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Cover Page nonprinting - shares	3 Months Ended
Cover Page nonprinting - shares	Mar. 31, 2020	Apr. 30, 2020
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Mar. 31, 2020
Document Transition Report	false
Entity Registrant Name	SI-BONE, Inc.
Entity Central Index Key	0001459839
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2020
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		28,427,133

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Current assets:
Cash and cash equivalents	$ 67,568	$ 10,435
Short-term investments	77,373	81,345
Accounts receivable, net of allowance for doubtful accounts of $272 and $238, respectively	9,361	11,720
Inventory	5,726	5,452
Prepaid expenses and other current assets	1,936	2,510
Total current assets	161,964	111,462
Long-term investments	1,274	1,278
Property and equipment, net	4,269	3,954
Other non-current assets	312	315
TOTAL ASSETS	167,819	117,009
Current liabilities:
Accounts payable	2,577	2,811
Accrued liabilities and other	9,284	11,605
Current portion of long-term borrowings	8,731	4,358
Total current liabilities	20,592	18,774
Long-term Debt, Excluding Current Maturities	30,557	34,865
Other long-term liabilities	400	362
TOTAL LIABILITIES	51,549	54,001
Commitments and contingencies
STOCKHOLDERS’ EQUITY
Preferred stock, $0.0001 par value; 5,000,000 shares authorized; no shares issued and outstanding	0	0
Common stock, $0.0001 par value; 100,000,000 shares authorized; 28,406,128 and 25,163,803 shares issued and outstanding, respectively	3	3
Additional paid-in capital	323,922	258,121
Accumulated other comprehensive income	697	464
Accumulated deficit	(208,352)	(195,580)
TOTAL STOCKHOLDERS’ EQUITY	116,270	63,008
TOTAL LIABILITIES AND STOCKHOLDERS’ EQUITY	$ 167,819	$ 117,009

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Statement of Financial Position [Abstract]
Allowance for doubtful accounts	$ 272	$ 238
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock authorized (in shares)	5,000,000	5,000,000
Preferred stock issued (in shares)	0	0
Preferred stock outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock authorized (in shares)	100,000,000	100,000,000
Common stock issued (in shares)	28,406,128
Common stock outstanding (in shares)	28,406,128
Shares, Outstanding		25,163,803

CONDENSED CONSOLIDATED STATEMENTS OF OPERATIONS AND COMPREHENSIVE LOSS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Income Statement [Abstract]
Revenue	$ 16,821	$ 14,991
Cost of goods sold	1,932	1,526
Gross profit	14,889	13,465
Operating expenses:
Sales and marketing	19,281	15,815
Research and development	2,090	1,683
General and administrative	5,400	4,766
Total operating expenses	26,771	22,264
Loss from operations	(11,882)	(8,799)
Interest and other income (expense), net:
Interest income	498	744
Interest expense	(1,231)	(1,230)
Other expense, net	(157)	(60)
Net loss	(12,772)	(9,345)
Other comprehensive income (loss):
Changes in foreign currency translation	12	(19)
Unrealized gain on marketable securities	221	25
Comprehensive loss	$ (12,539)	$ (9,339)
Net loss per share, basic and diluted (in dollars per share)	$ (0.47)	$ (0.38)
Weighted-average number of common shares used to compute basic and diluted net loss per share (in shares)	27,252,409	24,390,648

CONDENSED CONSOLIDATED STATEMENTS OF CHANGES IN REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Accumulated Deficit
Stockholders' equity (deficit), beginning of period at Dec. 31, 2018	$ 90,192	$ 3	$ 246,927	$ 439	$ (157,177)
Stockholders' equity (deficit), beginning of period (in shares) at Dec. 31, 2018		24,450,757
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon exercise of stock options, net of shares withheld	125		125
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)		46,809
Stock-based compensation	1,871		1,871
Vesting of early exercised stock options	66		66
Additional accrual of IPO related costs	(160)		(160)
Foreign currency translation	(19)			(19)
Unrealized gain on marketable securities	25			25
Net loss	(9,345)				(9,345)
Stockholders' equity (deficit), ending of period (in shares) at Mar. 31, 2019		24,497,566
Stockholders' equity (deficit), ending of period at Mar. 31, 2019	82,755	$ 3	248,829	445	(166,522)
Stockholders' equity (deficit), beginning of period at Dec. 31, 2019	$ 63,008	$ 3	258,121	464	(195,580)
Stockholders' equity (deficit), beginning of period (in shares) at Dec. 31, 2019	25,163,803
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock from public offering, net of underwriting discounts, commissions and offering costs	$ 62,978		62,978
Issuance of common stock from public offering, net of underwriting discounts, commissions and offering costs (in shares)		3,135,053
Issuance of common stock upon exercise of stock options, net of shares withheld	$ 174		174
Issuance of common stock upon exercise of stock options, net of shares withheld (in shares)	43,334	43,334
Issuance of common stock upon vesting of restricted stock units	$ 0
Issuance of common stock upon vesting of restricted stock units (in shares)		63,938
Stock-based compensation	2,622		2,622
Vesting of early exercised stock options	27		27
Foreign currency translation	12			12
Unrealized gain on marketable securities	221			221
Net loss	(12,772)				(12,772)
Stockholders' equity (deficit), ending of period (in shares) at Mar. 31, 2020		28,406,128
Stockholders' equity (deficit), ending of period at Mar. 31, 2020	$ 116,270	$ 3	$ 323,922	$ 697	$ (208,352)

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Cash flows from operating activities
Net loss	$ (12,772)	$ (9,345)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation	2,622	1,871
Depreciation and amortization	249	193
Bad debts expense	192	0
Accretion on marketable securities	(25)	(479)
Amortization of debt issuance costs	65	65
Loss on sale and disposal of property and equipment	0	97
Changes in operating assets and liabilities:
Accounts receivable	2,207	87
Inventory	(256)	(165)
Prepaid expenses and other assets	581	(167)
Accounts payable	76	451
Accrued liabilities and other	(2,294)	314
Net cash used in operating activities	(9,355)	(7,078)
Cash flows from investing activities
Maturities of marketable securities	21,000	17,600
Purchases of marketable securities	(16,777)	(22,741)
Purchases of property and equipment	(884)	(412)
Net cash provided by (used in) investing activities	3,339	(5,553)
Cash flows from financing activities
Proceeds from follow-on public offering, net of underwriting discounts, commissions and offering costs	62,978	0
Proceeds from the exercise of stock options	174	125
Net cash provided by financing activities	63,152	125
Effect of exchange rate changes on cash and cash equivalents	(3)	(53)
Net decrease in cash and cash equivalents	57,133	(12,559)
Cash and cash equivalents at
Beginning of period	10,435	25,120
End of period	67,568	12,561
Supplemental disclosure of non-cash information
Vesting of early exercised stock options	27	66
Purchases of property and equipment included in accounts payable and accrued liabilities	52	140
Public offering costs included in accounts payable	$ 0	$ 167

The Company and Nature of Business	3 Months Ended
The Company and Nature of Business	Mar. 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. In October 2018, the Company completed its initial public offering ("IPO"), by issuing 8,280,000 shares of common stock, at an offering price of $15.00 per share, for net proceeds of $113.4 million after deducting underwriting discounts and commissions and offering costs. In January 2020, the Company received $50.3 million of net proceeds, after deducting the underwriting discounts and commissions, from its public offering of 4,300,000 shares of the Company's common stock at a public offering price of $21.50 per share, of which 2,490,053 shares were offered and sold by the Company. Further, in February 2020, the underwriters fully exercised their option to purchase 645,000 shares of the Company's common stock at a public offering price of $21.50 per share for an additional net proceeds of $13.0 million to the Company, after deducting underwriting discounts and commissions. The total public offering costs incurred in connection with the follow-on offering were allocated based on the gross proceeds received by the Company and the other selling shareholders on a pro-rated basis. Public offering cost of $0.4 million allocated to selling of shares by the Company was charged against the gross proceeds received from the follow-on offering. Public offering costs of $0.2 million allocated to selling of shares by the selling shareholders was recognized as transaction costs within general and administrative expenses on the unaudited condensed consolidated statements of operations in the three months ended March 31, 2020.

