CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Total	Common Stock	Paid-In Capital	Accumulated Other Comprehensive Loss	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2020		128,138,311
Beginning balance at Dec. 31, 2020	$ 146,379	$ 1,282	$ 643,269	$ 0	$ (498,172)
Common stock Issued upon exercise of warrants (in shares)		1,863,058
Issuance of common stock upon exercise of warrants	1,117	$ 18	1,099
Non-cash stock-based compensation	562		562
Issuance of common stock under stock plans, net of taxes ( in shares)		(121,499)
Issuance of common stock under stock plans, net of taxes		$ (1)	1
Other comprehensive loss	0
Net loss	(10,057)				(10,057)
Issuance of common stock, net of issuance costs (in shares)		68,170,579
Issuance of common stock, net of issuance costs	457,690	$ 682	457,008
Ending balance (in shares) at Mar. 31, 2021		198,050,449
Ending balance at Mar. 31, 2021	595,691	$ 1,981	1,101,939	0	(508,229)
Beginning balance (in shares) at Dec. 31, 2021		201,988,662
Beginning balance at Dec. 31, 2021	547,255	$ 2,020	1,103,224	(614)	(557,375)
Common stock Issued upon exercise of warrants (in shares)		4,677
Issuance of common stock upon exercise of warrants	3		3
Non-cash stock-based compensation	4,044		4,044
Issuance of common stock under stock plans, net of taxes ( in shares)		(240,617)
Issuance of common stock under stock plans, net of taxes	(221)	$ (1)	(220)
Other comprehensive loss	(973)			(973)
Net loss	(15,673)				(15,673)
Ending balance (in shares) at Mar. 31, 2022		201,752,722
Ending balance at Mar. 31, 2022	$ 534,435	$ 2,019	$ 1,107,051	$ (1,587)	$ (573,048)