STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid In Capital	Accumulated Deficit
Balance at Dec. 31, 2020	$ 123,982	$ 215	$ 887,868	$ (764,101)
Balance (in shares) at Dec. 31, 2020		214,591,906
Stock-based compensation	2,197		2,197
Exercise of employee stock options	1,016		1,016
Exercise of employee stock options (in shares)		352,442
Restricted stock awards (in shares)		313,326
Net loss	(21,554)			(21,554)
Balance at Mar. 31, 2021	105,641	$ 215	891,081	(785,655)
Balance (in shares) at Mar. 31, 2021		215,257,674
Balance at Dec. 31, 2021	58,057	$ 216	900,693	(842,852)
Balance (in shares) at Dec. 31, 2021		216,127,443
Stock-based compensation	853		853
Cancelled restricted common stock (in shares)		(176,882)
Net loss	(9,788)			(9,788)
Balance at Mar. 31, 2022	$ 49,122	$ 216	$ 901,546	$ (852,640)
Balance (in shares) at Mar. 31, 2022		215,950,561