Condensed Statements of Redeemable Convertible Preferred Stock and Stockholders' Equity (Deficit) (unaudited) - USD ($) $ in Thousands	Total	Redeemable Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive Income
Beginning balance at Dec. 31, 2018	$ (134,553)		$ 1	$ 4,557	$ (139,111)	$ 0
Beginning balance (in shares) at Dec. 31, 2018			1,135,310
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	375			375
Exercise of stock options (in shares)			251,305
Stock-based compensation	262			262
Net loss	(24,158)				(24,158)
Comprehensive loss	(24,158)				(24,158)
Unrealized gains on investments, net	0
Ending balance at Mar. 31, 2019	(158,074)		$ 1	5,194	(163,269)	0
Ending balance (in shares) at Mar. 31, 2019			1,386,615
Temporary equity, beginning balance at Dec. 31, 2018		$ 105,235
Temporary equity, beginning balance (in shares) at Dec. 31, 2018		21,233,190
Increase (Decrease) in Temporary Equity [Roll Forward]
Exercise of warrants		$ 30
Exercise of warrants (in shares)		4,915
Temporary equity, ending balance at Mar. 31, 2019		$ 105,265
Temporary equity, ending balance (in shares) at Mar. 31, 2019		21,238,105
Beginning balance at Dec. 31, 2019	71,891		$ 31	263,384	(191,526)	2
Beginning balance (in shares) at Dec. 31, 2019			31,255,267
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options	$ 274			274
Exercise of stock options (in shares)	140,370		140,370
Stock-based compensation	$ 1,293			1,293
Net loss	(9,941)				(9,941)
Unrealized gains on investments, net	440					440
Ending balance at Mar. 31, 2020	$ 63,957		$ 31	$ 264,951	$ (201,467)	$ 442
Ending balance (in shares) at Mar. 31, 2020			31,395,637