Note 1 - General and Basis of Presentation (Details Textual) € in Millions			1 Months Ended					3 Months Ended			9 Months Ended		12 Months Ended
	Sep. 11, 2016 USD ($)	Mar. 30, 2016	Oct. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jul. 31, 2016 USD ($) MWh	Jul. 31, 2016 EUR (€) MWh	Jun. 30, 2015 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Apr. 30, 2015	Dec. 31, 2014 USD ($)
Senior Unsecured Bonds [Member] | Series 2 Bonds [Member]
Proceeds from Issuance of Unsecured Debt	$ 67,000,000
Debt Instrument, Interest Rate, Stated Percentage	3.70%
Senior Unsecured Bonds [Member] | Series 3 Bonds [Member]
Proceeds from Issuance of Unsecured Debt	$ 137,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.45%
Senior Unsecured Bonds [Member] | Nonoperating Income (Expense) [Member]
Amortization of Debt Discount (Premium)									$ 300,000		$ 300,000
Senior Unsecured Bonds [Member]
Proceeds from Issuance of Unsecured Debt	$ 204,000,000								250,000,000
Loss on Debt Prepayment									5,000,000
Prepayment Penalty Charges									5,000,000
Ormat Funding Corp [Member] | Other Nonoperating Income (Expense) [Member]
Amortization of Debt Issuance Costs							$ 500,000
Ormat Funding Corp [Member]
Repayments of Secured Debt							30,600,000
Gain (Loss) on Extinguishment of Debt							$ 1,700,000
Nonoperating Income (Expense) [Member]
Gain (Loss) on Repurchase of Debt Instrument				$ 600,000
Geothermie Bouillante SA (“GB”) [Member] | Ormat Systems LTD and Caisse des Depots et Consignations (CDC) [Member]
Business Acquisition, Percentage of Voting Interests Acquired					80.00%
Geothermie Bouillante SA (“GB”) [Member] | Ormat Systems Ltd [Member]
Business Combination, Co-acquisition, Percentage of Ownership Interest Allocated					75.00%
Geothermie Bouillante SA (“GB”) [Member] | Caisse des Depots et Consignations (CDC) [Member]
Business Combination, Co-acquisition, Percentage of Ownership Interest Allocated					25.00%
Geothermie Bouillante SA (“GB”) [Member] | Subsequent Event [Member]
Payments to Acquire Businesses, Net of Cash Acquired			$ 2,000,000
Geothermie Bouillante SA (“GB”) [Member] | After Further Invest in Two Years [Member]
Business Combination, Expected Ownership Interest					63.75%
Payments to Acquire Additional Interest in Subsidiaries					$ 8,400,000	€ 7.5
Geothermie Bouillante SA (“GB”) [Member] | Service Agreements [Member]
Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Finite-Lived Intangibles					$ 33,000,000
Geothermie Bouillante SA (“GB”) [Member]
Expected Power Generating Capacity | MWh					14.75	14.75
Power Utilization | MWh					13	13
Number of Exploration Licenses Owned					2
Business Acquisition, Expansion Capacity | MWh					45
Business Acquisition, Percentage of Voting Interests Acquired					60.00%
Business Combination, Expected Ownership Interest					85.00%
Payments to Acquire Businesses, Net of Cash Acquired									20,600,000
Payments to Acquire Businesses, Additional Amount Subject to Achievement of Agreed upon Production Thresholds					$ 13,400,000	€ 12.0
Power Purchase Agreements Term					15 years	15 years
Goodwill					$ 7,100,000
Redeemable Noncontrolling Interest, Equity, Carrying Amount				5,000,000					5,000,000		5,000,000
Stockholders' Equity Attributable to Noncontrolling Interest				8,300,000					8,300,000		8,300,000
Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual									4,100,000		4.10
Scenario, Forecast [Member] | Second Phase of Don Campbell [Member]
Proceeds from Divestiture of Businesses								$ 43,000,000
Rabbit Hill Project Entity [Member]
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions		85.00%
Subsidiary or Equity Method Investee, Cumulative Percentage Ownership after All Transactions, Subsequent to Reaching Certain IRR Achievements		50.10%
