CONDENSED 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, 2019	$ 135,155	$ 200	$ 1,214,835	$ (1,080,012)	$ 132
Balances (in shares) at Dec. 31, 2019		199,814,581
Increase (Decrease) in Stockholders' Equity
Net loss	(16,355)			(16,355)
Other comprehensive (loss) income	(256)				(256)
Issuance of common stock in connection with at market offering, net of issuance costs	686		686
Issuance of common stock in connection with at market offering, net of issuance costs (in shares)		530,228
Stock-based compensation related to issuance of common stock and options in exchange for services	16		16
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)		6,039
Stock-based compensation for equity- based awards to employees and directors	1,568		1,568
Balances at Mar. 31, 2020	120,814	$ 200	1,217,105	(1,096,367)	(124)
Balances (in shares) at Mar. 31, 2020		200,350,848
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) income	(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 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