Note 1 - General and Basis of Presentation - Customers as a Percentage of Total Revenues (Details) - Revenue Benchmark [Member] - Customer Concentration Risk [Member]	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Sierra Pacific Power Company And Nevada Power Company [Member]
Percent of revenues	15.80%	15.40%	18.70%	17.10%
Southern California Public Power Authority [Member]
Percent of revenues	21.30%	19.50%	23.90%	19.80%
Kenya Power and Lighting Co LTD [Member]
Percent of revenues	16.10%	18.20%	16.30%	16.50%