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, 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	(75,617)			(75,617)
Other comprehensive loss	(54)				(54)
Issuance of common stock, pre-funded warrant and warrants to purchase common stock in public offering, net of issuance costs	140,184	$ 107	140,077
Issuance of common stock, pre-funded warrant and warrants to purchase common stock in public offering, net of issuance costs (in shares)		107,049,375
Issuance of common stock in connection with at market offering, net of issuance costs	4,075	$ 3	4,072
Issuance of common stock in connection with at market offering, net of issuance costs (in shares)		3,496,616
Issuance of common stock in connection exercise of warrants	16		16
Issuance of common stock in connection exercise of warrants (in shares)		12,500
Stock-based compensation related to issuance of common stock and options in exchange for services	85		85
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)		17,986
Issuances of common stock under equity plans	208		208
Issuances of common stock under equity plans (in shares)		175,795
Stock-based compensation for equity-based awards to employees and directors	6,895		6,895
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	(116,112)			(116,112)
Other comprehensive loss	(251)				(251)
Issuance of common stock in connection with at market offering, net of issuance costs	20,385	$ 11	20,374
Issuance of common stock in connection with at market offering, net of issuance costs (in shares)		10,571,556
Issuance of common stock in connection exercise of warrants	2,479	$ 2	2,477
Issuance of common stock in connection exercise of warrants (in shares)		1,906,341
Stock-based compensation related to issuance of common stock and options in exchange for services	91		91
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)		20,783
Issuances of common stock under equity plans	797	$ 1	796
Issuances of common stock under equity plans (in shares)		666,058
Stock-based compensation for equity-based awards to employees and directors	8,080		8,080
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	323,731,591
Increase (Decrease) in Stockholders' Equity
Net loss	$ (141,901)			(141,901)
Other comprehensive loss	(68)				(68)
Foreign currency translation adjustment	22				22
Issuance of common stock, pre-funded warrant and warrants to purchase common stock in public offering, net of issuance costs	69,916	$ 53	69,863
Issuance of common stock, pre-funded warrant and warrants to purchase common stock in public offering, net of issuance costs (in shares)		53,333,334
Issuance of common stock in connection exercise of warrants	15,163	$ 12	15,151
Issuance of common stock in connection exercise of warrants (in shares)		11,663,387
Stock-based compensation related to issuance of common stock and options in exchange for services	264		264
Stock-based compensation related to issuance of common stock and options in exchange for services (in shares)		15,962
Issuances of common stock under equity plans	2,185	$ 1	2,184
Issuances of common stock under equity plans (in shares)		1,518,250
Stock-based compensation for equity-based awards to employees and directors	8,001		8,001
Balances at Dec. 31, 2022	$ 79,998	$ 390	$ 1,493,469	$ (1,413,642)	$ (219)
Balances (in shares) at Dec. 31, 2022	390,262,524	390,262,524