Note 1 - General and Basis of Presentation (Details Textual)		1 Months Ended	3 Months Ended			6 Months Ended		12 Months Ended
	Mar. 30, 2016	Jun. 30, 2015 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($)	Jun. 30, 2015 USD ($)	Dec. 31, 2015 USD ($)	Apr. 29, 2015	Dec. 31, 2014 USD ($)
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
Scenario, Forecast [Member] | Second Phase of Don Campbell [Member]
Proceeds from Divestiture of Businesses			$ 43,000,000
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
Reclassification out of Accumulated Other Comprehensive Income [Member]
Net Income (Loss) Attributable to Parent				$ 2,000	$ 8,000	$ 5,000	$ 15,000
Interest Expense				6,000	14,000	10,000	25,000
Income Tax Expense (Benefit)				4,000	$ 5,000	5,000	$ 10,000
Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss), Net of Tax				582,000		582,000
UNITED STATES
Cash, Cash Equivalents, and Short-term Investments				18.60		18.60		$ 19
Foreign Countries [Member]
Cash, Cash Equivalents, and Short-term Investments				186.60		186.60		181
Accounts Receivable, Net, Current				34.70		34.70		27.80
Maximum [Member]
Cash, FDIC Insured Amount				$ 250,000		$ 250,000		$ 250,000
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Primary Customers [Member]
Concentration Risk, Percentage						59.00%		66.00%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Sierra Pacific Power Company And Nevada Power Company [Member]
Concentration Risk, Percentage				19.10%	20.10%	21.10%	21.90%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Kenya Power And Lighting Co LTD [Member]
Concentration Risk, Percentage				17.10%	15.40%	17.20%	16.50%
Sales Revenue, Net [Member] | Customer Concentration Risk [Member] | Southern California Edison Company [Member]
Concentration Risk, Percentage				10.40%	4.10%	11.20%	4.90%
Repayments of Secured Debt							$ 30,638,000
Net Income (Loss) Attributable to Parent				$ 24,349,000	$ 14,414,000	53,620,000	24,446,000
Interest Expense				18,401,000	18,859,000	34,424,000	36,687,000
Income Tax Expense (Benefit)				7,890,000	6,056,000	17,399,000	11,515,000
Accumulated Other Comprehensive Income (Loss), Net of Tax				(12,838,000)		(12,838,000)		$ (7,667,000)
Exploration Abandonment and Impairment Expense				863,000	0	1,420,000	174,000
Cash, Cash Equivalents, and Short-term Investments		$ 137,665,000		192,556,000	$ 137,665,000	192,556,000	$ 137,665,000	185,919,000		$ 40,230,000
Accounts Receivable, Net, Current				$ 59,042,000		59,042,000		$ 55,301,000
Provision for Doubtful Accounts						$ 0