee stock purchase plan (in shares) \| shares						137,377	168,457
Issuance of common stock related to employee stock purchase plan \| $						$ 1,915	$ 2,203
Stock-based compensation expense \| $						$ 11,927	7,464
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price of option as percent of fair market value when individual owns more than 10% of shares outstanding (percent)						110.00%
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Percentage of ownership of outstanding shares for alternate terms						10.00%
Stock option term (in years)						10 years
Stock option term when grantee holds more than 10% of shares outstanding (in years)						5 years
Award vesting period (in years)						4 years
Unrecognized compensation cost, expected period for recognition (in years)						1 year 10 months 24 days
Incentive Stock Options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price of option as percent of fair market value (percent)						100.00%
Nonqualified Stock Options \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Exercise price of option as percent of fair market value (percent)						85.00%
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, expected period for recognition (in years)						2 years 10 months 24 days
Unrecognized compensation cost \| $					$ 19,300	$ 19,300
Restricted Stock Units \| Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)						2 years
Restricted Stock Units \| Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period (in years)						4 years
2018 Equity Incentive Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual increase in shares reserved as percentage of prior year-end shares outstanding (percent)					5.00%	5.00%
Increase in number of shares reserved for future issuance (in shares) \| shares		1,222,538	1,258,190
Shares available for future grants (in shares) \| shares					2,843,814	2,843,814
2018 Equity Incentive Plan \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in number of shares reserved for future issuance (in shares) \| shares	1,629,161
2018 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Annual increase in shares reserved as percentage of prior year-end shares outstanding (percent)					1.00%	1.00%
Annual increase in shares reserved, maximum (in shares) \| shares					555,555	555,555
Unrecognized compensation cost \| $					$ 200	$ 200
Purchase price of common stock as a percent of fair market value (percent)						85.00%
Employees stock purchase program offering period interval (in months)				6 months	12 months
Number of purchase periods in offering interval \| purchase_period					2
Number of shares reserved for issuance (in shares) \| shares					705,618	705,618		515,307
Accrued compensation and related expenses for employee payroll deductions \| $					$ 400	$ 400	200
Stock-based compensation expense \| $						$ 1,200	$ 800
2018 ESPP \| Subsequent Event
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Increase in number of shares reserved for future issuance (in shares) \| shares	325,832

Stock-Based Compensation - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Number of Shares
Beginning balance (in shares)	2,718,971	2,641,198
Options granted (in shares)	26,236	638,983
Options exercised (in shares)	(323,701)	(444,924)
Options canceled and forfeited (in shares)	(15,549)	(116,286)
Ending balance (in shares)	2,405,957	2,718,971
Options vested and exercisable (in shares)	2,069,020
Options vested and expected to vest (in shares)	2,390,755
Weighted-Average Exercise Price
Beginning balance (in dollars per share)	$ 8.02	$ 4.27
Options granted (in dollars per share)	17.31	20.89
Options exercised (in dollars per share)	4.52	3.36
Options canceled and forfeited (in dollars per share)	17.07	11.30
Ending balance (in dollars per share)	8.54	$ 8.02
Options vested and exercisable (in dollars per share)	6.85
Options vested and expected to vest (in dollars per share)	$ 8.36
Weighted-Average Remaining Contractual Life and Aggregate Intrinsic Value
Weighted-average remaining contractual life, options outstanding (in years)	5 years 9 months 18 days
Weighted-average remaining contractual life, options vested and exercisable (in years)	5 years 4 months 24 days
Weighted-average remaining contractual life, options vested and expected to vest (in years)	6 years
Aggregate intrinsic value, options outstanding	$ 51,402
Aggregate intrinsic value, options vested and exercisable	47,689
Aggregate intrinsic value, options vested and expected to vest	$ 51,493