Summary of Significant Accounting Policies

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Summary of Significant Accounting Policies

Basis of Presentation and Principles of Consolidation

The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP have been condensed or omitted, and accordingly the balance sheet as of December 31, 2019 has been derived from the audited consolidated financial statements at that date but does not include all of the information required by GAAP for complete financial statements. These unaudited interim condensed consolidated financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments that are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the three months ended March 31, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 or for any other interim period or for any other future year.

The accompanying condensed consolidated financial statements should be read in conjunction with the audited financial statements and related notes thereto for the year ended December 31, 2019 contained in the Company’s Annual Report on Form 10-K filed with the SEC on March 11, 2020.

Risks and Uncertainties

In late 2019, SARS-CoV-2, a novel strain of coronavirus which causes the disease COVID-19, was reported in China, and in March 2020 the World Health Organization declared it a pandemic. 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 is in its early stages and information is rapidly evolving. The Company's customers which include hospitals and medical centers are diverting resources to treat COVID-19 patients and deferring elective surgical procedures, both of which are likely to impact the Company's revenues as well as receivable collections and inventory obsolescence. Furthermore, capital markets and economies worldwide have also been negatively impacted by the COVID-19 pandemic, and it is likely that it could cause a local and/or global recession. Such economic disruption could have a material adverse effect on the Company's business. Policymakers around the globe have responded with fiscal policy actions to support the healthcare industry and economy as a whole. The magnitude and overall effectiveness of these actions remains uncertain.

The severity of the impact of the COVID-19 pandemic on the Company's business will depend on a number of factors, including, but not limited to, the duration and severity of the pandemic and the extent and severity of the impact on the Company's customers, all of which are uncertain and cannot be predicted. The Company's future results of operations and liquidity could be adversely impacted by delays in payments of outstanding receivable amounts beyond normal payment terms, supply chain disruptions and uncertain demand, excess and obsolete inventory, and the impact of any initiatives and programs that the Company may undertake to address financial and operations challenges faced by its customers.

Use of Estimates

The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Significant accounting estimates and management judgments reflected in the consolidated financial statements include: fair value of assets and liabilities; analysis of the allowance for doubtful accounts; inventory valuation; valuation of deferred tax assets, including related valuation allowances; stock-based compensation; and useful lives of long lived assets. Estimates are based on historical experience, where applicable and other assumptions believed to be reasonable by the management. Actual results could differ from those estimates.

Significant Accounting Policies

The Company’s significant accounting policies are disclosed in the Company’s Annual Report on Form 10-K for the year ended December 31, 2019. There have been no material changes to these accounting policies.

JOBS Act Accounting Election

As an emerging growth company under the Jumpstart Our Business Startups Act of 2012 (the "JOBS Act"), the Company is eligible to take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies. The Company has elected to take advantage of the extended transition period for adopting new or revised accounting standards that have different effective dates for public and private companies. Those standards apply to companies until the earlier of the date that it is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, these condensed consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. The Company continues to be an emerging growth company until December 31, 2023, unless one of the following occurs: (i) if the Company's total annual gross revenues are $1.07 billion or more; or (ii) the Company has issued more than $1.0 billion in non-convertible debt in the past three years; or (iii) the Company becomes a "large accelerated filer," as defined in Rule 12b-2 of the Exchange Act.

Segments

The Company manages and operates as one reportable segment. The Company derives substantially all of its revenue from sales to customers in the U.S. Revenue by geography is based on billing address of the customer. No single country outside the U.S. accounts for more than 10% of the total revenue during the periods presented. Long-lived assets held outside the U.S. are immaterial. The table below summarizes the Company's revenue by geography:


	Three Months Ended March 31,
	2020		2019
	(in thousands)
United States	$	15,297	$	13,450
International	1,524		1,541
	$	16,821	$	14,991

Adoption of New Revenue Recognition Standard

The Company adopted the new revenue recognition standards ("ASC 606") using the modified retrospective method effective for the year ended December 31, 2019. This approach was applied to all contracts that were not completed as of January 1, 2019. As an emerging growth company that elected to take advantage of the JOBS Act accounting election, the Company was not required to adopt the new revenue standard in the interim reporting periods on the year of adoption and is not required, and intends not, to revise its 2019 interim periods which were reported under previous revenue recognition standards ("ASC 605"). The adoption of ASC 606 did not result in a material impact on the Company’s condensed consolidated financial statements and no adjustment was made to the opening balance of accumulated deficit at January 1, 2019. ASC 606's core principle is that a reporting entity will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. As it relates to product sales where the Company's sales representative delivers the product at the point of implantation at hospital or medical facilities, which represents majority of the Company's revenue, the Company continues to recognize the revenue upon completion of the procedure and authorization by the customer, net of rebates and price discounts. As it relates to sale of products through distributors and hospitals where product is ordered in advance of the procedure, the Company continues to recognize the revenue upon shipments to the customers, net of rebates and price discounts. Additionally, ASC 606 requires the capitalization of costs to obtain a contract, primarily sales commissions, and amortization of these costs over the contract period or estimated customer life. The Company’s sales commissions paid to its sales representatives is generally based on the surgeries performed. The Company applied the practical expedient that permits an entity to expense the cost to obtain a contract as incurred when the expected amortization is one year or less. As such, the Company recognize sales commission as expense when incurred.

The Company disaggregates revenues from contracts with customers into geographical regions. The Company determined that disaggregating revenue into these categories depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by regional economic factors. For information regarding revenue by geography, refer to Segments in “Note 2 - Summary of Significant Accounting Policies" in the accompanying Notes to Condensed Consolidated Financial Statements.

Recently Issued Accounting Standards Not Yet Effective

In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2016-02, Leases (Topic 842), which requires that lessee's recognize a right-of-use asset and a lease liability for all leases with lease terms greater than twelve months in the balance sheet. A lease liability is a lessee's obligation to make lease payments arising from a lease, measured on a discounted basis; and a right-of-use asset is an asset that represents the lessee’s right to use, or control use of, a specified asset for the lease term for all leases (with the exception of short-term leases) at the adoption date. In July 2018, the FASB issued ASU 2018-10 and ASU 2018-11, which provides clarification on the narrow aspects of the guidance and provide an additional transition method to adopt the new leases standard. The new transition method allows an entity to recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. In March 2019, the FASB issued ASU 2019-01, which provides clarification on implementation issues associated with adopting ASU 2016-02. The new leases standard must be adopted using a modified retrospective transition method and allows for the application of the new guidance at the beginning of the earliest comparative period presented or at the adoption date. In November 2019, the FASB issued ASU 2019-10, which revised the mandatory effective dates of the new lease standard. For public companies, the new guidance remained 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, 2020 and interim periods within fiscal years beginning after December 15, 2021. Early adoption is still permitted for any interim or annual financial statements not yet issued.

As an emerging growth company, the new lease standard is now effective for the Company for the fiscal year ending December 31, 2021 and interim periods within fiscal year ending December 31, 2022. The Company is currently evaluating the impact of this standard on its consolidated financial statements including the timing of its adoption. The Company anticipates to elect several practical expedients that permit the Company not to reassess (1) whether a contract is or contains a lease, (2) the classification of existing leases, and (3) whether previously capitalized initial direct costs would qualify for capitalization under ASC 842. The Company expects that the adoption of this new standard will have a material impact on its balance sheet. The most significant impact would be the recognition of operating lease right-of-use assets and liability. The standard is not expected to have a material impact to the Company's consolidated statements of income and cash flows.

