Note 4 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2024	Dec. 31, 2023
Finance liability - Dixie Valley	$ 224.2	$ 207.2
Deposit	20.0	20.9
Hapoalim 2024 Loan Agreement [Member]
Loans	75.9
Mizrahi Loan Agreement [Member]
Loans	61.2	61.4
HSBC 2024 Loan Agreement [Member]
Loans	126.5
Mizrahi Loan Agreement 2023 [Member]
Loans	51.8	52.0
Mammoth Senior Secured Notes [Member]
Loans	137.4
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 Loan DFC [Member]
Loans	111.6	116.4
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
Other Long-term Debt [Member]
Senior Unsecured Bond	6.7	6.8
Fair Value, Inputs, Level 1 [Member]
Finance liability - Dixie Valley	0.0	0.0
Deposit	20.0	20.9
Fair Value, Inputs, Level 1 [Member] | Hapoalim 2024 Loan Agreement [Member]
Loans	0.0
Fair Value, Inputs, Level 1 [Member] | Mizrahi Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | HSBC 2024 Loan Agreement [Member]
Loans	0.0
Fair Value, Inputs, Level 1 [Member] | Mizrahi Loan Agreement 2023 [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Mammoth Senior Secured Notes [Member]
Loans	0.0
Fair Value, Inputs, Level 1 [Member] | Convertible Senior Notes [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | HSBC Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Hapoalim Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Discount Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Olkaria III Loan DFC [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Platanares Loan - OPIC [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | OFC Senior Secured Notes [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | USG Prudential - NV [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | USG Prudential - ID [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | USG DOE [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured Bond	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Senior Unsecured Loan [Member]
Senior Unsecured Bond	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Other Long-term Debt [Member]
Senior Unsecured Bond	0.0	0.0
Fair Value, Inputs, Level 2 [Member]
Finance liability - Dixie Valley	0.0	0.0
Deposit	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Hapoalim 2024 Loan Agreement [Member]
Loans	0.0
Fair Value, Inputs, Level 2 [Member] | Mizrahi Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | HSBC 2024 Loan Agreement [Member]
Loans	0.0
Fair Value, Inputs, Level 2 [Member] | Mizrahi Loan Agreement 2023 [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Mammoth Senior Secured Notes [Member]
Loans	0.0
Fair Value, Inputs, Level 2 [Member] | Convertible Senior Notes [Member]
Notes	417.4	444.6
Fair Value, Inputs, Level 2 [Member] | HSBC Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Hapoalim Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Discount Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Olkaria III Loan DFC [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Platanares Loan - OPIC [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | OFC Senior Secured Notes [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | USG Prudential - NV [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | USG Prudential - ID [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | USG DOE [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured Bond	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Senior Unsecured Loan [Member]
Senior Unsecured Bond	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Other Long-term Debt [Member]
Senior Unsecured Bond	0.0	0.0
Fair Value, Inputs, Level 3 [Member]
Finance liability - Dixie Valley	224.2	207.2
Deposit	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Hapoalim 2024 Loan Agreement [Member]
Loans	75.9
Fair Value, Inputs, Level 3 [Member] | Mizrahi Loan Agreement [Member]
Loans	61.2	61.4
Fair Value, Inputs, Level 3 [Member] | HSBC 2024 Loan Agreement [Member]
Loans	126.5
Fair Value, Inputs, Level 3 [Member] | Mizrahi Loan Agreement 2023 [Member]
Loans	51.8	52.0
Fair Value, Inputs, Level 3 [Member] | Mammoth Senior Secured Notes [Member]
Loans	137.4
Fair Value, Inputs, Level 3 [Member] | Convertible Senior Notes [Member]
Notes	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | HSBC Loan Agreement [Member]
Loans	30.1	33.8
Fair Value, Inputs, Level 3 [Member] | Hapoalim Loan Agreement [Member]
Loans	76.0	75.0
Fair Value, Inputs, Level 3 [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans	93.5	99.7
Fair Value, Inputs, Level 3 [Member] | Discount Loan Agreement [Member]
Loans	63.2	69.9
Fair Value, Inputs, Level 3 [Member] | Olkaria III Loan DFC [Member]
Loans	111.6	116.4
Fair Value, Inputs, Level 3 [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	22.0	21.6
Fair Value, Inputs, Level 3 [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	19.3	19.0
Fair Value, Inputs, Level 3 [Member] | Platanares Loan - OPIC [Member]
Loans	68.8	71.3
Fair Value, Inputs, Level 3 [Member] | OFC Senior Secured Notes [Member]
Notes	128.9	134.2
Fair Value, Inputs, Level 3 [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	50.5	52.3
Fair Value, Inputs, Level 3 [Member] | USG Prudential - NV [Member]
Notes	22.0	22.3
Fair Value, Inputs, Level 3 [Member] | USG Prudential - ID [Member]
Notes	51.2	54.1
Fair Value, Inputs, Level 3 [Member] | USG DOE [Member]
Notes	28.2	30.0
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured Bond	198.5	202.8
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Loan [Member]
Senior Unsecured Bond	139.7	150.4
Fair Value, Inputs, Level 3 [Member] | Other Long-term Debt [Member]
Senior Unsecured Bond	$ 6.7	$ 6.8