CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Beginning balance, value at Dec. 31, 2019	$ 9,201	$ 271	$ 704,351	$ (695,421)
Beginning balance, shares at Dec. 31, 2019		271,177,000
Shares issued for exercise of options	72		72
Shares issued for exercise of options (in shares)		351,000
Shares issued for vested restricted stock units (in shares)		150,000
Share-based compensation	2,366		2,366
Net loss	(56,849)			(56,849)
Ending balance, value at Mar. 31, 2020	(45,210)	$ 271	706,789	(752,270)
Ending balance, shares at Mar. 31, 2020		271,678,000
Beginning balance, value at Dec. 31, 2019	9,201	$ 271	704,351	(695,421)
Beginning balance, shares at Dec. 31, 2019		271,177,000
Net loss	(141,437)
Ending balance, value at Sep. 30, 2020	(116,033)	$ 273	720,552	(836,858)
Ending balance, shares at Sep. 30, 2020		272,812,000
Beginning balance, value at Mar. 31, 2020	(45,210)	$ 271	706,789	(752,270)
Beginning balance, shares at Mar. 31, 2020		271,678,000
Shares issued for exercise of options	95	$ 1	94
Shares issued for exercise of options (in shares)		313,000
Shares issued for vested restricted stock units (in shares)		303,000
Share-based compensation	3,003		3,003
Net loss	(51,976)			(51,976)
Ending balance, value at Jun. 30, 2020	(94,088)	$ 272	709,886	(804,246)
Ending balance, shares at Jun. 30, 2020		272,294,000
Shares issued for exercise of warrants and options, net of cashless exercises	106	$ 1	105
Shares issued for exercise of warrants and options, net of cashless exercises (in shares)		518,000
Warrants issued in relation to debt financing agreement	7,428		7,428
Share-based compensation	3,133		3,133
Net loss	(32,612)			(32,612)
Ending balance, value at Sep. 30, 2020	(116,033)	$ 273	720,552	(836,858)
Ending balance, shares at Sep. 30, 2020		272,812,000
Beginning balance, value at Dec. 31, 2020	$ (124,001)	$ 300	754,644	(878,945)
Beginning balance, shares at Dec. 31, 2020	299,765,000	299,765,000
Shares issued for sale of common stock, net of cost, value	$ 150,899	$ 93	150,806
Shares issued for sale of common stock, net of cost, shares		92,870,000
Shares issued for exercise of warrants and options, net of cashless exercises	50		50
Shares issued for exercise of warrants and options, net of cashless exercises (in shares)		503,000
Shares issued for vested restricted stock units (in shares)		52,000
Share-based compensation	2,957		2,957
Net loss	(39,383)			(39,383)
Ending balance, value at Mar. 31, 2021	(9,478)	$ 393	908,457	(918,328)
Ending balance, shares at Mar. 31, 2021		393,190,000
Beginning balance, value at Dec. 31, 2020	$ (124,001)	$ 300	754,644	(878,945)
Beginning balance, shares at Dec. 31, 2020	299,765,000	299,765,000
Shares issued for exercise of options (in shares)	61,000
Net loss	$ (129,455)
Ending balance, value at Sep. 30, 2021	$ (57,360)	$ 425	950,615	(1,008,400)
Ending balance, shares at Sep. 30, 2021	424,879,000	424,879,000
Beginning balance, value at Mar. 31, 2021	$ (9,478)	$ 393	908,457	(918,328)
Beginning balance, shares at Mar. 31, 2021		393,190,000
Shares issued for sale of common stock, net of cost, value	163		163
Shares issued for sale of common stock, net of cost, shares		125,000
Shares issued for exercise of warrants and options, net of cashless exercises	228	$ 1	227
Shares issued for exercise of warrants and options, net of cashless exercises (in shares)		600,000
Shares issued for exercise of options	21		21
Shares issued for exercise of options (in shares)		54,000
Shares issued for vested restricted stock units		$ 1	(1)
Shares issued for vested restricted stock units (in shares)		929,000
Shares issued for sale of common stock related to employee stock purchase plan	134		134
Shares issued for sale of common stock related to employee stock purchase plan (in shares)		150,000
Share-based compensation	2,510		2,510
Net loss	(42,652)			(42,652)
Ending balance, value at Jun. 30, 2021	(49,074)	$ 395	911,511	(960,980)
Ending balance, shares at Jun. 30, 2021		395,048,000
Shares issued for sale of common stock, net of cost, value	31,819	$ 29	31,790
Shares issued for sale of common stock, net of cost, shares		28,770,000
Shares issued for exercise of options	3		3
Shares issued for exercise of options (in shares)		7,000
Shares issued for vested restricted stock units		$ 1	(1)
Shares issued for vested restricted stock units (in shares)		1,054,000
Share-based compensation	7,312		7,312
Net loss	(47,420)			(47,420)
Ending balance, value at Sep. 30, 2021	$ (57,360)	$ 425	$ 950,615	$ (1,008,400)
Ending balance, shares at Sep. 30, 2021	424,879,000	424,879,000