Note 5 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Finance liability - Dixie Valley	$ 230.4	$ 248.4
Deposits	15.0	17.1
Mizrahi Loan Agreement [Member]
Loans	78.1
HSBC Loan Agreement [Member]
Loans	44.5	50.4
Convertible Senior Notes [Member]
Notes	431.3
Hapoalim Loan Agreement [Member]
Loans	101.5	117.8
Discount Loan Agreement [Member]
Loans	88.6	100.2
Olkaria III Loan DFC [Member]
Loans	146.0	166.5
Olkaria IV Loan - DEG 2 [Member]
Loans		34.1
Olkaria IV Loan - DEG 3 [Member]
Loans		30.1
Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	29.5
Platanares Loan - OPIC [Member]
Loans	86.2	98.2
Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	26.0
Amatitlan Loan [Member]
Loans	17.1	19.8
OFC Senior Secured Notes [Member]
Notes	159.7	183.3
Don A. Campbell 1 ("DAC1") [Member]
Notes	60.7	69.8
USG Prudential - NV [Member]
Notes	25.3	28.9
USG Prudential - ID [Member]
Notes	16.3	17.3
USG DOE [Member]
Notes	34.9	39.9
Senior Unsecured Bonds [Member]
Senior Unsecured debt	273.7	578.9
Senior Unsecured Loan [Member]
Senior Unsecured debt	179.5	204.3
Plumstriker Loan Agreement [Member]
Loans	13.2	14.8
Other Long-term Debt [Member]
Senior Unsecured debt	10.6	13.3
Fair Value, Inputs, Level 1 [Member]
Finance liability - Dixie Valley	0.0	0.0
Deposits	15.0	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 IV Loan - DEG 2 [Member]
Loans		0.0
Fair Value, Inputs, Level 1 [Member] | Olkaria IV Loan - DEG 3 [Member]
Loans		0.0
Fair Value, Inputs, Level 1 [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	0.0
Fair Value, Inputs, Level 1 [Member] | Platanares Loan - OPIC [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 1 [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	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]
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
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	431.3
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 IV Loan - DEG 2 [Member]
Loans		0.0
Fair Value, Inputs, Level 2 [Member] | Olkaria IV Loan - DEG 3 [Member]
Loans		0.0
Fair Value, Inputs, Level 2 [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	0.0
Fair Value, Inputs, Level 2 [Member] | Platanares Loan - OPIC [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	0.0
Fair Value, Inputs, Level 2 [Member] | Amatitlan Loan [Member]
Loans	17.1	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	13.2	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]
Finance liability - Dixie Valley	230.4	248.4
Deposits	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Mizrahi Loan Agreement [Member]
Loans	78.1
Fair Value, Inputs, Level 3 [Member] | HSBC Loan Agreement [Member]
Loans	44.5	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	101.5	117.8
Fair Value, Inputs, Level 3 [Member] | Discount Loan Agreement [Member]
Loans	88.6	100.2
Fair Value, Inputs, Level 3 [Member] | Olkaria III Loan DFC [Member]
Loans	146.0	166.5
Fair Value, Inputs, Level 3 [Member] | Olkaria IV Loan - DEG 2 [Member]
Loans		34.1
Fair Value, Inputs, Level 3 [Member] | Olkaria IV Loan - DEG 3 [Member]
Loans		30.1
Fair Value, Inputs, Level 3 [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	29.5
Fair Value, Inputs, Level 3 [Member] | Platanares Loan - OPIC [Member]
Loans	86.2	98.2
Fair Value, Inputs, Level 3 [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	26.0
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	159.7	183.3
Fair Value, Inputs, Level 3 [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	60.7	69.8
Fair Value, Inputs, Level 3 [Member] | USG Prudential - NV [Member]
Notes	25.3	28.9
Fair Value, Inputs, Level 3 [Member] | USG Prudential - ID [Member]
Notes	16.3	17.3
Fair Value, Inputs, Level 3 [Member] | USG DOE [Member]
Notes	34.9	39.9
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt	273.7	578.9
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	179.5	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	$ 10.6	$ 13.3