Other - (Schedule of Operating Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2022	Mar. 31, 2021
Other [Abstract]
Energy revenues	$ 115,085	$ 90,834
Renewable energy credits	17	9
Demand revenues	98,565	93,900
Total revenues from sales to member distribution cooperatives	213,667	184,743
Energy revenues	3,767	6,191
Renewable energy credits		183
Total revenues from sales to non-members	3,767	6,374
Total operating revenues	$ 217,434	$ 191,117
Type of Revenue [Extensible List]	us-gaap:ElectricityMember	us-gaap:ElectricityMember