CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Accumulated Deficit	Accumulated Other Comprehensive (Loss) Income
Beginning balance (in shares) at Dec. 31, 2020		91,502,461
Beginning balance at Dec. 31, 2020	$ 130,670	$ 915	$ 1,176,647	$ (1,046,889)	$ (3)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Recognition of stock-based compensation	1,099		1,099
Exercise of stock options (in shares)		31,811
Exercise of stock options	79	$ 1	78
Unrealized gain (loss) on marketable securities	(6)				(6)
Net loss	(9,927)			(9,927)
Ending balance (in shares) at Mar. 31, 2021		91,534,272
Ending balance at Mar. 31, 2021	$ 121,915	$ 916	1,177,824	(1,056,816)	(9)
Beginning balance (in shares) at Dec. 31, 2021	91,645,369	91,645,369
Beginning balance at Dec. 31, 2021	$ 90,707	$ 916	1,182,225	(1,092,325)	(109)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Recognition of stock-based compensation	$ 1,718		1,718
Exercise of stock options (in shares)	0	0
Exercise of stock options	$ 0	$ 0	0
Unrealized gain (loss) on marketable securities	(342)				(342)
Net loss	$ (16,109)			(16,109)
Ending balance (in shares) at Mar. 31, 2022	91,645,369	91,645,369
Ending balance at Mar. 31, 2022	$ 75,974	$ 916	$ 1,183,943	$ (1,108,434)	$ (451)