Note 4 - Fair Value of Financial Instruments - Fair Value of Long-term Debt Approximates Its Carrying Amount, Exceptions (Details) - USD ($) $ in Millions		Mar. 31, 2023	Dec. 31, 2022
Finance liability - Dixie Valley		$ 213.3	$ 219.8
Mizrahi Loan Agreement [Member]
Loans		71.4	71.4
Convertible Senior Notes [Member]
Notes		485.4	505.3
HSBC Loan Agreement [Member]
Loans		36.6	40.3
Hapoalim Loan Agreement [Member]
Loans		92.4	91.1
Hapoalim Loan Agreement 2023 [Member]
Loans		100.0
Discount Loan Agreement [Member]
Loans		74.5	81.1
Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans		26.9	26.5
Olkaria III plant 1 Loan - DEG 3 [Member]
Loans		23.7	23.3
Platanares Loan - OPIC [Member]
Loans		78.0	80.2
Amatitlan Loan [Member]
Loans		13.8	14.7
Don A. Campbell 1 ("DAC1") [Member]
Notes		55.8	57.4
USG Prudential - NV [Member]
Notes		23.5	23.7
USG Prudential - ID [Member]
Notes		54.6	56.8
USG DOE [Member]
Notes		31.1	32.8
Senior Unsecured Bonds [Member]
Senior Unsecured debt		232.1	235.1
Senior Unsecured Loan [Member]
Senior Unsecured debt		156.1	166.4
Plumstriker Loan Agreement [Member]
Loans		10.9	11.2
Estimate of Fair Value Measurement [Member]
Finance liability - Dixie Valley		213.3	219.8
Other long-term debt		8.8	9.2
Estimate of Fair Value Measurement [Member] | Mizrahi Loan Agreement [Member]
Loans		71.4	71.4
Estimate of Fair Value Measurement [Member] | Convertible Senior Notes [Member]
Notes		485.4	505.3
Estimate of Fair Value Measurement [Member] | HSBC Loan Agreement [Member]
Loans		36.6	40.3
Estimate of Fair Value Measurement [Member] | Hapoalim Loan Agreement [Member]
Loans		92.4	91.1
Estimate of Fair Value Measurement [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans		100.0	0.0
Estimate of Fair Value Measurement [Member] | Discount Loan Agreement [Member]
Loans		74.5	81.1
Estimate of Fair Value Measurement [Member] | Olkaria III OPIC [Member]
Loans		129.7	134.2
Estimate of Fair Value Measurement [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans		26.9	26.5
Estimate of Fair Value Measurement [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans		23.7	23.3
Estimate of Fair Value Measurement [Member] | Platanares Loan - OPIC [Member]
Loans		78.0	80.2
Estimate of Fair Value Measurement [Member] | Amatitlan Loan [Member]
Loans		13.8	14.7
Estimate of Fair Value Measurement [Member] | OFC Two Senior Secured Notes [Member]
Notes		145.0	149.8
Estimate of Fair Value Measurement [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes		55.8	57.4
Estimate of Fair Value Measurement [Member] | USG Prudential - NV [Member]
Notes		23.5	23.7
Estimate of Fair Value Measurement [Member] | USG Prudential - ID [Member]
Notes		54.6	56.8
Estimate of Fair Value Measurement [Member] | USG DOE [Member]
Notes		31.1	32.8
Estimate of Fair Value Measurement [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt		232.1	235.1
Estimate of Fair Value Measurement [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt		156.1	166.4
Estimate of Fair Value Measurement [Member] | Plumstriker Loan Agreement [Member]
Loans		10.9	11.2
Reported Value Measurement [Member]
Finance liability - Dixie Valley	[1]	236.1	242.0
Other long-term debt	[1]	9.4	10.4
Reported Value Measurement [Member] | Mizrahi Loan Agreement [Member]
Loans	[1]	70.3	70.3
Reported Value Measurement [Member] | Convertible Senior Notes [Member]
Notes	[1]	431.3	431.3
Reported Value Measurement [Member] | HSBC Loan Agreement [Member]
Loans	[1]	39.3	42.9
Reported Value Measurement [Member] | Hapoalim Loan Agreement [Member]
Loans	[1]	98.2	98.2
Reported Value Measurement [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans		100.0	0.0
Reported Value Measurement [Member] | Discount Loan Agreement [Member]
Loans	[1]	81.3	87.5
Reported Value Measurement [Member] | Olkaria III OPIC [Member]
Loans	[1]	134.2	138.7
Reported Value Measurement [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	[1]	27.5	27.5
Reported Value Measurement [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	[1]	24.0	24.0
Reported Value Measurement [Member] | Platanares Loan - OPIC [Member]
Loans	[1]	77.8	79.9
Reported Value Measurement [Member] | Amatitlan Loan [Member]
Loans	[1]	14.9	15.8
Reported Value Measurement [Member] | OFC Two Senior Secured Notes [Member]
Notes	[1]	153.3	158.0
Reported Value Measurement [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	[1]	61.1	62.7
Reported Value Measurement [Member] | USG Prudential - NV [Member]
Notes	[1]	24.8	25.0
Reported Value Measurement [Member] | USG Prudential - ID [Member]
Notes	[1]	59.8	61.6
Reported Value Measurement [Member] | USG DOE [Member]
Notes	[1]	31.4	32.8
Reported Value Measurement [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt	[1]	249.0	255.8
Reported Value Measurement [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	[1]	166.4	174.8
Reported Value Measurement [Member] | Plumstriker Loan Agreement [Member]
Loans	[1]	$ 11.1	$ 11.4

[1] Carrying amount value excludes the related deferred financing costs.