Note 7 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2023	Dec. 31, 2022
Financing Liability - Dixie Valley	$ 207.2	$ 219.8
Deposits	20.9	13.9
Mizrahi Loan Agreement [Member]
Loans	61.4	71.4
Mizrahi Loan Agreement 2023 [Member]
Loans	52.0
Convertible Senior Notes [Member]
Notes	444.6	505.3
HSBC Loan Agreement [Member]
Loans	33.8	40.3
Hapoalim Loan Agreement [Member]
Loans	75.0	91.1
Discount Loan Agreement [Member]
Loans	69.9	81.1
Hapoalim Loan Agreement 2023 [Member]
Loans	99.7
Olkaria III Loan DFC [Member]
Loans	116.4	134.2
Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	21.6	26.5
Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	19.0	23.3
Platanares Loan - OPIC [Member]
Loans	71.3	80.2
Amatitlan Loan [Member]
Loans		14.7
OFC Senior Secured Notes [Member]
Notes	134.2	149.8
Don A. Campbell 1 ("DAC1") [Member]
Notes	52.3	57.4
USG Prudential - NV [Member]
Notes	22.3	23.7
USG Prudential - ID [Member]
Notes	54.1	56.8
USG DOE [Member]
Notes	30.0	32.8
Senior Unsecured Bonds [Member]
Senior Unsecured debt	202.8	235.1
Senior Unsecured Loan [Member]
Senior Unsecured debt	150.4	166.4
Plumstriker Loan Agreement [Member]
Loans		11.2
Other Long-term Debt [Member]
Senior Unsecured debt	6.8	9.2
Fair Value, Inputs, Level 1 [Member]
Financing Liability - Dixie Valley	0.0	0.0
Deposits	20.9	13.9
Fair Value, Inputs, Level 1 [Member] | Mizrahi Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Mizrahi Loan Agreement 2023 [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] | Discount Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans	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] | Amatitlan Loan [Member]
Loans		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 debt	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Plumstriker Loan Agreement [Member]
Loans		0.0
Fair Value, Inputs, Level 1 [Member] | Other Long-term Debt [Member]
Senior Unsecured debt	0.0	0.0
Fair Value, Inputs, Level 2 [Member]
Financing Liability - Dixie Valley	0.0	0.0
Deposits	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Mizrahi Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Mizrahi Loan Agreement 2023 [Member]
Loans	0.0
Fair Value, Inputs, Level 2 [Member] | Convertible Senior Notes [Member]
Notes	444.6	505.3
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] | Discount Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans	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] | Amatitlan Loan [Member]
Loans		14.7
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 debt	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Plumstriker Loan Agreement [Member]
Loans		11.2
Fair Value, Inputs, Level 2 [Member] | Other Long-term Debt [Member]
Senior Unsecured debt	0.0	0.0
Fair Value, Inputs, Level 3 [Member]
Financing Liability - Dixie Valley	207.2	219.8
Deposits	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Mizrahi Loan Agreement [Member]
Loans	61.4	71.4
Fair Value, Inputs, Level 3 [Member] | Mizrahi Loan Agreement 2023 [Member]
Loans	52.0
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	33.8	40.3
Fair Value, Inputs, Level 3 [Member] | Hapoalim Loan Agreement [Member]
Loans	75.0	91.1
Fair Value, Inputs, Level 3 [Member] | Discount Loan Agreement [Member]
Loans	69.9	81.1
Fair Value, Inputs, Level 3 [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans	99.7
Fair Value, Inputs, Level 3 [Member] | Olkaria III Loan DFC [Member]
Loans	116.4	134.2
Fair Value, Inputs, Level 3 [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	21.6	26.5
Fair Value, Inputs, Level 3 [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	19.0	23.3
Fair Value, Inputs, Level 3 [Member] | Platanares Loan - OPIC [Member]
Loans	71.3	80.2
Fair Value, Inputs, Level 3 [Member] | Amatitlan Loan [Member]
Loans		0.0
Fair Value, Inputs, Level 3 [Member] | OFC Senior Secured Notes [Member]
Notes	134.2	149.8
Fair Value, Inputs, Level 3 [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	52.3	57.4
Fair Value, Inputs, Level 3 [Member] | USG Prudential - NV [Member]
Notes	22.3	23.7
Fair Value, Inputs, Level 3 [Member] | USG Prudential - ID [Member]
Notes	54.1	56.8
Fair Value, Inputs, Level 3 [Member] | USG DOE [Member]
Notes	30.0	32.8
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt	202.8	235.1
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	150.4	166.4
Fair Value, Inputs, Level 3 [Member] | Plumstriker Loan Agreement [Member]
Loans		0.0
Fair Value, Inputs, Level 3 [Member] | Other Long-term Debt [Member]
Senior Unsecured debt	$ 6.8	$ 9.2