Northleaf Geothermal Holdings, Northleaf [Member]
Equity Method Investment, Ownership Percentage														36.75%
Number of Power Plants Acquired														9
Recovered Energy Generation Assets														3
Foreign Tax Authority [Member] | KENYA | Minimum [Member]
Extended Period for Deduction of Tax Losses, Term										5 years
Foreign Tax Authority [Member] | KENYA | Maximum [Member]
Extended Period for Deduction of Tax Losses, Term										10 years
Foreign Tax Authority [Member] | KENYA
Investment Deduction Percentage										150.00%
KENYA
Investment Deduction Percentage										50.00%
Deferred Foreign Income Tax Expense (Benefit)										$ 49,400,000
UNITED STATES
Cash, Cash Equivalents, and Short-term Investments				35,200,000					35,200,000		35,200,000		$ 19,000,000
Foreign Countries [Member]
Cash, Cash Equivalents, and Short-term Investments				72,400,000					72,400,000		72,400,000		181,000,000
Accounts Receivable, Net, Current				36,300,000					36,300,000		36,300,000		27,800,000
Maximum [Member]
Cash, FDIC Insured Amount				250,000,000					250,000,000		250,000,000		$ 250,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Net Income (Loss) Attributable to Parent									2,000	7,000	7,000	$ 22,000
Interest Expense									3,000	10,000	11,000	35,000
Income Tax Expense (Benefit)									1,000	$ 3,000	4,000	$ 13,000
Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax				$ 582,000					$ 582,000		$ 582,000
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Primary Customers [Member]
Concentration Risk, Percentage											60.00%		66.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Sierra Pacific Power Company And Nevada Power Company [Member]
Concentration Risk, Percentage									14.40%	15.30%	18.60%	19.30%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Kenya Power And Lighting Co LTD [Member]
Concentration Risk, Percentage									15.10%	13.50%	16.40%	15.40%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Southern California Public Power Authority [Member]
Concentration Risk, Percentage									7.70%	3.30%	9.90%	4.30%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Hyundai (Sarulla Goethermal Power Project) [Member]
Concentration Risk, Percentage									24.00%	22.00%	14.00%	16.00%
Proceeds from Issuance of Unsecured Debt											$ 203,483,000
Debt Instrument, Interest Rate, Stated Percentage				7.00%					7.00%		7.00%		7.00%
Amortization of Debt Discount (Premium)											$ (513,000)	(230,000)
Payments to Acquire Businesses, Net of Cash Acquired											18,135,000
Goodwill				$ 7,071,000					$ 7,071,000		7,071,000
Redeemable Noncontrolling Interest, Equity, Carrying Amount				4,972,000					4,972,000		4,972,000
Stockholders' Equity Attributable to Noncontrolling Interest				95,913,000					95,913,000		95,913,000		93,873,000
Debt Instrument, Repurchased Face Amount				6,800,000					6,800,000		6,800,000
Repayments of Secured Debt											6,815,000	30,638,000
Net Income (Loss) Attributable to Parent									12,080,000	$ 72,139,000	65,700,000	96,585,000
Interest Expense									17,137,000	17,748,000	51,561,000	54,435,000
Income Tax Expense (Benefit)									11,988,000	(38,211,000)	29,387,000	(26,696,000)
Accumulated Other Comprehensive Income (Loss), Net of Tax				(11,503,000)					(11,503,000)		(11,503,000)		(7,667,000)
Exploration Abandonment and Impairment Expense									1,294,000	185,000	2,714,000	359,000
Cash, Cash Equivalents, and Short-term Investments				90,066,000					90,066,000	$ 171,541,000	90,066,000	$ 171,541,000	185,919,000		$ 40,230,000
Accounts Receivable, Net, Current				$ 65,198,000					$ 65,198,000		65,198,000		$ 55,301,000
Provision for Doubtful Accounts											$ 0