Note 11 - Long-term Debt and Credit Agreements (Details Textual)										1 Months Ended												6 Months Ended	12 Months Ended
	Mar. 22, 2018 USD ($)	Dec. 21, 2016 USD ($)	Nov. 29, 2016 USD ($)	Jul. 31, 2015 USD ($) MWh	Nov. 30, 2013 USD ($)	Sep. 26, 2013	Feb. 28, 2013 USD ($)	Nov. 30, 2012 USD ($)	Feb. 29, 2012 USD ($)	Oct. 31, 2018 USD ($) MWh	Sep. 30, 2017 USD ($)	Sep. 29, 2016 USD ($)	May 31, 2016 USD ($)	Aug. 18, 2014 USD ($)	Jun. 30, 2014 USD ($)	May 31, 2013 USD ($)	Nov. 30, 2012 USD ($)	Oct. 31, 2011 USD ($)	Aug. 31, 2011 USD ($)	Mar. 30, 2009 USD ($)	Dec. 31, 2005 USD ($)	Jun. 30, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)	Dec. 31, 2014 USD ($)	Jun. 30, 2018	May 31, 2017 USD ($)	Oct. 20, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)	Dec. 13, 2015 USD ($)	Aug. 29, 2014 USD ($)	Aug. 23, 2012 USD ($)	Sep. 30, 2011 USD ($)	Feb. 29, 2004 USD ($)
Letters of Credit Outstanding, Amount																							$ 229,600,000
Repayments of Secured Debt																								$ 14,270,000	$ 6,815,000
Repayments of Long-term Debt, Total																							62,774,000	66,223,000	62,052,000
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Total																							81,000	135,000	141,000
Proceeds from Issuance of Unsecured Debt																									203,483,000
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio																							3.21
Stockholders' Equity Attributable to Parent, Ending Balance																							$ 1,319,837,000	1,211,378,000
Percentage Of Company Assets																							46.30%
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance																							$ 1,445,096,000	1,295,700,000	1,168,272,000						$ 1,087,307,000
Payments of Dividends, Total																							$ 26,800,000
Interest Rate Cap [Member]
Payments for Derivative Instrument, Financing Activities														$ 1,500,000
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax, Total																										$ 900,000
Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Tax, Total																										$ 600,000
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net																									$ 100,000							$ 100,000
Covenant Requirement Minimum [Member]
Amount Available For Dividend Distribution Percent Of Cumulative Net Income																							35
Stockholders' Equity Attributable to Parent, Ending Balance																							$ 600,000,000
Percentage Of Company Assets																							25.00%
Maximum [Member] | Covenant Requirement Minimum [Member]
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio																							6
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited1 [Member]
Debt Instrument, Term				12 years
Debt Instrument, Face Amount				$ 42,000,000
Power Utilization | MWh				20
Debt Instrument, Payment Frequency				12 years
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited1 [Member] | Covenant Requirement Minimum [Member]
Debt Services, Coverage Ratio				1.15
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited1 [Member] | Covenant Required to not Limit Dividends [Member]
Debt Services, Coverage Ratio				1.25
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited1 [Member] | Minimum [Member]
Debt Instrument, Prepayment Premium Percentage				0.50%
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited1 [Member] | Maximum [Member]
Debt Instrument, Prepayment Premium Percentage				1.00%
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited1 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Guaranteed [Member]
Debt Instrument, Basis Spread on Variable Rate				4.35%
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited1 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Not Guaranteed [Member]
Debt Instrument, Basis Spread on Variable Rate				4.75%
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited1 [Member] | London Interbank Offered Rate (LIBOR) [Member] | Minimum [Member]
Debt Instrument, Basis Spread on Variable Rate				1.25%
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited [Member]
Debt Instrument, Face Amount																																		$ 310,000,000
Long-term Debt, Gross																							$ 29,800,000
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited [Member] | Historical [Member]
Debt Services, Coverage Ratio																							1.58
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited [Member] | Projected [Member]
Debt Services, Coverage Ratio																							1.59
Loan Agreement With OPIC [Member]
