Note 4 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Sep. 30, 2023	Dec. 31, 2022
Finance liability - Dixie Valley	$ 201.4	$ 219.8
Deposits	21.2	13.9
Mizrahi Loan Agreement [Member]
Loans	65.2	71.4
Convertible Senior Notes [Member]
Notes	419.8	505.3
HSBC Loan Agreement [Member]
Loans	35.9	40.3
Hapoalim Loan Agreement [Member]
Loans	83.2	91.1
Hapoalim Loan Agreement 2023 [Member]
Loans	97.1
Discount Loan Agreement [Member]
Loans	67.9	81.1
Olkaria III Loan DFC [Member]
Loans	118.9	134.2
Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	24.2	26.5
Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	21.3	23.3
Platanares Loan - OPIC [Member]
Loans	72.1	80.2
Amatitlan Loan [Member]
Loans		14.7
OFC Senior Secured Notes [Member]
Notes	135.6	149.8
Don A. Campbell 1 ("DAC1") [Member]
Notes	52.5	57.4
USG Prudential - NV [Member]
Notes	22.2	23.7
USG Prudential - ID [Member]
Notes	52.0	56.8
USG DOE [Member]
Notes	29.0	32.8
Senior Unsecured Bonds [Member]
Senior Unsecured debt	190.4	235.1
Senior Unsecured Loan [Member]
Senior Unsecured debt	145.3	166.4
Other Long-term Debt [Member]
Senior Unsecured debt	7.5	9.2
Plumstriker Loan Agreement [Member]
Loans		11.2
Fair Value, Inputs, Level 1 [Member]
Finance liability - Dixie Valley	0.0	0.0
Deposits	21.2	13.9
Fair Value, Inputs, Level 1 [Member] | Mizrahi Loan Agreement [Member]
Loans	0.0	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
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] | 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] | Other Long-term Debt [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 2 [Member]
Finance 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] | Convertible Senior Notes [Member]
Notes	419.8	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] | Hapoalim Loan Agreement 2023 [Member]
Loans	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] | 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] | Other Long-term Debt [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 3 [Member]
Finance liability - Dixie Valley	201.4	219.8
Deposits	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Mizrahi Loan Agreement [Member]
Loans	65.2	71.4
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	35.9	40.3
Fair Value, Inputs, Level 3 [Member] | Hapoalim Loan Agreement [Member]
Loans	83.2	91.1
Fair Value, Inputs, Level 3 [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans	97.1
Fair Value, Inputs, Level 3 [Member] | Discount Loan Agreement [Member]
Loans	67.9	81.1
Fair Value, Inputs, Level 3 [Member] | Olkaria III Loan DFC [Member]
Loans	118.9	134.2
Fair Value, Inputs, Level 3 [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	24.2	26.5
Fair Value, Inputs, Level 3 [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	21.3	23.3
Fair Value, Inputs, Level 3 [Member] | Platanares Loan - OPIC [Member]
Loans	72.1	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	135.6	149.8
Fair Value, Inputs, Level 3 [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	52.5	57.4
Fair Value, Inputs, Level 3 [Member] | USG Prudential - NV [Member]
Notes	22.2	23.7
Fair Value, Inputs, Level 3 [Member] | USG Prudential - ID [Member]
Notes	52.0	56.8
Fair Value, Inputs, Level 3 [Member] | USG DOE [Member]
Notes	29.0	32.8
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt	190.4	235.1
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	145.3	166.4
Fair Value, Inputs, Level 3 [Member] | Other Long-term Debt [Member]
Senior Unsecured debt	$ 7.5	9.2
Fair Value, Inputs, Level 3 [Member] | Plumstriker Loan Agreement [Member]
Loans		$ 0.0