Cover - shares	9 Months Ended
Cover - shares	Sep. 30, 2019	Nov. 08, 2019
Cover page.
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2019
Document Transition Report	false
Entity File Number	001-39049
Entity Registrant Name	EXAGEN INC.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	20-0434866
Entity Central Index Key	0001274737
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q3
Amendment Flag	false
Entity Address, Address Line One	1261 Liberty Way,
Entity Address, Address Line Two	Suite C
Entity Address, City or Town	Vista
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	92081
City Area Code	(760)
Local Phone Number	560-1501
Title of 12(b) Security	Common Stock, par value $0.001 per share
Trading Symbol	XGN
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Interactive Data Current	Yes
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		12,560,990

Condensed Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Current assets:
Cash and cash equivalents	$ 77,828	$ 13,164
Accounts receivable, net	6,238	5,952
Prepaid expenses and other current assets	1,686	2,196
Total current assets	85,752	21,312
Property and equipment, net	1,314	1,566
Goodwill	5,506	5,506
Other assets	172	503
Total assets	92,744	28,887
Current liabilities:
Accounts payable	1,213	1,279
Accrued liabilities	6,449	3,923
Proceeds received prior to issuance of Series G redeemable convertible preferred stock	0	3,750
Total current liabilities	7,662	8,952
Borrowings-non-current portion, net of discounts and debt issuance costs	25,677	24,617
Redeemable convertible preferred stock warrant liabilities	0	1,503
Deferred taxes	245	245
Other non-current liabilities	510	304
Total liabilities	34,094	35,621
Commitments and contingencies (Note 6)
Stockholders’ equity:
Preferred stock	0	0
Common stock	13	0
Additional paid-in capital	219,831	40,598
Accumulated deficit	(161,194)	(152,564)
Total stockholders' equity (deficit)	58,650	(111,966)
Total liabilities, redeemable convertible preferred stock and stockholders' equity (deficit)	92,744	28,887
Temporary Equity, Carrying Amount, Attributable to Parent	$ 0	$ 105,232

Unaudited Condensed Statements of Operations - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Income Statement [Abstract]
Revenue	$ 10,439	$ 8,223	$ 30,173	$ 22,799
Operating expenses:
Costs of revenue (excluding amortization of purchased technology)	4,783	3,852	14,217	11,376
Selling, general and administrative expenses	7,306	4,932	20,787	14,419
Research and development expenses	507	525	1,610	1,592
Amortization of intangible assets	0	47	0	141
Total operating expenses	12,596	9,356	36,614	27,528
Loss from operations	(2,157)	(1,133)	(6,441)	(4,729)
Interest expense	909	704	2,720	2,098
Change in fair value of financial instruments	(200)	55	267	55
Other income, net	125	26	264	77
Net loss	(3,141)	(1,756)	(8,630)	(6,695)
Accretion of redeemable convertible preferred stock	(338)	(2,768)	(4,640)	(6,462)
Deemed dividend recorded in connection with financing transactions	(13,601)	0	(13,601)	(1,152)
Net Income (Loss) Available to Common Stockholders, Basic	(17,080)	(4,524)	(26,871)	(14,309)
Net loss attributable to common stockholders (diluted)	$ (17,080)	$ (4,524)	$ (26,871)	$ (14,309)
Net loss per share:
Net loss per share, basic and diluted (USD per share)	$ (11.29)	$ (71.80)	$ (48.70)	$ (227.11)
Weighted average shares:
Weighted-average number of shares used to compute net loss per share, basic and diluted (Note 2)	1,513,189	63,005	551,730	63,005

Unaudited Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2017	497,691,757
Beginning balance at Dec. 31, 2017	$ 92,046
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	$ 1,382
Issuance of Series G redeemable convertible preferred stock for aggregate proceeds, net of issuance costs (in shares)	34,914,327
Issuance of Series G redeemable convertible preferred stock for aggregate proceeds, net of issuance costs	$ 3,868
Ending balance (in shares) at Mar. 31, 2018	532,606,084
Ending balance at Mar. 31, 2018	$ 97,296
Beginning balance (in shares) at Dec. 31, 2017		63,005
Beginning balance at Dec. 31, 2017	(96,684)	$ 0	$ 50,954	$ (147,638)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	1,382		1,382
Stock-based compensation	46		46
Issuance of Series H redeemable convertible preferred stock for aggregate proceeds of $0.047 per share, net of issuance costs of $318 (Note 8)	(1,152)		(1,152)
Net loss	(2,793)			(2,793)
Ending balance (in shares) at Mar. 31, 2018		63,005
Ending balance at Mar. 31, 2018	$ (98,879)	$ 0	48,466	(147,345)
Beginning balance (in shares) at Dec. 31, 2017	497,691,757
Beginning balance at Dec. 31, 2017	$ 92,046
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	$ 6,462
Ending balance (in shares) at Sep. 30, 2018	532,606,084
Ending balance at Sep. 30, 2018	$ 102,376
Beginning balance (in shares) at Dec. 31, 2017		63,005
Beginning balance at Dec. 31, 2017	(96,684)	$ 0	50,954	(147,638)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net loss	(6,695)
Ending balance (in shares) at Sep. 30, 2018		63,005
Ending balance at Sep. 30, 2018	$ (107,807)	$ 0	43,440	(151,247)
Beginning balance (in shares) at Mar. 31, 2018	532,606,084
Beginning balance at Mar. 31, 2018	$ 97,296
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	$ 2,312
Ending balance (in shares) at Jun. 30, 2018	532,606,084
Ending balance at Jun. 30, 2018	$ 99,608
Beginning balance (in shares) at Mar. 31, 2018		63,005
Beginning balance at Mar. 31, 2018	(98,879)	$ 0	48,466	(147,345)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	2,312		2,312
Stock-based compensation	44		44
Net loss	(2,146)			(2,146)
Ending balance (in shares) at Jun. 30, 2018		63,005
Ending balance at Jun. 30, 2018	(103,293)	$ 0	46,198	(149,491)
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	$ 2,768
Ending balance (in shares) at Sep. 30, 2018	532,606,084
Ending balance at Sep. 30, 2018	$ 102,376
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	2,768		2,768
Stock-based compensation	10		10
Net loss	(1,756)			(1,756)
Ending balance (in shares) at Sep. 30, 2018		63,005
Ending balance at Sep. 30, 2018	$ (107,807)	$ 0	43,440	(151,247)
Beginning balance (in shares) at Dec. 31, 2018	532,606,084
Beginning balance at Dec. 31, 2018	$ 105,232
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	$ 2,114
Issuance of Series G redeemable convertible preferred stock for aggregate proceeds, net of issuance costs (in shares)	97,646,289
Issuance of Series G redeemable convertible preferred stock for aggregate proceeds, net of issuance costs	$ 7,520
Ending balance (in shares) at Mar. 31, 2019	630,252,373
Ending balance at Mar. 31, 2019	$ 114,866
Beginning balance (in shares) at Dec. 31, 2018	63,005	63,005
Beginning balance at Dec. 31, 2018	$ (111,966)	$ 0	40,598	(152,564)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	2,114		2,114
Exercise of stock options (in Shares)		24
Exercise of stock options	0	$ 0
Stock-based compensation	12		12
Net loss	(2,704)			(2,704)
Ending balance (in shares) at Mar. 31, 2019		63,029
Ending balance at Mar. 31, 2019	$ (116,772)	$ 0	38,496	(155,268)
Beginning balance (in shares) at Dec. 31, 2018	532,606,084
Beginning balance at Dec. 31, 2018	$ 105,232
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	$ 4,640
Ending balance (in shares) at Sep. 30, 2019	0
Ending balance at Sep. 30, 2019	$ 0
Beginning balance (in shares) at Dec. 31, 2018	63,005	63,005
Beginning balance at Dec. 31, 2018	$ (111,966)	$ 0	40,598	(152,564)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options (in Shares)	50
Net loss	$ (8,630)
Ending balance (in shares) at Sep. 30, 2019	12,559,492	12,559,492
Ending balance at Sep. 30, 2019	$ 58,650	$ 13	219,831	(161,194)
Beginning balance (in shares) at Mar. 31, 2019	630,252,373
Beginning balance at Mar. 31, 2019	$ 114,866
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	$ 2,188
Issuance of Series G redeemable convertible preferred stock for aggregate proceeds, net of issuance costs (in shares)	51,282,048
Issuance of Series G redeemable convertible preferred stock for aggregate proceeds, net of issuance costs	$ 3,972
Ending balance (in shares) at Jun. 30, 2019	681,534,421
Ending balance at Jun. 30, 2019	$ 121,026
Beginning balance (in shares) at Mar. 31, 2019		63,029
Beginning balance at Mar. 31, 2019	(116,772)	$ 0	38,496	(155,268)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	2,188		2,188
Exercise of stock options (in Shares)		26
Exercise of stock options	0	$ 0
Stock-based compensation	11		11
Net loss	(2,785)			(2,785)
Ending balance (in shares) at Jun. 30, 2019		63,055
Ending balance at Jun. 30, 2019	(121,734)	$ 0	36,319	(158,053)
Increase (Decrease) in Temporary Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	$ 338
Issuance of Series G redeemable convertible preferred stock for aggregate proceeds, net of issuance costs (in shares)	233,446,519
Issuance of Series G redeemable convertible preferred stock for aggregate proceeds, net of issuance costs	$ 3,941
Deemed dividend recognized on beneficial conversion features of Series H redeemable convertible preferred stock (Note 8)	$ 6,741
Deemed dividend from conversion of Series G to Series H redeemable convertible preferred stock (Note 8) (in shares)	97,592,739
Conversion of preferred stock to common stock in connection with initial public offering (Note 8) (in shares)	1,012,573,679
Conversion of preferred stock to common stock in connection with initial public offering (Note 8)	$ 138,906
Ending balance (in shares) at Sep. 30, 2019	0
Ending balance at Sep. 30, 2019	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Accretion of redeemable convertible preferred stock	338		338
Stock-based compensation	62		62
Issuance of Series H redeemable convertible preferred stock for aggregate proceeds of $0.047 per share, net of issuance costs of $318 (Note 8)	6,741		6,741
Deemed dividend recognized on beneficial conversion features of Series H redeemable convertible preferred stock (Note 8)	6,741		6,741
Deemed Dividend	6,860
Deemed dividend from conversion of Series G to Series H redeemable convertible preferred stock (Note 8)	6,860		6,860
Stock issued upon conversion of redeemable convertible preferred shares (in shares)		7,816,643
Conversion of preferred stock to common stock in connection with initial public offering (Note 8)	138,906	$ 8	138,898
Issuance of common stock in initial public offering, net of underwriting discount, commissions and issuance costs (Note 9) (in shares)		4,140,000
Issuance of common stock in initial public offering, net of underwriting discount, commissions and issuance costs (Note 9)	50,518	$ 4	50,514
Net exercise of common stock warrants (in shares)		539,794
Net exercise of common stock warrants	511	$ 1	510
Reclassification of redeemable convertible preferred stock warrant liabilities as equity	726		726
Net loss	$ (3,141)			(3,141)
Ending balance (in shares) at Sep. 30, 2019	12,559,492	12,559,492
Ending balance at Sep. 30, 2019	$ 58,650	$ 13	$ 219,831	$ (161,194)

