Note 5 - Fair Value of Financial Instruments - Fair Value of Long-term Debt Approximates Its Carrying Amount, Exceptions (Details) - USD ($) $ in Millions	Jun. 30, 2022	Dec. 31, 2021
Finance liability - Dixie Valley	$ 230.4	$ 248.4
Mizrahi Loan Agreement [Member]
Loans	78.1
Convertible Senior Notes [Member]
Notes	431.3
HSBC Loan Agreement [Member]
Loans	44.5	50.4
Hapoalim Loan Agreement [Member]
Loans	101.5	117.8
Discount Loan Agreement [Member]
Loans	88.6	100.2
Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	29.5
Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	26.0
Platanares Loan - OPIC [Member]
Loans	86.2	98.2
Amatitlan Loan [Member]
Loans	17.1	19.8
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
Estimate of Fair Value Measurement [Member]
Finance liability - Dixie Valley	230.4	248.4
Other long-term debt	10.6	13.3
Estimate of Fair Value Measurement [Member] | Mizrahi Loan Agreement [Member]
Loans	78.1	0.0
Estimate of Fair Value Measurement [Member] | Convertible Senior Notes [Member]
Notes	431.3	0.0
Estimate of Fair Value Measurement [Member] | HSBC Loan Agreement [Member]
Loans	44.5	50.4
Estimate of Fair Value Measurement [Member] | Hapoalim Loan Agreement [Member]
Loans	101.5	117.8
Estimate of Fair Value Measurement [Member] | Discount Loan Agreement [Member]
Loans	88.6	100.2
Estimate of Fair Value Measurement [Member] | Olkaria III OPIC [Member]
Loans	146.0	166.5
Estimate of Fair Value Measurement [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	29.5	34.1
Estimate of Fair Value Measurement [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	26.0	30.1
Estimate of Fair Value Measurement [Member] | Platanares Loan - OPIC [Member]
Loans	86.2	98.2
Estimate of Fair Value Measurement [Member] | Amatitlan Loan [Member]
Loans	17.1	19.8
Estimate of Fair Value Measurement [Member] | OFC Two Senior Secured Notes [Member]
Notes	159.7	183.3
Estimate of Fair Value Measurement [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	60.7	69.8
Estimate of Fair Value Measurement [Member] | USG Prudential - NV [Member]
Notes	25.3	28.9
Estimate of Fair Value Measurement [Member] | USG Prudential - ID [Member]
Notes	16.3	17.3
Estimate of Fair Value Measurement [Member] | USG DOE [Member]
Notes	34.9	39.9
Estimate of Fair Value Measurement [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt	273.7	578.9
Estimate of Fair Value Measurement [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	179.5	204.3
Estimate of Fair Value Measurement [Member] | Plumstriker Loan Agreement [Member]
Loans	13.2	14.8
Reported Value Measurement [Member]
Finance liability - Dixie Valley	249.1	252.9
Other long-term debt	11.2	13.6
Reported Value Measurement [Member] | Mizrahi Loan Agreement [Member]
Loans	75.0	0.0
Reported Value Measurement [Member] | Convertible Senior Notes [Member]
Notes	431.3	0.0
Reported Value Measurement [Member] | HSBC Loan Agreement [Member]
Loans	46.4	50.0
Reported Value Measurement [Member] | Hapoalim Loan Agreement [Member]
Loans	107.1	116.1
Reported Value Measurement [Member] | Discount Loan Agreement [Member]
Loans	93.8	100.0
Reported Value Measurement [Member] | Olkaria III OPIC [Member]
Loans	147.7	156.7
Reported Value Measurement [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	30.0	32.5
Reported Value Measurement [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	26.2	28.4
Reported Value Measurement [Member] | Platanares Loan - OPIC [Member]
Loans	84.0	88.1
Reported Value Measurement [Member] | Amatitlan Loan [Member]
Loans	17.5	19.3
Reported Value Measurement [Member] | OFC Two Senior Secured Notes [Member]
Notes	164.9	173.3
Reported Value Measurement [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	64.8	67.9
Reported Value Measurement [Member] | USG Prudential - NV [Member]
Notes	25.8	26.3
Reported Value Measurement [Member] | USG Prudential - ID [Member]
Notes	16.4	17.3
Reported Value Measurement [Member] | USG DOE [Member]
Notes	34.2	35.5
Reported Value Measurement [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt	257.1	539.6
Reported Value Measurement [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	183.2	191.6
Reported Value Measurement [Member] | Plumstriker Loan Agreement [Member]
Loans	$ 13.2	$ 14.7