Note 8 - Business Segments (Details Textual) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Jun. 30, 2023 USD ($)	Jun. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Number of Reportable Segments			3
Revenue from Contract with Customer, Including Assessed Tax	$ 194,796	$ 169,078	$ 380,028	$ 352,788
Goodwill	90,456		90,456		$ 90,325
Electricity Segment [Member]
Goodwill	85,800	85,600	85,800	85,600
Electricity Segment [Member] | Accounted for Under ASC 606 [Member]
Revenue from Contract with Customer, Including Assessed Tax	30,200	23,200	62,900	46,000
Energy Storage and Management Services [Member]
Goodwill	4,600	4,600	4,600	4,600
Product Segment [Member]
Goodwill	$ 0	$ 0	$ 0	$ 0