Fair Value of Financial Instruments (Detail) (USD $) In Millions, unless otherwise specified	Dec. 31, 2012
Fair Value of Financial Instruments [Line Items]
Other long-term debt	$ 36.7
Revolving credit lines with banks	73.6
Deposits	21.7
Amatitlan Geothermal Power Plant
Fair Value of Financial Instruments [Line Items]
Loan	38.9
Ormat Funding Corp. ("OFC")
Fair Value of Financial Instruments [Line Items]
Senior secured notes	105.0
OrCal Geothermal Inc. ("OrCal")
Fair Value of Financial Instruments [Line Items]
Senior secured notes	77.3
OFC 2 LLC ("OFC 2")
Fair Value of Financial Instruments [Line Items]
Senior secured notes	131.2
Senior Unsecured Bonds
Fair Value of Financial Instruments [Line Items]
Senior Unsecured Bonds	273.2
Institutional Investors
Fair Value of Financial Instruments [Line Items]
Other long-term debt	27.7
Olkaria III loan
Fair Value of Financial Instruments [Line Items]
Loan	48.8
Fair Value, Inputs, Level 1
Fair Value of Financial Instruments [Line Items]
Deposits	21.7
Fair Value, Inputs, Level 2
Fair Value of Financial Instruments [Line Items]
Other long-term debt	36.7
Revolving credit lines with banks	73.6
Fair Value, Inputs, Level 2 | Ormat Funding Corp. ("OFC")
Fair Value of Financial Instruments [Line Items]
Senior secured notes	105.0
Fair Value, Inputs, Level 3 | Amatitlan Geothermal Power Plant
Fair Value of Financial Instruments [Line Items]
Loan	38.9
Fair Value, Inputs, Level 3 | OrCal Geothermal Inc. ("OrCal")
Fair Value of Financial Instruments [Line Items]
Senior secured notes	77.3
Fair Value, Inputs, Level 3 | OFC 2 LLC ("OFC 2")
Fair Value of Financial Instruments [Line Items]
Senior secured notes	131.2
Fair Value, Inputs, Level 3 | Senior Unsecured Bonds
Fair Value of Financial Instruments [Line Items]
Senior Unsecured Bonds	273.2
Fair Value, Inputs, Level 3 | Institutional Investors
Fair Value of Financial Instruments [Line Items]
Other long-term debt	27.7
Fair Value, Inputs, Level 3 | Olkaria III loan
Fair Value of Financial Instruments [Line Items]
Loan	$ 48.8