Note 9 - Business Segments - Summarized Financial Information Concerning Reportable Segments (Details) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2022		Mar. 31, 2021		Dec. 31, 2021
Revenue		$ 183,710		$ 166,352
Operating income (loss)		45,078		49,889
Segment assets at period end		4,414,189	[1],[2]	3,859,213	[1],[2]	$ 4,425,678
Segment Reconciling Items [Member]
Revenue	[3]	0		0
Segment assets at period end		112,522		104,519
Electricity Segment [Member]
Revenue		162,525		144,988
Operating income (loss)		47,575		47,749
Segment assets at period end	[1],[2]	4,093,759		3,577,745
Electricity Segment [Member] | Segment Reconciling Items [Member]
Revenue	[3]	0		0
Segment assets at period end		112,522		104,519
Product Segment [Member]
Revenue		14,628		8,643
Operating income (loss)		(1,575)		(1,211)
Segment assets at period end	[1],[2]	140,957		140,039
Product Segment [Member] | Segment Reconciling Items [Member]
Revenue	[3]	20,903		25,334
Segment assets at period end		0		0
Other Segments [Member]
Revenue		6,557		12,721
Operating income (loss)		(922)		3,351
Segment assets at period end	[1],[2]	179,473		141,429
Other Segments [Member] | Segment Reconciling Items [Member]
Revenue	[3]	0		0
Segment assets at period end		0		0
UNITED STATES
Revenue	[4]	123,201		113,550
UNITED STATES | Electricity Segment [Member]
Revenue	[4]	116,109		98,976
UNITED STATES | Product Segment [Member]
Revenue	[4]	535		1,853
UNITED STATES | Other Segments [Member]
Revenue	[4]	6,557		12,721
Non-US [Member]
Revenue	[5]	60,509		52,802
Non-US [Member] | Electricity Segment [Member]
Revenue	[5]	46,416		46,012
Non-US [Member] | Product Segment [Member]
Revenue	[5]	14,093		6,790
Non-US [Member] | Other Segments [Member]
Revenue	[5]	$ 0		$ 0

[1] Electricity segment assets include goodwill in the amount of $86.0 million and $20.1 million as of March 31, 2022 and 2021, respectively. Energy Storage segment assets include goodwill in the amount of $4.6 million and $4.1 as of March 31, 2022 and 2021, respectively. No goodwill is included in the Product segment assets as of March 31, 2022 and 2021.

[2] Including unconsolidated investments

[3] Intersegment revenue are fully eliminated in consolidation.

[4] Electricity segment revenues in the United States are all accounted under lease accounting except for $22.8 million and $19.2 million for the three months ended March 31, 2022 and 2021, 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.