STATEMENTS OF REDEEMABLE CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY (DEFICIT) - USD ($)	Total	Common Stock	Treasury Stock	Additional Paid-in Capital	Accumulated Deficit	Redeemable Convertible Preferred Stock
Redeemable convertible preferred stock, beginning balance at Dec. 31, 2016						$ 89,567,000
Redeemable convertible preferred stock, beginning balance, shares at Dec. 31, 2016						9,131,999
Temporary equity, Accretion of redeemable preferred stock to redemption value						$ 67,000
Redeemable convertible preferred stock, ending balance at Dec. 31, 2017	$ 89,633,543					$ 89,634,000
Redeemable convertible preferred stock, ending balance, shares at Dec. 31, 2017	9,131,999					9,131,999
Beginning balance at Dec. 31, 2016	$ (87,182,000)	$ 1,000	$ (24,000)	$ 1,659,000	$ (88,818,000)
Beginning balance, shares at Dec. 31, 2016		773,208	(29,967)
Exercises of stock options	3,000			3,000
Exercises of stock options, shares		2,547
Stock-based compensation	77,000			77,000
Accretion of redeemable preferred stock to redemption value	(67,000)			(67,000)
Net loss	(10,247,000)				(10,247,000)
Ending balance at Dec. 31, 2017	$ (97,416,000)	$ 1,000	$ (24,000)	1,672,000	(99,065,000)
Ending balance, shares at Dec. 31, 2017	745,788	775,755	(29,967)
Issuance of redeemable preferred stock						$ 14,890,000
Issuance of redeemable preferred stock, shares						1,842,959
Issuance of redeemable preferred stock upon conversion of promissory notes						$ 19,778,000
Issuance of redeemable preferred stock upon conversion of promissory notes, shares						2,080,209
Exercises of warrants						$ 1,212,000
Exercises of warrants, shares						144,948
Temporary equity, Accretion of redeemable preferred stock to redemption value						$ 95,000
Temporary equity, conversion of redeemable convertible preferred stock into common stock						$ (125,609,000)
Temporary equity, conversion of redeemable convertible preferred stock into common stock, shares						(13,200,115)
Redeemable convertible preferred stock, ending balance, shares at Dec. 31, 2018	0
Conversion of redeemable convertible preferred stock warrants into common stock warrants	$ 3,346,000			3,346,000
Conversion of redeemable convertible preferred stock into common stock	125,609,000	$ 13,000		125,596,000
Conversion of redeemable convertible preferred stock into common stock, shares		13,225,048
Issuance of common stock in initial public offering, net	42,974,000	$ 10,000		42,964,000
Issuance of common stock in initial public offering, net, shares		9,864,666
Exercises of warrants for common stock, net	(69,000)	$ 1,000		(70,000)
Exercises of warrants for common stock, net (in shares)		619,086
Exercises of stock options	92,000			92,000
Exercises of stock options, shares		43,687
Stock-based compensation	332,000			332,000
Accretion of redeemable preferred stock to redemption value	(95,000)			(95,000)
Net loss	(23,846,000)				(23,846,000)
Ending balance at Dec. 31, 2018	$ 50,927,000	$ 25,000	$ (24,000)	$ 173,837,000	$ (122,911,000)
Ending balance, shares at Dec. 31, 2018	24,498,275	24,528,242	(29,967)