Unaudited Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
Unaudited Statements of Cash Flows - USD ($) $ in Thousands	Sep. 30, 2019	Sep. 30, 2018
Cash flows from operating activities:
Net loss	$ (8,630)	$ (6,695)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	480	576
Amortization of debt discount and debt issuance costs	575	425
Non-cash interest expense	484	380
Revaluation of warrant liabilities	(267)	(55)
Loss on disposal of assets	20	0
Stock-based compensation	85	100
Changes in assets and liabilities:
Increase (Decrease) in Accounts Receivable	(286)	(1,168)
Increase (Decrease) in Prepaid Expense and Current Other Assets	510	(590)
Increase (Decrease) in Other Noncurrent Assets	(24)	(8)
Accounts payable	174	(392)
Accrued and other liabilities	1,095	(5)
Net cash used in operating activities	(5,784)	(7,432)
Cash flows from investing activities:
Purchases of property and equipment	(377)	(128)
Proceeds from sale of property and equipment	300	0
Purchases of short-term investments	0	(2,000)
Maturities of short-term investments	0	1,000
Net cash used in investing activities	(77)	(1,128)
Cash flows from financing activities:
Repayments of Long-term Capital Lease Obligations	(94)	(17)
Proceeds from initial public offering, net of issuance costs	52,195	0
Net cash provided by financing activities	70,525	2,699
Increase (decrease) in cash, cash equivalents and restricted cash	64,664	(5,861)
Cash, cash equivalents and restricted cash, beginning of period	13,264	11,341
Cash, cash equivalents and restricted cash, end of period	77,928	5,480
Supplemental disclosure of cash flow information:
Cash paid for interest expense	1,661	1,293
Supplemental disclosure of non-cash items:
Accretion to redemption value of redeemable convertible preferred stock	4,640	6,462
Equipment Purchased Under Capital Lease	412	289
Cost incurred, but not paid, in connection with capital expenditures	71	207
Conversion of redeemable convertible preferred stock	138,906	0
Net exercise of common and preferred stock warrants	511	0
Deferred offering costs included in accounts payable and accrued liabilities	1,677	0
Reclassification of redeemable convertible preferred stock warrant liabilities as equity	726	0
Adjustment upon adoption of ASC 606	0	3,086
Series F redeemable convertible preferred stock
Cash flows from financing activities:
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	0	2,716
Supplemental disclosure of non-cash items:
Deemed dividend from issuance of Series F redeemable convertible preferred stock	0	1,152
Series G redeemable convertible preferred stock
Cash flows from financing activities:
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	7,742	0
Supplemental disclosure of non-cash items:
Deemed dividend from conversion/issuance of redeemable convertible preferred stock	6,860	0
Conversion of Series G to Series H redeemable convertible preferred stock	11,875	0
Series H redeemable convertible preferred stock
Cash flows from financing activities:
Proceeds from issuance of redeemable convertible preferred stock, net of issuance costs	10,682	0
Supplemental disclosure of non-cash items:
Deemed dividend recognized for beneficial conversion features of Series H redeemable convertible preferred stock	$ 6,741	$ 0

Condensed Balance Sheets - (Parenthetical) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Convertible preferred stock
Shares outstanding (in shares)	0	532,606,084
Preferred stock
Par value (in dollars per share)	$ 0.001	$ 0.001
Shares authorized (in shares)	10,000,000	0
Shares issued (in shares)	0	0
Shares outstanding (in shares)	0	0
Common stock
Par value (in dollars per share)	$ 0.001	$ 0.001
Shares authorized (in shares)	200,000,000	1,470,000,000
Shares issued (in shares)	12,559,492	63,005
Shares outstanding (in shares)	12,559,492	63,005
Redeemable Convertible Preferred Stock
Convertible preferred stock
Par value (in dollars per share)	$ 0.001	$ 0.001
Shares authorized (in shares)	750,300,000	750,300,000
Shares outstanding (in shares)		532,606,084
Liquidation preference	$ 0	$ 163,316
Shares issued (in shares)	0

Organization - (Notes)	9 Months Ended
Organization - (Notes)	Sep. 30, 2019
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Organization	Organization Description of Business Exagen Inc. (the Company) was incorporated under the laws of the state of New Mexico in 2002, under the name Exagen Corporation. In 2003, Exagen Corporation changed its state of incorporation from New Mexico to Delaware by merging with and into Exagen Diagnostics, Inc., pursuant to which the Company changed its name to Exagen Diagnostics, Inc. In January 2019, the Company changed its name to Exagen Inc. The Company is dedicated to transforming the care continuum for patients suffering from debilitating and chronic autoimmune diseases by enabling timely differential diagnosis and optimizing therapeutic intervention. Initial Public Offering On September 23, 2019, the Company closed its initial public offering (the IPO) of 4,140,000 shares of its common stock at a price to the public of $14.00 per share, including the exercise in full by the underwriters of their option to purchase 540,000 additional shares of the Company's common stock. Including the exercise of the option to purchase additional shares, the aggregate net proceeds to the Company from the offering was approximately $50.5 million, net of underwriting discounts, commissions and other estimated offering expenses, for aggregate expenses of approximately $7.5 million. In addition, an aggregate of 7,816,643 shares of common stock, excluding warrant conversions, were issued to the holders of the Company's Series A-3, Series B-3, Series C, Series D, Series E, Series F and Series H redeemable convertible preferred stockholders upon the automatic conversion of all shares of redeemable convertible preferred stock to common stock. Reverse Stock Split On September 6, 2019, the Company effected a one-for-183.635 reverse stock split of its common stock (the Reverse Stock Split). The par value and the authorized shares of the common stock were not adjusted as a result of the Reverse Stock Split. All issued and outstanding common stock and the conversion ratio of the redeemable convertible preferred stock have been retroactively adjusted to reflect this Reverse Stock Split for all periods presented in the accompanying condensed financial statements and notes to the condensed financial statements. Liquidity The Company has suffered recurring losses and negative cash flows from operating activities since inception. The Company anticipates that it will continue to incur net losses into the foreseeable future. At September 30, 2019, the Company had cash and cash equivalents of $77.8 million and had an accumulated deficit of $161.2 million, respectively. Since inception, the Company has financed its operations primarily through private placements of preferred securities, the sale of common stock through its IPO and debt financing arrangements. Based on the Company's current business plan, management believes that its existing capital resources will be sufficient to fund the Company's obligations for at least the next twelve months. To execute its business plans, the Company may need additional funding to support its continuing operations and pursue its growth strategy. Until such time as the Company can achieve significant cash flows from operations, if ever, it expects to finance its operations through the sale of its stock, debt financings or other strategic transactions. Although the Company has been successful in raising capital in the past, there is no assurance that it will be successful in obtaining such additional financing on terms acceptable to the Company, if at all. The terms of any financing may adversely affect the holdings or the rights of the Company's stockholders. If the Company is unable to obtain funding, the Company could be forced to delay, reduce or eliminate some or all of its programs, product portfolio expansion plans or commercialization efforts, which could have a material adverse effect on the Company's business, operating results and financial condition and the Company's ability to achieve its intended business objectives.

Summary Of Significant Accounting Policies - (Notes)

9 Months Ended

Sep. 30, 2019

Accounting Policies [Abstract]

Summary Of Significant Accounting Policies

Note 2. Summary of Significant Accounting Policies

Basis of Presentation and Use of Estimates

The accompanying interim condensed balance sheet as of September 30, 2019, the condensed statements of operations and the condensed statements of redeemable convertible preferred stock and stockholders' equity (deficit) for the three and nine months ended September 30, 2019 and 2018 and cash flows for the nine months ended September 30, 2019 and 2018 and the related footnote disclosure are unaudited and have been prepared in accordance with the rules and regulations of the Securities and Exchange Commission (SEC), and with accounting principles generally accepted in the United States (GAAP) applicable to interim financial statements. In management's opinion, the unaudited interim condensed financial statements have been prepared on the same basis as the audited financial statements and include all adjustments, which include only normal recurring adjustments, necessary for the fair presentation of the Company's financial position as of September 30, 2019 and its results of operations for the three and nine months ended September 30, 2019 and 2018 and cash flows for the nine months ended September 30, 2019 and 2018 in accordance with GAAP. The results for the nine months ended September 30, 2019 are not necessarily indicative of the results expected for the full fiscal year or any other interim period. The year-end condensed balance sheet data was derived from audited financial statements, but does not include all disclosures required by accounting principles generally accepted in the United States of America. These unaudited condensed financial statements should be read in conjunction with the Company’s audited financial statements for the year ended December 31, 2018, included in its Prospectus dated September 18, 2019 filed with the SEC on September 20, 2019.

The preparation of the accompanying condensed financial statements requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities, the disclosure of contingent assets and liabilities as of the date of the condensed financial statements, and the reported amounts of revenue and expenses during the reporting period.

Significant estimates and assumptions made in the accompanying condensed financial statements include, but are not limited to revenue recognition, the fair value of financial instruments measured at fair value, the recoverability of its long-lived assets (including goodwill), net deferred tax assets (and related valuation allowance), and for periods prior to the IPO, the fair value of the Company's common stock and redeemable convertible preferred stock. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates.

Concentration of Credit Risk and Other Risk and Uncertainties

Financial instruments that potentially subject the Company to credit risk consist principally of cash, cash equivalents, and accounts receivable. Substantially all the Company's cash and cash equivalents are held at one financial institution that management believes is of high credit quality. Such deposits may, at times, exceed federally insured limits.

Significant payers are those which represent more than 10% of the Company's total revenue or accounts receivable balance at each respective balance sheet date. For each significant payer, revenue as a percentage of total revenue and accounts receivable as a percentage of total accounts receivable are as follows:


	Revenue
	Three Months Ended September 30,						Nine Months Ended September 30,
	2019		2018		2019		2018
Medicare	25	%	30	%	26	%	31	%
Blue Shield	13	%	14	%	13	%	14	%
United Healthcare	10	%	12	%	10	%	13	%
Medicare Advantage	12	%	12	%	11	%	11	%


	Accounts Receivable
	September 30, 2019		December 31, 2018

Medicare	23	%	26	%
Blue Shield	16	%	16	%
United Healthcare	9	%	11	%
Medicare Advantage	8	%	11	%

For the three months ended September 30, 2019 and 2018, approximately 83%, and 86%, respectively, of the Company's revenue was related to the AVISE^® CTD test. For the nine months ended September 30, 2019 and 2018, approximately 83% and 86%, respectively, of the Company's revenue was related to the AVISE^® CTD test.

The Company is dependent on key suppliers for certain laboratory materials. An interruption in the supply of these materials would temporarily impact the Company's ability to perform testing services.

Disaggregation of Revenue

The following table includes the Company's revenues as disaggregated by payer category (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2019		2018		2019		2018
Revenue:
Healthcare insurers	$	6,188	$	5,408	$	17,716	$	15,023
Government	2,665		2,524		7,964		7,013
Client	1,007		171		3,200		428
Other(1)	148		120		458		335
Janssen (SIMPONI^®)	431		—		835		—
Total revenue	$	10,439	$	8,223	$	30,173	$	22,799

(1)Includes patient self-pay that is immaterial.

Fair Value Measurements

The carrying value of the Company's cash and cash equivalents, other assets and accrued liabilities approximate fair value due to the short-term nature of these items. Based on the borrowing rates currently available to the Company for debt with similar terms and consideration of default and credit risk, the carrying value of the Company's long-term borrowings approximates its fair value, which is considered a Level 2 input.

Fair value is defined as the exchange price that would be received for an asset or an exit price paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs.

The fair value hierarchy defines a three-level valuation hierarchy for disclosure of fair value measurements as follows:

Level 1 - Unadjusted quoted prices in active markets for identical assets or liabilities;

Level 2 - Inputs other than quoted prices included within Level I that are observable, unadjusted quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and

Level 3 - Unobservable inputs that are supported by little or no market activity for the related assets or liabilities.

The categorization of a financial instrument within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement.

The Company's redeemable convertible preferred stock warrant liabilities were measured at fair value on a recurring basis and were classified as Level 3 liabilities. The Company recorded subsequent adjustments to reflect the increase or decrease in estimated fair value at each reporting date in current period earnings.

Cash, Cash Equivalents and Restricted Cash

The Company considers all highly-liquid investments purchased with a remaining maturity date upon acquisition of three months or less to be cash equivalents and are stated at cost, which approximates fair value.

In 2016, the Company entered into an arrangement with a financial institution with which it has an existing banking relationship whereby in exchange for the issuance of corporate credit cards, the Company agreed to obtain a $0.1 million certificate of deposit with this financial institution as collateral for the balances borrowed on these credit cards. The Company has classified the value of this certificate of deposit (including all interest earned thereon) within other assets in the accompanying balance sheets. The Company has the right to terminate the credit card program at any time. Upon termination of the credit card program and repayment of all outstanding balances owed, the Company may redeem the certificate of deposit (and all interest earned thereon).

