Note 9 - Business Segments - Summarized Financial Information Concerning Reportable Segments (Details) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2021		Sep. 30, 2020		Sep. 30, 2021		Sep. 30, 2020		Dec. 31, 2020
Revenues		$ 158,842		$ 158,947		$ 472,095		$ 525,960
Operating income (loss)		35,988		51,686		114,496		160,818
Segment assets at period end		4,359,366	[1],[2]	3,520,947	[1],[2]	4,359,366	[1],[2]	3,520,947	[1],[2]	$ 3,888,987
Segment Reconciling Items [Member]
Revenues	[3]	0		0		0		0
Segment assets at period end		109,725		91,277		109,725		91,277
Electricity Segment [Member]
Revenues		142,651		123,660		421,503		395,201
Operating income (loss)		38,409		50,847		116,176		155,352
Segment assets at period end	[1],[2]	4,064,679		3,236,631		4,064,679		3,236,631
Electricity Segment [Member] | Segment Reconciling Items [Member]
Revenues	[3]	0		0		0		0
Segment assets at period end		109,725		91,277		109,725		91,277
Product Segment [Member]
Revenues		10,527		29,625		26,580		120,737
Operating income (loss)		(1,115)		1,285		(2,753)		8,960
Segment assets at period end	[1],[2]	125,167		148,106		125,167		148,106
Product Segment [Member] | Segment Reconciling Items [Member]
Revenues	[3]	14,147		36,839		90,519		95,948
Segment assets at period end		0		0		0		0
Other Segments [Member]
Revenues		5,664		5,662		24,012		10,022
Operating income (loss)		(1,306)		(446)		1,073		(3,494)
Segment assets at period end	[1],[2]	169,520		136,210		169,520		136,210
Other Segments [Member] | Segment Reconciling Items [Member]
Revenues	[3]	0		0		0		0
Segment assets at period end		0		0		0		0
UNITED STATES
Revenues	[4]	105,755		79,277		313,143		256,733
UNITED STATES | Electricity Segment [Member]
Revenues	[4]	98,550		73,180		285,090		245,299
UNITED STATES | Product Segment [Member]
Revenues	[4]	1,541		435		4,041		1,412
UNITED STATES | Other Segments [Member]
Revenues	[4]	5,664		5,662		24,012		10,022
Non-US [Member]
Revenues	[5]	53,087		79,670		158,952		269,227
Non-US [Member] | Electricity Segment [Member]
Revenues	[5]	44,101		50,480		136,413		149,902
Non-US [Member] | Product Segment [Member]
Revenues	[5]	8,986		29,190		22,539		119,325
Non-US [Member] | Other Segments [Member]
Revenues	[5]	$ 0		$ 0		$ 0		$ 0

[1] Electricity segment assets include goodwill in the amount of $86.7 million and $20.1 million as of September 30, 2021 and 2020, respectively, $66.6 million of which were added in the third quarter of 2021 as a result of the geothermal asset purchase transaction as further detailed under Note 1 to the condensed consolidated financial statements. Energy Storage segment assets include goodwill in the amount of $4.6 million and $3.5 as of September 30, 2021 and 2020, respectively. No goodwill is included in the Product segment assets as of September 30, 2021 and 2020.??

[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 $19.0 million and $59.0 million for the three and nine months ended September 30, 2021, respectively, and $15.0 and $47.4 million for the three and nine months ended September 30, 2020 , 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.