Condensed Consolidated Statements of Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	Common stock	Additional paid-in capital	Treasury stock	Accumulated other comprehensive income (loss)	Accumulated deficit
Beginning balance (in shares) at Dec. 31, 2018		5,193,915		418,981
Beginning balance at Dec. 31, 2018	$ (149,753)	$ 6	$ 7,290	$ 0	$ 0	$ (157,049)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		1,335
Exercise of common stock options	12		12
Accretion of preferred stock to redemption value	(46)		(46)
Stock-based compensation	1,137		1,137
Net loss	(11,573)					(11,573)
Ending balance (in shares) at Mar. 31, 2019		5,195,250		418,981
Ending balance at Mar. 31, 2019	(160,223)	$ 6	8,393	$ 0	0	(168,622)
Beginning balance (in shares) at Dec. 31, 2018		5,193,915		418,981
Beginning balance at Dec. 31, 2018	(149,753)	$ 6	7,290	$ 0	0	(157,049)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Reclassification of warrants to additional paid-in capital	476
Net loss	(43,324)
Ending balance (in shares) at Sep. 30, 2019		23,517,446		418,981
Ending balance at Sep. 30, 2019	74,344	$ 24	274,693	$ 0	0	(200,373)
Beginning balance (in shares) at Mar. 31, 2019		5,195,250		418,981
Beginning balance at Mar. 31, 2019	(160,223)	$ 6	8,393	$ 0	0	(168,622)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		44,697
Exercise of common stock options	211		211
Conversion of preferred stock to common stock upon closing of the initial public offering (in shares)		14,641,997
Conversion of preferred stock to common stock upon closing of the initial public offering	197,888	$ 15	197,873
Issuance of common stock, net of issuance costs (in shares)		3,571,428
Issuance of common stock, net of issuance costs	64,532	$ 3	64,529
Reclassification of warrants to additional paid-in capital	476		476
Exercise of common stock warrant (in shares)		45,414
Exercise of common stock warrant	0
Stock-based compensation	1,507		1,507
Net loss	(14,447)					(14,447)
Ending balance (in shares) at Jun. 30, 2019		23,498,786		418,981
Ending balance at Jun. 30, 2019	89,944	$ 24	272,989	$ 0	0	(183,069)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		18,660
Exercise of common stock options	26		26
Stock-based compensation	1,678		1,678
Net loss	(17,304)					(17,304)
Ending balance (in shares) at Sep. 30, 2019		23,517,446		418,981
Ending balance at Sep. 30, 2019	74,344	$ 24	274,693	$ 0	0	(200,373)
Beginning balance (in shares) at Dec. 31, 2019		23,607,797		418,981
Beginning balance at Dec. 31, 2019	60,224	$ 24	276,286	$ 0	0	(216,086)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Stock-based compensation	1,599		1,599
Net loss	(15,009)					(15,009)
Ending balance (in shares) at Mar. 31, 2020		23,607,797		418,981
Ending balance at Mar. 31, 2020	46,814	$ 24	277,885	$ 0	0	(231,095)
Beginning balance (in shares) at Dec. 31, 2019		23,607,797		418,981
Beginning balance at Dec. 31, 2019	$ 60,224	$ 24	276,286	$ 0	0	(216,086)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)	4,071
Reclassification of warrants to additional paid-in capital	$ 0
Net loss	(41,338)
Ending balance (in shares) at Sep. 30, 2020		37,919,824		418,981
Ending balance at Sep. 30, 2020	88,762	$ 38	346,152	$ 0	(4)	(257,424)
Beginning balance (in shares) at Mar. 31, 2020		23,607,797		418,981
Beginning balance at Mar. 31, 2020	46,814	$ 24	277,885	$ 0	0	(231,095)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options (in shares)		3,166
Exercise of common stock options	0
Issuance of common stock, net of issuance costs (in shares)		13,055,264
Issuance of common stock, net of issuance costs	58,085	$ 13	58,072
Stock-based compensation	1,956		1,956
Net loss	(13,892)					(13,892)
Ending balance (in shares) at Jun. 30, 2020		36,666,227		418,981
Ending balance at Jun. 30, 2020	92,963	$ 37	337,913	$ 0	0	(244,987)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock, net of issuance costs (in shares)		1,253,597
Issuance of common stock, net of issuance costs	6,868	$ 1	6,867
Stock-based compensation	1,372		1,372
Unrealized loss on available-for-sale securities	(4)				(4)
Net loss	(12,437)					(12,437)
Ending balance (in shares) at Sep. 30, 2020		37,919,824		418,981
Ending balance at Sep. 30, 2020	$ 88,762	$ 38	$ 346,152	$ 0	$ (4)	$ (257,424)