Note 8 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions - USD ($) $ in Millions	Dec. 31, 2015	Dec. 31, 2014
Senior Secured Notes:
Loan from institutional investors	$ 6.7	$ 10.0
Olkaria III - DEG [Member]
Senior Secured Notes:
Loan from institutional investors	24.2	32.2
Olkaria III - DEG [Member] | Estimate of Fair Value Measurement [Member]
Note 8 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions [Line Items]
Loan	24.2	32.2
Olkaria III - DEG [Member] | Reported Value Measurement [Member]
Note 8 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions [Line Items]
Loan	23.7	31.6
Olkaria III - OPIC [Member]
Senior Secured Notes:
Loan from institutional investors	262.6	279.4
Olkaria III - OPIC [Member] | Estimate of Fair Value Measurement [Member]
Note 8 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions [Line Items]
Loan	262.6	279.4
Olkaria III - OPIC [Member] | Reported Value Measurement [Member]
Note 8 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions [Line Items]
Loan	264.6	282.6
Amatitlan Member
Senior Secured Notes:
Loan from institutional investors	41.7
Amatitlan Member | Estimate of Fair Value Measurement [Member]
Note 8 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions [Line Items]
Loan	41.7	0.0
Amatitlan Member | Reported Value Measurement [Member]
Note 8 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions [Line Items]
Loan	40.3	0.0
Ormat Funding Corp [Member]
Senior Secured Notes:
Loan from institutional investors	31.6	71.4
Ormat Funding Corp [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	31.6	71.4
Ormat Funding Corp [Member] | Reported Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	30.0	67.2
Orcal Geothermal Inc [Member]
Senior Secured Notes:
Loan from institutional investors	43.8	55.5
Orcal Geothermal Inc [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	43.8	55.5
Orcal Geothermal Inc [Member] | Reported Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	43.3	55.1
OFC Two Senior Secured Notes [Member]
Senior Secured Notes:
Loan from institutional investors	231.1	238.8
OFC Two Senior Secured Notes [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	231.1	238.8
OFC Two Senior Secured Notes [Member] | Reported Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	262.0	272.5
Senior Unsecured Bonds Member
Senior Secured Notes:
Loan from institutional investors	264.5	265.4
Senior Unsecured Bonds Member | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Unsecured Bonds	264.5	265.4
Senior Unsecured Bonds Member | Reported Value Measurement [Member]
Senior Secured Notes:
Senior Unsecured Bonds	250.0	250.4
Institutional Investors [Member]
Senior Secured Notes:
Loan from institutional investors		12.2
Institutional Investors [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Loan from institutional investors	0.0	12.2
Institutional Investors [Member] | Reported Value Measurement [Member]
Senior Secured Notes:
Loan from institutional investors	$ 0.0	$ 11.9