Cash, cash equivalents and restricted cash presented in the accompanying condensed statements of cash flows consist of the following (in thousands):


	September 30, 2019		December 31, 2018

Cash and cash equivalents	$	77,828	$	13,164
Restricted cash	100		100
	$	77,928	$	13,264

Deferred Offering Costs

As of December 31, 2018, the Company deferred offering costs of $0.4 million consisting of legal, accounting and other fees and costs directly attributable to its IPO, which are recorded within other assets in the accompanying condensed balance sheet. As of September 30, 2019, the deferred offering costs were offset against the proceeds received upon the completion of the IPO.

Redeemable Convertible Preferred Stock

Prior to the completion of the IPO, the Company had multiple classes of redeemable convertible preferred stock, all of which were classified as temporary equity in the accompanying condensed balance sheet as the redemption of the shares were outside of the Company's control. Redeemable convertible preferred stock which was redeemable on or after a certain date at the option of the holder was accreted to its redemption value from the date of issuance to the earliest redemption date.

In connection with the completion of the IPO in September 2019, all outstanding shares of redeemable convertible preferred stock were automatically converted into an aggregate of 7,816,643 shares of common stock, excluding warrant conversions.

Redeemable Convertible Preferred Stock Warrants

Prior to the completion of the IPO, the Company accounted for its redeemable convertible preferred stock warrants as liabilities based upon the characteristics and provisions of each instrument. The redeemable convertible preferred stock warrants were recorded at their fair value on the date of issuance and were revalued on each subsequent balance sheet date, with fair value changes recognized as increases or reductions in the statements of operations. Upon the completion of the IPO, all remaining outstanding warrants to purchase shares of redeemable convertible preferred stock were automatically converted into warrants to purchase shares of common stock. As such, the warrants no longer require liability accounting and the then fair value of the warrant liability was reclassified into stockholders’ equity.

The Company performed the final remeasurement of the warrant liabilities as of the IPO closing date. See Note 7 for the amounts associated with the fair value measurements and Note 5 for further discussion on the remaining warrants.

Revenue Recognition

Substantially all of the Company's revenue has been derived from sales of its testing products and is primarily comprised of a high volume of relatively low-dollar transactions. The Company primarily markets its testing products to rheumatologists and their physician assistants in the United States. The healthcare professionals who order the Company's testing products and to whom test results are reported are generally not responsible for payment for these products. The parties that pay for these services (the Payers) consist of healthcare insurers, government payers (primarily Medicare and Medicaid), client payers (i.e., hospitals, other laboratories, etc.), and patient self-pay. The Company's service is a single performance obligation that is completed upon the delivery of test results to the prescribing physician which triggers revenue recognition

Payers are billed at the Company's list price. Net revenues recognized consist of amounts billed net of allowances for differences between amounts billed and the estimated consideration the Company expects to receive from such payers. The process for estimating revenues and the ultimate collection of accounts receivable involves significant judgment and estimation. The Company follows a standard process, which considers historical denial and collection experience, insurance reimbursement policies and other factors, to estimate allowances and implicit price concessions, recording adjustments in the current period as changes in estimates. Further adjustments to the allowances, based on actual receipts, is recorded upon settlement. The transaction price is estimated using an expected value method on a portfolio basis. The Company's portfolios are grouped per payer (i.e. each individual third-party insurance, Medicare, client payers, patient self-pay, etc.) and per test basis.

Collection of the Company's net revenues from payers is normally a function of providing complete and correct billing information to the healthcare insurers and generally occurs within 30 to 90 days of billing. Contracts do not contain significant financing components based on the typical period of time between performance of services and collection of consideration.

The Company early adopted Accounting Standards Codification (ASC) Topic 606, Revenue from Contracts with Customers (Topic 606) as of January 1, 2018 using a cumulative-effect adjustment to the opening balance of accumulated deficit and accounts receivable of $3.1 million.

Janssen Promotion Agreement

In December 2018, the Company entered into a co-promotion agreement with Janssen (the Janssen agreement) to co-promote SIMPONI^® in the United States. The Company recognized revenue of approximately $0.4 million and $0.8 million during the three and nine months ended September 30, 2019, respectively. The related expenses for marketing SIMPONI^® are included in selling, general and administrative expenses and are expensed as incurred.

Research and Development

Costs associated with research and development activities are expensed as incurred and include, but are not limited to, personnel-related expenses, including stock-based compensation expense, materials, laboratory supplies, consulting costs, costs associated with setting up and conducting clinical studies and allocated overhead including rent and utilities.

Advertising and Marketing Costs

Costs associated with advertising and marketing activities are expensed as incurred. Total advertising and marketing costs were approximately $0.4 million for the three months ended September 30, 2019 and 2018, and $1.1 million for the nine months ended September 30, 2019 and 2018, and are included in selling, general and administrative expenses in the accompanying condensed statements of operations.

Shipping and Handling Costs

Costs incurred for shipping and handling are included in costs of revenue in the accompanying condensed statements of operations and totaled approximately $0.4 million and $0.3 million for the three months ended September 30, 2019 and 2018, respectively, and $1.1 million and $0.9 million for the nine months ended September 30, 2019 and 2018, respectively.

Stock-Based Compensation

The Company recognizes compensation expense for all stock-based awards to employees and directors based on the grant-date estimated fair values over the requisite service period of the awards (usually the vesting

period) on a straight-line basis. The fair value of stock options is determined using the Black-Scholes-Merton (BSM) option pricing model, which requires management to make certain assumptions regarding a number of complex and subjective variables. Equity award forfeitures are recorded as they occur.

The BSM option pricing model incorporates various estimates, including the fair value of the Company's common stock, expected volatility, expected term and risk-free interest rates. The weighted-average expected term of options was calculated using the simplified method. This decision was based on the lack of relevant historical data due to the Company's limited historical experience. In addition, due to the Company's limited historical data, the estimated volatility incorporates the historical volatility over the expected term of the award of comparable companies whose share prices are publicly available. The risk-free interest rate for periods within the contractual term of the option is based on the U.S. Treasury yield in effect at the time of grant. The dividend yield was zero, as the Company has never declared or paid dividends and has no plans to do so in the foreseeable future.

Upon the effective date of the IPO, the Company began using the closing price of its common stock as the fair value of its common stock on the corresponding date. Prior to the completion of the IPO in September 2019, due to the absence of a public market for the Company's common stock, it was necessary to estimate the fair value of the common stock underlying the Company's stock-based awards when performing fair value calculations using the BSM option pricing model. The fair value of the common stock underlying the Company's stock-based awards was assessed on each grant date by the Company's board of directors (Board of Directors).

Comprehensive Loss

Comprehensive loss is defined as a change in equity of a business enterprise during a period, resulting from transactions from nonowner sources. There have been no items qualifying as other comprehensive loss and, therefore, for all periods presented, the Company's comprehensive loss was the same as its reported net loss.

Net Loss Per Share

Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. Diluted net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Potentially dilutive common stock equivalents are comprised of redeemable convertible preferred stock, warrants for the purchase of redeemable convertible preferred and common stock and options outstanding under the Company's stock option plans. For the three and nine months ended September 30, 2019 and 2018, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as the inclusion of the potentially dilutive securities would be antidilutive.

Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common stock equivalent shares):


	Three Months Ended September 30,			Nine Months Ended September 30,
	2019	2018	2019	2018
Redeemable convertible preferred stock	—	5,202,940	—	5,202,940
Warrants to purchase redeemable convertible preferred stock	—	203,549	—	203,549
Warrants to purchase common stock	461,273	934,789	461,273	934,789
Common stock options	1,475,006	69,885	1,475,006	69,885
Total	1,936,279	6,411,163	1,936,279	6,411,163

Segment Reporting

Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations as, and manages its business in, one operating segment.

Recent Accounting Pronouncements

From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company's financial position or results of operations upon adoption.

In February 2016, the FASB issued Accounting Standards Update (ASU) 2016-02, Leases (Topic 842). The new topic supersedes Topic 840, Leases, and increases transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and requires disclosures of key information about leasing arrangements. In July 2018, the FASB issued ASU 2018-10, Codification Improvements to Topic 842, which provides narrow amendments to clarify how to apply certain aspects of the new lease standard, and ASU 2018-11, Leases: Targeted Improvements, which was issued to provide relief to companies from restating comparative periods. Pursuant to this ASU, in the period of adoption the Company will not restate comparative periods presented in its condensed financial statements. The effective date of this guidance for public companies is for reporting periods beginning after December 15, 2018. Topic 842 mandates a modified retrospective transition method. The Company intends to adopt the new lease standard using a cumulative effect to accumulated deficit and will elect the package of practical expedients, which among other things will allow the Company to carry forward its historical lease classification. The Company is currently evaluating the impact of Topic 842 on its condensed financial statements.

In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement: Disclosure Framework--Changes to the Disclosure Requirements for Fair Value Measurement, which adds and modifies certain disclosure requirements for fair value measurements. Under the new guidance, 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, or valuation processes for Level 3 fair value measurements. However, public companies will be required to disclose the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and related changes in unrealized gains and losses included in other comprehensive income. This update is effective for annual periods beginning after December 15, 2019, and interim periods within those periods, and early adoption is permitted. The Company is currently evaluating the impact of ASU 2018-13 on its condensed financial statements.

Borrowings - (Notes)

9 Months Ended

Sep. 30, 2019

Debt Disclosure [Abstract]

Borrowings

2017 Term Loan

In September 2017, the Company executed a term loan agreement (the 2017 Term Loan) with Innovatus Life Sciences Lending Fund I, LP (Innovatus) and borrowed $20.0 million, $17.8 million of which was immediately used to repay the Company's existing loan with Capital Royalty Partners II L.P. and its affiliates. On December 7, 2018, the Company borrowed an additional $5.0 million under the 2017 Term Loan. At September 30, 2019, no additional amounts remain available to borrow under the 2017 Term Loan.

The interest rate on all borrowings under the 2017 Term Loan is 11.0%, of which 2.5% is paid in-kind in the form of additional term loans, or PIK Loans, until September of 2019, after which interest accrues at an annual rate of 11.0%. The Company has estimated the effective interest rate of this loan to be approximately 14%. Accrued interest is due and payable monthly, unless the Company elects to pay PIK interest. The outstanding principal and accrued interest on the 2017 Term Loan will be repaid in twenty-four equal monthly installments commencing in October 2020. Upon repayment of the final installment under the 2017 Term Loan, the Company is required to pay an additional fee of $1.0 million. This obligation is being accreted into interest expense over the term of 2017 Term Loan using the effective interest method. For the three months ended September 30, 2019 and 2018, the Company issued PIK Loans totaling $0.2 million and $0.1 million, respectively. For the nine months ended September 30, 2019 and 2018, the Company issued PIK Loans totaling $0.5 million and $0.4 million, respectively.

If the 2017 Term Loan is prepaid after September 7, 2019, but before September 7, 2020, the 2017 Term Loan requires a prepayment premium of 3% of the aggregate outstanding principal. The prepayment premium decreases by 1% during each subsequent twelve-month period after September 7, 2020.

The 2017 Term Loan is collateralized by a first priority security interest on substantially all of the Company's assets, including intellectual property. The affirmative covenants of the 2017 Term Loan require that the Company timely file taxes, maintain good standing and government compliance, maintain liability and other insurance, provide prompt notification of significant corporate events, and furnish audited financial statements within 150 days of fiscal year end without qualification as to the scope of the audit or as to going concern and without any other similar qualification.

The affirmative covenants require that the Company achieve a specified level of revenue, and either (i) gross margins, or (ii) gross profits (collectively referred to as the Interest Only Milestones), as measured quarterly on a rolling twelve month basis, and commencing with the quarter ending December 31, 2017 (1) the interest rate on the 2017 Term Loan will increase by 8% and (2) repayment will commence on the date it is determined the Interest Only Milestones have not been met and over the following eighteen months in equal monthly installments. The consequences of failing to achieve the Interest Only Milestones will be waived if, within sixty days of failing to achieve the Interest Only Milestones, the Company issues additional equity securities or subordinated debt with net proceeds of at least $9.5 million. In addition, the 2017 Term Loan requires that the Company maintain certain levels of minimum liquidity. If the Company has achieved the Interest Only Milestones, the Company is required to maintain an unrestricted cash balance of $2.0 million. If the Interest Only Milestones are not met, the Company must maintain unrestricted cash balances totaling at least the trailing four months cash used to fund operating activities.

