CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Common Stock	Additional Paid-In Capital	Accumulated Other Comprehensive Income.	Accumulated Deficit	Total
Balance at Dec. 31, 2018	$ 12	$ 1,083,903	$ 2,583	$ (962,438)	$ 124,060
Balance (in shares) at Dec. 31, 2018	11,957,635
Increase (Decrease) in Stockholders' Equity
Shares issued under stock option and employee stock purchase plans		9			9
Shares issued under stock option and employee stock purchase plans (in shares)	3,285
Shares issued in connection with at the market agreement	$ 5	16,243			16,248
Shares issued in connection with at the market agreement (in shares)	5,011,157
Stock-based compensation		4,551			4,551
Unrealized gain (loss) on marketable securities			36		36
Net loss				(50,878)	(50,878)
Balance at Dec. 31, 2019	$ 17	1,104,706	2,619	(1,013,316)	94,026
Balance (in shares) at Dec. 31, 2019	16,972,077
Increase (Decrease) in Stockholders' Equity
Shares issued under stock option and employee stock purchase plans		434			434
Shares issued under stock option and employee stock purchase plans (in shares)	122,076
Shares issued in connection with at the market agreement	$ 8	29,423			29,431
Shares issued in connection with at the market agreement (in shares)	7,125,004
Shares issued in underwritten offering, net	$ 15	141,346			141,361
Shares issued in underwritten offering, net (in shares)	15,384,614
Stock-based compensation		3,915			3,915
Unrealized gain (loss) on marketable securities			(30)		(30)
Net loss				(59,780)	(59,780)
Balance at Dec. 31, 2020	$ 40	1,279,824	2,589	(1,073,096)	$ 209,357
Balance (in shares) at Dec. 31, 2020	39,603,771				39,603,771
Increase (Decrease) in Stockholders' Equity
Shares issued under stock option and employee stock purchase plans		2,479			$ 2,479
Shares issued under stock option and employee stock purchase plans (in shares)	281,189
Shares issued in underwritten offering, net	$ 7	269,886			269,893
Shares issued in underwritten offering, net (in shares)	6,845,238
Stock-based compensation		8,953			8,953
Unrealized gain (loss) on marketable securities			(695)		(695)
Net loss				(70,511)	(70,511)
Balance at Dec. 31, 2021	$ 47	$ 1,561,142	$ 1,894	$ (1,143,607)	$ 419,476
Balance (in shares) at Dec. 31, 2021	46,730,198				46,730,198