Note 19 - Business Segments - Revenue From Major Customers (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Revenue	[1]	$ 746,044	$ 719,267	$ 692,812
Southern California Public Power Authority [Member]
Revenue	[2]	$ 133,725	$ 109,208	$ 70,100
Percentage of revenues	[2]	17.90%	15.20%	10.10%
Sierra Pacific Power Company And Nevada Power Company [Member]
Revenue	[2],[3]	$ 125,486	$ 116,149	$ 125,424
Percentage of revenues	[2],[3]	16.80%	16.10%	18.10%
Kenya Power and Lighting Co LTD [Member]
Revenue	[2]	$ 121,661	$ 119,094	$ 110,243
Percentage of revenues	[2]	16.30%	16.60%	15.90%

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

[2] Revenues reported in Electricity segment.

[3] Subsidiaries of NV Energy, Inc.