The negative covenants provide, among other things, that without the prior consent of Innovatus subject to certain exceptions, the Company may not dispose of certain assets, engage in certain business combinations or acquisitions, incur additional indebtedness or encumber any of the Company's property, pay dividends on the Company's capital stock or make prohibited investments. The 2017 Term Loan agreement provides that an event of default will occur if, among other triggers, (i) the Company defaults in the payment of any amount payable under the agreement when due, (ii) there occurs any circumstance(s) that could reasonably be expected to result in a material adverse effect on the Company's business, operations or condition, or on the Company's ability to perform its obligations under the agreement, (iii) the Company becomes insolvent, (iv) the Company undergoes a change in control or (v) the Company breaches any negative covenants or certain affirmative covenants in the agreement or, subject to a cure period, otherwise neglects to perform or observe any material item in the agreement.

At September 30, 2019, the Company was in compliance with all covenants of the 2017 Term Loan.

Upon an event of default in any of the 2017 Term Loan covenants, the repayment of the 2017 Term Loan may be accelerated and the applicable interest rate will be increased by 4.0% until the default is cured. Although repayment of the 2017 Term Loan can be accelerated under certain circumstances, the Company believes acceleration of this loan is not probable as of the date of these condensed financial statements. Accordingly, the Company has reflected the amounts of the 2017 Term Loan due beyond twelve months of the balance sheet date as non-current.

In connection with the 2017 Term Loan, the Company paid issuance costs of $0.4 million to Innovatus and an additional $0.1 million to third parties. These fees were recorded as discounts to the carrying value of the 2017 Term Loan. The Company also issued Innovatus warrants (i) on the closing date of the 2017 Term Loan, to purchase 15,384,615 shares of Series F redeemable convertible preferred stock at an exercise price of $0.078 per share and (ii) on December 7, 2018, to purchase 3,846,154 shares of Series F redeemable convertible preferred stock at an exercise price of $0.078 per share (Note 5). These warrants are immediately exercisable and will expire if unexercised seven years after their issuance. The fair value of the warrants on each of their dates of issuance, determined using BSM option pricing model, was recorded as a discount to long-term debt and an offsetting amount recognized as a liability. The resulting debt discount is being amortized to interest expense using the effective interest method over the term of the 2017 Term Loan. In connection with the completion of the IPO in September 2019, the Series F redeemable convertible preferred stock warrants automatically converted into warrants exercisable for an aggregate of 104,722 shares of common stock.

Future Minimum Payments on the Outstanding Borrowings

Future minimum aggregate payments, including interest, for outstanding borrowings under the 2017 Term Loan are as follows (in thousands):


	September 30, 2019
2019 (remaining)	$	725
2020	6,125
2021	14,937
2022	11,250
Total	33,037
Less:
Unamortized debt discount and issuance costs	(484)
Interest	(6,876)
Total borrowings, net of discounts and debt issuance costs	$	25,677

Commitment and Contingencies - (Notes)	9 Months Ended
Commitment and Contingencies - (Notes)	Sep. 30, 2019
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Leases The Company leases approximately 14,000 square feet of office and laboratory space in Vista, California, under a lease that expires in January 2021, with options to extend the lease for two additional 36-month periods. In addition, the Company also leases approximately 19,500 square feet of office space in Vista, California, under a lease that expires in January 2021 with an option to extend the lease for an additional 24-month period. The Company's lease payments under each of these leases are subject to escalation clauses. For the three months ended September 30, 2019 and 2018, rent expense was $0.1 million. For the nine months ended September 30, 2019 and 2018, rent expense was $0.3 million. Acquisition-related liabilities In connection with the acquisition of the medical diagnostics division of Cypress Bioscience, Inc. in 2010, the Company was required to pay certain amounts in the event that certain revenue milestones were achieved and upon the first commercial sale of a product associated with this acquisition. The acquisition also included amounts that may be due under several licensing agreements. All milestone payments other than one have been paid as of December 31, 2017. The remaining milestone obligation is for an additional $2.0 million payment due to Prometheus Laboratories, Inc. (Prometheus) for which the fair value was determined to be zero at September 30, 2019 and December 31, 2018. In addition, the Company has ongoing royalty payment obligations on net sales of products which incorporate certain acquired technologies ranging from 2.5% to 7.5%. Future royalties payable under these arrangements are limited to the lesser of an aggregate of $4.2 million (including an upfront payment of $100,000) or the total royalties earned through January 1, 2024. Licensing Agreements The Company has licensed technology for use in its diagnostic tests. In addition to the milestone payments required by these agreements as described above, individual license agreements generally provide for ongoing royalty payments on net sales of products which incorporate licensed technology, as defined, ranging from 3.0% to 20.0%. Royalties are accrued when earned and recorded in costs of revenue in the accompanying condensed statement of operations. Supply Agreement In January 2018, the Company entered into a supply agreement with one supplier for reagents which includes a minimum annual purchase commitment of $3.25 million for each of the three years covered by the agreement, which terminates in 2021. Contingencies In the normal course of business, the Company enters into contracts and agreements that contain a variety of representations and warranties and provide for general indemnifications; including subpoenas and other civil investigative demands, from governmental agencies, Medicare or Medicaid payers and managed care organizations reviewing billing practices or requesting comment on allegations of billing irregularities that are brought to their attention through billing audits or third parties. The Company's exposure under these agreements is unknown because it involves claims that may be made against the Company in the future, but have not yet been made. The Company accrues a liability for such matters when it is probable that future expenditures will be made and such expenditures can be reasonably estimated. Litigation The Company is not a party to any litigation and does not have contingent reserves established for any litigation liabilities.

Fair Value Measurements - (Notes)

9 Months Ended

Sep. 30, 2019

Fair Value Disclosures [Abstract]

Fair Value Measurements

The following table sets forth the Company's financial instruments that were measured at fair value on a recurring basis within the fair value hierarchy (in thousands):


	September 30, 2019
	Total		Level 1		Level 2	Level 3
Assets:
Money market funds	$	71,950	$	71,950	—	—


	December 31, 2018
	Total		Level 1		Level 2	Level 3
	(As Revised)					(As Revised)
Assets:
Money market funds	$	8,618	$	8,618	—	—
Liabilities:
Redeemable convertible preferred stock warrant liabilities	$	1,503	—		—	$	1,503

The fair value of the Company's money market funds is based on quoted market prices.

The following table includes a roll-forward of the financial instruments measured on a recurring basis and classified within Level 3 of the fair value hierarchy (in thousands):


	Liability Classified Warrants
	(As Revised)
Balances at December 31, 2017	$	896
Issuance of warrants to purchase shares of Series F redeemable convertible preferred stock in connection with 2017 Term Loan (Note 4)	289
Remeasurement of financial instruments	318
Balances at December 31, 2018	1,503
Remeasurement of financial instruments	(267)
Net exercise of preferred stock warrants	(510)
Reclassification of liability classified warrants to stockholders' equity (deficit)	(726)
Balance at September 30, 2019	$	—

Changes in the fair value of the Company's liability classified warrants are recorded in the line item change in fair value of financial instruments in the accompanying condensed statement of operations.

- 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

Redeemable Convertible Preferred Stock	9 Months Ended
Redeemable Convertible Preferred Stock	Sep. 30, 2019
Temporary Equity Disclosure [Abstract]
Redeemable Convertible Preferred Stock	Redeemable Convertible Preferred Stock On January 2, 2019, the Company amended and restated its restated certificate of incorporation to, among other things, increase its authorized shares of convertible preferred stock from 750,300,000 to 955,500,000 shares, of which 205,200,000 shares are designated as Series G convertible preferred stock and set forth the rights, preferences and privileges of the Series G convertible preferred stock. On July 11, 2019, the Company amended and restated its restated certificate of incorporation to among other things, increase its authorized shares of convertible preferred stock from 955,500,000 to 1,038,667,059 shares, of which 479,967,595 shares are designated as Series H redeemable convertible preferred stock and set forth the rights, preferences and privileges of the Series H redeemable convertible preferred stock. Upon completion of the Company's IPO in September 2019, an aggregate of 7,816,643 shares of common stock, excluding warrant conversions, were issued to the holders of the Company's Series A-3, Series B-3, Series C, Series D, Series E, Series F and Series H redeemable convertible preferred stockholders upon the automatic conversion of all shares of redeemable convertible preferred stock to common stock. As a result, no shares of redeemable convertible preferred stock remain outstanding at September 30, 2019. Series F Financing In December 2017, the Company's Board of Directors authorized a third tranche closing of the issuance to existing preferred stockholders in connection with the Company's Series F financing, which was completed between December 2017 and January 2018. In December 2017, a group of existing investors of the Company purchased 54,246,756 shares of Series F redeemable convertible preferred stock at a per share price of $0.078 for aggregate gross proceeds of approximately $4.2 million. In early January 2018, a group of existing stockholders of the Company purchased an additional 34,914,327 shares of Series F redeemable convertible preferred stock at a per share price of $0.078 for aggregate gross proceeds of approximately $2.7 million. The Company concluded that the third tranche closing of the Series F preferred stock purchase agreement contained a single freestanding financial instrument, shares of Series F redeemable convertible preferred stock, and the Company determined there were no embedded features requiring bifurcation in the shares of Series F redeemable convertible preferred stock issued in the third tranche closing. The Company accounted for the difference between the estimated fair value and the $0.078 per share purchase price of shares of Series F redeemable convertible preferred stock issued in the third tranche closing as a deemed dividend since all investors in the third closing are existing preferred stockholders of the Company, and the Company did not identify any elements to the transaction which it believes were compensatory in nature. As a result, the Company recognized a deemed dividend in the amount of $1.2 million in the first quarter of 2018, that was recorded as additional paid-in capital (in the absence of retained earnings) in the accompanying condensed statement of redeemable convertible preferred stock and stockholders’ deficit. Series G Financing In January 2019, the Company entered into an agreement with new and certain existing preferred stockholders to issue shares of Series G redeemable convertible preferred stock in multiple separate closings at per share price of $0.078 in each closing. Shares of Series G redeemable convertible preferred stock were issuable under the Series G preferred stock purchase agreement until the earlier of March 31, 2019 or the issuance of all authorized shares of Series G redeemable convertible preferred stock, as specified in the Company's amended and restated certificate of incorporation. In January 2019 and March 2019, the Company sold 88,030,905 and 9,615,384 shares, respectively, of Series G redeemable convertible preferred stock for aggregate gross proceeds of approximately $7.6 million to new and existing investors, of which $3.75 million of gross proceeds were received as of December 31, 2018 and are included in the accompanying December 31, 2018 balance sheet. In May 2019, the Company sold an additional 51,282,048 shares of Series G redeemable convertible preferred stock for aggregate gross proceeds of approximately $4.0 million to existing investors. In addition, in May 2019, the Series G preferred stock purchase agreement was amended to include the right of the Company to require certain holders of Series G redeemable convertible preferred stock to purchase an additional 32,051,280 shares of Series G redeemable convertible preferred stock at $0.078 per share, for total aggregate proceeds of $2.5 million, at any time after July 31, 2019 and prior to May 31, 2020. This right terminated in connection with the issuance of the Series H redeemable convertible stock in July 2019. The Company concluded that the closings of the Series G preferred stock purchase agreement in January and March 2019, contained a single freestanding financial instrument, shares of Series G redeemable convertible preferred stock, and the Company determined there were no embedded features requiring bifurcation in the shares of Series G redeemable convertible preferred stock issued. The Company concluded the closing in May 2019 contained two freestanding financial instruments, shares of Series G redeemable convertible preferred stock and the Company call right, and the Company concluded there were no embedded features requiring bifurcation in the shares of Series G redeemable convertible preferred stock issued. The Company call right was deemed to have nominal value since it was with insiders with knowledge of the imminent closing of Series H redeemable convertible stock. Series H Financing In July 2019, the Company entered into an agreement with a new investor to issue shares of Series H redeemable convertible preferred stock at a per share price of $0.04712. Pursuant to the terms of the agreement, the new investor purchased 233,446,519 shares of Series H redeemable convertible preferred stock for gross proceeds of approximately $11.0 million. In connection with the Series H financing, the Company converted all of the 148,928,337 outstanding shares of the Company's Series G redeemable convertible preferred stock into 246,521,076 shares of Series H redeemable convertible preferred stock on a dollar-for-dollar basis. The Company concluded that the closing of the Series H preferred stock purchase agreement contained a single freestanding financial instrument, shares of Series H redeemable convertible preferred stock, and the Company determined there were no embedded features requiring bifurcation in the shares of Series H redeemable convertible preferred stock issued at closing. The Company accounted for the difference between the effective conversion price of $0.04712 and the fair value of the underlying common stock at the commitment date as a beneficial conversion feature, which was immediately accreted as a deemed dividend. As a result, the Company recognized a beneficial conversion feature in the amount of $6.7 million in the third quarter of 2019, that was recorded as additional paid-in capital (in the absence of retained earnings) in the accompanying condensed statement of redeemable convertible preferred stock and stockholders’ equity (deficit). Additionally, the Company concluded that the conversion of shares of Series G into shares of Series H redeemable convertible preferred stock in connection with the issuance of Series H redeemable convertible preferred stock represented an extinguishment of the Series G shares. As a result, the Company recognized a deemed dividend for the extinguishment charge in the amount of $6.9 million in the third quarter of 2019, that was recorded as additional paid-in capital (in the absence of retained earnings) in the accompanying condensed statement of redeemable convertible preferred stock and stockholders' equity (deficit).

