Note 8 - Business Segments - Summarized Financial Information Concerning Reportable Segments (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2024		Mar. 31, 2023		Dec. 31, 2023
Revenue		$ 224,166		$ 185,232
Operating income (loss)		52,583		53,166
Segment assets at period end		5,516,844	[1],[2]	5,015,270	[1],[2]	$ 5,208,279
Investment in unconsolidated companies		127,386		119,185		$ 125,439
Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment [Member]
Revenue	[2]	0		0
Electricity Segment [Member]
Revenue		191,253		170,310
Operating income (loss)		52,681		57,008
Segment assets at period end	[1],[2]	4,961,483		4,648,303
Investment in unconsolidated companies		127,386		119,185
Electricity Segment [Member] | Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment [Member]
Revenue	[2]	0		0
Product Segment [Member]
Revenue		24,832		10,042
Operating income (loss)		842		(1,505)
Segment assets at period end	[1],[2]	190,210		161,428
Investment in unconsolidated companies		0		0
Product Segment [Member] | Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment [Member]
Revenue	[2]	20,597		7,772
Energy Storage Segment [Member]
Revenue		8,081		4,880
Operating income (loss)		(940)		(2,337)
Segment assets at period end	[1],[2]	365,151		205,539
Investment in unconsolidated companies		0		0
Energy Storage Segment [Member] | Segment Reporting, Reconciling Item, Excluding Corporate Nonsegment [Member]
Revenue	[2]	0		0
UNITED STATES
Revenue	[3]	152,773		128,732
UNITED STATES | Electricity Segment [Member]
Revenue	[3]	143,816		122,411
UNITED STATES | Product Segment [Member]
Revenue	[3]	876		1,441
UNITED STATES | Energy Storage Segment [Member]
Revenue	[3]	8,081		4,880
Non-US [Member]
Revenue	[4]	71,393		56,500
Non-US [Member] | Electricity Segment [Member]
Revenue	[4]	47,437		47,899
Non-US [Member] | Product Segment [Member]
Revenue	[4]	23,956		8,601
Non-US [Member] | Energy Storage Segment [Member]
Revenue	[4]	$ 0		$ 0

[1] Electricity segment assets include goodwill in the amount of $146.5 million and $85.8 million as of March 31, 2024 and 2023, respectively. Energy Storage segment assets include goodwill in the amount of $4.6 million and $4.6 million as of March 31, 2024 and 2023, respectively. No goodwill is included in the Product segment assets as of March 31, 2024 and 2023.

[2] Intersegment revenues are fully eliminated in consolidation.

[3] Electricity segment revenues in the United States are all accounted for under lease accounting except for $44.8 million in three months ended March 31, 2024, and $32.7 million for the three months ended March 31, 2023, that are accounted for under ASC 606. Product and Energy Storage segment revenues in the United States are accounted for under ASC 606, Revenue from Contracts with Customers ("ASC 606"), except for Energy Storage revenues of $0.7 million for the three months ended March 31, 2024, and none for the three months ended March 31, 2023, that are accounted for under lease accounting.

[4] Electricity segment revenues in foreign countries are all accounted for under lease accounting. Product segment revenues in foreign countries are all accounted for under ASC 606.