Note 1 - Business and Significant Accounting Policies 1 (Details Textual) - USD ($) $ / shares in Units, $ in Thousands					1 Months Ended	2 Months Ended	12 Months Ended
	Feb. 19, 2021	Nov. 30, 2020	Nov. 30, 2020	Nov. 18, 2020	Feb. 28, 2022	Feb. 28, 2022	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Debt Securities, Available-for-sale, Total							$ 43,343	$ 0
Cash, FDIC Insured Amount							31,000	18,900
Cash, Uninsured Amount							64,300	72,400
Accounts Receivable, after Allowance for Credit Loss, Current, Total							122,944	149,170
Interest Costs Capitalized							14,582	10,409	$ 3,285
Amortization of Debt Issuance Costs							3,200	3,500	5,400
Write off of Deferred Debt Issuance Cost							0	0	$ 0
Impairment of Long-Lived Assets to be Disposed of							0
Accumulated Other Comprehensive Income (Loss), Foreign Currency Translation Adjustment, Net of Tax, Ending Balance							1,200	$ (900)
Revenue, Remaining Performance Obligation, Amount							$ 53,000
Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount (in shares)							142,400	369,700	360,500
Payments of Dividends, Total							$ 27,000	$ 22,500	$ 22,400
Common Stock, Dividends, Per Share, Cash Paid (in dollars per share)							$ 0.48	$ 0.44	$ 0.44
Common Stock, Par or Stated Value Per Share (in dollars per share)				$ 0.001			$ 0.001	$ 0.001
Proceeds from Issuance of Common Stock							$ 311	$ 339,471	$ 0
Loss from Catastrophes	$ 9,100
General and Administrative Expense [Member]
Accounts Receivable, Credit Loss Expense (Reversal)							3,000
Electricity Segment [Member] | Puna Geothermal Power Plant [Member]
Business Interruption Insurance Recovery, Gross							15,800	28,600
Underwriting Agreement [Member]
Stock Issued During Period, Shares, New Issues (in shares)				4,150,000
Shares Issued, Price Per Share (in dollars per share)				$ 74.00
Proceeds from Issuance of Common Stock		$ 339,500
Underwriting Agreement [Member] | Underwriters [Member]
Stock Issued During Period, Shares, New Issues (in shares)			622,500
Shares Issued, Price Per Share (in dollars per share)		$ 74.00	$ 74.00
Galena 2 Power Purchase Agreement [Member]
Termination Fees							$ 0	$ 0	$ 0
Minimum [Member]
Finite-Lived Intangible Asset, Useful Life (Year)							6 years
Standard Product Warranty, Term (Year)							1 year
Minimum [Member] | Viridity Energy, Inc. [Member]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life (Year)							6 years
Maximum [Member]
Finite-Lived Intangible Asset, Useful Life (Year)							19 years
Standard Product Warranty, Term (Year)							2 years
Maximum [Member] | Viridity Energy, Inc. [Member]
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life (Year)							19 years
Power Plants [Member] | Minimum [Member]
Property, Plant and Equipment, Useful Life (Year)							15 years
Power Plants [Member] | Maximum [Member]
Property, Plant and Equipment, Useful Life (Year)							30 years
Kenya Power and Lighting Co LTD [Member]
Accounts Receivable, Past Due							$ 25,500
Accounts Receivable, Past Due, Average Number of Days Overdue (Day)							63 days
Kenya Power and Lighting Co LTD [Member] | Subsequent Event [Member]
Proceeds, Overdue Accounts Receivable						$ 22,900
ENNE [Member]
Accounts Receivable, Past Due							$ 20,700
ENNE [Member] | Subsequent Event [Member]
Proceeds, Overdue Accounts Receivable					$ 2,900
Accounts Receivable [Member] | Customer Concentration Risk [Member] | Primary Customers [Member]
Concentration Risk, Percentage							58.00%	65.00%
Non-US [Member]
Accounts Receivable, after Allowance for Credit Loss, Current, Total							$ 77,500	$ 111,300
Cash and Cash Equivalents [Member]
Debt Securities, Available-for-sale, Total							$ 3,700