Stock Option Plan

9 Months Ended

Sep. 30, 2019

Share-based Payment Arrangement [Abstract]

Stock Option Plan

In December 2012, the Company's Board of Directors adopted the 2013 Stock Option Plan (the Plan). Pursuant to the Plan, employees, consultants, and directors may be granted either incentive stock options or non-qualified stock options to purchase shares of the Company's common stock. In July 2019, the number of shares reserved for issuance under the Plan was increased from 669,806 to 1,663,681 shares.

In September 2019, the Company's Board of Directors adopted, and the Company's stockholders approved, the 2019 Incentive Award Plan (the 2019 Plan). Under the 2019 Plan, the Company may grant stock options, stock appreciation rights, restricted stock, restricted stock units and other awards to individuals who are then employees, officers, non-employee directors or consultants of the Company or its subsidiaries. A total of (i) 2,011,832 shares of common stock plus (ii) shares subject to awards granted under the 2013 Plan on or before the effective date of the 2019 Plan became available for issuance under the 2019 Plan and will initially be reserved for issuance under the 2019 Plan. In addition, the number of shares of common stock available for issuance under the 2019 Plan will be increased annually on the first day of each fiscal year during the term of the 2019 Plan, beginning with the 2020 fiscal year, by an amount equal to 4% of the total number of shares of capital stock outstanding on December 31st of the preceding calendar year or such smaller amount as the Board of Directors may determine. As of September 30, 2019, 1,199,631 shares remained available for future awards.

The options generally expire ten years after the date of grant and are exercisable to the extent vested. Vesting is established by the Board of Directors and is generally four years from the date of grant.

Activity under the Company's stock option plans is set forth below:


	Number of Options	Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding, December 31, 2018	661,180	$	1.22	9.52	$	6,198
Granted	814,339	$	13.99
Exercised	(50)	$	1.84
Forfeited	(310)	$	5.75
Expired	(153)	$	37.20
Outstanding, September 30, 2019	1,475,006	$	8.26	8.89	$	10,993
Vested and expected to vest, September 30, 2019	1,475,006	$	8.26	8.89	$	10,993
Options exercisable, September 30, 2019	20,464	$	30.74	4.56	$	23

The intrinsic value is calculated as the difference between the fair value of the Company's common stock and the exercise price of the stock options.

Stock-Based Compensation Expense

The fair value of employee stock options was estimated using the following assumptions to determine the fair value of stock options granted:


	Three Months Ended September 30,			Nine Months Ended September 30,
	2019	2018	2019	2018
Expected volatility	59%	70%	59%	70%
Risk-free interest rate	2.0%	2.6%	2.0%-2.6%	1.4% - 2.6%
Dividend yield	—	—	—	—
Expected term (in years)	5.75-6.08	6.08	5.75-6.08	6.08

Total non-cash stock-based compensation expense recorded related to options granted in the condensed statement of operations is as follows (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2019		2018		2019		2018
Cost of revenue	$	4	$	1	$	6	$	11
Selling, general and administrative	55		9		73		83
Research and development	3		—		6		6
Total	$	62	$	10	$	85	$	100

As of September 30, 2019, total unrecognized compensation cost was $6.4 million, which is expected to be recognized over a remaining weighted-average vesting period of 3.5 years.

Employee Stock Purchase Plan

In September 2019, the Board of Directors adopted the Employee Stock Purchase Plan (the ESPP). The ESPP became effective on the day the ESPP was adopted by the Company's Board of Directors. The ESPP permits participants to purchase common stock through payroll deductions of up to 20% of their eligible compensation. A total of 120,000 shares of common stock was initially reserved for issuance under the ESPP. In addition, the number of shares of common stock available for issuance under the ESPP will be annually increased on the first day of each fiscal year during the term of the ESPP, beginning with the 2020 fiscal year, by an amount equal to 1% of the total number capital stock outstanding on December 31 of the preceding calendar year or such smaller other amount as the Board of Directors may determine. There has been no stock-based compensation expense incurred related to the ESPP for the three and nine months ended September 30, 2019.

Related Parties	9 Months Ended
Related Parties	Sep. 30, 2019
Related Party Transactions [Abstract]
Related Parties	Related PartiesThe Company entered into a consulting services agreement, as amended, with a member of the Company's Board of Directors under which this board member provides certain scientific consulting services to the Company. Under this agreement, as amended in June 2018, this board member is compensated at a bi-weekly rate of $5,000 (plus reimbursement for certain administrative and travel related expenses) and received options to purchase 544 shares of common stock in November 2017, the commencement date of the agreement. Total amounts paid to this board member under this agreement for the three months ended September 30, 2019 and 2018 and the nine months ended September 30, 2019 and 2018, were $30,000, $30,000, $95,000, and $91,000, respectively, which was recorded in research and development expenses in the accompanying condensed statements of operations. The Company accounted for the grant of options as an award to a non-employee and measures compensation cost for this award based on the value of the award at the date the consulting services are complete. The options granted to this board member were granted at an exercise price of $0.367 (the estimated fair value of share of common stock on the grant date using an OPM model), and vests over a three-year term expected to coincide with the period the board member is expected to provide consulting services to the Company. The estimated fair value of the awards and related compensation cost recognized during the three and nine months ended September 30, 2019 and 2018 was immaterial. All compensation cost related to these awards is recorded in research and development expenses in the accompanying condensed statements of operations. Effective July 12, 2019, this consultant no longer serves on the Company's Board of Directors. In September 2011, the Company entered into a license agreement with the Company's Chief Scientific Officer, and a related company, De Novo Diagnostics, Inc. The license agreement, covering novel methods for monitoring low-dose methotrexate therapy, relates to technology developed by the Company's Chief Scientific Officer prior to joining the Company. The technology has yet to be used by the Company. Under the agreement, the Company's Chief Scientific Officer will be eligible to receive up to $0.6 million upon the achievement of certain sales milestones and an ongoing royalty of 5% on sales. The third tranche closing of the Series F financing and the closings of the Series G financing described in Note 8 were issued to existing holders of the Company's redeemable convertible preferred stock.

