Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Current assets
Cash and cash equivalents	$ 22,358	$ 25,552
Prepaid expenses and other current assets	1,029	835
Total current assets	23,387	26,387
Property, plant and equipment, net	175,172	173,816
Operating lease right-of-use assets, net	450	590
Other non-current assets, net	22,661	21,312
Total assets	221,670	222,105
Current liabilities
Accounts payable	516	281
Share-based compensation liability	182	182
Accrued liabilities and other current liabilities	2,815	5,791
Current common stock warrant liabilities	3,291	1,376
Current operating lease liabilities	440	596
Total current liabilities	7,244	8,226
Non-current common stock warrant liabilities	7,620	2,587
Other non-current liabilities	23,000	23,000
Total liabilities	37,864	33,813
Commitments and contingencies (Note 12)
Stockholders’ equity
Common stock, $0.0001 par value; Authorized: 480.0 million shares at March 31, 2022 and December 31, 2021; Issued and outstanding: 121.6 million shares and 120.8 million shares at March 31, 2022 and December 31, 2021, respectively	12	12
Treasury stock: 541,258 shares and 346,126 shares at March 31, 2022 and December 31, 2021, respectively, at cost	(1,779)	(1,315)
Preferred stock, $0.0001 par value; Authorized: 0.5 million, after designation of the Convertible Preferred Stock; Issued and outstanding: none at March 31, 2022 and December 31, 2021	0	0
Additional paid-in-capital	183,138	191,264
Accumulated deficit	(181,506)	(170,069)
Total stockholders’ equity	(135)	19,892
Total liabilities, convertible preferred stock and stockholders’ equity	221,670	222,105
Series A Convertible Preferred Stock [Member]
Current liabilities
Convertible Preferred Stock	66,016	63,791
Series B Convertible Preferred Stock [Member]
Current liabilities
Convertible Preferred Stock	66,725	64,602
Series C Convertible Preferred Stock [Member]
Current liabilities
Convertible Preferred Stock	$ 51,200	$ 40,007