Note 8 - Business Segments - Summarized Financial Information Concerning Reportable Segments (Details) - USD ($) $ in Thousands		3 Months Ended				6 Months Ended
		Jun. 30, 2023		Jun. 30, 2022		Jun. 30, 2023		Jun. 30, 2022		Dec. 31, 2022
Revenue		$ 194,796		$ 169,078		$ 380,028		$ 352,788
Operating income (loss)		24,224		38,607		77,390		83,685
Segment assets at period end		5,010,644	[1],[2]	4,541,976	[1],[2]	5,010,644	[1],[2]	4,541,976	[1],[2]	$ 4,611,579
UNITED STATES
Revenue		114,476	[3]	113,818	[3]	243,208		237,019
Non-US [Member]
Revenue		80,320	[4]	55,260	[4]	136,820		115,769
Segment Reconciling Items [Member]
Revenue		0	[5]	0	[5]	0		0
Segment assets at period end		126,451		114,699		126,451		114,699
Electricity Segment [Member] | Operating Segments [Member]
Revenue		155,324		151,195		325,634		313,720
Operating income (loss)		28,661		40,466		85,669		88,041
Segment assets at period end	[1],[2]	4,576,437		4,222,340		4,576,437		4,222,340
Electricity Segment [Member] | Operating Segments [Member] | UNITED STATES
Revenue		106,209	[3]	105,193	[3]	228,620		221,302
Electricity Segment [Member] | Operating Segments [Member] | Non-US [Member]
Revenue		49,115	[4]	46,002	[4]	97,014		92,418
Electricity Segment [Member] | Segment Reconciling Items [Member]
Revenue		0	[5]	0	[5]	0		0
Segment assets at period end		126,451		114,699		126,451		114,699
Product Segment [Member] | Operating Segments [Member]
Revenue		33,458		10,392		43,500		25,020
Operating income (loss)				(2,276)		(3,802)		(3,851)
Segment assets at period end	[1],[2]	182,437		122,221		182,437		122,221
Product Segment [Member] | Operating Segments [Member] | UNITED STATES
Revenue		2,253	[3]	1,134	[3]	3,694		1,669
Operating income (loss)		(2,297)
Product Segment [Member] | Operating Segments [Member] | Non-US [Member]
Revenue		31,205	[4]	9,258	[4]	39,806		23,351
Product Segment [Member] | Segment Reconciling Items [Member]
Revenue		12,918	[5]	22,097	[5]	20,690		43,000
Segment assets at period end		0		0		0		0
Other Segments [Member] | Operating Segments [Member]
Revenue		6,014		7,491		10,894		14,048
Operating income (loss)		(2,140)		417		(4,477)		(505)
Segment assets at period end	[1],[2]	251,770		197,415		251,770		197,415
Other Segments [Member] | Operating Segments [Member] | UNITED STATES
Revenue		6,014	[3]	7,491	[3]	10,894		14,048
Other Segments [Member] | Operating Segments [Member] | Non-US [Member]
Revenue		0	[4]	0	[4]	0		0
Other Segments [Member] | Segment Reconciling Items [Member]
Revenue		0	[5]	0	[5]	0		0
Segment assets at period end		$ 0		$ 0		$ 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] 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.

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

[5] Intersegment revenues are fully eliminated in consolidation.