Note 2 - Business Acquisitions - Fair Value of Amounts of Identified Assets and Liabilities Assumed in a Business Combination (Details) - USD ($) $ in Thousands		Dec. 31, 2021	Jul. 13, 2021	Dec. 31, 2020	Jul. 20, 2020	Dec. 31, 2019
Goodwill, Ending Balance		$ 89,954		$ 24,566		$ 20,140
Goodwill (2)		$ 89,954		$ 24,566		$ 20,140
Two Contracted Geothermal Assets in Nevada [Member]
Cash and cash equivalents and restricted cash			$ 10,900
Trade receivables and others (1)	[1]		8,600
Deferred income taxes			23,600
Property, plant and equipment and construction-in-process			152,000
Intangible assets (2)	[2]		191,600
Goodwill, Ending Balance	[3]		65,400
Total assets acquired			452,100
Accounts payable, accrued expenses and others			6,600
Financing liability (4)	[4]		258,400
Asset retirement obligation			5,300
Total liabilities assumed			270,300
Total assets acquired, and liabilities assumed, net			181,800
Property, plant and equipment, net			152,000
Goodwill (2)	[3]		65,400
Liabilities assumed			$ (270,300)
Pomona Energy Storage [Member]
Trade receivables and others (1)					$ 1,000
Property, plant and equipment and construction-in-process					20,100
Intangible assets (2)	[5]				20,400
Goodwill, Ending Balance	[6]				4,100
Total liabilities assumed					2,200
Total assets acquired, and liabilities assumed, net					43,400
Property, plant and equipment, net					20,100
Goodwill (2)	[6]				4,100
Total assets acquired					45,600
Liabilities assumed					$ (2,200)

[1] The gross amount of receivables due under the Dixie Valley and Beowawe PPAs is $7.8 million. These receivables were fully collected during the third quarter of 2021.

[2] Intangible assets are related to the long-term electricity PPAs described above and are amortized over the term of those PPAs.

[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.

[4] Financing liability is related to a sale and leaseback transaction entered into by the Seller in September 2015 under which it sold and leased back the undivided interests in the Dixie Valley power plant asset through June 2038. The lease transaction was accounted for by the Seller as a finance lease due to the Seller's continued involvement and management of the power plant and the existence of an early buy-out option in September 2024, which continues to be applicable to the Company. As per the accounting guidance, the Company retained the Seller's accounting of a "failed" sale and leaseback transaction and accordingly accounted for the liability as a financing liability. This financing liability, as well as the related power plant asset, were measured at their acquisition-date fair value.

[5] Intangible assets of $18.0 million are related to a long-term energy storage resource adequacy agreement with Southern California Edison and are depreciated over a period of approximately 6.5 years. The remaining $2.4 million is related to certain other contract rights.

[6] Goodwill is primarily related to certain potential future economic benefits arising from assets acquired. Goodwill is allocated to the Energy Storage segment and is deductible for tax purposes.