Note 18 - Business Segments (Details Textual) $ in Thousands		3 Months Ended	12 Months Ended
		Sep. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)	Dec. 31, 2020 USD ($)	Dec. 31, 2019 USD ($)	Jul. 13, 2021 USD ($)
Number of Reportable Segments			3
Revenue from Contract with Customer, Including Assessed Tax	[1]		$ 663,084	$ 705,342	$ 746,044
Goodwill, Ending Balance			89,954	24,566	20,140
Goodwill, Acquired During Period	[2]		65,441	4,107
Two Contracted Geothermal Assets in Nevada [Member]
Goodwill, Ending Balance	[3]					$ 65,400
Electricity Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax			585,771	541,393	540,333
Goodwill, Ending Balance			85,300	20,500	20,100
Electricity Segment [Member] | Two Contracted Geothermal Assets in Nevada [Member]
Goodwill, Acquired During Period		$ 65,400
Electricity Segment [Member] | Accounting Standards Update 2014-09 [Member]
Revenue from Contract with Customer, Including Assessed Tax			83,400	68,100	61,300
Energy Storage and Management Services [Member]
Goodwill, Ending Balance			4,600	4,100	0
Product Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax			46,920	148,125	191,009
Goodwill, Ending Balance			$ 0	$ 0	$ 0

[1] Revenues as reported in the geographic area in which they originate.

[2] Goodwill acquired in 2021 and 2020 is related to the purchase of geothermal assets from TG Geothermal Portfolio, LLC and the Pomona storage facility purchase transaction, respectively, as further described in Note 2 to the consolidated financial statements.

[3] Goodwill is primarily related to the expected synergies and potential cost savings in operations as a result of the purchase transaction. The goodwill is allocated to the Electricity segment and is deductible for tax purposes pending the exercise of the financial lease buy-out option as described below.