Note 1 - General and Basis of Presentation (Details)								1 Months Ended	3 Months Ended				6 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2015 USD ($) shares	Aug. 05, 2015 USD ($)	Jul. 31, 2015 USD ($)	Apr. 30, 2015 USD ($)	Feb. 15, 2015 USD ($) shares	Jun. 20, 2014 USD ($)	Mar. 26, 2014 USD ($)	Jun. 30, 2015 USD ($)	Sep. 30, 2015 USD ($) shares	Sep. 30, 2014 USD ($)	Jun. 30, 2014 USD ($)	Mar. 31, 2014 USD ($)	Jun. 30, 2015	Jun. 30, 2014	Sep. 30, 2015 USD ($) shares	Sep. 30, 2014 USD ($)	Dec. 31, 2014 USD ($) shares	Feb. 14, 2015 shares	Feb. 11, 2015	Dec. 31, 2013 USD ($)
Note 1 - General and Basis of Presentation (Details) [Line Items]
Extended Period for Deduction of Tax Losses Term															10 years
Repayments of Secured Debt															$ 30,638,000	$ 12,860,000
Proceeds from Sales of Business, Affiliate and Productive Assets																35,250,000
Noncontrolling Interest, Increase from Subsidiary Equity Issuance																257,000
															$ 156,761,000
Percentage of Public Float Before Transition to Noncontrolled Public Company																			40.00%
Percentage of Public Float After Transition to Noncontrolled Public Company					76.00%
Share Exchange Shares Granted Per Share (in Shares) | shares					0.2592
Common Stock, Shares, Issued (in Shares) | shares	49,035,593				3,000,000				49,035,593						49,035,593		45,537,162
Common Stock, Shares, Outstanding (in Shares) | shares	49,035,593				48,500,000				49,035,593						49,035,593		45,537,162	45,500,000
Sale of Stock, Consideration Received on Transaction					$ 15,400,000
Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax									$ 7,000	$ 35,000					$ 22,000	107,000
Interest Expense									17,748,000	22,494,000					54,435,000	65,084,000
Income Tax Expense (Benefit)									(38,211,000)	6,444,000					(26,696,000)	17,731,000
Exploration Abandonment and Impairment Expense									185,000						359,000	8,107,000
Cash, Cash Equivalents, and Short-term Investments	$ 171,541,000								171,541,000	42,451,000					171,541,000	42,451,000	$ 40,230,000			$ 57,354,000
Accounts Receivable, Net, Current	52,313,000								52,313,000						52,313,000		48,609,000
Provision for Doubtful Accounts															$ 0
Crump Geyser and North Valley [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Business Combination, Consideration Transferred		$ 1,500,000
Business Acquisition, Percentage of Voting Interests Acquired		50.00%
Business Acquisition, Noncontrolling Interest Reclassified to Equity		$ 1,000,000
Business Acquisition, Amount Recorded in Additional Paid in Capital		$ 200,000
KENYA
Note 1 - General and Basis of Presentation (Details) [Line Items]
Investment Deduction Percentage															50.00%
Deferred Foreign Income Tax Expense (Benefit)									49,400,000						$ 49,400,000
UNITED STATES
Note 1 - General and Basis of Presentation (Details) [Line Items]
Cash, Cash Equivalents, and Short-term Investments	41,071,000								41,071,000						41,071,000		23,488,000
Foreign Countries [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Cash, Cash Equivalents, and Short-term Investments	134,986,000								134,986,000						134,986,000		24,304,000
Accounts Receivable, Net, Current	$ 22,981,000								22,981,000						22,981,000		$ 21,935,000
Additional Paid-in Capital [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
															71,291,000
Noncontrolling Interest [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Noncontrolling Interest, Increase from Subsidiary Equity Issuance																257,000
															85,470,000
Maximum [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Cash, FDIC Insured Amount																				$ 250,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Interest Expense									10,000	57,000					35,000	173,000
Income Tax Expense (Benefit)									$ 3,000	$ 22,000					$ 13,000	$ 66,000
Northleaf Geothermal Holdings (Northleaf) [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Equity Method Investment, Ownership Percentage				36.75%
Number of Power Plants Acquired				9
Recovered Energy Generation Assets				3
Business Combination, Consideration Transferred				$ 162,300,000
Proceeds from Sales of Business, Affiliate and Productive Assets				156,800,000
Business Acquisition, Transaction Costs				5,500,000
Business Combination, Bargain Purchase, Gain Recognized, Amount				102,100,000
