Fair Value of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Mar. 31, 2012
Fair Value, Measurement Inputs, Disclosure [Line Items]
Other long-term debt	$ 50.0
Deposits	21.1
Revolving lines of credit	227.6
Olkaria III
Fair Value, Measurement Inputs, Disclosure [Line Items]
Loan	80.3
Amatitlan
Fair Value, Measurement Inputs, Disclosure [Line Items]
Loan	36.6
Ormat Funding Corp. ("OFC")
Fair Value, Measurement Inputs, Disclosure [Line Items]
Senior secured notes	118.7
OrCal Geothermal Inc. ("OrCal")
Fair Value, Measurement Inputs, Disclosure [Line Items]
Senior secured notes	85.8
OFC 2 LLC ("OFC 2")
Fair Value, Measurement Inputs, Disclosure [Line Items]
Senior secured notes	125.0
Senior Unsecured Bonds
Fair Value, Measurement Inputs, Disclosure [Line Items]
Senior Unsecured Bonds	238.7
Institutional Investors
Fair Value, Measurement Inputs, Disclosure [Line Items]
Other long-term debt	32.5
Fair Value, Inputs, Level 1
Fair Value, Measurement Inputs, Disclosure [Line Items]
Deposits	21.1
Fair Value, Inputs, Level 2
Fair Value, Measurement Inputs, Disclosure [Line Items]
Revolving lines of credit	227.6
Fair Value, Inputs, Level 2 | Ormat Funding Corp. ("OFC")
Fair Value, Measurement Inputs, Disclosure [Line Items]
Senior secured notes	118.7
Fair Value, Inputs, Level 3
Fair Value, Measurement Inputs, Disclosure [Line Items]
Other long-term debt	50.0
Fair Value, Inputs, Level 3 | Olkaria III
Fair Value, Measurement Inputs, Disclosure [Line Items]
Loan	80.3
Fair Value, Inputs, Level 3 | Amatitlan
Fair Value, Measurement Inputs, Disclosure [Line Items]
Loan	36.6
Fair Value, Inputs, Level 3 | OrCal Geothermal Inc. ("OrCal")
Fair Value, Measurement Inputs, Disclosure [Line Items]
Senior secured notes	85.8
Fair Value, Inputs, Level 3 | OFC 2 LLC ("OFC 2")
Fair Value, Measurement Inputs, Disclosure [Line Items]
Senior secured notes	125.0
Fair Value, Inputs, Level 3 | Senior Unsecured Bonds
Fair Value, Measurement Inputs, Disclosure [Line Items]
Senior Unsecured Bonds	238.7
Fair Value, Inputs, Level 3 | Institutional Investors
Fair Value, Measurement Inputs, Disclosure [Line Items]
Other long-term debt	$ 32.5