In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. FASB issued ASU 2019-05 in May 2019 and ASU 2019-08 in November 2019 for codification improvements of Topic 326. The new standard revises the accounting requirements related to the measurement of credit losses and will require organizations to measure all expected credit losses for financial assets based on historical experience, current conditions and reasonable and supportable forecasts about collectability. Assets must be presented in the financial statements at the net amount expected to be collected. In November 2019, the FASB issued ASU 2019-10, which defers the effective date of ASU 2016-13 for public companies that are eligible to be smaller reporting companies and all other companies, to fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. In February 2020, the FASB issued ASU 2020-02, which provides guidance regarding methodologies, documentation, and internal controls related to expected credit losses. The Company is currently evaluating the impact of this standard on its consolidated financial statements, but do not expect the standard will have a material impact on the Company's consolidated financial statements.

In June 2018, the FASB issued ASU 2018-07, Improvements to Non-employee Share-Based Payment Accounting. ASU 2018-07 expands the scope of Topic 718, Compensation-Stock Compensation, to include share-based payments issued to non-employees for goods or services. Consequently, the accounting for share-based payments to non-employees and employees will be substantially aligned. ASU 2018-07 supersedes Subtopic 505-50, Equity-Based Payments to Non-Employees. For public business entities, the amendments are effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. For all other entities, the amendments are effective for fiscal years beginning after December 15, 2019, and interim periods within fiscal years beginning after December 15, 2020. Early adoption is permitted, but no earlier than a company’s adoption date of ASC 606. The Company is currently assessing the impact of this new guidance but does not expect it to have a material impact on its consolidated financial statements, and anticipates adopting the standard for the fiscal year ending December 31, 2020.

In August 2018, the FASB issued ASU 2018-13, Fair Value Measurements, which eliminates, adds or modifies certain disclosure requirements for fair value measurements. Entities will no longer be required to disclose the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, but will be required to disclose the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. This 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 is currently assessing the impact of this new guidance but does not expect it to have a material impact on its consolidated financial statements, and anticipates adopting the standard for the fiscal year ending December 31, 2020.

Marketable Securities

3 Months Ended

Mar. 31, 2020

Investments, Debt and Equity Securities [Abstract]

Marketable Securities

All of the Company's marketable securities were available-for-sale and were classified based on their maturities. Marketable securities with remaining maturities at the date of purchase of three months or less are classified as cash equivalents. Short term investments are securities that original maturity or remaining maturity is greater than three months and not more than twelve months. Long-term investments are securities for which the original maturity or remaining maturity is greater than twelve months.

The table below summarizes the marketable securities:


	March 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses		Aggregate Fair Value
	(in thousands)
Money market funds	$	62,194	$	—	$	—	$	62,194

Cash equivalents	62,194		—		—		62,194

U.S. treasury securities	52,025		323		—		52,348
Corporate bonds	11,816		4		(47)		11,773
Commercial paper	13,252		—		—		13,252
Short-term investments	77,093		327		(47)		77,373

Corporate bonds	1,278		—		(4)		1,274
Long-term investments	1,278		—		(4)		1,274
Total marketable securities	$	140,565	$	327	$	(51)	$	140,841


	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 March 31, 2020 and December 31, 2019 mature in April 2021.

Unrealized gains and losses on available-for-sale securities are recorded in accumulated other comprehensive income (loss) on the condensed consolidated balance sheets. The Company evaluates its investments to assess whether those in unrealized loss positions are other-than-temporarily impaired. The Company considers impairments to be other-than-temporary if it is related to deterioration in credit risk or if it is likely the Company will sell the securities before the recovery of their cost basis. The Company did not identify any of its marketable securities as other-than-temporarily impaired as of March 31, 2020 and December 31, 2019.

Fair Value Measurement

3 Months Ended

Mar. 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 or liabilities that required fair value hierarchy measurements and disclosures for the periods presented.

The table below summarizes the fair value of the Company’s marketable securities measured at fair value on a recurring basis based on the three-tier fair value hierarchy:







	March 31, 2020
	Level 1		Level 2		Level 3		Total
	(in thousands)
Marketable securities
Money market funds	$	62,194	$	—	$	—	$	62,194
U.S. treasury securities	52,348		—		—		52,348
Corporate bonds	—		13,047		—		13,047
Commercial paper	—		13,252		—		13,252
Total marketable securities	$	114,542	$	26,299	$	—	$	140,841

	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

3 Months Ended

Mar. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Balance Sheet Components

Inventory

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

Property and Equipment, net:


	March 31, 2020		December 31, 2019
	(in thousands)
Machinery and equipment	$	4,999	$	4,613
Construction in progress	1,994		1,854
Computer and office equipment	605		598
Leasehold improvements	502		497
Furniture and fixtures	189		187
	8,289		7,749
Less: Accumulated depreciation and amortization	(4,020)		(3,795)
	$	4,269	$	3,954

Depreciation expense was $0.2 million and $0.2 million for the three months ended March 31, 2020 and 2019, respectively.

Accrued Liabilities and Other:


	March 31, 2020		December 31, 2019
	(in thousands)
Accrued compensation and related expenses	$	4,717	$	7,274
Accrued litigation expense	3,200		3,200
Accrued professional services	571		392
Others	796		739
	$	9,284	$	11,605

Commitments and Contingencies

3 Months Ended

Mar. 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 2026. Further, the Company also leases vehicles under operating lease arrangements for certain of its sales personnel in Europe which expire various times in 2020 to 2023.

Rent expense is recorded over the lease terms on a straight-line basis. Rent expense charged to operations under operating leases was $0.3 million and $0.3 million for three months ended March 31, 2020 and 2019, respectively.

The table below summarizes aggregate future minimum lease payments under all leases as of March 31, 2020:


Year ending December 31,	(in thousands)
2020 (remaining nine months)	$	850
2021	1,024
2022	952
2023	866
2024	867
Thereafter	363
	$	4,922

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 $0.2 million and $0.4 million as of March 31, 2020 and December 31, 2019, respectively.

Legal Proceedings

On February 6, 2019, a putative class action captioned Eric B. Fromer Chiropractic, Inc. ("Plaintiff") v. SI-BONE, Inc. (Civil Action No. 5:19-cv-633-SVK), was filed in the U.S. District Court, Northern District of California. The 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. On December 23, 2019 the parties filed a joint stipulation of dismissal of the case in the District Court in the Northern District of California 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.

As this lawsuit is being resolved through a negotiated settlement and class resolution process, the Company believes that it will incur a loss associated with resolution of the claims against it. The Company has accrued litigation expense of $3.2 million during the year ended December 31, 2019 within general and administrative expenses in the consolidated financial statements. The accrual reflects the estimable and probable costs that the Company may incur based on estimated claims submitted by members of the settlement class, as defined in the Settlement Agreement. As of March 31, 2020, the total accrued litigation expense remained the same as of December 31, 2019. The final disposition of the lawsuit may result in a loss in excess of the aggregate recorded amount.

Indemnification

The Company enters into standard indemnification arrangements in the ordinary course of business. Pursuant to these arrangements, the Company indemnifies, holds harmless, and agrees to reimburse the indemnified parties for losses suffered or incurred by the indemnified party, in connection with any trade secret, copyright, patent or other intellectual property infringement claim by any third-party with respect to the Company’s technology. The term of these indemnification agreements is generally perpetual. The maximum potential amount of future payments the Company could be required to make under these agreements is not determinable because it involves claims that may be made against the Company in the future, but have not yet been made.

