Note 11 - Long-term Debt, Credit Agreements and Commercial Paper (Details Textual) $ in Thousands, ₪ in Billions												1 Months Ended		12 Months Ended
		Jul. 20, 2020 USD ($)	Apr. 06, 2020 USD ($)	Jul. 03, 2019 USD ($)	May 30, 2019	Apr. 09, 2019 USD ($)	Mar. 25, 2019 USD ($)	Mar. 22, 2018 USD ($)	Dec. 21, 2016 USD ($)	Jul. 31, 2015 USD ($) MWh	Feb. 29, 2012	Oct. 31, 2018 MWh	May 31, 2013	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Jul. 01, 2020 USD ($)	Jul. 01, 2020 ILS (₪)	May 13, 2020 USD ($)	Apr. 30, 2020 USD ($)	Apr. 20, 2020 USD ($)	May 04, 2019 USD ($)	Apr. 29, 2019	Apr. 04, 2019 USD ($)	Jan. 04, 2019 USD ($)	Apr. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)	May 31, 2017 USD ($)	Nov. 29, 2016 USD ($)	Oct. 20, 2016 USD ($)	Sep. 30, 2016 USD ($)	May 31, 2016 USD ($)	Aug. 29, 2014 USD ($)	Aug. 23, 2012 USD ($)	Oct. 31, 2011 USD ($)	Sep. 30, 2011 USD ($)	Aug. 31, 2011 USD ($)
Letters of Credit Outstanding, Amount														$ 190,300
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio														2.36
Proceeds from Issuance of Commercial Paper				$ 50,000										$ 0	$ 50,000	$ 0
Stockholders' Equity Attributable to Parent, Ending Balance														$ 1,805,985	1,392,420
Percentage Of Company Assets														49.90%
Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest, Ending Balance														$ 1,941,437	1,515,410	1,445,096											$ 1,319,535
Payments of Dividends, Total														$ 22,500	$ 22,400	$ 26,800
Covenant Requirement Minimum [Member]
Amount Available For Dividend Distribution Percent Of Cumulative Net Income														50
Stockholders' Equity Attributable to Parent, Ending Balance														$ 750,000
Percentage Of Company Assets														25.00%
London Interbank Offered Rate (LIBOR) [Member] | Commercial Paper [Member]
Debt Instrument, Basis Spread on Variable Rate				0.75%
Maximum [Member] | Covenant Requirement Minimum [Member]
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio														6
Maximum [Member] | Commercial Paper [Member]
Debt Instrument, Term (Year)				5 years
Minimum [Member] | Commercial Paper [Member]
Debt Instrument, Term (Year)				90 days
Pomona Energy Storage [Member]
Business Combination, Consideration Transferred, Total		$ 43,400
Senior Unsecured Bonds, Series 4 [Member]
Debt Instrument, Face Amount														$ 289,800			$ 289,800	₪ 1
Debt Instrument, Number of Annual Payments																	10	10
Debt Instrument, Interest Rate, Stated Percentage														3.35%
Long-term Debt, Gross														$ 311,000
Senior Unsecured Bonds, Series 4 [Member] | Cross Currency Interest Rate Contract [Member]
Derivative, Fixed Interest Rate																	4.34%	4.34%
Senior Unsecured Bonds, Series 2 [Member]
Debt Instrument, Face Amount																															$ 67,000
Senior Unsecured Bonds, Series 3 [Member]
Debt Instrument, Face Amount			$ 51,100											$ 218,000					$ 15,300		$ 14,500										$ 137,000
Proceeds from Issuance of Long-term Debt, Total			$ 50,000
Debt Instrument, Interest Rate, Stated Percentage			4.45%											4.45%
Long-term Debt, Gross														$ 218,000
Senior Unsecured Loan (Migdal) [Member]
Debt Instrument, Face Amount								$ 100,000						$ 100,000
Debt Instrument, Interest Rate, Stated Percentage	[1]													4.80%
Debt Instrument, Periodic Payment, Total								4,200
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid								$ 37,000
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								$ 750,000
Stockholders Equity to Total Assets, Ratio								25.00%
Stockholders Equity, Debt Covenant, Minimum Threshold to Pay Dividends								$ 800,000
Dividends to Net Income, Ratio								50.00%
Long-term Debt, Gross														$ 100,000
Senior Unsecured Loan (Migdal) [Member] | Maximum [Member]
Debt Instrument, Increase in Stated Interest Rate								1.00%
Senior Unsecured Loan (Migdal) [Member] | Minimum [Member]
Debt Instrument, Interest Rate, Stated Percentage								4.80%
Additional Migdal Loan [Member]
Debt Instrument, Face Amount							$ 50,000							$ 50,000
Debt Instrument, Interest Rate, Stated Percentage	[1]													4.60%
Debt Instrument, Periodic Payment, Total							2,100
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid							$ 18,500
Long-term Debt, Gross														$ 50,000
Second Addendum Migdal Loan [Member]
Debt Instrument, Face Amount														$ 50,000						$ 50,000
Debt Instrument, Interest Rate, Stated Percentage	[1]													5.44%
Debt Instrument, Periodic Payment Terms, Balloon Payment to be Paid																				18,500
Debt Instrument, Principal to Be Repaid in Installments																				$ 31,500
Debt Instrument, Number of Semi-annual Payments																				15
Long-term Debt, Gross														$ 50,000
DEG 2 Facility Agreement [Member]
Debt Instrument, Interest Rate, Stated Percentage									6.28%
Line of Credit Facility, Maximum Borrowing Capacity																														$ 50,000
Proceeds from Lines of Credit, Total									$ 50,000
DEG 3 Loan Agreement [Member]
Debt Instrument, Interest Rate, Stated Percentage																									6.04%
DEG 3 Loan Agreement [Member] | OrPower 4, Inc [Member]
Debt Instrument, Face Amount																									$ 41,500
Loan Agreement With OPIC the Olkaria III Power Plant [Member]
