Note 5 - Fair Value of Financial Instruments - Fair Value of Financial Instruments (Details) - USD ($) $ in Millions	Mar. 31, 2022	Dec. 31, 2021
Finance liability - Dixie Valley	$ 245.2
Deposits	16.2	$ 17.1
HSBC Loan Agreement [Member]
Loans	46.8
Olkaria III Loan DFC [Member]
Loans	161.2	166.5
Hapoalim Loan Agreement [Member]
Loans	117.8
Olkaria IV Loan - DEG 2 [Member]
Loans		34.1
Discount Loan Agreement [Member]
Loans	94.0
Olkaria IV Loan - DEG 3 [Member]
Loans		30.1
Platanares Loan - OPIC [Member]
Loans	95.6	98.2
Amatitlan Loan [Member]
Loans	18.6	19.8
Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	34.4
OFC Senior Secured Notes [Member]
Notes	178.1	183.3
Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	30.3
Don A. Campbell 1 ("DAC1") [Member]
Notes	68.0	69.8
USG Prudential - NV [Member]
Notes	28.6	28.9
USG Prudential - ID [Member]
Notes	16.2	17.3
USG DOE [Member]
Notes	38.3	39.9
Senior Unsecured Bonds [Member]
Senior Unsecured debt	569.5	578.9
Senior Unsecured Loan [Member]
Senior Unsecured debt	193.5	204.3
Plumstriker Loan Agreement [Member]
Loans	14.5	14.8
Other Long-term Debt [Member]
Senior Unsecured debt	12.1	13.3
Fair Value, Inputs, Level 1 [Member]
Finance liability - Dixie Valley	0.0
Deposits	16.2	17.1
Fair Value, Inputs, Level 1 [Member] | HSBC Loan Agreement [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] | Hapoalim Loan Agreement [Member]
Loans	0.0
Fair Value, Inputs, Level 1 [Member] | Olkaria IV Loan - DEG 2 [Member]
Loans		0.0
Fair Value, Inputs, Level 1 [Member] | Discount Loan Agreement [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] | 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] | Olkaria III Plant 4 Loan - DEG 2 [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] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	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
Deposits	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | HSBC Loan Agreement [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] | Hapoalim Loan Agreement [Member]
Loans	0.0
Fair Value, Inputs, Level 2 [Member] | Olkaria IV Loan - DEG 2 [Member]
Loans		0.0
Fair Value, Inputs, Level 2 [Member] | Discount Loan Agreement [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] | Platanares Loan - OPIC [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 2 [Member] | Amatitlan Loan [Member]
Loans	18.6	19.8
Fair Value, Inputs, Level 2 [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	0.0
Fair Value, Inputs, Level 2 [Member] | OFC Senior Secured Notes [Member]
Notes	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] | 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	14.5	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	245.2
Deposits	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | HSBC Loan Agreement [Member]
Loans	46.8
Fair Value, Inputs, Level 3 [Member] | Olkaria III Loan DFC [Member]
Loans	161.2	166.5
Fair Value, Inputs, Level 3 [Member] | Hapoalim Loan Agreement [Member]
Loans	117.8
Fair Value, Inputs, Level 3 [Member] | Olkaria IV Loan - DEG 2 [Member]
Loans		34.1
Fair Value, Inputs, Level 3 [Member] | Discount Loan Agreement [Member]
Loans	94.0
Fair Value, Inputs, Level 3 [Member] | Olkaria IV Loan - DEG 3 [Member]
Loans		30.1
Fair Value, Inputs, Level 3 [Member] | Platanares Loan - OPIC [Member]
Loans	95.6	98.2
Fair Value, Inputs, Level 3 [Member] | Amatitlan Loan [Member]
Loans	0.0	0.0
Fair Value, Inputs, Level 3 [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	34.4
Fair Value, Inputs, Level 3 [Member] | OFC Senior Secured Notes [Member]
Notes	178.1	183.3
Fair Value, Inputs, Level 3 [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	30.3
Fair Value, Inputs, Level 3 [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	68.0	69.8
Fair Value, Inputs, Level 3 [Member] | USG Prudential - NV [Member]
Notes	28.6	28.9
Fair Value, Inputs, Level 3 [Member] | USG Prudential - ID [Member]
Notes	16.2	17.3
Fair Value, Inputs, Level 3 [Member] | USG DOE [Member]
Notes	38.3	39.9
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt	569.5	578.9
Fair Value, Inputs, Level 3 [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	193.5	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	$ 12.1	$ 13.3