The Company has entered into indemnification agreements with its directors and officers that may require the Company to indemnify its directors and officers against liabilities that may arise by reason of their status or service as directors or officers, other than liabilities arising from willful misconduct of the individual.

The Company has not incurred costs to defend lawsuits or settle claims related to these indemnification agreements. No liability associated with such indemnifications has been recorded to date.

Borrowings

3 Months Ended

Mar. 31, 2020

Debt Disclosure [Abstract]

Borrowings

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


	March 31, 2020		December 31, 2019
	(in thousands)
Principal outstanding	$	40,000	$	40,000
Less: Unamortized debt issuance costs	(712)		(777)
Outstanding debt, net of debt issuance costs	$	39,288	$	39,223
Classified as:
Current portion of long-term borrowings	$	8,731	$	4,358
Long-term borrowings	$	30,557	$	34,865

The outstanding debt is related to a term loan entered by the Company with Biopharma Credit Investments IV Sub LP, or Pharmakon, in October 2017 for total loan proceeds of $40.0 million. The term loan includes an interest-only period for 35 months through September 2020 and is then repaid in equal quarterly principal payments plus interest through December 2022 and carries a fixed interest rate of 11.5%. The term loan includes a pre-payment fee equal to the remaining interest due for the first 30 months of the agreement if it is prepaid within the first 30 months, a 2% prepayment penalty for months 31-48, and a 1% penalty for months 49-60. The loan is a senior obligation secured with a blanket first lien on the assets of the Company. The effective interest rate for the three months ended March 31, 2020 and 2019 was 12.3% and 12.2%, respectively.

The table below summarizes annual future minimum principal payments under the loan agreement as of March 31, 2020:


Year ending December 31,	(in thousands)
2020 (remaining nine months)	$	4,444
2021	17,778
2022	17,778
Total future minimum payments	40,000
Less: Amount representing debt issuance costs	(712)
Long-term borrowings	$	39,288

The term loan requires the Company to maintain a minimum cash balance of $5.0 million and to meet either minimum net sales or trailing 12-month consolidated earnings before interest, taxes, depreciation, and amortization targets. The Company was in compliance with all debt covenants as of March 31, 2020. Due to uncertainties surrounding the impact of the COVID-19 pandemic, there is a substantial risk that the Company may not meet the remaining minimum net sales or the trailing 12-month consolidated EBITDA targets in future quarters. If the Company is not in compliance with these requirements, the loan may become due immediately at Pharmakon's option.

Stock-Based Incentive Compensation Plans

3 Months Ended

Mar. 31, 2020

Share-based Payment Arrangement [Abstract]

Stock-Based Incentive Compensation Plans

Stock Options

The table below summarizes the stock option activity for the three months ended March 31, 2020:


	Number of Shares	Weighted- Average Exercise Price
Outstanding as of December 31, 2019	2,718,971	$8.02
Granted	26,236	17.31
Exercised	(43,334)	4.03
Canceled and forfeited	(1,319)	12.87
Outstanding as of March 31, 2020	2,700,554	8.17

As of March 31, 2020, there was $5.0 million of unrecognized compensation cost related to stock options granted. These costs are expected to be recognized over a period of approximately 2.4 years.

The table below summarizes the weighted average grant date fair value per share and the assumptions used to estimate the grant date fair value of the stock options granted during the respective periods using the Black-Scholes option-pricing model:


	Three Months Ended March 31,
	2020					2019
Weighted average grant date fair value per share	$8.37					$10.40
Expected term (years)	5.5	to	7.0	5.0	to	7.0
Expected volatility	46.74%	to	47.20%	42.00%	to	47.00%
Risk-free interest rate	1.56%	to	1.64%	2.52%	to	2.59%
Dividend yield	—%					—%

Early Exercise of Unvested Stock Options

Early exercises of stock options are subject to a right of repurchase by the Company of any unvested shares. The repurchase rights lapse over the original vesting period of the options. The Company accounts for the cash received in consideration for the early exercised options as a liability included in accrued liabilities, which is then reclassified to stockholders’ equity as the options vest. As of March 31, 2020 and December 31, 2019, the Company had a total of 15,567 and 21,404 shares of common stock, respectively, subject to repurchase under the 2008 Stock Option Plan and $0.1 million and $0.1 million, respectively, of associated liabilities for the repurchase.

Restricted Stock Units

The table below summarizes restricted stock units activity for the three months ended March 31, 2020:


	Number of Shares	Weighted Average Grant Date Fair Value
Outstanding as of December 31, 2019	543,041	$19.72
Granted	868,683	20.43
Vested	(63,938)	21.00
Canceled and forfeited	(5,575)	18.43
Outstanding as of March 31, 2020	1,342,211	20.13

As of March 31, 2020, there was a total unrecognized compensation cost of $23.4 million related to the restricted stock units granted. These costs are expected to be recognized over a period of approximately 3.5 years.

Employee Stock Purchase Plan

The Company's 2018 Employee Stock Purchase Plan (the "ESPP") allows eligible employees to purchase shares of the Company's common stock through payroll deductions at the price equal to 85% of the lesser of the fair market value of the stock as of the first date or the ending date of each six month offering period. The offer period generally commence in May and November. As of March 31, 2020 and December 31, 2019, total accumulated ESPP related employee payroll deductions amounted to $0.9 million and $0.2 million, respectively, which were included within accrued compensation and related expenses in the condensed consolidated balance sheets. On March 26, 2020, the Company's Board of Directors approved the amendment of the terms of future offerings under the ESPP, among other things, to provide that the offering set to commence in May 2020 be twelve months in duration and consist of two purchase periods, provide for automatic enrollment in a new offering, and increase the maximum number of shares that may be purchased on any single purchase date.

Stock-Based Compensation

The table below presents the detail of stock-based compensation expense amounts included in the condensed consolidated statements of operations:


	Three Months Ended March 31,
	2020		2019
	(in thousands)
Cost of goods sold	$	71	$	42
Sales and marketing	1,141		670
Research and development	240		96
General and administrative	1,170		1,063
	$	2,622	$	1,871

Net Loss Per Share of Common Stock

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

Net Loss Per Share of Common Stock

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


	Three Months Ended March 31,
	2020		2019
	(in thousands, except share and per share data)
Net loss	$	(12,772)	$	(9,345)

Weighted-average shares used to compute basic and diluted net loss per share	27,252,409		24,390,648

Net loss per share, basic and diluted	$	(0.47)	$	(0.38)

Because the Company has reported a net loss in all periods presented, outstanding stock options, restricted stock units, shares subject to repurchase, ESPP purchase rights and common stock warrants are anti-dilutive and therefore diluted net loss per common share is the same as basic net loss per common share for the periods presented. The following anti-dilutive common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented:


	Three Months Ended March 31,
	2020	2019
Stock options	2,700,554	3,047,130
Restricted stock units	1,342,211	531,669
Shares subject to repurchase	15,567	59,193
ESPP purchase rights	65,442	—
Common stock warrants	118,122	118,122
	4,241,896	3,756,114

Related Party Transactions	3 Months Ended
Related Party Transactions	Mar. 31, 2020
Related Party Transactions [Abstract]
Related Party Transactions	Related Party Transaction On February 24, 2020, the Company entered into a joint development agreement (the "Development Agreement") with SeaSpine Orthopedics Corporation ("SeaSpine") to develop a next generation device for sacropelvic fixation. Mr. Keith Valentine, who serves as the President, Chief Executive Officer and a member of the board of directors of SeaSpine, also serves as a member of the Company's Board of Directors since August 2015. Pursuant to the development plan, SeaSpine shall use reasonable efforts to assist in the development of the potential product offering, including licensing certain existing intellectual property to be incorporated into such product. Under the terms of the Development Agreement, the Company agreed to make monthly payments to SeaSpine to reimburse for full time resources employed by SeaSpine responsible to conduct the development activities. For the three months ended March 31, 2020, the Company expensed $22,000 of the reimbursement charges from SeaSpine, which was recorded within research and development expense in the condensed consolidated statement of operations. The outstanding liability to SeaSpine as of March 31, 2020 amounted to $10,000, recorded within accrued liabilities and other in the condensed consolidated balance sheet. Certain intellectual property developed pursuant to the project plan will be owned by the Company, certain intellectual property developed pursuant to the project plan will be owned by SeaSpine, and other intellectual property developed pursuant to the project plan will be jointly owned by SeaSpine and the Company. The Company also agreed to provide SeaSpine a royalty-free, worldwide, perpetual, non-exclusive license of certain of the Company's intellectual property incorporated into the product to be developed. The Company also agreed to pay SeaSpine a product royalty, in an amount specified in the Development Agreement, for each resulting product sold for a period of 10 years beginning on the initial market launch. The term of the Development Agreement shall continue until the expiration of all royalty terms, unless earlier terminated by either party, as provided for by the Development Agreement.

