Note 5 - Fair Value of Financial Instruments (Details) - Fair Value of Financial Instruments - USD ($) $ in Millions	Sep. 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
Revolving lines of credit		20.3
Senior Secured Notes:
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	28.5	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	266.4	279.4
Amatitlan Loan [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	43.2
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	36.0	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	53.3	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	234.2	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	262.0	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	6.2	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
Revolving lines of credit		20.3
Fair Value, Inputs, Level 2 [Member] | Amatitlan Loan [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	43.2
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	36.0	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	28.5	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	266.4	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	53.3	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	234.2	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	262.0	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	$ 6.2	$ 12.2