Note 4 - Fair Value of Financial Instruments - Fair Value of Long-term Debt Approximates Its Carrying Amount, Exceptions (Details) - USD ($) $ in Millions		Mar. 31, 2024	Dec. 31, 2023
Finance liability - Dixie Valley		$ 224.2	$ 207.2
HSBC 2024 Loan Agreement [Member]
Loans		126.5
Mammoth Senior Secured Notes [Member]
Loans		137.4
Mizrahi Loan Agreement [Member]
Loans		61.2	61.4
Mizrahi Loan Agreement 2023 [Member]
Loans		51.8	52.0
Convertible Senior Notes [Member]
Notes		417.4	444.6
HSBC Loan Agreement [Member]
Loans		30.1	33.8
Hapoalim Loan Agreement [Member]
Loans		76.0	75.0
Hapoalim Loan Agreement 2023 [Member]
Loans		93.5	99.7
Discount Loan Agreement [Member]
Loans		63.2	69.9
Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans		22.0	21.6
Olkaria III plant 1 Loan - DEG 3 [Member]
Loans		19.3	19.0
Platanares Loan - OPIC [Member]
Loans		68.8	71.3
OFC Senior Secured Notes [Member]
Notes		128.9	134.2
Don A. Campbell 1 ("DAC1") [Member]
Notes		50.5	52.3
USG Prudential - NV [Member]
Notes		22.0	22.3
USG Prudential - ID [Member]
Notes		51.2	54.1
USG DOE [Member]
Notes		28.2	30.0
Senior Unsecured Bonds [Member]
Senior Unsecured Bond		198.5	202.8
Senior Unsecured Loan [Member]
Senior Unsecured Bond		139.7	150.4
Estimate of Fair Value Measurement [Member]
Finance liability - Dixie Valley		224.2	207.2
Other long-term debt		6.7	6.8
Estimate of Fair Value Measurement [Member] | Hapoalim Loan Agreement 2024 [Member]
Loans		75.9	0.0
Estimate of Fair Value Measurement [Member] | HSBC 2024 Loan Agreement [Member]
Loans		126.5	0.0
Estimate of Fair Value Measurement [Member] | Mammoth Senior Secured Notes [Member]
Loans		137.4	0.0
Estimate of Fair Value Measurement [Member] | Mizrahi Loan Agreement [Member]
Loans		61.2	61.4
Estimate of Fair Value Measurement [Member] | Mizrahi Loan Agreement 2023 [Member]
Loans		51.8	52.0
Estimate of Fair Value Measurement [Member] | Convertible Senior Notes [Member]
Notes		417.4	444.6
Estimate of Fair Value Measurement [Member] | HSBC Loan Agreement [Member]
Loans		30.1	33.8
Estimate of Fair Value Measurement [Member] | Hapoalim Loan Agreement [Member]
Loans		76.0	75.0
Estimate of Fair Value Measurement [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans		93.5	99.7
Estimate of Fair Value Measurement [Member] | Discount Loan Agreement [Member]
Loans		63.2	69.9
Estimate of Fair Value Measurement [Member] | Olkaria III OPIC [Member]
Loans		111.6	116.4
Estimate of Fair Value Measurement [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans		22.0	21.6
Estimate of Fair Value Measurement [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans		19.3	19.0
Estimate of Fair Value Measurement [Member] | Platanares Loan - OPIC [Member]
Loans		68.8	71.3
Estimate of Fair Value Measurement [Member] | OFC Senior Secured Notes [Member]
Notes		128.9	134.2
Estimate of Fair Value Measurement [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes		50.5	52.3
Estimate of Fair Value Measurement [Member] | USG Prudential - NV [Member]
Notes		22.0	22.3
Estimate of Fair Value Measurement [Member] | USG Prudential - ID [Member]
Notes		51.2	54.1
Estimate of Fair Value Measurement [Member] | USG DOE [Member]
Notes		28.2	30.0
Estimate of Fair Value Measurement [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured Bond		198.5	202.8
Estimate of Fair Value Measurement [Member] | Senior Unsecured Loan [Member]
Senior Unsecured Bond		139.7	150.4
Reported Value Measurement [Member]
Finance liability - Dixie Valley		223.3	225.8
Other long-term debt	[1]	6.8	7.7
Reported Value Measurement [Member] | Hapoalim Loan Agreement 2024 [Member]
Loans	[1]	75.0	0.0
Reported Value Measurement [Member] | HSBC 2024 Loan Agreement [Member]
Loans		125.0	0.0
Reported Value Measurement [Member] | Mammoth Senior Secured Notes [Member]
Loans		135.1	0.0
Reported Value Measurement [Member] | Mizrahi Loan Agreement [Member]
Loans	[1]	60.9	60.9
Reported Value Measurement [Member] | Mizrahi Loan Agreement 2023 [Member]
Loans		50.0	50.0
Reported Value Measurement [Member] | Convertible Senior Notes [Member]
Notes	[1]	431.3	431.3
Reported Value Measurement [Member] | HSBC Loan Agreement [Member]
Loans	[1]	32.1	35.7
Reported Value Measurement [Member] | Hapoalim Loan Agreement [Member]
Loans		80.4	80.4
Reported Value Measurement [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans		90.0	95.0
Reported Value Measurement [Member] | Discount Loan Agreement [Member]
Loans	[1]	68.8	75.0
Reported Value Measurement [Member] | Olkaria III OPIC [Member]
Loans	[1]	116.2	120.7
Reported Value Measurement [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	[1]	22.5	22.5
Reported Value Measurement [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	[1]	19.7	19.7
Reported Value Measurement [Member] | Platanares Loan - OPIC [Member]
Loans	[1]	69.6	71.7
Reported Value Measurement [Member] | OFC Senior Secured Notes [Member]
Notes		142.5	142.5
Reported Value Measurement [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes		55.8	57.4
Reported Value Measurement [Member] | USG Prudential - NV [Member]
Notes	[1]	23.8	23.9
Reported Value Measurement [Member] | USG Prudential - ID [Member]
Notes		57.2	58.9
Reported Value Measurement [Member] | USG DOE [Member]
Notes	[1]	28.7	30.2
Reported Value Measurement [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured Bond	[1]	217.3	220.6
Reported Value Measurement [Member] | Senior Unsecured Loan [Member]
Senior Unsecured Bond	[1]	$ 149.6	$ 158.0

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