Note 1 - General and Basis of Presentation - Fair Value of Amounts of Identified Assets and Liabilities Assumed in a Business Combination (Details) - USD ($) $ in Thousands		Jun. 30, 2018	Apr. 24, 2018	Dec. 31, 2017
Goodwill (2)		$ 40,133		$ 21,037
U.S. Geothermal [Member]
Cash and cash equivalents and restricted cash			$ 37,900
Working capital			(8,200)
Property, plant and equipment and construction-in-process			77,300
Intangible assets (1)	[1]		127,000
Deferred tax liability			(4,900)
Long-term term debt, net of deferred transaction costs			(98,300)
Asset retirement obligation			(9,000)
Total identifiable assets and liabilities acquired			121,800
Goodwill (2)	[2]		$ 19,300

[1] Intangible assets are primarily related to long-term electricity power purchase agreements and depreciated over an average of 19 years.

[2] Goodwill is primarily related to the expected synergies in operation as a result of the purchase transaction and is allocated to the Electricity segment.