Note 18 - Business Segments - Revenue From Major Customers (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Revenue	[1]	$ 663,084	$ 705,342	$ 746,044
Southern California Public Power Authority [Member]
Revenue	[2]	$ 157,318	$ 145,450	$ 133,725
Percentage of revenues	[2]	23.70%	20.60%	17.90%
Sierra Pacific Power Company And Nevada Power Company [Member]
Revenue	[2],[3]	$ 120,206	$ 123,734	$ 125,486
Percentage of revenues	[2],[3]	18.10%	17.50%	16.80%
Kenya Power and Lighting Co LTD [Member]
Revenue	[2]	$ 102,844	$ 115,474	$ 121,661
Percentage of revenues	[2]	15.50%	16.40%	16.30%

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

[2] Revenues reported in Electricity segment.

[3] Subsidiaries of NV Energy, Inc.