Income Taxes	3 Months Ended
Income Taxes	Mar. 31, 2020
Income Tax Disclosure [Abstract]
Income Taxes	Income TaxesIn determining quarterly provisions for income taxes, the Company uses the annual estimated effective tax rate applied to the actual year-to-date profit or loss, adjusted for discrete items arising in that quarter. The Company updates its estimate of its annual effective tax rate at the end of each quarterly period. The estimate takes into account annual forecasted income (loss) before income taxes, the geographic mix of income (loss) before income taxes and any significant permanent tax items. The Company did not have provision for income taxes for the three months ended March 31, 2020 and 2019. The Company continues to maintain a full valuation allowance against its net deferred tax assets due to the uncertainty surrounding realization of such assets. The Company accounts for the uncertainty in income taxes by utilizing a comprehensive model for the recognition, measurement, presentation and disclosure in financial statements of any uncertain tax positions that have been taken or are expected to be taken on an income tax return. There had been no changes in the estimated uncertain tax benefits recorded as of December 31, 2019.

Subsequent Events	3 Months Ended
Subsequent Events	Mar. 31, 2020
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events Impact of COVID-19 OutbreakAs discussed in Note 2 - "Risk and Uncertainties" in the accompanying Notes to Condensed Consolidated Financial Statements, 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 is in its incipient stages and information is rapidly evolving. As of the date of issuance of the unaudited condensed consolidated financial statements, the Company is not aware of any specific event or circumstance that would require the Company to update its estimates, judgments or revise the carrying value of its assets or liabilities. These estimates may change, as new events occur and additional information is obtained, and are recognized in the consolidated financial statements as soon as they become known. Actual results could differ from those estimates and any such differences may be material to the Company's consolidated financial statements.

Summary of Significant Accounting Policies (Policies)	3 Months Ended
Summary of Significant Accounting Policies (Policies)	Mar. 31, 2020
Accounting Policies [Abstract]
Basis of Presentation	The accompanying unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States of America (“U.S. GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (“SEC”) regarding interim financial reporting. As permitted under those rules, certain footnotes or other financial information that are normally required by U.S. GAAP have been condensed or omitted, and accordingly the balance sheet as of December 31, 2019 has been derived from the audited consolidated financial statements at that date but does not include all of the information required by GAAP for complete financial statements.
Principles of Consolidation	These unaudited interim condensed consolidated financial statements have been prepared on the same basis as the Company’s annual financial statements and, in the opinion of management, reflect all adjustments that are necessary for a fair statement of the Company’s consolidated financial information. The results of operations for the three months ended March 31, 2020 are not necessarily indicative of the results to be expected for the year ending December 31, 2020 or for any other interim period or for any other future year.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the date of the financial statements and the reported amounts of revenue and expenses during the reporting period. Significant accounting estimates and management judgments reflected in the consolidated financial statements include: fair value of assets and liabilities; analysis of the allowance for doubtful accounts; inventory valuation; valuation of deferred tax assets, including related valuation allowances; stock-based compensation; and useful lives of long lived assets. Estimates are based on historical experience, where applicable and other assumptions believed to be reasonable by the management. Actual results could differ from those estimates.
JOBS Act Accounting Election	JOBS Act Accounting Election As an emerging growth company under the Jumpstart Our Business Startups Act of 2012 (the "JOBS Act"), the Company is eligible to take advantage of certain exemptions from various reporting requirements that are applicable to other public companies that are not emerging growth companies. The Company has elected to take advantage of the extended transition period for adopting new or revised accounting standards that have different effective dates for public and private companies. Those standards apply to companies until the earlier of the date that it is (i) no longer an emerging growth company or (ii) affirmatively and irrevocably opt out of the extended transition period provided in the JOBS Act. As a result, these condensed consolidated financial statements may not be comparable to companies that comply with the new or revised accounting pronouncements as of public company effective dates. The Company continues to be an emerging growth company 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	SegmentsThe Company manages and operates as one reportable segment.
Adoption of New Revenue Recognition Standard	Adoption of New Revenue Recognition Standard The Company adopted the new revenue recognition standards ("ASC 606") using the modified retrospective method effective for the year ended December 31, 2019. This approach was applied to all contracts that were not completed as of January 1, 2019. As an emerging growth company that elected to take advantage of the JOBS Act accounting election, the Company was not required to adopt the new revenue standard in the interim reporting periods on the year of adoption and is not required, and intends not, to revise its 2019 interim periods which were reported under previous revenue recognition standards ("ASC 605"). The adoption of ASC 606 did not result in a material impact on the Company’s condensed consolidated financial statements and no adjustment was made to the opening balance of accumulated deficit at January 1, 2019. ASC 606's core principle is that a reporting entity will recognize revenue when it transfers promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. As it relates to product sales where the Company's sales representative delivers the product at the point of implantation at hospital or medical facilities, which represents majority of the Company's revenue, the Company continues to recognize the revenue upon completion of the procedure and authorization by the customer, net of rebates and price discounts. As it relates to sale of products through distributors and hospitals where product is ordered in advance of the procedure, the Company continues to recognize the revenue upon shipments to the customers, net of rebates and price discounts. Additionally, ASC 606 requires the capitalization of costs to obtain a contract, primarily sales commissions, and amortization of these costs over the contract period or estimated customer life. The Company’s sales commissions paid to its sales representatives is generally based on the surgeries performed. The Company applied the practical expedient that permits an entity to expense the cost to obtain a contract as incurred when the expected amortization is one year or less. As such, the Company recognize sales commission as expense when incurred. The Company disaggregates revenues from contracts with customers into geographical regions. The Company determined that disaggregating revenue into these categories depicts how the nature, amount, timing and uncertainty of revenue and cash flows are affected by regional economic factors. For information regarding revenue by geography, refer to Segments in “Note 2 - Summary of Significant Accounting Policies" in the accompanying Notes to Condensed Consolidated Financial Statements.
Recent Accounting Standards	Recently Issued Accounting Standards Not Yet Effective In February 2016, the Financial Accounting Standards Board (“FASB”) issued Accounting Standards Update ("ASU") 2016-02, Leases (Topic 842), which requires that lessee's recognize a right-of-use asset and a lease liability for all leases with lease terms greater than twelve months in the balance sheet. A lease liability is a lessee's obligation to make lease payments arising from a lease, measured on a discounted basis; and a right-of-use asset is an asset that represents the lessee’s right to use, or control use of, a specified asset for the lease term for all leases (with the exception of short-term leases) at the adoption date. In July 2018, the FASB issued ASU 2018-10 and ASU 2018-11, which provides clarification on the narrow aspects of the guidance and provide an additional transition method to adopt the new leases standard. The new transition method allows an entity to recognize a cumulative-effect adjustment to the opening balance of retained earnings in the period of adoption. In March 2019, the FASB issued ASU 2019-01, which provides clarification on implementation issues associated with adopting ASU 2016-02. The new leases standard must be adopted using a modified retrospective transition method and allows for the application of the new guidance at the beginning of the earliest comparative period presented or at the adoption date. In November 2019, the FASB issued ASU 2019-10, which revised the mandatory effective dates of the new lease standard. For public companies, the new guidance remained 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, 2020 and interim periods within fiscal years beginning after December 15, 2021. Early adoption is still permitted for any interim or annual financial statements not yet issued. As an emerging growth company, the new lease standard is now effective for the Company for the fiscal year ending December 31, 2021 and interim periods within fiscal year ending December 31, 2022. The Company is currently evaluating the impact of this standard on its consolidated financial statements including the timing of its adoption. The Company anticipates to elect several practical expedients that permit the Company not to reassess (1) whether a contract is or contains a lease, (2) the classification of existing leases, and (3) whether previously capitalized initial direct costs would qualify for capitalization under ASC 842. The Company expects that the adoption of this new standard will have a material impact on its balance sheet. The most significant impact would be the recognition of operating lease right-of-use assets and liability. The standard is not expected to have a material impact to the Company's consolidated statements of income and cash flows. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments. FASB issued ASU 2019-05 in May 2019 and ASU 2019-08 in November 2019 for codification improvements of Topic 326. The new standard revises the accounting requirements related to the measurement of credit losses and will require organizations to measure all expected credit losses for financial assets based on historical experience, current conditions and reasonable and supportable forecasts about collectability. Assets must be presented in the financial statements at the net amount expected to be collected. In November 2019, the FASB issued ASU 2019-10, which defers the effective date of ASU 2016-13 for public companies that are eligible to be smaller reporting companies and all other companies, to fiscal years beginning after December 15, 2022, including interim periods within those fiscal years. In February 2020, the FASB issued ASU 2020-02, which provides guidance regarding methodologies, documentation, and internal controls related to expected credit losses. The Company is currently evaluating the impact of this standard on its consolidated financial statements, but do not expect the standard will have a material impact on the Company's consolidated financial statements. In June 2018, the FASB issued ASU 2018-07, Improvements to Non-employee Share-Based Payment Accounting. ASU 2018-07 expands the scope of Topic 718, Compensation-Stock Compensation, to include share-based payments issued to non-employees for goods or services. Consequently, the accounting for share-based payments to non-employees and employees will be substantially aligned. ASU 2018-07 supersedes Subtopic 505-50, Equity-Based Payments to Non-Employees. For public business entities, the amendments are effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. For all other entities, the amendments are effective for fiscal years beginning after December 15, 2019, and interim periods within fiscal years beginning after December 15, 2020. Early adoption is permitted, but no earlier than a company’s adoption date of ASC 606. The Company is currently assessing the impact of this new guidance but does not expect it to have a material impact on its consolidated financial statements, and anticipates adopting the standard for the fiscal year ending December 31, 2020. In August 2018, the FASB issued ASU 2018-13, Fair Value Measurements, which eliminates, adds or modifies certain disclosure requirements for fair value measurements. Entities will no longer be required to disclose the amount of and reasons for transfers between Level 1 and Level 2 of the fair value hierarchy, but will be required to disclose the range and weighted average used to develop significant unobservable inputs for Level 3 fair value measurements. This 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 is currently assessing the impact of this new guidance but does not expect it to have a material impact on its consolidated financial statements, and anticipates adopting the standard for the fiscal year ending December 31, 2020.

