Note 8 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Financing Liability - Dixie Valley	$ 219.8	$ 248.4
Deposits	13.9	17.1
Mizrahi Loan Agreement [Member]
Loans	71.4
HSBC Loan Agreement [Member]
Loans	40.3	50.4
Convertible Senior Notes [Member]
Notes	505.3
Hapoalim Loan Agreement [Member]
Loans	91.1	117.8
Discount Loan Agreement [Member]
Loans	81.1	100.2
Olkaria III Loan DFC [Member]
Loans	134.2	166.5
Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	26.5	34.1
Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	23.3	30.1
Platanares Loan - OPIC [Member]
Loans	80.2	98.2
Amatitlan Loan [Member]
Loans	14.7	19.8
OFC Senior Secured Notes [Member]
Notes	149.8	183.3
Don A. Campbell 1 ("DAC1") [Member]
Notes	57.4	69.8
USG Prudential - NV [Member]
Notes	23.7	28.9
USG Prudential - ID [Member]
Notes	56.8	17.3
USG DOE [Member]
Notes	32.8	39.9
Senior Unsecured Bonds [Member]
Senior Unsecured debt	235.1	578.9
Senior Unsecured Loan [Member]
Senior Unsecured debt	166.4	204.3
Plumstriker Loan Agreement [Member]
Loans	11.2	14.8
Other Long-term Debt [Member]
Senior Unsecured debt	9.2	13.3
Fair Value, Inputs, Level 1 [Member]
Financing Liability - Dixie Valley	0.0	0.0
Deposits	13.9	17.1
Fair Value, Inputs, Level 1 [Member] | Mizrahi Loan Agreement [Member]
Loans	0.0
Fair Value, Inputs, Level 1 [Member] | HSBC Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Convertible Senior Notes [Member]
Notes	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] | 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	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	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
Fair Value, Inputs, Level 2 [Member] | HSBC Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Convertible Senior Notes [Member]
Notes	505.3
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] | 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	19.8
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	14.8
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	219.8	248.4
Deposits	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Mizrahi Loan Agreement [Member]
Loans	71.4
Fair Value, Inputs, Level 3 [Member] | HSBC Loan Agreement [Member]
Loans	40.3	50.4
Fair Value, Inputs, Level 3 [Member] | Convertible Senior Notes [Member]
Notes	0.0
Fair Value, Inputs, Level 3 [Member] | Hapoalim Loan Agreement [Member]
Loans	91.1	117.8
Fair Value, Inputs, Level 3 [Member] | Discount Loan Agreement [Member]
Loans	81.1	100.2
Fair Value, Inputs, Level 3 [Member] | Olkaria III Loan DFC [Member]
Loans	134.2	166.5
Fair Value, Inputs, Level 3 [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	26.5	34.1
Fair Value, Inputs, Level 3 [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	23.3	30.1
Fair Value, Inputs, Level 3 [Member] | Platanares Loan - OPIC [Member]
Loans	80.2	98.2
Fair Value, Inputs, Level 3 [Member] | Amatitlan Loan [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | OFC Senior Secured Notes [Member]
Notes	149.8	183.3
Fair Value, Inputs, Level 3 [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	57.4	69.8
Fair Value, Inputs, Level 3 [Member] | USG Prudential - NV [Member]
Notes	23.7	28.9
Fair Value, Inputs, Level 3 [Member] | USG Prudential - ID [Member]
Notes	56.8	17.3
Fair Value, Inputs, Level 3 [Member] | USG DOE [Member]
Notes	32.8	39.9
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt	235.1	578.9
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	166.4	204.3
Fair Value, Inputs, Level 3 [Member] | Plumstriker Loan Agreement [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Other Long-term Debt [Member]
Senior Unsecured debt	$ 9.2	$ 13.3