Note 8 - Business Segments (Details Textual) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Dec. 31, 2022 USD ($)
Number of Reportable Segments			3
Revenue from Contract with Customer, Including Assessed Tax	$ 208,056	$ 175,885	$ 588,084	$ 528,673
Goodwill	90,269		90,269		$ 90,325
Electricity Segment [Member]
Goodwill	85,600	85,100	85,600	85,100
Electricity Segment [Member] | Accounted for Under ASC 606 [Member]
Revenue from Contract with Customer, Including Assessed Tax	27,300	25,600	90,200	71,600
Energy Storage and Management Services [Member]
Goodwill	4,600	4,600	4,600	4,600
Product Segment [Member]
Goodwill	$ 0	$ 0	$ 0	$ 0