Debt Services, Coverage Ratio																							1.7
Long-term Debt, Gross																							$ 210,600,000
Restricted Cash and Cash Equivalents, Current, Total																							2,600,000	3,700,000
Letters of Credit Outstanding, Amount																							$ 16,100,000
Loan Agreement With OPIC [Member] | In The First Two Years After the Plant Commercial Operation Date [Member]
Debt Instrument, Prepayment Premium Percentage																							2.00%
Debt Instrument, Interest Rate, Stated Percentage																							6.12%
Loan Agreement With OPIC [Member] | Third Year After the Plant 2 Commercial Operation Date [Member]
Debt Instrument, Prepayment Premium Percentage																							1.00%
Loan Agreement With OPIC [Member] | Historical [Member]
Debt Services, Coverage Ratio																							2.87
Loan Agreement With OPIC [Member] | Projected [Member]
Debt Services, Coverage Ratio																							3.03
Loan Agreement With OPIC [Member] | Tranche One [Member]
Debt Instrument, Face Amount								$ 85,000,000									$ 85,000,000
Long-term Debt, Gross																							$ 56,600,000
Prepayment Deposit On Debt																	20,500,000
Loan Agreement With OPIC [Member] | Tranche Two [Member]
Long-term Debt, Gross								135,000,000									135,000,000						$ 121,800,000
Proceeds from Issuance of Debt							$ 45,000,000
Debt Instrument, Interest Rate, Stated Percentage																							6.31%
Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net																							$ 6,310,000
Loan Agreement With OPIC [Member] | Tranche Three [Member]
Debt Instrument, Face Amount								45,000,000									45,000,000
Long-term Debt, Gross																							$ 32,200,000
Proceeds from Issuance of Debt					$ 45,000,000
Loan Agreement With OPIC [Member] | Threshold For Loan Default [Member]
Debt Services, Coverage Ratio																							1.1
Loan Agreement With OPIC [Member] | Minimum [Member] | Historical [Member]
Debt Services, Coverage Ratio																							1.4
Olkaria III DEG [Member]
Debt Instrument, Face Amount																				$ 105,000,000
Debt Instrument, Basis Spread on Variable Rate																				4.00%
Debt Instrument, Interest Rate, Stated Percentage																				6.90%
Payment for Debt Extinguishment or Debt Prepayment Cost											$ 100,000
Repayments of Long-term Debt, Total											11,800,000
Olkaria III DEG [Member] | Tranche One [Member]
Debt Instrument, Face Amount								180,000,000									$ 180,000,000
Prepayment Penalty Charges								$ 1,500,000
Platanares Finance Agreement [Member] | OPIC [Member]
Long-term Debt, Gross																							$ 112,700,000
Prepayment Deposit On Debt																							$ 5,000,000
Proceeds from Issuance of Debt										$ 114,700,000
Debt Instrument, Interest Rate, Stated Percentage										7.02%
Debt Agreement, Maximum Borrowing Capacity										$ 124,700,000
Debt Instrument, Prepayment Premium Percentage, First or Second Year																							2.00%
Debt Instrument, Prepayment Premium Percentage, Third Year																							1.00%
Platanares Finance Agreement [Member] | Historical [Member] | OPIC [Member]
Debt Services, Coverage Ratio																							1.1
Platanares Finance Agreement [Member] | Projected [Member] | OPIC [Member]
Debt Services, Coverage Ratio																							1.5
Platanares Finance Agreement [Member] | Debt Service Reserve [Member] | OPIC [Member]
Restricted Cash and Cash Equivalents, Current, Total																							$ 13,400,000
Letters of Credit Outstanding, Amount																							0
Platanares Finance Agreement [Member] | Well Drilling Reserve [Member] | OPIC [Member]
Restricted Cash and Cash Equivalents, Current, Total																							2,000,000
Letters of Credit Outstanding, Amount																							$ 0
Platanares Finance Agreement [Member] | Threshold For Loan Default [Member] | OPIC [Member]
Debt Services, Coverage Ratio																							1.2
Platanares Finance Agreement [Member] | Maximum [Member] | Scenario, Forecast [Member] | OPIC [Member]
Proceeds from Issuance of Debt																						$ 10,000,000
Platanares [Member]
Current Power Generation | MWh										35
Ormat Funding Corp [Member]
Debt Instrument, Face Amount																																				$ 190,000,000
Repayments of Secured Debt											14,300,000
Payment for Debt Extinguishment or Debt Prepayment Cost											$ 1,300,000
Ormat Funding Corp [Member] | Mammoth Complex [Member]
Percentage of Financing Acquisition Cost																																				50.00%
