Note 1 - General and Basis of Presentation (Tables)

6 Months Ended

Jun. 30, 2023

Notes Tables

Schedule of Cash and Cash Equivalents [Table Text Block]

	June 30,		December 31,
	2023		2022
	(Dollars in thousands)
Cash and cash equivalents	$	275,066	$	95,872
Restricted cash and cash equivalents		120,316		130,804
Total Cash and cash equivalents and restricted cash and cash equivalents	$	395,382	$	226,676

Schedules of Concentration of Risk, by Risk Factor [Table Text Block]

	Three Months Ended June 30,						Six Months Ended June 30,
	2023			2022			2023			2022
Southern California Public Power Authority (“SCPPA”)		21.0	%		21.3	%		23.8	%		21.6	%
Sierra Pacific Power Company and Nevada Power Company		15.9			18.1			17.9			18.6
Kenya Power and Lighting Co. Ltd. ("KPLC")		14.4			15.5			14.4			14.8

Accounts Receivable, Allowance for Credit Loss [Table Text Block]

	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
	(Dollars in thousands)				(Dollars in thousands)
Beginning balance of the allowance for expected credit losses	$	90	$	90	$	90	$	90
Change in the provision for expected credit losses for the period		—		—		—		—
Ending balance of the allowance for expected credit losses	$	90	$	90	$	90	$	90

Contract with Customer, Contract Asset, Contract Liability, and Receivable [Table Text Block]

	June 30,			December 31,
	2023			2022
	(Dollars in thousands)
Contract assets (*)	$	21,786		$	16,405
Contract liabilities (*)	$	(18,651	)	$	(8,785	)

Operating Lease, Lease Income [Table Text Block]

	Three Months Ended June 30,				Six Months Ended June 30,
	2023		2022		2023		2022
	(Dollars in thousands)				(Dollars in thousands)
Lease income relating to lease payments from operating leases	$	125,140	$	127,472	$	262,761	$	267,153