Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments - USD ($) $ in Millions	Jun. 30, 2015	Dec. 31, 2014
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	$ 8.3	$ 10.0
Senior Secured Notes:
Revolving credit lines with banks		20.3
Deposits	15.8	17.3
Olkaria III - DEG [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	28.2	32.2
Olkaria III - OPIC [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	267.5	279.4
Ormat Funding Corp [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	32.4	71.4
Orcal Geothermal Inc [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	52.5	55.5
OFC Two Senior Secured Notes [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	232.3	238.8
Senior Unsecured Bonds Member
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	267.3	265.4
Institutional Investors [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	8.1	12.2
Fair Value, Inputs, Level 1 [Member]
Senior Secured Notes:
Deposits	15.8	17.3
Fair Value, Inputs, Level 2 [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	8.3	10.0
Senior Secured Notes:
Revolving credit lines with banks		20.3
Fair Value, Inputs, Level 2 [Member] | Ormat Funding Corp [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	32.4	71.4
Fair Value, Inputs, Level 3 [Member] | Olkaria III - DEG [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	28.2	32.2
Fair Value, Inputs, Level 3 [Member] | Olkaria III - OPIC [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	267.5	279.4
Fair Value, Inputs, Level 3 [Member] | Orcal Geothermal Inc [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	52.5	55.5
Fair Value, Inputs, Level 3 [Member] | OFC Two Senior Secured Notes [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	232.3	238.8
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Bonds Member
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	267.3	265.4
Fair Value, Inputs, Level 3 [Member] | Institutional Investors [Member]
Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments [Line Items]
Fair value levels-secured,unsecured and long term debt	$ 8.1	$ 12.2