Consolidated Statements of Changes in Stockholders' Equity - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balances at Dec. 31, 2018	$ 67,428	$ 2	$ 184,314	$ (27)	$ (116,861)
Balances (in shares) at Dec. 31, 2018		24,140
Issuance of common stock in connection with employee stock purchase plan	307		307
Issuance of common stock in connection with employee stock purchase plan (in shares)		45
Issuance of common stock in connection with exercise of stock options	1,143		1,143
Issuance of common stock in connection with exercise of stock options (in shares)		274
Issuance of common stock and pre-funded warrants in connection with public and at-the-market offerings, net of offering costs	64,503	$ 1	64,502
Issuance of common stock and pre-funded warrants in connection with public and at-the-market offerings, net of offering costs (in shares)		4,625
Stock-based compensation expense	4,876		4,876
Foreign currency translation adjustment	0
Unrealized (loss) gain on marketable securities	78			78
Net loss	(78,254)				(78,254)
Balances at Dec. 31, 2019	60,081	$ 3	255,142	51	(195,115)
Balances (in shares) at Dec. 31, 2019		29,084
Issuance of common stock in connection with employee stock purchase plan	366		366
Issuance of common stock in connection with employee stock purchase plan (in shares)		60
Issuance of common stock in connection with exercise of stock options	490		490
Issuance of common stock in connection with exercise of stock options (in shares)		127
Issuance of common stock and pre-funded warrants in connection with public and at-the-market offerings, net of offering costs	153,572	$ 2	153,570
Issuance of common stock and pre-funded warrants in connection with public and at-the-market offerings, net of offering costs (in shares)		18,688
Stock-based compensation expense	6,256		6,256
Foreign currency translation adjustment	19			19
Unrealized (loss) gain on marketable securities	(59)			(59)
Net loss	(80,893)				(80,893)
Balances at Dec. 31, 2020	139,832	$ 5	415,824	11	(276,008)
Balances (in shares) at Dec. 31, 2020		47,959
Issuance of common stock in connection with employee stock purchase plan	454		454
Issuance of common stock in connection with employee stock purchase plan (in shares)		83
Issuance of common stock in connection with exercise of stock options	$ 1,449		1,449
Issuance of common stock in connection with exercise of stock options (in shares)	313,095	313
Issuance of common stock and pre-funded warrants in connection with public and at-the-market offerings, net of offering costs (in shares)		1,000
Stock-based compensation expense	$ 8,038		8,038
Foreign currency translation adjustment	(1)			(1)
Unrealized (loss) gain on marketable securities	(30)			(30)
Net loss	(65,801)				(65,801)
Balances at Dec. 31, 2021	$ 83,941	$ 5	$ 425,765	$ (20)	$ (341,809)
Balances (in shares) at Dec. 31, 2021		49,355