CONSOLIDATED STATEMENTS OF STOCKHOLDERS' (DEFICIT) - USD ($) $ in Thousands	Total	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Deficit [Member]
Beginning balance, value at Dec. 31, 2018	$ 97,524	$ 240	$ 616,560	$ (519,276)
Beginning balance, shares at Dec. 31, 2018		240,462,000
Shares issued for sale of common stock, net of cost	77,031	$ 30	77,001
Shares issued for sale of common stock, net of cost (in shares)		29,900,000
Shares issued for exercise of warrants, net of cashless exercises		$ 1	(1)
Shares issued for exercise of warrants, net of cashless exercises (in shares)		471,000
Shares issued for exercise of options	$ 109		109
Shares issued for exercise of options (in shares)	344,000	344,000
Share-based payment award compensation costs	$ 10,682		10,682
Net loss	(176,145)			(176,145)
Ending balance, value at Dec. 31, 2019	9,201	$ 271	704,351	(695,421)
Ending balance, shares at Dec. 31, 2019		271,177,000
Shares issued for sale of common stock, net of cost	31,703	$ 27	31,676
Shares issued for sale of common stock, net of cost (in shares)		26,953,000
Shares issued for exercise of options	$ 272	$ 1	271
Shares issued for exercise of options (in shares)	1,182,000	1,182,000
Shares issued for vested restricted and performance stock units		$ 1	(1)
Shares issued for vested restricted and performance stock units (in shares)		453,000
Warrants issued in relation to debt financing agreement	$ 7,668		7,668
Share-based payment award compensation costs	10,679		10,679
Net loss	(183,524)			(183,524)
Ending balance, value at Dec. 31, 2020	$ (124,001)	$ 300	754,644	(878,945)
Ending balance, shares at Dec. 31, 2020	299,765,000	299,765,000
Shares issued for sale of common stock, net of cost	$ 184,115	$ 122	183,993
Shares issued for sale of common stock, net of cost (in shares)		121,765,000
Shares issued for exercise of warrants, net of cashless exercises	278	$ 1	277
Shares issued for exercise of warrants, net of cashless exercises (in shares)		1,103,000
Shares issued for exercise of options	$ 44		44
Shares issued for exercise of options (in shares)	111,000	111,000
Shares issued for vested restricted and performance stock units		$ 7	(7)
Shares issued for vested restricted and performance stock units (in shares)		6,806,000
Shares issued for sale of common stock related to employee stock purchase plan	$ 233		233
Shares issued for sale of common stock related to employee stock purchase plan (in shares)		336,000
Share-based payment award compensation costs	18,125		18,125
Net loss	(172,415)			(172,415)
Ending balance, value at Dec. 31, 2021	$ (93,621)	$ 430	$ 957,309	$ (1,051,360)
Ending balance, shares at Dec. 31, 2021	429,886,000	429,886,000