Summary of Significant Accounting Policies (Tables)

3 Months Ended

Mar. 31, 2020

Accounting Policies [Abstract]

Schedule of Revenue by Geography

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


	Three Months Ended March 31,
	2020		2019
	(in thousands)
United States	$	15,297	$	13,450
International	1,524		1,541
	$	16,821	$	14,991

Marketable Securities (Tables)

3 Months Ended

Mar. 31, 2020

Investments, Debt and Equity Securities [Abstract]

Schedule of Marketable Securities

The table below summarizes the marketable securities:


	March 31, 2020
	Amortized Cost		Unrealized Gains		Unrealized Losses		Aggregate Fair Value
	(in thousands)
Money market funds	$	62,194	$	—	$	—	$	62,194

Cash equivalents	62,194		—		—		62,194

U.S. treasury securities	52,025		323		—		52,348
Corporate bonds	11,816		4		(47)		11,773
Commercial paper	13,252		—		—		13,252
Short-term investments	77,093		327		(47)		77,373

Corporate bonds	1,278		—		(4)		1,274
Long-term investments	1,278		—		(4)		1,274
Total marketable securities	$	140,565	$	327	$	(51)	$	140,841


	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)

3 Months Ended

Mar. 31, 2020

Fair Value Disclosures [Abstract]

Schedule of Marketable Securities Measured at Fair Value on Recurring Basis

The table below summarizes the fair value of the Company’s marketable securities measured at fair value on a recurring basis based on the three-tier fair value hierarchy:







	March 31, 2020
	Level 1		Level 2		Level 3		Total
	(in thousands)
Marketable securities
Money market funds	$	62,194	$	—	$	—	$	62,194
U.S. treasury securities	52,348		—		—		52,348
Corporate bonds	—		13,047		—		13,047
Commercial paper	—		13,252		—		13,252
Total marketable securities	$	114,542	$	26,299	$	—	$	140,841

	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)

3 Months Ended

Mar. 31, 2020

Organization, Consolidation and Presentation of Financial Statements [Abstract]

Schedule of Property and Equipment, Net

Property and Equipment, net:


	March 31, 2020		December 31, 2019
	(in thousands)
Machinery and equipment	$	4,999	$	4,613
Construction in progress	1,994		1,854
Computer and office equipment	605		598
Leasehold improvements	502		497
Furniture and fixtures	189		187
	8,289		7,749
Less: Accumulated depreciation and amortization	(4,020)		(3,795)
	$	4,269	$	3,954

Schedule of Accrued Liabilities and Other

Accrued Liabilities and Other:


	March 31, 2020		December 31, 2019
	(in thousands)
Accrued compensation and related expenses	$	4,717	$	7,274
Accrued litigation expense	3,200		3,200
Accrued professional services	571		392
Others	796		739
	$	9,284	$	11,605

Commitments and Contingencies (Tables)

3 Months Ended

Mar. 31, 2020

Commitments and Contingencies Disclosure [Abstract]

Schedule of Aggregate Future Minimum Lease Payments

The table below summarizes aggregate future minimum lease payments under all leases as of March 31, 2020:


Year ending December 31,	(in thousands)
2020 (remaining nine months)	$	850
2021	1,024
2022	952
2023	866
2024	867
Thereafter	363
	$	4,922

Borrowings (Tables)

3 Months Ended

Mar. 31, 2020

Debt Disclosure [Abstract]

Schedule of Outstanding Borrowings

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


	March 31, 2020		December 31, 2019
	(in thousands)
Principal outstanding	$	40,000	$	40,000
Less: Unamortized debt issuance costs	(712)		(777)
Outstanding debt, net of debt issuance costs	$	39,288	$	39,223
Classified as:
Current portion of long-term borrowings	$	8,731	$	4,358
Long-term borrowings	$	30,557	$	34,865

Schedule of Annual Future Minimum Principal Payments Under Loan Agreements

The table below summarizes annual future minimum principal payments under the loan agreement as of March 31, 2020:


Year ending December 31,	(in thousands)
2020 (remaining nine months)	$	4,444
2021	17,778
2022	17,778
Total future minimum payments	40,000
Less: Amount representing debt issuance costs	(712)
Long-term borrowings	$	39,288

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02.22)
-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 45
-Paragraph 1A
-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28541-108399

