Note 9 - Business Segments (Details Textual) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2021 USD ($)	Dec. 31, 2021 USD ($)
Number of Reportable Segments			3
Revenue from Contract with Customer, Including Assessed Tax	$ 169,078	$ 146,901	$ 352,788	$ 313,253
Goodwill, Ending Balance	90,200		90,200		$ 89,954
Electricity Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax	151,195	133,864	313,720	278,852
Goodwill, Ending Balance	85,600	20,200	85,600	20,200
Electricity Segment [Member] | Accounted for Under ASC 606 [Member]
Revenue from Contract with Customer, Including Assessed Tax	23,200	20,800	46,000	40,000
Energy Storage and Management Services [Member]
Goodwill, Ending Balance	4,600	4,600	4,600	4,600
Product Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax	10,392	7,410	25,020	16,053
Goodwill, Ending Balance	$ 0	$ 0	$ 0	$ 0