Note 9 - Business Segments (Details Textual) $ in Thousands	3 Months Ended
	Mar. 31, 2022 USD ($)	Mar. 31, 2021 USD ($)	Dec. 31, 2021 USD ($)
Number of Reportable Segments	3
Revenue from Contract with Customer, Including Assessed Tax	$ 183,710	$ 166,352
Goodwill, Ending Balance	90,591		$ 89,954
Electricity Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax	162,525	144,988
Goodwill, Ending Balance	86,000		20,100
Electricity Segment [Member] | Accounting Standards Update 2014-09 [Member]
Revenue from Contract with Customer, Including Assessed Tax	22,800	19,200
Energy Storage and Management Services [Member]
Goodwill, Ending Balance	4,600		4,100
Product Segment [Member]
Revenue from Contract with Customer, Including Assessed Tax	14,628	$ 8,643
Goodwill, Ending Balance	$ 0		$ 0