Note 2 - Business Acquisitions - Summary of Pro Forma Information Related to a Business Combination (Details) - Two Contracted Geothermal Assets in Nevada [Member] - USD ($) $ in Millions	12 Months Ended
Dec. 31, 2021	Dec. 31, 2020
Business Acquisition, Pro Forma Revenue	$ 690.6	$ 760.6
Net income attributable to the Company's stockholders	69.6	84.3
Electricity Segment [Member]
Business Acquisition, Pro Forma Revenue	$ 613.3	$ 596.6

The pro forma net Income or Loss for the period as if the business combination or combinations had been completed at the beginning of a period.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(3)
-URI https://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(2)
-URI https://asc.fasb.org/extlink&oid=79982066&loc=d3e1392-128463

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration