Note 7 - Fair Value of Financial Instruments - Fair Value of Long-term Debt Approximates Its Carrying Amount, Exceptions (Details) - USD ($) $ in Millions		Dec. 31, 2023	Dec. 31, 2022
Financing Liability - Dixie Valley		$ 207.2	$ 219.8
Mizrahi Loan Agreement [Member]
Loans		61.4	71.4
Mizrahi Loan Agreement 2023 [Member]
Loans		52.0
Convertible Senior Notes [Member]
Notes		444.6	505.3
HSBC Loan Agreement [Member]
Loans		33.8	40.3
Hapoalim Loan Agreement [Member]
Loans		75.0	91.1
Hapoalim Loan Agreement 2023 [Member]
Loans		99.7
Discount Loan Agreement [Member]
Loans		69.9	81.1
Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans		21.6	26.5
Olkaria III plant 1 Loan - DEG 3 [Member]
Loans		19.0	23.3
Platanares Loan - OPIC [Member]
Loans		71.3	80.2
Amatitlan Loan [Member]
Loans			14.7
OFC Senior Secured Notes [Member]
Notes		134.2	149.8
Don A. Campbell 1 ("DAC1") [Member]
Notes		52.3	57.4
USG Prudential - NV [Member]
Notes		22.3	23.7
USG Prudential - ID [Member]
Notes		54.1	56.8
USG DOE [Member]
Notes		30.0	32.8
Senior Unsecured Bonds [Member]
Senior Unsecured debt		202.8	235.1
Senior Unsecured Loan [Member]
Senior Unsecured debt		150.4	166.4
Plumstriker Loan Agreement [Member]
Loans			11.2
Estimate of Fair Value Measurement [Member]
Financing Liability - Dixie Valley		207.2	219.8
Other long-term debt		6.8	9.2
Estimate of Fair Value Measurement [Member] | Mizrahi Loan Agreement [Member]
Loans		61.4	71.4
Estimate of Fair Value Measurement [Member] | Mizrahi Loan Agreement 2023 [Member]
Loans		52.0	0.0
Estimate of Fair Value Measurement [Member] | Convertible Senior Notes [Member]
Notes		444.6	505.3
Estimate of Fair Value Measurement [Member] | HSBC Loan Agreement [Member]
Loans		33.8	40.3
Estimate of Fair Value Measurement [Member] | Hapoalim Loan Agreement [Member]
Loans		75.0	91.1
Estimate of Fair Value Measurement [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans		99.7	0.0
Estimate of Fair Value Measurement [Member] | Discount Loan Agreement [Member]
Loans		69.9	81.1
Estimate of Fair Value Measurement [Member] | Olkaria III OPIC [Member]
Loans		116.4	134.2
Estimate of Fair Value Measurement [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans		21.6	26.5
Estimate of Fair Value Measurement [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans		19.0	23.3
Estimate of Fair Value Measurement [Member] | Platanares Loan - OPIC [Member]
Loans		71.3	80.2
Estimate of Fair Value Measurement [Member] | Amatitlan Loan [Member]
Loans		0.0	14.7
Estimate of Fair Value Measurement [Member] | OFC Senior Secured Notes [Member]
Loans		134.2	149.8
Estimate of Fair Value Measurement [Member] | Don A. Campbell 1 ("DAC1") [Member]
Loans		52.3	57.4
Estimate of Fair Value Measurement [Member] | USG Prudential - NV [Member]
Notes		22.3	23.7
Estimate of Fair Value Measurement [Member] | USG Prudential - ID [Member]
Notes		54.1	56.8
Estimate of Fair Value Measurement [Member] | USG DOE [Member]
Notes		30.0	32.8
Estimate of Fair Value Measurement [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt		202.8	235.1
Estimate of Fair Value Measurement [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt		150.4	166.4
Estimate of Fair Value Measurement [Member] | Plumstriker Loan Agreement [Member]
Loans		0.0	11.2
Reported Value Measurement [Member]
Financing Liability - Dixie Valley		225.8	242.0
Other long-term debt	[1]	7.7	10.4
Reported Value Measurement [Member] | Mizrahi Loan Agreement [Member]
Loans	[1]	60.9	70.3
Reported Value Measurement [Member] | Mizrahi Loan Agreement 2023 [Member]
Loans		50.0	0.0
Reported Value Measurement [Member] | Convertible Senior Notes [Member]
Notes	[1]	431.3	431.3
Reported Value Measurement [Member] | HSBC Loan Agreement [Member]
Loans	[1]	35.7	42.9
Reported Value Measurement [Member] | Hapoalim Loan Agreement [Member]
Loans	[1]	80.4	98.2
Reported Value Measurement [Member] | Hapoalim Loan Agreement 2023 [Member]
Loans		95.0	0.0
Reported Value Measurement [Member] | Discount Loan Agreement [Member]
Loans	[1]	75.0	87.5
Reported Value Measurement [Member] | Olkaria III OPIC [Member]
Loans	[1]	120.7	138.7
Reported Value Measurement [Member] | Olkaria III Plant 4 Loan - DEG 2 [Member]
Loans	[1]	22.5	27.5
Reported Value Measurement [Member] | Olkaria III plant 1 Loan - DEG 3 [Member]
Loans	[1]	19.7	24.0
Reported Value Measurement [Member] | Platanares Loan - OPIC [Member]
Loans	[1]	71.7	79.9
Reported Value Measurement [Member] | Amatitlan Loan [Member]
Loans	[1]	0.0	15.8
Reported Value Measurement [Member] | OFC Senior Secured Notes [Member]
Loans		142.5	158.0
Reported Value Measurement [Member] | Don A. Campbell 1 ("DAC1") [Member]
Loans		57.4	62.7
Reported Value Measurement [Member] | USG Prudential - NV [Member]
Notes	[1]	23.9	25.0
Reported Value Measurement [Member] | USG Prudential - ID [Member]
Notes		58.9	61.6
Reported Value Measurement [Member] | USG DOE [Member]
Notes	[1]	30.2	32.8
Reported Value Measurement [Member] | Senior Unsecured Bonds [Member]
Senior Unsecured debt	[1]	220.6	255.8
Reported Value Measurement [Member] | Senior Unsecured Loan [Member]
Senior Unsecured debt	[1]	158.0	174.8
Reported Value Measurement [Member] | Plumstriker Loan Agreement [Member]
Loans	[1]	$ 0.0	$ 11.4

[1] Carrying amount value excludes the related deferred financing costs.