Summary Of Significant Accounting Policies - Policies	9 Months Ended
Summary Of Significant Accounting Policies - Policies	Sep. 30, 2019
Accounting Policies [Abstract]
Concentration of Credit Risk and Other Risk and Uncertainties	Concentration of Credit Risk and Other Risk and Uncertainties Financial instruments that potentially subject the Company to credit risk consist principally of cash, cash equivalents, and accounts receivable. Substantially all the Company's cash and cash equivalents are held at one financial institution that management believes is of high credit quality. Such deposits may, at times, exceed federally insured limits.
Fair Value Measurements	Fair Value Measurements The carrying value of the Company's cash and cash equivalents, other assets and accrued liabilities approximate fair value due to the short-term nature of these items. Based on the borrowing rates currently available to the Company for debt with similar terms and consideration of default and credit risk, the carrying value of the Company's long-term borrowings approximates its fair value, which is considered a Level 2 input. Fair value is defined as the exchange price that would be received for an asset or an exit price paid to transfer a liability in the principal or most advantageous market for the asset or liability in an orderly transaction between market participants on the measurement date. Valuation techniques used to measure fair value must maximize the use of observable inputs and minimize the use of unobservable inputs. The fair value hierarchy defines a three-level valuation hierarchy for disclosure of fair value measurements as follows: Level 1 - Unadjusted quoted prices in active markets for identical assets or liabilities; Level 2 - Inputs other than quoted prices included within Level I that are observable, unadjusted quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the related assets or liabilities; and Level 3 - Unobservable inputs that are supported by little or no market activity for the related assets or liabilities. The categorization of a financial instrument within the valuation hierarchy is based upon the lowest level of input that is significant to the fair value measurement. The Company's redeemable convertible preferred stock warrant liabilities were measured at fair value on a recurring basis and were classified as Level 3 liabilities. The Company recorded subsequent adjustments to reflect the increase or decrease in estimated fair value at each reporting date in current period earnings.
Cash, Cash Equivalents and Restricted Cash	Cash, Cash Equivalents and Restricted Cash The Company considers all highly-liquid investments purchased with a remaining maturity date upon acquisition of three months or less to be cash equivalents and are stated at cost, which approximates fair value.
Redeemable Convertible Preferred Stock	Redeemable Convertible Preferred Stock Prior to the completion of the IPO, the Company had multiple classes of redeemable convertible preferred stock, all of which were classified as temporary equity in the accompanying condensed balance sheet as the redemption of the shares were outside of the Company's control. Redeemable convertible preferred stock which was redeemable on or after a certain date at the option of the holder was accreted to its redemption value from the date of issuance to the earliest redemption date.
Revenue Recognition	Revenue Recognition Substantially all of the Company's revenue has been derived from sales of its testing products and is primarily comprised of a high volume of relatively low-dollar transactions. The Company primarily markets its testing products to rheumatologists and their physician assistants in the United States. The healthcare professionals who order the Company's testing products and to whom test results are reported are generally not responsible for payment for these products. The parties that pay for these services (the Payers) consist of healthcare insurers, government payers (primarily Medicare and Medicaid), client payers (i.e., hospitals, other laboratories, etc.), and patient self-pay. The Company's service is a single performance obligation that is completed upon the delivery of test results to the prescribing physician which triggers revenue recognition Payers are billed at the Company's list price. Net revenues recognized consist of amounts billed net of allowances for differences between amounts billed and the estimated consideration the Company expects to receive from such payers. The process for estimating revenues and the ultimate collection of accounts receivable involves significant judgment and estimation. The Company follows a standard process, which considers historical denial and collection experience, insurance reimbursement policies and other factors, to estimate allowances and implicit price concessions, recording adjustments in the current period as changes in estimates. Further adjustments to the allowances, based on actual receipts, is recorded upon settlement. The transaction price is estimated using an expected value method on a portfolio basis. The Company's portfolios are grouped per payer (i.e. each individual third-party insurance, Medicare, client payers, patient self-pay, etc.) and per test basis. Collection of the Company's net revenues from payers is normally a function of providing complete and correct billing information to the healthcare insurers and generally occurs within 30 to 90 days of billing. Contracts do not contain significant financing components based on the typical period of time between performance of services and collection of consideration. The Company early adopted Accounting Standards Codification (ASC) Topic 606, Revenue from Contracts with Customers (Topic 606) as of January 1, 2018 using a cumulative-effect adjustment to the opening balance of accumulated deficit and accounts receivable of $3.1 million.
Research and Development	Research and Development Costs associated with research and development activities are expensed as incurred and include, but are not limited to, personnel-related expenses, including stock-based compensation expense, materials, laboratory supplies, consulting costs, costs associated with setting up and conducting clinical studies and allocated overhead including rent and utilities.
Advertising and Marketing Cost	Advertising and Marketing Costs Costs associated with advertising and marketing activities are expensed as incurred. Total advertising and marketing costs were approximately $0.4 million for the three months ended September 30, 2019 and 2018, and $1.1 million for the nine months ended September 30, 2019 and 2018, and are included in selling, general and administrative expenses in the accompanying condensed statements of operations.
Stock-Based Compensation	Stock-Based Compensation The Company recognizes compensation expense for all stock-based awards to employees and directors based on the grant-date estimated fair values over the requisite service period of the awards (usually the vesting period) on a straight-line basis. The fair value of stock options is determined using the Black-Scholes-Merton (BSM) option pricing model, which requires management to make certain assumptions regarding a number of complex and subjective variables. Equity award forfeitures are recorded as they occur. The BSM option pricing model incorporates various estimates, including the fair value of the Company's common stock, expected volatility, expected term and risk-free interest rates. The weighted-average expected term of options was calculated using the simplified method. This decision was based on the lack of relevant historical data due to the Company's limited historical experience. In addition, due to the Company's limited historical data, the estimated volatility incorporates the historical volatility over the expected term of the award of comparable companies whose share prices are publicly available. The risk-free interest rate for periods within the contractual term of the option is based on the U.S. Treasury yield in effect at the time of grant. The dividend yield was zero, as the Company has never declared or paid dividends and has no plans to do so in the foreseeable future. Upon the effective date of the IPO, the Company began using the closing price of its common stock as the fair value of its common stock on the corresponding date. Prior to the completion of the IPO in September 2019, due to the absence of a public market for the Company's common stock, it was necessary to estimate the fair value of the common stock underlying the Company's stock-based awards when performing fair value calculations using the BSM option pricing model. The fair value of the common stock underlying the Company's stock-based awards was assessed on each grant date by the Company's board of directors (Board of Directors).
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as a change in equity of a business enterprise during a period, resulting from transactions from nonowner sources. There have been no items qualifying as other comprehensive loss and, therefore, for all periods presented, the Company's comprehensive loss was the same as its reported net loss.
Net Loss Per Share	Net Loss Per Share Basic net loss per share attributable to common stockholders is calculated by dividing the net loss attributable to common stockholders by the weighted-average number of common shares outstanding during the period. Diluted net loss per share attributable to common stockholders is computed by dividing the net loss attributable to common stockholders by the weighted-average number of common stock equivalents outstanding for the period determined using the treasury-stock and if-converted methods. Potentially dilutive common stock equivalents are comprised of redeemable convertible preferred stock, warrants for the purchase of redeemable convertible preferred and common stock and options outstanding under the Company's stock option plans. For the three and nine months ended September 30, 2019 and 2018, there is no difference in the number of shares used to calculate basic and diluted shares outstanding as the inclusion of the potentially dilutive securities would be antidilutive.
Segment Reporting	Segment Reporting Operating segments are identified as components of an enterprise about which separate discrete financial information is available for evaluation by the chief operating decision-maker in making decisions regarding resource allocation and assessing performance. The Company views its operations as, and manages its business in, one operating segment.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the Financial Accounting Standards Board (FASB), or other standard setting bodies and adopted by the Company as of the specified effective date. Unless otherwise discussed, the impact of recently issued standards that are not yet effective will not have a material impact on the Company's financial position or results of operations upon adoption. In February 2016, the FASB issued Accounting Standards Update (ASU) 2016-02, Leases (Topic 842). The new topic supersedes Topic 840, Leases, and increases transparency and comparability among organizations by recognizing lease assets and lease liabilities on the balance sheet and requires disclosures of key information about leasing arrangements. In July 2018, the FASB issued ASU 2018-10, Codification Improvements to Topic 842, which provides narrow amendments to clarify how to apply certain aspects of the new lease standard, and ASU 2018-11, Leases: Targeted Improvements, which was issued to provide relief to companies from restating comparative periods. Pursuant to this ASU, in the period of adoption the Company will not restate comparative periods presented in its condensed financial statements. The effective date of this guidance for public companies is for reporting periods beginning after December 15, 2018. Topic 842 mandates a modified retrospective transition method. The Company intends to adopt the new lease standard using a cumulative effect to accumulated deficit and will elect the package of practical expedients, which among other things will allow the Company to carry forward its historical lease classification. The Company is currently evaluating the impact of Topic 842 on its condensed financial statements. In August 2018, the FASB issued ASU No. 2018-13, Fair Value Measurement: Disclosure Framework--Changes to the Disclosure Requirements for Fair Value Measurement, which adds and modifies certain disclosure requirements for fair value measurements. Under the new guidance, 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, or valuation processes for Level 3 fair value measurements. However, public companies will be required to disclose the range and weighted average of significant unobservable inputs used to develop Level 3 fair value measurements, and related changes in unrealized gains and losses included in other comprehensive income. This update is effective for annual periods beginning after December 15, 2019, and interim periods within those periods, and early adoption is permitted. The Company is currently evaluating the impact of ASU 2018-13 on its condensed financial statements.

Summary Of Significant Accounting Policies - (Tables)

9 Months Ended

Sep. 30, 2019

Accounting Policies [Abstract]

Schedule of Concentration of Risk, by Risk Factor and Significant Payer

For each significant payer, revenue as a percentage of total revenue and accounts receivable as a percentage of total accounts receivable are as follows:


	Revenue
	Three Months Ended September 30,						Nine Months Ended September 30,
	2019		2018		2019		2018
Medicare	25	%	30	%	26	%	31	%
Blue Shield	13	%	14	%	13	%	14	%
United Healthcare	10	%	12	%	10	%	13	%
Medicare Advantage	12	%	12	%	11	%	11	%


	Accounts Receivable
	September 30, 2019		December 31, 2018

Medicare	23	%	26	%
Blue Shield	16	%	16	%
United Healthcare	9	%	11	%
Medicare Advantage	8	%	11	%

Disaggregation of Revenue

The following table includes the Company's revenues as disaggregated by payer category (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2019		2018		2019		2018
Revenue:
Healthcare insurers	$	6,188	$	5,408	$	17,716	$	15,023
Government	2,665		2,524		7,964		7,013
Client	1,007		171		3,200		428
Other(1)	148		120		458		335
Janssen (SIMPONI^®)	431		—		835		—
Total revenue	$	10,439	$	8,223	$	30,173	$	22,799

(1)Includes patient self-pay that is immaterial.

Schedule of Restricted Cash and Cash Equivalents

Cash, cash equivalents and restricted cash presented in the accompanying condensed statements of cash flows consist of the following (in thousands):


	September 30, 2019		December 31, 2018

Cash and cash equivalents	$	77,828	$	13,164
Restricted cash	100		100
	$	77,928	$	13,264

Schedule of Cash and Cash Equivalents

Cash, cash equivalents and restricted cash presented in the accompanying condensed statements of cash flows consist of the following (in thousands):


	September 30, 2019		December 31, 2018

Cash and cash equivalents	$	77,828	$	13,164
Restricted cash	100		100
	$	77,928	$	13,264

Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share

Potentially dilutive securities not included in the calculation of diluted net loss per share because to do so would be anti-dilutive are as follows (in common stock equivalent shares):


	Three Months Ended September 30,			Nine Months Ended September 30,
	2019	2018	2019	2018
Redeemable convertible preferred stock	—	5,202,940	—	5,202,940
Warrants to purchase redeemable convertible preferred stock	—	203,549	—	203,549
Warrants to purchase common stock	461,273	934,789	461,273	934,789
Common stock options	1,475,006	69,885	1,475,006	69,885
Total	1,936,279	6,411,163	1,936,279	6,411,163

Other Financial Information - (Tables)

9 Months Ended

Sep. 30, 2019

Other Financial Information [Abstract]

Prepaid expenses table

Prepaid expenses and other current assets consist of the following (in thousands):


	September 30, 2019		December 31, 2018
Diagnostic testing supplies	$	916	$	1,174
Prepaid product royalties	137		176
Prepaid maintenance and insurance contracts	619		698
Other prepaid assets	14		148
Prepaid and other current assets	$	1,686	$	2,196

Property and equipment

Property and equipment consist of the following (in thousands):


	September 30, 2019		December 31, 2018
Furniture and fixtures	$	25	$	25
Laboratory equipment	2,228		1,855
Computer equipment and software	851		796
Leasehold improvements	423		399
Construction in progress	71		310
Total property and equipment	3,598		3,385
Less: accumulated depreciation and amortization	(2,284)		(1,819)
Property and equipment, net	$	1,314	$	1,566

Accrued liabilities

Accrued liabilities consist of the following (in thousands):


	September 30, 2019		December 31, 2018
Accrued payroll and related expenses	$	2,850	$	2,111
Accrued deferred offering costs	1,598		355
Accrued interest	182		178
Accrued purchases of goods and services	292		243
Accrued royalties	708		602
Accrued clinical study activity	43		146
Capital lease obligations, current portion	179		81
Other accrued liabilities	597		207
Accrued liabilities	$	6,449	$	3,923

Fair Value Measures and Disclosures (Tables)

9 Months Ended

Sep. 30, 2019

Fair Value Disclosures [Abstract]

Schedule of Fair Value, Financial Instrument Measured on a Recurring Basis

The following table sets forth the Company's financial instruments that were measured at fair value on a recurring basis within the fair value hierarchy (in thousands):


	September 30, 2019
	Total		Level 1		Level 2	Level 3
Assets:
Money market funds	$	71,950	$	71,950	—	—


	December 31, 2018
	Total		Level 1		Level 2	Level 3
	(As Revised)					(As Revised)
Assets:
Money market funds	$	8,618	$	8,618	—	—
Liabilities:
Redeemable convertible preferred stock warrant liabilities	$	1,503	—		—	$	1,503

Schedule of Fair Value, Financial Instruments Measured on Recurring Basis, Level 3 Hierarchy

The following table includes a roll-forward of the financial instruments measured on a recurring basis and classified within Level 3 of the fair value hierarchy (in thousands):


	Liability Classified Warrants
	(As Revised)
Balances at December 31, 2017	$	896
Issuance of warrants to purchase shares of Series F redeemable convertible preferred stock in connection with 2017 Term Loan (Note 4)	289
Remeasurement of financial instruments	318
Balances at December 31, 2018	1,503
Remeasurement of financial instruments	(267)
Net exercise of preferred stock warrants	(510)
Reclassification of liability classified warrants to stockholders' equity (deficit)	(726)
Balance at September 30, 2019	$	—

Stock Option Plan (Tables)

9 Months Ended

Sep. 30, 2019

Share-based Payment Arrangement [Abstract]

Schedule of Stock Option Activity

Activity under the Company's stock option plans is set forth below:


	Number of Options	Weighted- Average Exercise Price		Weighted- Average Remaining Contractual Term (Years)	Aggregate Intrinsic Value
Outstanding, December 31, 2018	661,180	$	1.22	9.52	$	6,198
Granted	814,339	$	13.99
Exercised	(50)	$	1.84
Forfeited	(310)	$	5.75
Expired	(153)	$	37.20
Outstanding, September 30, 2019	1,475,006	$	8.26	8.89	$	10,993
Vested and expected to vest, September 30, 2019	1,475,006	$	8.26	8.89	$	10,993
Options exercisable, September 30, 2019	20,464	$	30.74	4.56	$	23

Schedule of Fair Value Assumptions, Stock Options

The fair value of employee stock options was estimated using the following assumptions to determine the fair value of stock options granted:


	Three Months Ended September 30,			Nine Months Ended September 30,
	2019	2018	2019	2018
Expected volatility	59%	70%	59%	70%
Risk-free interest rate	2.0%	2.6%	2.0%-2.6%	1.4% - 2.6%
Dividend yield	—	—	—	—
Expected term (in years)	5.75-6.08	6.08	5.75-6.08	6.08

Schedule of Non-cash Stock-based Compensation Expense

Total non-cash stock-based compensation expense recorded related to options granted in the condensed statement of operations is as follows (in thousands):


	Three Months Ended September 30,						Nine Months Ended September 30,
	2019		2018		2019		2018
Cost of revenue	$	4	$	1	$	6	$	11
Selling, general and administrative	55		9		73		83
Research and development	3		—		6		6
Total	$	62	$	10	$	85	$	100

