Note 11 - Long-term Debt and Credit Agreements - Long-term Debt (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
	$ 622,145	$ 681,548
Less current portion	(54,720)	(53,729)
Non current portion	567,425	627,819
Recourse Debt	306,419	274,983
Less current portion	(54,587)	(12,242)
Non current portion	251,832	262,741
Other Loans, Limited and Non-recourse [Member]
Non-Recourse Debt	7,252	6,368
Loan Agreement With OPIC the Olkaria III Power Plant [Member]
Non-Recourse Debt	228,635	246,630
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited [Member]
Non-Recourse Debt	33,251	36,750
Ormat Funding Corp [Member]
Non-Recourse Debt		17,026
OrCal Geothermal Inc [Member]
Non-Recourse Debt	32,142	35,181
Don A. Campbell 1 ("DAC1") [Member]
Non-Recourse Debt	88,339	92,361
OFC Two Senior Secured Notes [Member]
Non-Recourse Debt	232,526	247,232
Senior Unsecured Bonds [Member]
Recourse Debt	204,332	204,332
Institutional Investors [Member]
Recourse Debt		3,333
Olkaria III DEG [Member]
Recourse Debt	50,000	65,789
Loan From Commercial Bank [Member]
Recourse Debt	587	1,529
Revolving Credit Lines With Banks [Member]
Recourse Debt	$ 51,500