Note 1 - Business and Significant Accounting Policies - Impact of Adoption (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Revenue	[1]	$ 734,159	$ 663,084	$ 705,342
Electricity [Member]
Revenue		631,727	585,771	541,393
Electricity [Member] | Accounting Standards Update 2016-02 [Member]
Revenue		529,264	502,355	473,260
Electricity and Product Revenue [Member] | Accounting Standards Update 2014-09 [Member]
Revenue		$ 204,895	$ 160,729	$ 232,082

[1] Revenues as reported in the geographic area in which they originate.