OrCal Senior Secured Notes [Member]
Debt Instrument, Face Amount																					$ 165,000,000
Proceeds from Issuance of Debt																					$ 161,100,000
Debt Instrument, Interest Rate, Stated Percentage																					6.21%
Restricted Cash and Cash Equivalents, Current, Total																							$ 0	1,900,000
Letters of Credit Outstanding, Amount																							$ 18,700,000	32,100,000
Debt Instrument, Issuance Costs																					$ 3,900,000
Debt Instrument, Redemption Price, Percentage																							100.00%
OrCal Senior Secured Notes [Member] | Historical [Member]
Debt Services, Coverage Ratio																							1.18
OrCal Senior Secured Notes [Member] | Projected [Member]
Debt Services, Coverage Ratio																							1.41
OrCal Senior Secured Notes [Member] | Debt Service Reserve Backing [Member]
Letters of Credit Outstanding, Amount																							$ 4,600,000	4,600,000
OrCal Senior Secured Notes [Member] | Minimum [Member]
Debt Services, Coverage Ratio																					1.25
OFC Two Senior Secured Notes [Member]
Debt Instrument, Face Amount																																			$ 350,000,000
Government Guarantee Percent																							80.00%
Debtor-in-Possession Financing, Letters of Credit Outstanding																							$ 20,000,000
OFC Two Senior Secured Notes [Member] | Senior Notes [Member]
Secured Debt, Total																							$ 217,800,000	$ 232,500,000
OFC Two Senior Secured Notes [Member] | Wholly Owned Subsidiaries With Project Debt [Member]
Debt Instrument, Face Amount																																	$ 140,000,000
Debt Instrument, Interest Rate, Stated Percentage																																	4.61%
OFC Two Senior Secured Notes [Member] | Historical [Member]
Debt Services, Coverage Ratio																							2.55				2.21
OFC Two Senior Secured Notes [Member] | Projected [Member]
Debt Services, Coverage Ratio																							2.09				2.18
OFC Two Senior Secured Notes [Member] | Phase One Series A Senior Notes [Member]
Debt Instrument, Face Amount																		$ 151,700,000
Proceeds from Issuance of Debt																		$ 141,100,000
Debt Instrument, Interest Rate, Stated Percentage																		4.687%
Repayments of Long-term Debt, Total															$ 4,300,000
Other Reserves																							$ 0										$ 28,000,000
OFC Two Senior Secured Notes [Member] | Maximum [Member] | Historical [Member]
Debt Services, Coverage Ratio																							1.2
OFC Two Senior Secured Notes [Member] | Maximum [Member] | Projected [Member]
Debt Services, Coverage Ratio																							1.5
Don A. Cambell Senior Secured Notes [Member]
Debt Instrument, Face Amount			$ 92,500,000
Proceeds from Issuance of Debt			$ 87,100,000
Debt Instrument, Interest Rate, Stated Percentage			4.03%
Secured Debt, Total																							$ 83,300,000
Debt Instrument, Minimum Prepay Amount			$ 2,000,000
Don A. Cambell Senior Secured Notes [Member] | Historical [Member]
Debt Services, Coverage Ratio																							1.35
Don A. Cambell Senior Secured Notes [Member] | Projected [Member]
Debt Services, Coverage Ratio																							1.69
Don A. Cambell Senior Secured Notes [Member] | Minimum [Member]
Debt Services, Coverage Ratio			1.2
Prudential Capital Group Agreement [Member]
Debt Instrument, Term													7 years
Debt Instrument, Face Amount													$ 20,000,000
Long-term Debt, Gross																							$ 18,900,000
Debt Instrument, Interest Rate, Stated Percentage													5.80%
Line of Credit Facility, Maximum Borrowing Capacity													$ 50,000,000
Debt Instrument, Remaining Balance													$ 16,000,000
DOE Loan Guarantee [Member]
Debt Instrument, Term																			21 years 182 days
Long-term Debt, Gross																							51,400,000
Debt Instrument, Interest Rate, Stated Percentage																			2.60%
Line of Credit Facility, Maximum Borrowing Capacity																			$ 96,800,000
Prudential Capital Purchase Agreement [member]
Debt Instrument, Term						24 years
Long-term Debt, Gross																							27,800,000
Debt Instrument, Interest Rate, Stated Percentage						6.75%
Senior Unsecured Bonds [Member]
Debt Instrument, Face Amount																														$ 67,000,000
Proceeds from Issuance of Unsecured Debt												$ 250,000,000
Senior Unsecured Bonds [Member] | Series 3 Bonds [Member]
Debt Instrument, Face Amount																														$ 137,000,000
Senior Unsecured Bonds, Series 2 [Member]
