Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Current assets
Cash and cash equivalents	$ 51,141	$ 62,789
Prepaid expenses and other current assets	1,570	1,149
Total current assets	52,711	63,938
Property, plant and equipment, net	243,870	218,646
Operating lease right-of-use assets, net	1,216	1,474
Other non-current assets, net	30,108	28,372
Total assets	327,905	312,430
Current liabilities
Accounts payable	1,854	1,084
Accrued liabilities and other current liabilities	28,661	23,184
Current common stock warrant liabilities	3,504	0
Current operating lease liabilities	873	1,093
Total current liabilities	34,892	25,361
Non-current common stock warrant liabilities	3,653	6,790
Non-current operating lease liabilities	395	465
Other non-current liabilities	23,000	23,000
Total liabilities	61,940	55,616
Commitments and contingencies (Note 13)
Stockholders’ equity
Common stock, $0.0001 par value Authorized: 480.0 million shares at March 31, 2023 and December 31, 2022; Issued and outstanding: 149.4 million shares and 143.5 million shares at March 31, 2023 and December 31, 2022, respectively	15	14
Treasury stock: 999,966 shares and 991,089 shares at March 31, 2023 and December 31, 2022, respectively, at cost	(4,634)	(4,587)
Preferred stock, $0.0001 par value Authorized: 0.5 million, after designation of the Convertible Preferred Stock Issued and outstanding: none at March 31, 2023 and December 31, 2022	0	0
Additional paid-in-capital	318,942	289,084
Accumulated deficit	(257,487)	(230,140)
Total stockholders’ equity	56,836	54,371
Total liabilities, convertible preferred stock and stockholders’ equity	327,905	312,430
Series A Convertible Preferred Stock [Member]
Current liabilities
Convertible Preferred Stock	75,532	73,026
Series B Convertible Preferred Stock [Member]
Current liabilities
Convertible Preferred Stock	75,798	73,408
Series C Convertible Preferred Stock [Member]
Current liabilities
Convertible Preferred Stock	$ 57,799	$ 56,009