Note 8 - Fair Value of Financial Instruments - Fair Value of Long-term Debt Approximates Its Carrying Amount, Exceptions (Details) - USD ($) $ in Millions	Dec. 31, 2022	Dec. 31, 2021
Financing Liability - Dixie Valley	$ 219.8	$ 248.4
Mizrahi Loan Agreement [Member]
Loans	71.4
Convertible Senior Notes [Member]
Notes	505.3
HSBC Loan Agreement [Member]
Loans	40.3	50.4
Hapoalim Loan Agreement [Member]
Loans	91.1	117.8
Discount Loan Agreement [Member]
Loans	81.1	100.2
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
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
Estimate of Fair Value Measurement [Member]
Financing Liability - Dixie Valley	219.8	248.4
Other long-term debt	9.2	13.3
Estimate of Fair Value Measurement [Member] | Mizrahi Loan Agreement [Member]
Loans	71.4	0.0
Estimate of Fair Value Measurement [Member] | Convertible Senior Notes [Member]
Notes	505.3	0.0
Estimate of Fair Value Measurement [Member] | HSBC Loan Agreement [Member]
Loans	40.3	50.4
Estimate of Fair Value Measurement [Member] | Hapoalim Loan Agreement [Member]
Loans	91.1	117.8
Estimate of Fair Value Measurement [Member] | Discount Loan Agreement [Member]
Loans	81.1	100.2
Estimate of Fair Value Measurement [Member] | Olkaria III OPIC [Member]
Loans	134.2	166.5
Estimate of Fair Value Measurement [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	26.5	34.1
Estimate of Fair Value Measurement [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	23.3	30.1
Estimate of Fair Value Measurement [Member] | Platanares Loan - OPIC [Member]
Loans	80.2	98.2
Estimate of Fair Value Measurement [Member] | Amatitlan Loan [Member]
Loans	14.7	19.8
Estimate of Fair Value Measurement [Member] | OFC 2 LLC ("OFC 2")[Member]
Notes	149.8	183.3
Estimate of Fair Value Measurement [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	57.4	69.8
Estimate of Fair Value Measurement [Member] | USG Prudential - NV [Member]
Notes	23.7	28.9
Estimate of Fair Value Measurement [Member] | USG Prudential - ID [Member]
Notes	56.8	17.3
Estimate of Fair Value Measurement [Member] | USG DOE [Member]
Notes	32.8	39.9
Estimate of Fair Value Measurement [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt	235.1	578.9
Estimate of Fair Value Measurement [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	166.4	204.3
Estimate of Fair Value Measurement [Member] | Plumstriker Loan Agreement [Member]
Loans	11.2	14.8
Reported Value Measurement [Member]
Financing Liability - Dixie Valley	242.0	252.9
Other long-term debt	10.4	13.6
Reported Value Measurement [Member] | Mizrahi Loan Agreement [Member]
Loans	70.3	0.0
Reported Value Measurement [Member] | Convertible Senior Notes [Member]
Notes	431.3	0.0
Reported Value Measurement [Member] | HSBC Loan Agreement [Member]
Loans	42.9	50.0
Reported Value Measurement [Member] | Hapoalim Loan Agreement [Member]
Loans	98.2	116.1
Reported Value Measurement [Member] | Discount Loan Agreement [Member]
Loans	87.5	100.0
Reported Value Measurement [Member] | Olkaria III OPIC [Member]
Loans	138.7	156.7
Reported Value Measurement [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	27.5	32.5
Reported Value Measurement [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	24.0	28.4
Reported Value Measurement [Member] | Platanares Loan - OPIC [Member]
Loans	79.9	88.1
Reported Value Measurement [Member] | Amatitlan Loan [Member]
Loans	15.8	19.3
Reported Value Measurement [Member] | OFC 2 LLC ("OFC 2")[Member]
Notes	158.0	173.3
Reported Value Measurement [Member] | Don A. Campbell 1 ("DAC1") [Member]
Notes	62.7	67.9
Reported Value Measurement [Member] | USG Prudential - NV [Member]
Notes	25.0	26.3
Reported Value Measurement [Member] | USG Prudential - ID [Member]
Notes	61.6	17.3
Reported Value Measurement [Member] | USG DOE [Member]
Notes	32.8	35.5
Reported Value Measurement [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt	255.8	539.6
Reported Value Measurement [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	174.8	191.6
Reported Value Measurement [Member] | Plumstriker Loan Agreement [Member]
Loans	$ 11.4	$ 14.7