Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Balances at Dec. 31, 2017	$ 50,337	$ 2	$ 122,950	$ (102)	$ (72,513)
Balances (in shares) at Dec. 31, 2017		16,670,000
Issuance of common stock in connection with employee stock purchase plan	207		207
Issuance of common stock in connection with employee stock purchase plan (in shares)		56,000
Issuance of common stock in connection with exercise of stock options	2,829		2,829
Issuance of common stock in connection with exercise of stock options (in shares)		521,000
Issuance of common stock in connection with public and at-the-market offerings, net of offering costs	54,048		54,048
Issuance of common stock in connection with public and at-the-market offerings, net of offering costs (in shares)		6,893,000
Stock-based compensation expense	4,280		4,280
Unrealized (loss) gain on marketable securities	75			75
Net loss	(44,348)				(44,348)
Balances at Dec. 31, 2018	67,428	$ 2	184,314	(27)	(116,861)
Balances (in shares) at Dec. 31, 2018		24,140,000
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)		45,000
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)		274,000
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)		4,625,000
Stock-based compensation expense	4,876		4,876
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		29,084,000
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)		60,000
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)	127,376	127,000
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)		18,688,000
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		47,959,000