Stock-Based Compensation - Outstanding Options and Exercisable Options Information by Range of Exercise Prices (Details)	12 Months Ended
	Dec. 31, 2020 $ / shares shares
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Options outstanding, number of shares (in shares) \| shares	2,405,957
Options outstanding, average remaining contractual life (years)	5 years 9 months 18 days
Options outstanding, weighted-average exercise price (in dollars per share)	$ 8.54
Options vested and exercisable, number of shares (in shares) \| shares	2,069,020
Options vested and exercisable, weighted-average exercise price (in dollars per share)	$ 6.85
$0.84-$3.69
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower limit (in dollars per share)	0.84
Exercise price, upper limit (in dollars per share)	$ 3.69
Options outstanding, number of shares (in shares) \| shares	465,071
Options outstanding, average remaining contractual life (years)	3 years 4 months 24 days
Options outstanding, weighted-average exercise price (in dollars per share)	$ 3.31
Options vested and exercisable, number of shares (in shares) \| shares	465,071
Options vested and exercisable, weighted-average exercise price (in dollars per share)	$ 3.31
$3.70-$4.41
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower limit (in dollars per share)	3.70
Exercise price, upper limit (in dollars per share)	$ 4.41
Options outstanding, number of shares (in shares) \| shares	689,903
Options outstanding, average remaining contractual life (years)	4 years 9 months 18 days
Options outstanding, weighted-average exercise price (in dollars per share)	$ 4.29
Options vested and exercisable, number of shares (in shares) \| shares	689,903
Options vested and exercisable, weighted-average exercise price (in dollars per share)	$ 4.29
$4.42-$5.31
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower limit (in dollars per share)	4.42
Exercise price, upper limit (in dollars per share)	$ 5.31
Options outstanding, number of shares (in shares) \| shares	458,812
Options outstanding, average remaining contractual life (years)	6 years 4 months 24 days
Options outstanding, weighted-average exercise price (in dollars per share)	$ 4.67
Options vested and exercisable, number of shares (in shares) \| shares	422,974
Options vested and exercisable, weighted-average exercise price (in dollars per share)	$ 4.67
$5.32-$20.51
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower limit (in dollars per share)	5.32
Exercise price, upper limit (in dollars per share)	$ 20.51
Options outstanding, number of shares (in shares) \| shares	356,271
Options outstanding, average remaining contractual life (years)	7 years 6 months
Options outstanding, weighted-average exercise price (in dollars per share)	$ 12.08
Options vested and exercisable, number of shares (in shares) \| shares	282,203
Options vested and exercisable, weighted-average exercise price (in dollars per share)	$ 11.00
$20.52-$22.00
Share-based Payment Arrangement, Option, Exercise Price Range [Line Items]
Exercise price, lower limit (in dollars per share)	20.52
Exercise price, upper limit (in dollars per share)	$ 22.00
Options outstanding, number of shares (in shares) \| shares	435,900
Options outstanding, average remaining contractual life (years)	8 years
Options outstanding, weighted-average exercise price (in dollars per share)	$ 22.00
Options vested and exercisable, number of shares (in shares) \| shares	208,869
Options vested and exercisable, weighted-average exercise price (in dollars per share)	$ 22.00

Stock-Based Compensation - Valuation Assumptions for Stock Options (Details) - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Black-Scholes option-pricing model assumptions
Weighted-average grant date fair value of options granted (in dollars per share)	$ 8.16	$ 9.78
Stock Options
Black-Scholes option-pricing model assumptions
Expected volatility, minimum (percent)	46.70%	41.70%
Expected volatility, maximum (percent)	47.20%	47.30%
Risk-free interest rate, minimum (percent)	1.60%	1.30%
Risk-free interest rate, maximum (percent)	1.60%	2.60%
Dividend yield (percent)	0.00%	0.00%
Stock Options \| Minimum
Black-Scholes option-pricing model assumptions
Expected term (in years)	5 years 6 months	5 years
Stock Options \| Maximum
Black-Scholes option-pricing model assumptions
Expected term (in years)	7 years	7 years

Stock-Based Compensation - Restricted Stock Unit Activity (Details) - Restricted Stock Units - $ / shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Number of Shares
Beginning balance (in shares)	543,041	53,436
Granted (in shares)	1,016,432	639,726
Vested (in shares)	(344,779)	(108,631)
Canceled and forfeited (in shares)	(49,399)	(41,490)
Ending balance (in shares)	1,165,295	543,041
Weighted- Average Grant Date Fair Value
Beginning balance (in dollars per share)	$ 19.72	$ 11.69
Granted (in dollars per share)	20.17	20.14
Vested (in dollars per share)	19.87	19.10
Canceled and forfeited (in dollars per share)	19.73	18.48
Ending balance (in dollars per share)	$ 20.07	$ 19.72

Stock-Based Compensation - Valuation Assumptions for ESPP Purchase Rights (Details) - ESPP Purchase Rights	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)		6 months
Expected volatility, minimum (percent)	38.30%	38.30%
Expected volatility, maximum (percent)	79.40%	58.40%
Risk-free interest rate, minimum (percent)	0.10%	1.60%
Risk-free interest rate, maximum (percent)	1.60%	2.40%
Dividend yield (percent)	0.00%	0.00%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	1 year

