Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Long-term Debt Approximates its Carrying Amount, Exceptions - USD ($) $ in Millions	Sep. 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	28.5	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	28.5	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	266.4	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	266.4	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	269.1	282.6
Amatitlan Loan [Member]
Senior Secured Notes:
Loan from institutional investors	43.2
Amatitlan Loan [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	43.2
Amatitlan Loan [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	41.1
Ormat Funding Corp [Member]
Senior Secured Notes:
Loan from institutional investors	36.0	71.4
Ormat Funding Corp [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	36.0	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	53.3	55.5
Orcal Geothermal Inc [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	53.3	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	234.2	238.8
OFC Two Senior Secured Notes [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	234.2	238.8
OFC Two Senior Secured Notes [Member] | Reported Value Measurement [Member]
Senior Secured Notes:
Senior Secured Notes	266.0	272.5
Senior Unsecured Bonds Member
Senior Secured Notes:
Loan from institutional investors	262.0	265.4
Senior Unsecured Bonds Member | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Senior Unsecured Bonds	262.0	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	6.2	12.2
Institutional Investors [Member] | Estimate of Fair Value Measurement [Member]
Senior Secured Notes:
Loan from institutional investors	6.2	12.2
Institutional Investors [Member] | Reported Value Measurement [Member]
Senior Secured Notes:
Loan from institutional investors	$ 6.0	$ 11.9