Organization - (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Sep. 23, 2019	Sep. 30, 2019	Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Cash and cash equivalents		$ 77,828	$ 13,164
Accumulated deficit		$ 161,194	$ 152,564
Common Stock
Subsidiary, Sale of Stock [Line Items]
Stock issued upon conversion of redeemable convertible preferred shares (in shares)		7,816,643
Common Stock \| IPO
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in public offering	4,140,000
Shares issued in public offering, price per share (in dollars per share)	$ 14.00
Proceeds from public offering, net	$ 50,500
Stock issued upon conversion of redeemable convertible preferred shares (in shares)	7,816,643
Common Stock \| Over-Allotment Option
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in public offering	540,000

Summary Of Significant Accounting Policies - Narrative (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Jan. 01, 2018
New Accounting Pronouncement, Early Adoption [Line Items]
Restricted cash	$ 100		$ 100		$ 100
Advertising Expense	400	$ 400	1,100	$ 1,100
Revenue	10,439	8,223	30,173	22,799
Cumulative effect of changes in accounting principle related to revenue recognition						$ 3,086
ASU 606
New Accounting Pronouncement, Early Adoption [Line Items]
Cumulative effect of changes in accounting principle related to revenue recognition						$ 3,100
Janssen (SIMPONI)
New Accounting Pronouncement, Early Adoption [Line Items]
Revenue	431	0	835	0
Shipping and Handling
New Accounting Pronouncement, Early Adoption [Line Items]
Cost of revenue	400	$ 300	1,100	$ 900
Other assets
New Accounting Pronouncement, Early Adoption [Line Items]
Restricted cash	$ 100		$ 100
IPO
New Accounting Pronouncement, Early Adoption [Line Items]
Deferred Offering Costs					$ 400

Summary Of Significant Accounting Policeies - Revenue by Major Payers (Details)	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Medicare \| Revenue Benchmark \| Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percent of total revenue	25.00%	30.00%	26.00%	31.00%
Medicare \| Accounts Receivable \| Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percent of total revenue			23.00%		26.00%
Blue Shield \| Revenue Benchmark \| Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percent of total revenue	13.00%	14.00%	13.00%	14.00%
Blue Shield \| Accounts Receivable \| Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percent of total revenue			16.00%		16.00%
United Healthcare \| Revenue Benchmark \| Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percent of total revenue	10.00%	12.00%	10.00%	13.00%
United Healthcare \| Accounts Receivable \| Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percent of total revenue			9.00%		11.00%
Medicare Advantage \| Revenue Benchmark \| Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percent of total revenue	12.00%	12.00%	11.00%	11.00%
Medicare Advantage \| Accounts Receivable \| Customer Concentration Risk
Disaggregation of Revenue [Line Items]
Percent of total revenue			8.00%		11.00%
AVISE CTD Test \| Revenue Benchmark \| Product Concentration Risk
Disaggregation of Revenue [Line Items]
Percent of total revenue	83.00%	86.00%	83.00%	86.00%

Summary Of Significant Accounting Policies - Cash, cash equivalents and restricted cash (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018	Sep. 30, 2018	Dec. 31, 2017
Accounting Policies [Abstract]
Cash and cash equivalents	$ 77,828	$ 13,164
Restricted cash	100	100
Total Cash, Cash Equivalents and Restricted Cash	$ 77,928	$ 13,264	$ 5,480	$ 11,341

Other Financial Information - Prepaid expenses (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Other Financial Information [Abstract]
Other current assets	$ 916	$ 1,174
Prepaid product royalties	137	176
Prepaid maintenance and insurance contracts	619	698
Other prepaid assets	14	148
Prepaid and other current assets	$ 1,686	$ 2,196

Other Financial Information - Property and equipment (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 3,598	$ 3,385
Less: accumulated depreciation and amortization	(2,284)	(1,819)
Property and equipment, net	1,314	1,566
Furniture and fixtures
Property, Plant and Equipment [Line Items]
Total property and equipment	25	25
Laboratory equipment
Property, Plant and Equipment [Line Items]
Total property and equipment	2,228	1,855
Computer equipment and software
Property, Plant and Equipment [Line Items]
Total property and equipment	851	796
Leasehold improvements
Property, Plant and Equipment [Line Items]
Total property and equipment	423	399
Construction in progress
Property, Plant and Equipment [Line Items]
Total property and equipment	$ 71	$ 310

Other Financial Information - Accrued liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Other Financial Information [Abstract]
Accrued payroll and related expenses	$ 2,850	$ 2,111
Accrued deferred offering costs	1,598	355
Accrued interest	182	178
Accrued purchases of goods and services	292	243
Accrued royalties	708	602
Accrued clinical study activity	43	146
Capital lease obligations, current portion	179	81
Other accrued liabilities	597	207
Accrued liabilities	$ 6,449	$ 3,923

Borrowings - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 07, 2018	Sep. 30, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2017
Debt Instrument [Line Items]
Warrants issued to purchase redeemable convertible preferred stock			461,273		461,273
Number of common shares to be called upon exercise of warrants			512,363		512,363
Series F redeemable convertible preferred stock
Debt Instrument [Line Items]
Number of common shares to be called upon exercise of warrants		104,722
Loan payable \| Capital Royalty Partners II LP
Debt Instrument [Line Items]
Loan repayment							$ 17,800
2017 Term loan \| Loan payable
Debt Instrument [Line Items]
Term loan, issuance costs		$ 100
2017 Term loan \| Loan payable \| Innovatus Life Sciences Lending Fund
Debt Instrument [Line Items]
Term loan borrowings	$ 5,000	20,000
Term loan, interest rate			1100.00%		1100.00%
Term loan, paid in-kind, interest rate			250.00%		250.00%
Term loan, effective interest rate			1400.00%		1400.00%
Term loan, fee incurred upon payment of final installment			$ 1,000		$ 1,000
Term loan, prepayment premium percentage			3.00%		3.00%
Term loan, annual reduction in prepayment penalty percentage			100.00%		100.00%
Term loan covenant, interest only milestones, increase to interest rate			800.00%		800.00%
Term loan covenant, minimum issuance of equity securities and subordinated debt			$ 9,500		$ 9,500
Term loan covenant, minimum unrestricted cash balance			$ 2,000		$ 2,000
Term loan covenant, increase to interest rate			400.00%		400.00%
Term loan, issuance costs		$ 400
2017 Term loan \| Loan payable \| Innovatus Life Sciences Lending Fund \| Series F redeemable convertible preferred stock
Debt Instrument [Line Items]
Warrants issued to purchase redeemable convertible preferred stock	3,846,154	15,384,615
Warrants issued to purchase redeemable convertible preferred stock, exercise price (in dollars per share)		$ 0.078
Number of common shares to be called upon exercise of warrants		104,722
2017 Term loan \| Paid in-kind note \| Innovatus Life Sciences Lending Fund
Debt Instrument [Line Items]
Term loan, paid in-kind loans issued			$ 200	$ 100	$ 500	$ 400

Borrowings - Future minimum payments (Details) $ in Thousands	Sep. 30, 2019 USD ($)
Debt Disclosure [Abstract]
2019 (remaining)	$ 725
2020	6,125
2021	14,937
2022	11,250
Total	33,037
Unamortized debt discount and issuance costs	484
Interest	6,876
Total borrowings, net of discounts and debt issuance costs	$ 25,677

Warrants to Purchase Common or Preferred Stock - Narrative (Details) - shares	1 Months Ended
	Sep. 30, 2019	Sep. 30, 2017
Temporary Equity [Line Items]
Number of common shares called upon exercise of warrants	512,363
Number of warrants exercised	569,184
Number of warrants unexercised and terminated	9,054
Series F redeemable convertible preferred stock
Temporary Equity [Line Items]
Number of common shares called upon exercise of warrants		104,722
Series D and Series E redeemable convertible preferred stock
Temporary Equity [Line Items]
Number of common shares called upon exercise of warrants	119,771
Net exercise of common stock warrants (in shares)	27,431

Warrants to Purchase Common or Preferred Stock - Outstanding warrants (Details)	Sep. 30, 2019 $ / shares shares
Class of Warrant or Right [Line Items]
Common stock warrants, shares	461,273
Warrant expiration January 19, 2026
Class of Warrant or Right [Line Items]
Common stock warrants, shares	282,402
Exercise Price \| $ / shares	$ 1.84
Warrant expiration March 31, 2026
Class of Warrant or Right [Line Items]
Common stock warrants, shares	74,018
Exercise Price \| $ / shares	$ 1.84
Warrant expiration April 1, 2026
Class of Warrant or Right [Line Items]
Common stock warrants, shares	131
Exercise Price \| $ / shares	$ 1.84
Warrant expiration September 8, 2024
Class of Warrant or Right [Line Items]
Common stock warrants, shares	83,778
Exercise Price \| $ / shares	$ 14.32
Warrant expiration December 7, 2025
Class of Warrant or Right [Line Items]
Common stock warrants, shares	20,944
Exercise Price \| $ / shares	$ 14.32

Commitment and Contingencies - Narrative (Details)	3 Months Ended		9 Months Ended
Commitment and Contingencies - Narrative (Details)	Sep. 30, 2019 USD ($) ft² leaseExtention	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) ft² leaseExtention	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Loss Contingencies [Line Items]
Rent expense	$ 100,000	$ 100,000	$ 300,000	$ 300,000
Minimum annual purchase commitment			$ 3,250,000
Purchase commitment, term			3 years
Minimum \| Licensing Agreements
Loss Contingencies [Line Items]
Royalty obligation, percent of net sales	3.00%		3.00%
Maximum
Loss Contingencies [Line Items]
Royalty obligation, percent of net sales	20.00%		20.00%
Prometheus Laboratories
Loss Contingencies [Line Items]
Remaining milestone obligation	$ 2,000,000.0		$ 2,000,000.0
Remaining milestone obligation, fair value	0		0		$ 0
Advance royalties payment	$ 100,000		$ 100,000
Prometheus Laboratories \| Minimum
Loss Contingencies [Line Items]
Royalty obligation, percent of net sales	2.50%		2.50%
Prometheus Laboratories \| Maximum
Loss Contingencies [Line Items]
Royalty obligation, percent of net sales	7.50%		7.50%
Future minimum royalty commitment	$ 4,200,000		$ 4,200,000
Office and Laboratory
Loss Contingencies [Line Items]
Operating lease, rentable area (square feet) \| ft²	14,000		14,000
Number of operating lease extensions \| leaseExtention	2		2
Operating lease, renewal term	36 months		36 months
Office
Loss Contingencies [Line Items]
Operating lease, rentable area (square feet) \| ft²	19,500		19,500
Operating lease, renewal term	24 months		24 months

Fair Value Measurements - Fair value measurement (Details) - Recurring - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Warrants
Liabilities:
Redeemable convertible preferred stock warrant liabilities		$ 1,503
Level 1 \| Warrants
Liabilities:
Redeemable convertible preferred stock warrant liabilities		0
Level 2 \| Warrants
Liabilities:
Redeemable convertible preferred stock warrant liabilities		0
Level 3 \| Warrants
Liabilities:
Redeemable convertible preferred stock warrant liabilities		1,503
Money market funds
Assets:
Money market funds	$ 71,950	8,618
Money market funds \| Level 1
Assets:
Money market funds	71,950	8,618
Money market funds \| Level 2
Assets:
Money market funds	0	0
Money market funds \| Level 3
Assets:
Money market funds	$ 0	$ 0

Fair Value Measurements- Fair value level 3 (Details) - USD ($) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Issuance of warrants to purchase shares of Series F redeemable convertible preferred stock in connection with 2017 Term Loan (Note 4)		$ 289
Level 3
Fair Value, Net Derivative Asset (Liability) Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 1,503	896
Issuance of warrants to purchase shares of Series F redeemable convertible preferred stock in connection with 2017 Term Loan (Note 4)		289
Remeasurement of financial instruments	(267)	318
Net exercise of preferred stock warrants	(510)
Reclassification of liability classified warrants to stockholders' equity (deficit)	(726)
Ending balance	$ 0	$ 1,503