Debt Instrument, Interest Rate, Stated Percentage																														3.70%
Senior Unsecured Bonds, Series 3 [Member]
Debt Instrument, Interest Rate, Stated Percentage																														4.45%
Migdal Loan [Member]
Debt Instrument, Face Amount	$ 100,000,000
Debt Instrument, Interest Rate, Stated Percentage	4.80%
Debt Instrument, Periodic Payment, Total	$ 4,200,000
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid	$ 37,000,000
Debt Instrument Increase in Stated Interest Rate if Rating is Downgraded to ILA Negative	0.50%
Debt Instrument Increase in Stated Interest Rate Each Additional Downgrade	0.25%
Debt Instrument Decrease in Stated Interest Rate for Each Rating Upgrade	0.25%
Debt to EBITDA Ratio Threshold for Rate Increase	4.5
Debt Instrument Increase in Stated Interest Rate if Debt to EBITDA Ratio Exceeds Threshold	0.50%
Debt to EBITDA Ratio Requirement	6
Stockholders Equity, Debt Covenant, Minimum Threshold	$ 650,000,000
Stockholders Equity to Total Assets, Ratio	25.00%
Stockholders Equity, Debt Covenant, Minimum Threshold to Pay Dividends	$ 800,000,000
Dividends to Net Income, Ratio	50.00%
Migdal Loan [Member] | Minimum [Member]
Debt Instrument, Interest Rate, Stated Percentage	4.80%
Migdal Loan [Member] | Maximum [Member]
Debt Instrument, Increase in Stated Interest Rate	1.00%
DEG 2 Facility Agreement [Member]
Debt Instrument, Interest Rate, Stated Percentage		6.28%
Debt Instrument, Minimum Prepay Amount		$ 5,000,000
Line of Credit Facility, Maximum Borrowing Capacity																													$ 50,000,000
Proceeds from Lines of Credit, Total		$ 50,000,000
Long-term Line of Credit, Total																							47,500,000
Credit Agreements With Eight Commercial Banks [Member]
Letters of Credit Outstanding, Amount																							229,600,000
Line of Credit Facility, Maximum Borrowing Capacity																							468,000,000
Long-term Line of Credit, Total																							159,000,000
Credit Agreements With Eight Commercial Banks [Member] | Extensions of Credit in The Form of Loans and/or Letters of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity																							233,000,000
Credit Agreements With Eight Commercial Banks [Member] | Letter of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity																							235,000,000
Credit Agreements With Eight Commercial Banks [Member] | Non - Committed [Member]
Long-term Line of Credit, Total																							14,100,000
Credit Agreements With Eight Commercial Banks [Member] | Union Bank, N.A. [Member]
Line of Credit Facility, Maximum Borrowing Capacity																							60,000,000
Credit Agreements With Eight Commercial Banks [Member] | HSBC Bank USA, N.A. [Member]
Line of Credit Facility, Maximum Borrowing Capacity																							$ 35,000,000
Union Bank, N.A. [Member]
Debt Services, Coverage Ratio																							2.94
Letters of Credit Outstanding, Amount																							$ 51,500,000
Line of Credit Facility, Maximum Borrowing Capacity									$ 60,000,000
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio																							2.91
Amount Available For Dividend Distribution Percent Of Cumulative Net Income									2														1.1
Union Bank, N.A. [Member] | Minimum [Member]
Debt Services, Coverage Ratio									1.35
Union Bank, N.A. [Member] | Maximum [Member]
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio									4.5
HSBC Bank USA, N.A. [Member]
Debt Services, Coverage Ratio																							2.94
Letters of Credit Outstanding, Amount																							$ 30,000,000
Line of Credit Facility, Maximum Borrowing Capacity																$ 35,000,000
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio																							2.91
Amount Available For Dividend Distribution Percent Of Cumulative Net Income																							1.1
Line of Credit Facility, Borrowing Capacity Increase																10,000,000
Line of Credit Facility, Capacity Available for Specific Purpose Other than for Trade Purchases																$ 10,000,000
HSBC Bank USA, N.A. [Member] | Minimum [Member]
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio																1.35
HSBC Bank USA, N.A. [Member] | Maximum [Member]
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio																4.5
Amount Available For Dividend Distribution Percent Of Cumulative Net Income																2
Surety Agreement [Member] | Chubb [Member]
Surety Bonds Available																												$ 200,000,000
Surety Bonds Outstanding																							$ 141,100,000