Condensed Consolidated Balance Sheets (Current Period Unaudited) (Parentheticals) - USD ($) $ in Thousands	Mar. 31, 2021	Dec. 31, 2020
Trade, allowance for credit losses	$ 597	$ 597
Property, plant and equipment, net	2,148,589	2,099,046
Construction-in-process	471,548	479,315
Operating leases right of use	15,627	16,347
Finance leases right of use	$ 8,336	$ 11,633
Common stock, par value (in dollars per share)	$ 0.001	$ 0.001
Common stock, shares authorized (in shares)	200,000,000	200,000,000
Common stock, shares issued (in shares)	55,984,392	55,983,259
Common stock, shares outstanding (in shares)	55,984,392	55,983,259
Variable Interest Entity, Primary Beneficiary [Member]
Property, plant and equipment, net	$ 2,012,052	$ 1,978,220
Construction-in-process	208,972	198,812
Operating leases right of use	4,589	4,712
Finance leases right of use	289	7,001
Senior Secured Notes [Member]
Deferred financing costs	5,082	5,318
Other Loans, Limited and Non-recourse [Member]
Deferred financing costs	8,132	8,557
Senior Unsecured Bonds [Member]
Deferred financing costs	1,996	2,086
Other Loans, Full Recourse [Member]
Deferred financing costs	$ 1,295	$ 1,340