Northleaf Geothermal Holdings (Northleaf) [Member] | Additional Paid-in Capital [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Noncontrolling Interest, Increase from Subsidiary Equity Issuance				71,300,000
Northleaf Geothermal Holdings (Northleaf) [Member] | Noncontrolling Interest [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
				$ 85,500,000
Primary Customers [Member] | Accounts Receivable [Member] | Customer Concentration Risk [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Concentration Risk, Percentage															73.70%		69.00%
Hawaii Electric Light Company [Member] | Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Concentration Risk, Percentage									15.30%	14.70%					19.30%	16.60%
Southern California Edison Company [Member] | Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Concentration Risk, Percentage									13.40%	19.90%			11.10%	15.20%
Kenya Power And Lighting Co Limited [Member] | Sales Revenue, Net [Member] | Customer Concentration Risk [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Concentration Risk, Percentage									13.50%	15.80%					15.40%	15.60%
Heber Solar Project [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Proceeds from Sales of Business, Affiliate and Productive Assets											$ 20,250,000	$ 15,000,000
Sales Price of Disposition							$ 35,250,000
Gain (Loss) on Sale of Project											$ 7,600,000
Aggregate Shares Issued [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Conversion of Stock, Shares Issued (in Shares) | shares					30,200,000
Shares Issued to Self, Deducted [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Conversion of Stock, Shares Issued (in Shares) | shares					27,200,000
Sale of Stock, Other Assets Received [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Sale of Stock, Consideration Received Per Transaction					$ 600,000
Sale of Stock, Land and Buildings Received [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Sale of Stock, Consideration Received Per Transaction					12,100,000
Sale of Stock, Liabilities Assumed [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Sale of Stock, Consideration Received Per Transaction					$ 500,000
Amatitlan Loan [Member] | Historical [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Debt Service Coverage Ratio	7.94
Amatitlan Loan [Member] | Projected [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Debt Service Coverage Ratio	1.97
Amatitlan Loan [Member] | Banco Industrial S.A. and Westrust Bank [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Debt Instrument, Term			12 years
Debt Instrument, Face Amount			$ 42,000,000
Debt Instrument Number of Quarterly Payments			48
Minimum Variable Interest Rate			1.25%
Debt Service Coverage Ratio			1.15
Loans Payable	$ 41,100,000								$ 41,100,000						$ 41,100,000
Amatitlan Loan [Member] | Banco Industrial S.A. and Westrust Bank [Member] | London Interbank Offered Rate (LIBOR) [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Debt Instrument, Basis Spread on Variable Rate			4.75%
Amatitlan Loan [Member] | Banco Industrial S.A. and Westrust Bank [Member] | London Interbank Offered Rate (LIBOR) [Member] | Rate Contingent on Guaranty to Lenders is Outstanding [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Debt Instrument, Basis Spread on Variable Rate			4.35%
Amatitlan Loan [Member] | Banco Industrial S.A. and Westrust Bank [Member] | Restricted Payments Limitations [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Debt Service Coverage Ratio			1.25
Ormat Funding Corp [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Repayments of Secured Debt								$ 30,600,000
Gains (Losses) on Extinguishment of Debt															1,700,000
Ormat Funding Corp [Member] | Other Nonoperating Income (Expense) [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Amortization of Financing Costs															$ 500,000
OFC Two Senior Secured Notes [Member]
Note 1 - General and Basis of Presentation (Details) [Line Items]
Repayments of Secured Debt						$ 4,300,000
Foreign Tax Authority [Member] | KENYA
Note 1 - General and Basis of Presentation (Details) [Line Items]
Investment Deduction Percentage															150.00%
Foreign Tax Authority [Member] | Minimum [Member] | KENYA
Note 1 - General and Basis of Presentation (Details) [Line Items]
Extended Period for Deduction of Tax Losses Term															5 years
Foreign Tax Authority [Member] | Maximum [Member] | KENYA
Note 1 - General and Basis of Presentation (Details) [Line Items]
Extended Period for Deduction of Tax Losses Term															10 years