CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-In Capital	Accumulated Deficit	Accumulated Other Comprehensive Gain (Loss)
Balances at Dec. 31, 2020	$ 210,947	$ 310	$ 1,366,188	$ (1,155,629)	$ 78
Balances (in shares) at Dec. 31, 2020		310,566,853
Increase (Decrease) in Stockholders' Equity
Net loss	(27,824)			(27,824)
Other comprehensive loss	(43)				(43)
Issuance of common stock in connection with at market offering, net of issuance costs	16,234	$ 8	16,226
Issuance of common stock in connection with at market offering, net of issuance costs (in shares)		7,948,505
Stock-based compensation related to issuance of common stock and options in exchange for services	25		25
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)		4,549
Issuance of common stock in connection with exercise of warrants	12		12
Issuance of common stock in connection exercise of warrants (in shares)		8,869
Issuance of common stock under equity plans	17		17
Issuances of common stock under equity plans (in shares)		16,232
Stock-based compensation for equity-based awards to employees and directors	1,794		1,794
Balances at Mar. 31, 2021	201,162	$ 318	1,384,262	(1,183,453)	35
Balances (in shares) at Mar. 31, 2021		318,545,008
Balances at Dec. 31, 2021	126,416	$ 324	1,398,006	(1,271,741)	(173)
Balances (in shares) at Dec. 31, 2021		323,731,591
Increase (Decrease) in Stockholders' Equity
Net loss	(30,098)			(30,098)
Other comprehensive loss	(538)				(538)
Stock-based compensation related to issuance of common stock and options in exchange for services	15		15
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)		5,284
Stock-based compensation for equity-based awards to employees and directors	1,692		1,692
Balances at Mar. 31, 2022	$ 97,487	$ 324	$ 1,399,713	$ (1,301,839)	$ (711)
Balances (in shares) at Mar. 31, 2022		323,736,875