Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Senior Secured Notes:
Loan from institutional investors	$ 8.3	$ 10.0
Olkaria III - DEG [Member]
Senior Secured Notes:
Loan from institutional investors	28.2	32.2
Olkaria III - DEG [Member] | Estimate of Fair Value Measurement [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions [Line Items]
Loan	28.2	32.2
Olkaria III - DEG [Member] | Reported Value Measurement [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions [Line Items]
Loan	27.6	31.6
Olkaria III - OPIC [Member]
Senior Secured Notes:
Loan from institutional investors	267.5	279.4
Olkaria III - OPIC [Member] | Estimate of Fair Value Measurement [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions [Line Items]
Loan	267.5	279.4
Olkaria III - OPIC [Member] | Reported Value Measurement [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions [Line Items]
Loan	273.6	282.6
Ormat Funding Corp [Member]
Senior Secured Notes:
Loan from institutional investors	32.4	71.4
Ormat Funding Corp [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	32.4	71.4
Ormat Funding Corp [Member] | Reported Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	33.3	67.2
Orcal Geothermal Inc [Member]
Senior Secured Notes:
Loan from institutional investors	52.5	55.5
Orcal Geothermal Inc [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	52.2	55.5
Orcal Geothermal Inc [Member] | Reported Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	51.8	55.1
OFC Two Senior Secured Notes [Member]
Senior Secured Notes:
Loan from institutional investors	232.3	238.8
OFC Two Senior Secured Notes [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	232.3	238.8
OFC Two Senior Secured Notes [Member] | Reported Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	268.1	272.5
Senior Unsecured Bonds Member
Senior Secured Notes:
Loan from institutional investors	267.3	265.4
Senior Unsecured Bonds Member | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Unsecured Bonds	267.3	265.4
Senior Unsecured Bonds Member | Reported Value Measurement [Member]
Senior Secured Notes:
Senior Unsecured Bonds	250.1	250.4
Institutional Investors [Member]
Senior Secured Notes:
Loan from institutional investors	8.1	12.2
Institutional Investors [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Loan from institutional investors	8.1	12.2
Institutional Investors [Member] | Reported Value Measurement [Member]
Senior Secured Notes:
Loan from institutional investors	$ 8.0	$ 11.9