Note 7 - Variable Interest Entities - Assets and Liabilities for the Company's 2015 Variable Interest Entity (Details) - USD ($) $ in Thousands		Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Restricted cash and cash equivalents		$ 34,262	$ 49,503
Property, plant and equipment, net		1,556,378	1,559,335
Construction-in-process		306,709	248,835
Total assets	[1]	2,461,569	2,273,982	$ 2,121,556
Accounts payable and accrued expenses		91,650	91,955
Long-term debt		956,532
Other long-term liabilities		21,294	1,776
Total liabilities		1,286,790	1,190,108
Property, plant and equipment, net		1,556,378	1,559,335
Construction-in-process		306,709	248,835
Variable Interest Entity, Primary Beneficiary [Member] | Project Debt [Member]
Restricted cash and cash equivalents		34,262	49,503
Other current assets		157,351	114,500
Property, plant and equipment, net		1,305,254	1,310,027
Construction-in-process		48,128	127,825
Other long-term assets		24,802	44,279
Total assets		1,569,797	1,646,134
Accounts payable and accrued expenses		10,900	11,404
Long-term debt		668,815	648,028
Other long-term liabilities		126,879	78,843
Total liabilities		806,594	738,275
Property, plant and equipment, net		1,305,254	1,310,027
Construction-in-process		48,128	127,825
Variable Interest Entity, Primary Beneficiary [Member] | Power Purchase Agreements [Member]
Restricted cash and cash equivalents
Other current assets		7,482	4,044
Property, plant and equipment, net		177,970	171,231
Construction-in-process		72,725	1,340
Other long-term assets			(1)
Total assets		258,177	176,614
Accounts payable and accrued expenses		3,992	2,931
Long-term debt
Other long-term liabilities		5,779	5,358
Total liabilities		9,771	8,289
Property, plant and equipment, net		177,970	171,231
Construction-in-process		$ 72,725	$ 1,340

[1] Including unconsolidated investments