Debt Instrument, Face Amount														310,000																				$ 310,000
Long-term Debt, Gross														174,700
Platanares Finance Agreement [Member]
Debt Instrument, Face Amount														$ 114,700
Debt Instrument, Interest Rate, Stated Percentage	[2]													7.02%
Long-term Debt, Gross														$ 96,300
Platanares Finance Agreement [Member] | OPIC [Member]
Debt Instrument, Face Amount																										$ 114,700
Current Power Generation (Megawatt-Hour) | MWh												35
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited1 [Member]
Debt Instrument, Face Amount										$ 42,000				42,000
Debt Instrument, Term (Year)										12 years
Power Utilization (Megawatt-Hour) | MWh										20
Debt Instrument Number of Quarterly Payments										48
Long-term Debt, Gross														$ 22,800
Loan Agreement with Banco Industrial S.A. and Westrust Bank (International) Limited1 [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate	[2]													4.35%
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] | Minimum [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate										1.25%
Plumstriker Loan Agreement [Member]
Debt Instrument, Face Amount														$ 23,500
Long-term Debt, Gross														$ 18,100
Plumstriker Loan Agreement [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate	[2]													3.50%
Plumstriker Loan Agreement [Member] | Plumstriker and its Two Subsidiaries [Member]
Debt Instrument, Face Amount																						$ 23,500
Debt Instrument, Equal Quarterly Principal Installments, Percentage of Loan					1.25%
Plumstriker Loan Agreement [Member] | Plumstriker and its Two Subsidiaries [Member] | London Interbank Offered Rate (LIBOR) [Member]
Debt Instrument, Basis Spread on Variable Rate					3.50%
Don A. Cambell Senior Secured Notes [Member]
Debt Instrument, Face Amount																													$ 92,500
OFC Two Senior Secured Notes [Member]
Debt Instrument, Face Amount																																			$ 151,700	$ 350,000
Government Guarantee Percent																																				80.00%
OFC Two Senior Secured Notes [Member] | Wholly Owned Subsidiaries With Project Debt [Member]
Debt Instrument, Face Amount																																	$ 140,000
Prudential Capital Group Agreement [Member]
Debt Instrument, Face Amount																																$ 20,000
Long-term Debt, Gross														$ 16,000
DOE Loan Guarantee [Member]
Line of Credit Facility, Maximum Borrowing Capacity																																					$ 96,800
Loan Agreement with Bpifrance [Member] | Guadeloupe 1 [Member]
Debt Instrument, Face Amount																								$ 8,900
Debt Instrument, Interest Rate, Stated Percentage																							1.93%
Long-term Debt, Gross														9,800
Loan Agreement with Société Général [Member] | Guadeloupe 1 [Member]
Debt Instrument, Face Amount						$ 8,900
Debt Instrument, Interest Rate, Stated Percentage						1.52%
Debt Instrument Number of Quarterly Payments						28
Long-term Debt, Gross														7,800
Credit Agreements With Eight Commercial Banks [Member]
Line of Credit Facility, Maximum Borrowing Capacity														623,000
Long-term Line of Credit, Total														0
Letters of Credit Outstanding, Amount														94,400
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														408,000
Credit Agreements With Eight Commercial Banks [Member] | Letter of Credit [Member]
Line of Credit Facility, Maximum Borrowing Capacity														120,000
Credit Agreements With Eight Commercial Banks [Member] | Union Bank, N.A. [Member]
Line of Credit Facility, Maximum Borrowing Capacity														60,000
Credit Agreements With Eight Commercial Banks [Member] | HSBC Bank USA, N.A. [Member]
Line of Credit Facility, Maximum Borrowing Capacity														35,000
Union Bank, N.A. [Member]
Line of Credit Facility, Maximum Borrowing Capacity														60,000
Long-term Line of Credit, Total														$ 57,900
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio														1.64
Debt Services, Coverage Ratio														5.05
Amount Available For Dividend Distribution Percent Of Cumulative Net Income											2.0			0.61
Union Bank, N.A. [Member] | Maximum [Member]
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio											4.5
Union Bank, N.A. [Member] | Minimum [Member]
Debt Services, Coverage Ratio											1.35
HSBC Bank USA, N.A. [Member]
Line of Credit Facility, Maximum Borrowing Capacity														$ 35,000
Long-term Line of Credit, Total														$ 27,900
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio														1.64
Debt Services, Coverage Ratio														5.05
Amount Available For Dividend Distribution Percent Of Cumulative Net Income														0.61
Line of Credit Facility, Borrowing Capacity Increase														$ 10,000
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													2.0
HSBC Bank USA, N.A. [Member] | Minimum [Member]
Debt To Earnings Before Interest Tax Depreciation And Amortization Ratio													1.35
Surety Agreement [Member] | Chubb [Member]
Surety Bonds Available																												$ 200,000
Surety Bonds Outstanding														$ 153,700

[1] payable semi-annually in arrears.

[2] payable quarterly