Note 8 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2016	Dec. 31, 2015
Deposits	$ 14.4	$ 15.9
Fair Value, Inputs, Level 1 [Member]
Deposits	14.4	15.9
Fair Value, Inputs, Level 2 [Member]
Deposits
Fair Value, Inputs, Level 3 [Member]
Deposits
Olkaria III DEG [Member]
Fair value levels-secured, unsecured and long term debt	16.3	24.2
Olkaria III DEG [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value levels-secured, unsecured and long term debt
Olkaria III DEG [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value levels-secured, unsecured and long term debt
Olkaria III DEG [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value levels-secured, unsecured and long term debt	16.3	24.2
Olkaria III OPIC [Member]
Fair value levels-secured, unsecured and long term debt	253.4	262.6
Olkaria III OPIC [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value levels-secured, unsecured and long term debt
Olkaria III OPIC [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value levels-secured, unsecured and long term debt
Olkaria III OPIC [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value levels-secured, unsecured and long term debt	253.4	262.6
Olkaria IV Loan - DEG 2 [Member]
Fair value levels-secured, unsecured and long term debt	50.9
Olkaria IV Loan - DEG 2 [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value levels-secured, unsecured and long term debt
Olkaria IV Loan - DEG 2 [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value levels-secured, unsecured and long term debt
Olkaria IV Loan - DEG 2 [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value levels-secured, unsecured and long term debt	50.9
Amatitlan Loan [Member]
Fair value levels-secured, unsecured and long term debt	37.3	41.7
Amatitlan Loan [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value levels-secured, unsecured and long term debt
Amatitlan Loan [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value levels-secured, unsecured and long term debt	37.3	41.7
Amatitlan Loan [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value levels-secured, unsecured and long term debt
Ormat Funding Corp [Member]
Fair value levels-secured, unsecured and long term debt	17.0	30.0
Ormat Funding Corp [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value levels-secured, unsecured and long term debt
Ormat Funding Corp [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value levels-secured, unsecured and long term debt	17.0	30.0
Ormat Funding Corp [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value levels-secured, unsecured and long term debt
Orcal Geothermal Inc [Member]
Fair value levels-secured, unsecured and long term debt	37.4	43.8
Orcal Geothermal Inc [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value levels-secured, unsecured and long term debt
Orcal Geothermal Inc [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value levels-secured, unsecured and long term debt
Orcal Geothermal Inc [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value levels-secured, unsecured and long term debt	37.4	43.8
OFC Two Senior Secured Notes [Member]
Fair value levels-secured, unsecured and long term debt	249.0	231.1
OFC Two Senior Secured Notes [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value levels-secured, unsecured and long term debt
OFC Two Senior Secured Notes [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value levels-secured, unsecured and long term debt
OFC Two Senior Secured Notes [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value levels-secured, unsecured and long term debt	249.0	231.1
Senior Unsecured Bonds [Member]
Fair value levels-secured, unsecured and long term debt	200.1	264.5
Senior Unsecured Bonds [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value levels-secured, unsecured and long term debt
Senior Unsecured Bonds [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value levels-secured, unsecured and long term debt
Senior Unsecured Bonds [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value levels-secured, unsecured and long term debt	200.1	264.5
Don A. Campbell 1 ("DAC1") [Member]
Fair value levels-secured, unsecured and long term debt	88.9
Don A. Campbell 1 ("DAC1") [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value levels-secured, unsecured and long term debt
Don A. Campbell 1 ("DAC1") [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value levels-secured, unsecured and long term debt
Don A. Campbell 1 ("DAC1") [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value levels-secured, unsecured and long term debt	88.9
Other Long-term Debt [Member]
Fair value levels-secured, unsecured and long term debt	10.4	6.7
Other Long-term Debt [Member] | Fair Value, Inputs, Level 1 [Member]
Fair value levels-secured, unsecured and long term debt
Other Long-term Debt [Member] | Fair Value, Inputs, Level 2 [Member]
Fair value levels-secured, unsecured and long term debt	3.3	6.7
Other Long-term Debt [Member] | Fair Value, Inputs, Level 3 [Member]
Fair value levels-secured, unsecured and long term debt	$ 7.1