Note 1 - Business and Significant Accounting Policies - Impact of Adoption (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue	[1]	$ 663,084	$ 705,342	$ 746,044
Electricity [Member]
Revenue		585,771	541,393	540,333
Electricity [Member] | Accounting Standards Update 2016-02 [Member]
Revenue		502,355	473,260	479,059
Electricity and Product Revenue [Member] | Accounting Standards Update 2014-09 [Member]
Revenue		$ 160,729	$ 232,082	$ 266,985

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