Note 9 - Property, Plant and Equipment and Construction-in-process - Property, Plant and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Property, plant and equipment	$ 2,436,858	$ 2,344,789
Asset retirement cost	8,669	7,961
Less accumulated depreciation	(880,480)	(785,454)
Property, plant and equipment, net	1,556,378	1,559,335
Land [Member]
Property, plant and equipment	31,904	31,465
Leasehold Improvements [Member]
Property, plant and equipment	3,848	3,691
Machinery and Equipment [Member]
Property, plant and equipment	152,821	133,457
Office Equipment [Member]
Property, plant and equipment	28,634	29,247
Automobiles [Member]
Property, plant and equipment	11,161	7,782
Geothermal And Recovered Energy Generation Power Plants [Member] \| UNITED STATES
Property, plant and equipment	1,658,195	1,637,081
Geothermal And Recovered Energy Generation Power Plants [Member] \| Foreign Countries [Member]
Property, plant and equipment	$ 541,626	$ 494,105

Amount of accumulated depreciation, depletion and amortization for physical assets used in the normal conduct of business to produce goods and services.

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The amount of asset retirement costs previously incurred and capitalized separately from the capitalized amount of the associated long-lived assets.

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