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

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 235
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.4-08.(e),(f))
-URI http://asc.fasb.org/extlink&oid=26873400&loc=d3e23780-122690

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
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-URI http://asc.fasb.org/extlink&oid=114775744&loc=d3e28551-108399

Reference 6: http://fasb.org/us-gaap/role/ref/legacyRef
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-Topic 505
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-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21521-112644

Reference 7: http://fasb.org/us-gaap/role/ref/legacyRef
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-Name Accounting Standards Codification
-Topic 505
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-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21538-112644

Reference 8: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 835
-SubTopic 30
-Section 55
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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
-Publisher FASB
-Name Accounting Standards Codification
-Topic 505
-SubTopic 10
-Section 50
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-URI http://asc.fasb.org/extlink&oid=109259400&loc=d3e21475-112644

+ Details

Stock-Based Incentive Compensation Plans (Tables)

3 Months Ended

Mar. 31, 2020

Share-based Payment Arrangement [Abstract]

Schedule of Stock Option Activity Under Stock Option Plan

The table below summarizes the stock option activity for the three months ended March 31, 2020:


	Number of Shares	Weighted- Average Exercise Price
Outstanding as of December 31, 2019	2,718,971	$8.02
Granted	26,236	17.31
Exercised	(43,334)	4.03
Canceled and forfeited	(1,319)	12.87
Outstanding as of March 31, 2020	2,700,554	8.17

Schedule of Valuation Assumptions Related to Stock Option Awards


	Three Months Ended March 31,
	2020					2019
Weighted average grant date fair value per share	$8.37					$10.40
Expected term (years)	5.5	to	7.0	5.0	to	7.0
Expected volatility	46.74%	to	47.20%	42.00%	to	47.00%
Risk-free interest rate	1.56%	to	1.64%	2.52%	to	2.59%
Dividend yield	—%					—%

Schedule of Restricted Stock Unit Activity

The table below summarizes restricted stock units activity for the three months ended March 31, 2020:


	Number of Shares	Weighted Average Grant Date Fair Value
Outstanding as of December 31, 2019	543,041	$19.72
Granted	868,683	20.43
Vested	(63,938)	21.00
Canceled and forfeited	(5,575)	18.43
Outstanding as of March 31, 2020	1,342,211	20.13

Schedule of Stock-Based Compensation

The table below presents the detail of stock-based compensation expense amounts included in the condensed consolidated statements of operations:


	Three Months Ended March 31,
	2020		2019
	(in thousands)
Cost of goods sold	$	71	$	42
Sales and marketing	1,141		670
Research and development	240		96
General and administrative	1,170		1,063
	$	2,622	$	1,871

Net Loss Per Share of Common Stock (Tables)

3 Months Ended

Mar. 31, 2020

Earnings Per Share [Abstract]

Schedule of Basic and Diluted Net Loss per Share

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


	Three Months Ended March 31,
	2020		2019
	(in thousands, except share and per share data)
Net loss	$	(12,772)	$	(9,345)

Weighted-average shares used to compute basic and diluted net loss per share	27,252,409		24,390,648

Net loss per share, basic and diluted	$	(0.47)	$	(0.38)

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

The following anti-dilutive common stock equivalents were excluded from the computation of diluted net loss per share for the periods presented:


	Three Months Ended March 31,
	2020	2019
Stock options	2,700,554	3,047,130
Restricted stock units	1,342,211	531,669
Shares subject to repurchase	15,567	59,193
ESPP purchase rights	65,442	—
Common stock warrants	118,122	118,122
	4,241,896	3,756,114

The Company and Nature of Business (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended			3 Months Ended
	Feb. 29, 2020	Jan. 31, 2020	Oct. 31, 2018	Mar. 31, 2020
IPO
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)			8,280,000
Public offering price (in dollars per share)			$ 15.00
Net proceeds from sale of stock			$ 113.4
Follow-on public offering
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)		2,490,053
Public offering price (in dollars per share)		$ 21.50
Net proceeds from sale of stock		$ 50.3
Public offering costs				$ 0.4
Follow-on public offering and secondary offering
Subsidiary, Sale of Stock [Line Items]
Number of shares in transaction, including shares in secondary offering		4,300,000
Underwriters option
Subsidiary, Sale of Stock [Line Items]
Number of shares issued (in shares)	645,000
Public offering price (in dollars per share)	$ 21.50
Net proceeds from sale of stock	$ 13.0
Secondary offering by selling shareholders
Subsidiary, Sale of Stock [Line Items]
Public offering costs				$ 0.2

Summary of Significant Accounting Policies - Segments (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2020 USD ($) segment	Mar. 31, 2019 USD ($)
Accounting Policies [Abstract]
Number of reportable segments \| segment	1
Number of operating segments \| segment	1
Disaggregation of Revenue [Line Items]
Revenue	$ 16,821	$ 14,991
United States
Disaggregation of Revenue [Line Items]
Revenue	15,297	13,450
International
Disaggregation of Revenue [Line Items]
Revenue	$ 1,524	$ 1,541

Marketable Securities (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Cash equivalents
Carrying Value	$ 62,194	$ 5,563
Short-term investments
Amortized Cost	77,093	81,291
Unrealized Gains	327	58
Unrealized Losses	(47)	(4)
Aggregate Fair Value	77,373	81,345
Long-term investments
Amortized Cost	1,278	1,278
Unrealized Gains	0	0
Unrealized Losses	(4)	0
Aggregate Fair Value	1,274	1,278
Total marketable securities, Amortized Cost	140,565	88,132
Total marketable securities, Unrealized Gains	327	58
Total marketable securities, Unrealized Losses	(51)	(4)
Total marketable securities, Aggregate Fair Value	140,841	88,186
Money market funds
Cash equivalents
Carrying Value	62,194	3,068
U.S. treasury securities
Short-term investments
Amortized Cost	52,025	67,051
Unrealized Gains	323	34
Unrealized Losses	0	(2)
Aggregate Fair Value	52,348	67,083
Corporate bonds
Short-term investments
Amortized Cost	11,816	9,075
Unrealized Gains	4	24
Unrealized Losses	(47)	(2)
Aggregate Fair Value	11,773	9,097
Long-term investments
Amortized Cost	1,278	1,278
Unrealized Gains	0	0
Unrealized Losses	(4)	0
Aggregate Fair Value	1,274	1,278
Commercial paper
Cash equivalents
Carrying Value		2,495
Short-term investments
Amortized Cost	13,252	5,165
Unrealized Gains	0	0
Unrealized Losses	0	0
Aggregate Fair Value	$ 13,252	$ 5,165

Fair Value Measurement - Marketable Securities Measured at Fair Value on Recurring Basis (Details) - Recurring - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Marketable securities
Marketable securities	$ 140,841	$ 88,186
Money market funds
Marketable securities
Marketable securities	62,194	3,068
U.S. treasury securities
Marketable securities
Marketable securities	52,348	67,083
Corporate bonds
Marketable securities
Marketable securities	13,047	10,375
Commercial paper
Marketable securities
Marketable securities	13,252	7,660
Level 1
Marketable securities
Marketable securities	114,542	70,151
Level 1 \| Money market funds
Marketable securities
Marketable securities	62,194	3,068
Level 1 \| U.S. treasury securities
Marketable securities
Marketable securities	52,348	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	26,299	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	13,047	10,375
Level 2 \| Commercial paper
Marketable securities
Marketable securities	13,252	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	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Property and Equipment, Net
Property and equipment, gross	$ 8,289		$ 7,749
Less: Accumulated depreciation and amortization	(4,020)		(3,795)
Property and equipment, net	4,269		3,954
Depreciation expense	200	$ 200
Machinery and equipment
Property and Equipment, Net
Property and equipment, gross	4,999		4,613
Construction in progress
Property and Equipment, Net
Property and equipment, gross	1,994		1,854
Computer and office equipment
Property and Equipment, Net
Property and equipment, gross	605		598
Leasehold improvements
Property and Equipment, Net
Property and equipment, gross	502		497
Furniture and fixtures
Property and Equipment, Net
Property and equipment, gross	$ 189		$ 187

