Consolidated Balance Sheets (Current Period Unaudited) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Current assets
Cash and cash equivalents	$ 39,290	$ 22,608
Prepaid expenses and other current assets	818	670
Total current assets	40,108	23,278
Property, plant and equipment, net	164,205	161,662
Operating lease right-of-use assets, net	290	429
Other non-current assets, net	17,478	16,299
Total assets	222,081	201,668
Current liabilities
Accounts payable	224	207
Share-based compensation liability	182	182
Accrued liabilities and other current liabilities	2,147	1,032
Current common stock warrant liabilities	4,520	3,290
Current operating lease liabilities	274	432
Total current liabilities	7,347	5,143
Non-current common stock warrant liabilities	2,499	874
Other non-current liabilities	23,000	22,916
Total liabilities	32,846	28,933
Commitments and contingencies (Note 12)
Stockholders’ equity
Common stock, $0.0001 par value Authorized: 480.0 million shares at March 31, 2021 and December 31, 2020 Issued and outstanding: 118.3 million shares and 117.8 million shares at March 31, 2021 and December 31, 2020, respectively	12	12
Treasury stock: 269,354 shares and 249,742 shares at March 31, 2021 and December 31, 2020, respectively, at cost	(1,075)	(1,031)
Preferred stock, $0.0001 par value Authorized: 0.8 million, after designation of the Series A, Series B and Series C Convertible Preferred Stock Issued and outstanding: none at March 31, 2021 and December 31, 2020	0	0
Additional paid-in-capital	202,176	209,481
Accumulated deficit	(151,688)	(148,030)
Total stockholders’ equity	49,425	60,432
Total liabilities, convertible preferred stock and stockholders’ equity	222,081	201,668
Series A Convertible Preferred Stock [Member]
Current liabilities
Convertible Preferred Stock	57,516	55,522
Series B Convertible Preferred Stock [Member]
Current liabilities
Convertible Preferred Stock	58,665	56,781
Series C Convertible Preferred Stock [Member]
Current liabilities
Convertible Preferred Stock	$ 23,629	$ 0