Redeemable Convertible Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands			1 Months Ended						3 Months Ended				9 Months Ended		12 Months Ended	15 Months Ended
	Sep. 23, 2019	Jan. 31, 2018	Jul. 31, 2019	May 31, 2019	Mar. 31, 2019	Jan. 31, 2019	Jan. 31, 2018	Dec. 31, 2017	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018	Mar. 31, 2019	Jan. 02, 2019	Jan. 01, 2019
Temporary Equity [Line Items]
Shares authorized (in shares)			1,038,667,059							955,500,000							955,500,000	750,300,000
Temporary Equity, Shares Redeemed upon Conversion									1,012,573,679
Deemed Dividend									$ 6,860
Beneficial conversion feature, temporary equity									$ 6,741
Common Stock
Temporary Equity [Line Items]
Stock issued upon conversion of redeemable convertible preferred shares (in shares)									7,816,643
Common Stock \| IPO
Temporary Equity [Line Items]
Stock issued upon conversion of redeemable convertible preferred shares (in shares)	7,816,643
Series G redeemable convertible preferred stock
Temporary Equity [Line Items]
Shares authorized (in shares)																	205,200,000
Number of shares sold, temporary equity				51,282,048	9,615,384	88,030,905
Sale of temporary equity, price per share (in dollars per share)						$ 0.078				$ 0.078	$ 0.078
Proceeds from sale of temporary equity				$ 4,000											$ 3,750	$ 7,600
Deemed dividend from conversion of Series G to Series H redeemable convertible preferred stock (Note 8)													$ 6,860	$ 0
Right to require mandatory purchase, temporary equity				32,051,280
Consideration to be received under mandatory purchase, temporary equity				$ 2,500
Temporary Equity, Shares Redeemed upon Conversion			148,928,337
Series F redeemable convertible preferred stock
Temporary Equity [Line Items]
Number of shares sold, temporary equity		34,914,327						54,246,756
Sale of temporary equity, price per share (in dollars per share)							$ 0.078	$ 0.078				$ 0.078
Proceeds from sale of temporary equity		$ 2,700						$ 4,200
Deemed Dividend												$ 1,200
Series H redeemable convertible preferred stock
Temporary Equity [Line Items]
Shares authorized (in shares)			479,967,595
Number of shares sold, temporary equity			233,446,519
Sale of temporary equity, price per share (in dollars per share)			$ 0.04712						$ 0.047
Proceeds from sale of temporary equity			$ 11,000
Shares issued upon conversion, temporary equity (in shares)			246,521,076
Beneficial conversion feature, temporary equity									$ 6,700				$ 6,741	$ 0

Stockholders' Equity (Deficit) (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	Sep. 23, 2019	Sep. 30, 2019	Jul. 31, 2019	Jun. 30, 2019	Jan. 31, 2019	Dec. 31, 2018
Subsidiary, Sale of Stock [Line Items]
Shares authorized (in shares)	200,000,000	200,000,000	1,970,000,000	1,675,200,000	1,675,200,000	1,470,000,000
Shares authorized (in shares)	10,000,000	10,000,000				0
Common Stock
Subsidiary, Sale of Stock [Line Items]
Stock issued upon conversion of redeemable convertible preferred shares (in shares)		7,816,643
IPO \| Common Stock
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in public offering	4,140,000
Shares issued in public offering, price per share (in dollars per share)	$ 14.00
Proceeds from public offering, net	$ 50,500
Stock issuance costs	$ 7,500
Stock issued upon conversion of redeemable convertible preferred shares (in shares)	7,816,643
Over-Allotment Option \| Common Stock
Subsidiary, Sale of Stock [Line Items]
Number of shares issued in public offering	540,000

Stock Option Plan - Narrative (Details) - USD ($)	3 Months Ended		9 Months Ended
Stock Option Plan - Narrative (Details) - USD ($)	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jul. 31, 2019	Jun. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, unrecognized compensation cost	$ 6,400,000		$ 6,400,000
Stock options, cost not yet recognized, remaining weighted average vesting period			3 years 6 months
Stock-based compensation expense	$ 62,000	$ 10,000	$ 85,000	$ 100,000
Employee Stock Purchase Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance under Stock Option Plan	120,000		120,000
Annual percentage increase in shares available for issuance under the Plan	100.00%		100.00%
Maximum Employee payroll deduction percentage	2000.00%		2000.00%
Stock-based compensation expense	$ 0		$ 0
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Stock options, expiration period			10 years
Stock options, vesting period			4 years
2013 Stock Option Plan \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance under Stock Option Plan					1,663,681	669,806
2019 Incentive Award Plan \| Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares reserved for issuance under Stock Option Plan	2,011,832		2,011,832
Annual percentage increase in shares available for issuance under the Plan	400.00%		400.00%
Shares that remain available for future awards	1,199,631		1,199,631

Stock Option Plan - Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding, December 31, 2018 (in Shares)	661,180
Granted (in Shares)	814,339
Exercised (in Shares)	(50)
Forfeited (in Shares)	(310)
Expired (in Shares)	(153)
Outstanding, September 30, 2019 (in Shares)	1,475,006	661,180
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding, December 31, 2018, Weighted Average Exercise Price (in dollars per share)	$ 1.22
Granted, Weighted Average Exercise Price (in dollars per share)	13.99
Exercised, Weighted Average Exercise Price (in dollars per share)	1.84
Forfeited, Weighted Average Exercise Price (in dollars per share)	5.75
Expired, Weighted Average Exercise Price (in dollars per share)	37.20
Outstanding, September 30, 2019, Weighted Average Exercise Price (in dollars per share)	$ 8.26	$ 1.22
Stock Options, Additional Disclosures [Abstract]
Outstanding, Weighted Average Remaining Contractual Term	8 years 10 months 20 days	9 years 6 months 7 days
Vested and expected to vest, Weighted Average Remaining Contractual Term	8 years 10 months 20 days
Options exercisable, Weighted Average Remaining Contractual Term	4 years 6 months 21 days
Outstanding, Aggregate Intrinsic Value	$ 10,993	$ 6,198
Vested and expected to vest, Aggregate Intrinsic Value	10,993
Options exercisable, Aggregate Intrinsic Value	$ 23
Vested and expected to vest, September 30, 2019 (in Shares)	1,475,006
Vested and expected to vest, September 30, 2019, Weighted Average Exercise Price (in dollars per share)	$ 8.26
Options exercisable, September 30, 2019 (in Shares)	20,464
Options exercised, September 30, 2019, Weighted Average Exercise Price (in dollars per share)	$ 30.74

Stock Option Plan - Fair Value Assumptions (Details)	3 Months Ended		9 Months Ended
Stock Option Plan - Fair Value Assumptions (Details)	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	59.00%	70.00%	59.00%	70.00%
Risk-free interest rate	2.00%	2.60%
Risk-free interest rate, minimum			2.00%	1.40%
Risk-free interest rate, maximum			2.60%	2.60%
Dividend yield	0.00%	0.00%	0.00%	0.00%
Expected term (in years)		6 years 29 days		6 years 29 days
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	5 years 9 months		5 years 9 months
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term (in years)	6 years 29 days		6 years 29 days

Related Parties (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 30, 2018	Nov. 30, 2017	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018
Related Party Transaction [Line Items]
Issued during period (in Shares)					814,339
Common stock options, exercise price (in dollars per share)					$ 13.99
Board Member \| Consulting services
Related Party Transaction [Line Items]
Expenses incurred with related party (bi-weekly rate)	$ 5		$ 30	$ 30	$ 95	$ 91
Issued during period (in Shares)		544
Common stock options, exercise price (in dollars per share)		$ 0.367
Stock options, vesting period					3 years
Chief Scientific Officer \| License Agreement
Related Party Transaction [Line Items]
Royalty obligation, percent of net sales			5.00%		5.00%
Milestone obligation			$ 600		$ 600

Accounting Changes and Error Corrections - Balance Sheet (Details) - USD ($) $ in Thousands	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Redeemable convertible preferred stock warrant liabilities	$ 0		$ 1,503	$ 1,503				$ 896
Total liabilities	34,094			35,621
Accumulated deficit	(161,194)			(152,564)
Total stockholders' deficit	$ 58,650	$ (121,734)	(116,772)	(111,966)	$ (107,807)	$ (103,293)	$ (98,879)	(96,684)
As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Redeemable convertible preferred stock warrant liabilities			2,680	2,680				896
Total liabilities				36,798
Accumulated deficit				(153,741)
Total stockholders' deficit				(113,143)
Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Redeemable convertible preferred stock warrant liabilities			$ (1,177)	(1,177)				$ 0
Total liabilities				(1,177)
Accumulated deficit				1,177
Total stockholders' deficit				$ 1,177

Accounting Changes and Error Corrections - Operations (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Change in fair value of financial instruments	$ (200)			$ 55			$ 267	$ 55	$ 318
Net loss	(3,141)	$ (2,785)	$ (2,704)	(1,756)	$ (2,146)	$ (2,793)	(8,630)	(6,695)
Net Income (Loss) Available to Common Stockholders, Basic	(17,080)			(4,524)			(26,871)	(14,309)
Net loss attributable to common stockholders (diluted)	$ (17,080)			$ (4,524)			$ (26,871)	$ (14,309)
Net loss per share, basic and diluted (USD per share)	$ (11.29)			$ (71.80)			$ (48.70)	$ (227.11)
As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Change in fair value of financial instruments									1,495
Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Change in fair value of financial instruments									$ (1,177)

- Definition

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

+ References + Details

Accounting Changes and Error Corrections - Warrant Liabilities (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Beginning balance			$ 1,503	$ 896	$ 896
Issuance of warrants to purchase shares of Series F redeemable convertible preferred stock in connection with 2017 Term Loan (Note 4)					289
Change in fair value of financial instruments	$ (200)	$ 55	267	55	318
Ending balance	$ 0		0		1,503
As Previously Reported
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Beginning balance			2,680	896	896
Issuance of warrants to purchase shares of Series F redeemable convertible preferred stock in connection with 2017 Term Loan (Note 4)					289
Change in fair value of financial instruments					1,495
Ending balance					2,680
Adjustment
Error Corrections and Prior Period Adjustments Restatement [Line Items]
Beginning balance			$ (1,177)	$ 0	0
Issuance of warrants to purchase shares of Series F redeemable convertible preferred stock in connection with 2017 Term Loan (Note 4)					0
Change in fair value of financial instruments					(1,177)
Ending balance					$ (1,177)

Stockholders' Equity (Deficit)	9 Months Ended
Stockholders' Equity (Deficit)	Sep. 30, 2019
Equity [Abstract]
Stockholders' Equity (Deficit)	Stockholders' Equity (Deficit) Common Stock Common stockholders are entitled to dividends as and when declared by the Board of Directors, subject to the rights of holders of all classes of stock outstanding having priority rights as to dividends. There have been no dividends declared to date. The holder of each share of common stock is entitled to one vote. On January 2, 2019, the Company amended and restated its restated certificate of incorporation to, among other things, increase its authorized shares of common stock from 1,470,000,000 to 1,675,200,000 shares. On July 11, 2019, the Company amended and restated its restated certificate of incorporation to, among other things, increase its authorized shares of common stock from 1,675,200,000 to 1,970,000,000 shares. The Company filed its amended and restated certificate of incorporation on September 23, 2019, authorizing 200,000,000 shares of common stock and 10,000,000 shares of preferred stock. On September 23, 2019, the Company closed its IPO of 4,140,000 shares of its common stock at a price to the public of $14.00 per share, including the exercise in full by the underwriters of their option to purchase 540,000 additional shares of the Company's common stock. Including the exercise of the option to purchase additional shares, the aggregate net proceeds to the Company from the offering was approximately $50.5 million, net of underwriting discounts, commissions and other estimated offering expenses, for aggregate expenses of approximately $7.5 million. In addition, an aggregate of 7,816,643 shares of common stock, excluding warrant conversions, were issued to the holders of the Company's Series A-3, Series B-3, Series C, Series D, Series E, Series F and Series H redeemable convertible preferred stockholders upon the automatic conversion of all shares of redeemable convertible preferred stock to common stock.

Label	Element	Value
Retained Earnings [Member]
Cumulative Effect of New Accounting Principle in Period of Adoption	us-gaap_CumulativeEffectOfNewAccountingPrincipleInPeriodOfAdoption	$ 3,086,000