Balance Sheet Components - Accrued Liabilities and Other (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Accrued Liabilities and Other
Accrued compensation and related expenses	$ 4,717	$ 7,274
Accrued litigation expense	3,200	3,200
Accrued professional services	571	392
Others	796	739
Accrued liabilities and other	$ 9,284	$ 11,605

Commitments and Contingencies - Narrative (Details) - USD ($)		3 Months Ended
	Feb. 06, 2019	Mar. 31, 2020	Mar. 31, 2019	Dec. 31, 2019
Other Commitments [Line Items]
Rent expense		$ 300,000	$ 300,000
Purchase commitments related to inventory		200,000		$ 400,000
Accrued litigation expense		3,200,000		$ 3,200,000
Statutory damages sought per violation of TCPA \| Eric B Fromer Chiropractic Inc Class Action [Member]
Other Commitments [Line Items]
Damages sought	$ 500
Treble damages sought per violation of TCPA \| Eric B Fromer Chiropractic Inc Class Action [Member]
Other Commitments [Line Items]
Damages sought	$ 1,500
Indemnification Agreement
Other Commitments [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	Mar. 31, 2020 USD ($)
Aggregate Future Minimum Lease Payments
2020 (remaining nine months)	$ 850
2021	1,024
2022	952
2023	866
2024	867
Thereafter	363
Total	$ 4,922

Borrowings - Narrative (Details) - Term Loan - Pharmakon Term Loan - USD ($) $ in Millions	1 Months Ended	3 Months Ended
	Oct. 31, 2017	Mar. 31, 2020	Mar. 31, 2019
Debt Instrument [Line Items]
Total loan proceeds	$ 40.0
Debt period payment, interest only period	35 months
Debt interest stated percentage (percent)	11.50%
Effective interest rate during the period (percent)		12.30%	12.20%
Debt covenant minimum cash balance	$ 5.0
Prepayment Penalty, 31-48 Months
Debt Instrument [Line Items]
Debt prepayment penalty percentage (percent)	2.00%
Prepayment Penalty, 49-60 Months
Debt Instrument [Line Items]
Debt prepayment penalty percentage (percent)	1.00%

Borrowings - Summary of Borrowings (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Debt Disclosure [Abstract]
Principal outstanding	$ 40,000	$ 40,000
Less: Unamortized debt issuance costs	(712)	(777)
Outstanding debt, net of debt issuance costs	39,288	39,223
Current portion of long-term borrowings	8,731	4,358
Long-term Debt, Excluding Current Maturities	$ 30,557	$ 34,865

Borrowings - Debt Maturity (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Maturities of Long-term Debt [Abstract]
2020 (remaining nine months)	$ 4,444
2021	17,778
2022	17,778
Total future minimum payments	40,000	$ 40,000
Less: Amount representing debt issuance costs	(712)	(777)
Outstanding debt, net of debt issuance costs	$ 39,288	$ 39,223

Stock-Based Incentive Compensation Plans - Narrative (Details) $ in Millions		3 Months Ended
	Mar. 26, 2020 purchase_period	Mar. 31, 2020 USD ($) shares	Dec. 31, 2019 USD ($) shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost		$ 5.0
Early exercise of stock options, share subject to repurchase (in shares) \| shares		15,567	21,404
Liability for early exercise of unvested stock options		$ 0.1	$ 0.1
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost, expected period for recognition (in years)		2 years 4 months 24 days
Restricted Stock Units
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Unrecognized compensation cost		$ 23.4
Unrecognized compensation cost, expected period for recognition (in years)		3 years 6 months
2018 ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Purchase price of common stock as a percent of fair market value (percent)		85.00%
Employee stock purchase program offering period interval (in months)		6 months
Accrued compensation and related expenses for employee payroll deductions		$ 0.9	$ 0.2
2018 Amended ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Employee stock purchase program offering period interval (in months)	12 months
Number of purchase periods in offering interval \| purchase_period	2

Stock-Based Incentive Compensation Plans - Stock Option Activity Under the Stock Option Plan (Details)	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Number of Shares
Outstanding, beginning of period (in shares) \| shares	2,718,971
Granted (in shares) \| shares	26,236
Exercised (in shares) \| shares	(43,334)
Canceled and forfeited (in shares) \| shares	(1,319)
Outstanding, end of period (in shares) \| shares	2,700,554
Weighted-Average Exercise Price
Outstanding, beginning of period (in dollars per share) \| $ / shares	$ 8.02
Granted (in dollars per share) \| $ / shares	17.31
Exercised (in dollars per share) \| $ / shares	4.03
Canceled and forfeited (in dollars per share) \| $ / shares	12.87
Outstanding, end of period (in dollars per share) \| $ / shares	$ 8.17

Stock-Based Incentive Compensation Plans - Weighted Average Grant Date Fair Value and Assumptions (Details) - $ / shares	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Weighted average grant date fair value per share and fair value assumptions for estimate fair value
Weighted average grant date fair value per share (in dollars per share)	$ 8.37	$ 10.40
Stock Options
Weighted average grant date fair value per share and fair value assumptions for estimate fair value
Expected volatility, minimum (percent)	46.74%	42.00%
Expected volatility, maximum (percent)	47.20%	47.00%
Risk-free interest rate, minimum (percent)	1.56%	2.52%
Risk-free interest rate, maximum (percent)	1.64%	2.59%
Dividend yield (percent)	0.00%	0.00%
Minimum \| Stock Options
Weighted average grant date fair value per share and fair value assumptions for estimate fair value
Expected term (years)	5 years 6 months	5 years
Maximum \| Stock Options
Weighted average grant date fair value per share and fair value assumptions for estimate fair value
Expected term (years)	7 years	7 years

Stock-Based Incentive Compensation Plans - Restricted Stock Units Activity (Details) - Restricted Stock Units	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Number of Shares
Outstanding, beginning of period (in shares) \| shares	543,041
Granted (in shares) \| shares	868,683
Vested (in shares) \| shares	(63,938)
Canceled and forfeited (in shares) \| shares	(5,575)
Outstanding, end of period (in shares) \| shares	1,342,211
Weighted Average Grant Date Fair Value
Outstanding, beginning of period (in dollars per share) \| $ / shares	$ 19.72
Granted (in dollars per share) \| $ / shares	20.43
Vested (in dollars per share) \| $ / shares	21.00
Canceled and forfeited (in dollars per share) \| $ / shares	18.43
Outstanding, end of period (in dollars per share) \| $ / shares	$ 20.13

Stock-Based Incentive Compensation Plans - Stock-Based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 2,622	$ 1,871
Cost of goods sold
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	71	42
Sales and marketing
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	1,141	670
Research and development
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	240	96
General and administrative
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock-based compensation expense	$ 1,170	$ 1,063

Net Loss Per Share of Common Stock - Schedule of Earnings Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended
	Mar. 31, 2020	Mar. 31, 2019
Earnings Per Share [Abstract]
Net loss	$ (12,772)	$ (9,345)
Weighted-average number of common shares used to compute basic and diluted net loss per share (in shares)	27,252,409	24,390,648
Net loss per share, basic and diluted (in dollars per share)	$ (0.47)	$ (0.38)

- 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	3 Months Ended
	Mar. 31, 2020	Mar. 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	4,241,896	3,756,114
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	2,700,554	3,047,130
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	1,342,211	531,669
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	15,567	59,193
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	65,442	0
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

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