Note 8 - Business Segments - Summarized Financial Information Concerning Reportable Segments (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2023		Mar. 31, 2022		Dec. 31, 2022
Revenue		$ 185,232		$ 183,710
Operating income (loss)		53,166		45,078
Segment assets at period end		5,015,270	[1],[2]	4,414,189	[1],[2]	$ 4,611,579
Segment Reconciling Items [Member]
Revenue	[3]	0		0
Segment assets at period end		119,185		112,522
Electricity Segment [Member]
Revenue		170,310		162,525
Operating income (loss)		57,008		47,575
Segment assets at period end	[1],[2]	4,648,303		4,093,759
Electricity Segment [Member] | Segment Reconciling Items [Member]
Revenue	[3]	0		0
Segment assets at period end		119,185		112,522
Product Segment [Member]
Revenue		10,042		14,628
Operating income (loss)		(1,505)		(1,575)
Segment assets at period end	[1],[2]	161,428		140,957
Product Segment [Member] | Segment Reconciling Items [Member]
Revenue	[3]	7,772		20,903
Segment assets at period end		0		0
Other Segments [Member]
Revenue		4,880		6,557
Operating income (loss)		(2,337)		(922)
Segment assets at period end	[1],[2]	205,539		179,473
Other Segments [Member] | Segment Reconciling Items [Member]
Revenue	[3]	0		0
Segment assets at period end		0		0
UNITED STATES
Revenue	[4]	128,732		123,201
UNITED STATES | Electricity Segment [Member]
Revenue	[4]	122,411		116,109
UNITED STATES | Product Segment [Member]
Revenue	[4]	1,441		535
UNITED STATES | Other Segments [Member]
Revenue	[4]	4,880		6,557
Non-US [Member]
Revenue	[5]	56,500		60,509
Non-US [Member] | Electricity Segment [Member]
Revenue	[5]	47,899		46,416
Non-US [Member] | Product Segment [Member]
Revenue	[5]	8,601		14,093
Non-US [Member] | Other Segments [Member]
Revenue	[5]	$ 0		$ 0

[1] Electricity segment assets include goodwill in the amount of $85.8 million and $86.0 million as of March 31, 2023 and 2022, respectively. Energy Storage segment assets include goodwill in the amount of $4.6 million and $4.6 as of March 31, 2023 and 2022, respectively. No goodwill is included in the Product segment assets as of March 31, 2023 and 2022.

[2] Including unconsolidated investments

[3] Intersegment revenues are fully eliminated in consolidation.

[4] Electricity segment revenues in the United States are all accounted under lease accounting except for $32.7 million for the three months ended March 31, 2023, and $22.8 million for the three months ended March 31, 2022, respectively, that are accounted under ASC 606. Product and Energy Storage segment revenues in the United States are accounted under ASC 606.

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