Note 8 - Property, Plant and Equipment and Construction-in-process - Property, Plant and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Property, plant and equipment	$ 3,225,949	$ 3,097,806
Asset retirement cost	19,824	11,448
Less accumulated depreciation	(1,254,534)	(1,138,228)
Property, plant and equipment, net	1,971,415	1,959,578
Land [Member]
Property, plant and equipment	38,049	38,060
Leasehold Improvements [Member]
Property, plant and equipment	7,757	5,718
Machinery and Equipment [Member]
Property, plant and equipment	230,465	208,646
Office Equipment [Member]
Property, plant and equipment	39,099	35,708
Vehicles [Member]
Property, plant and equipment	8,021	22,074
Geothermal And Recovered Energy Generation Power Plants [Member] \| UNITED STATES
Property, plant and equipment	2,160,910	2,065,377
Geothermal And Recovered Energy Generation Power Plants [Member] \| Foreign Countries [Member]
Property, plant and equipment	$ 721,824	$ 710,775

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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