Stock-Based Compensation - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 11,927	$ 7,464
Cost of goods sold
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	331	185
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	5,527	3,335
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,139	516
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 4,930	$ 3,428

Employee Benefit Plan (Details) - 401(k) Plan - USD ($)	12 Months Ended
Employee Benefit Plan (Details) - 401(k) Plan - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Defined Contribution Plan Disclosure [Line Items]
Employer matching contribution, percentage of eligible compensation	3.00%
Employer matching contribution, maximum amount per employee	$ 1,000
Employer contributions	$ 200,000	$ 100,000

Net Loss Per Share of Common Stock - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Earnings Per Share [Abstract]
Net loss	$ (43,697)	$ (38,403)
Weighted-average number of common shares used to compute basic and diluted net loss per share (in shares)	29,059,171	24,705,980
Net loss per share, basic and diluted (in dollars per share)	$ (1.50)	$ (1.55)

- Definition

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

+ References

+ Details

Net Loss Per Share of Common Stock - Antidilutive Securities Excluding from Computation of Earnings Per Share (Details) - shares	12 Months Ended
	Dec. 31, 2020	Dec. 31, 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	3,778,250	3,466,980
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	2,405,957	2,718,971
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	1,165,295	543,041
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	5,836	21,404
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	83,040	65,442
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

Income Taxes - Components of Loss Before Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Components of loss before income taxes
Domestic	$ (41,708)	$ (37,709)
Foreign	(1,989)	(694)
Loss before income taxes	$ (43,697)	$ (38,403)

Income Taxes - Components of Deferred Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Deferred tax expense:
Federal	$ 9,855	$ 8,523
State	2,711	1,569
Foreign	583	(200)
Total deferred income taxes	13,149	9,892
Change in deferred tax valuation allowance	(13,149)	(9,892)
Net deferred income tax	$ 0	$ 0

Income Taxes - Reconciliation of Effective Income Tax Rate (Details)	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Effective Income Tax Rate Reconciliation
Tax at statutory federal rate (percent)	(21.00%)	(21.00%)
State tax, net of federal benefit (percent)	(6.20%)	(4.10%)
Tax credits (percent)	(0.70%)	(0.70%)
Change in deferred tax valuation allowance (percent)	30.10%	25.80%
Stock compensation (percent)	(1.20%)	(1.50%)
Foreign rate differences (percent)	(1.30%)	0.50%
Other (percent)	0.30%	1.00%
Total income tax expense (percent)	0.00%	0.00%

Income Taxes - Temporary Differences and Carryforwards and Deferred Tax Assets (Details) - USD ($) $ in Thousands	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Deferred Tax Assets
Net operating loss carryforwards	$ 52,331	$ 42,032
Research and development credits	3,160	2,428
Accruals and reserves	5,450	4,222
Stock compensation	2,395	1,512
Depreciation and amortization	117	110
Total deferred tax assets	63,453	50,304
Less: Valuation allowance	(63,453)	(50,304)	$ (40,412)
Total deferred tax asset, net of valuation allowance	$ 0	$ 0

Income Taxes - Changes in Valuation Allowance (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Changes in Valuation Allowance
Valuation allowance, beginning balance	$ 50,304	$ 40,412
Additions during the period	13,149	9,892
Valuation allowance, ending balance	$ 63,453	$ 50,304

Income Taxes - Narrative (Details) - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Line Items]
Limited net operating loss carryforwards	$ 1,400,000
Deferred liability for social security taxes, CARES Act	1,000,000.0
Accrued interest related to unrecognized tax benefits	0	$ 0
Federal
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	200,500,000
Credit carryforwards	2,500,000
State
Income Tax Disclosure [Line Items]
Net operating loss carryforwards	165,000,000.0
Credit carryforwards	$ 2,500,000

Income Taxes - Uncertain Income Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019
Uncertain income tax positions [Roll Forward]
Balance at beginning of the year	$ 1,287	$ 1,084
Increases related to current year's tax positions	226	203
Balance at end of the year	$ 1,513	$ 1,287

Related Party Transactions (Details) - SeaSpine - Joint development agreement - USD ($)		12 Months Ended
	Feb. 24, 2020	Dec. 31, 2020
Related Party Transaction [Line Items]
Reimbursement charges expensed		$ 118,000
Outstanding liability to SeaSpine		$ 0
Term of product royalty sales period (in years)	10 years