Other - (Schedule of Operating Revenues) (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2024	Jun. 30, 2023
Accounting Policies [Abstract]
Energy revenues Formula rate	$ 122,351	$ 125,321	$ 266,976	$ 282,160
Renewable energy credits Formula rate	91	90	201	173
Demand revenues Formula rate	124,297	108,946	239,991	212,644
Total Formula rate revenues	246,739	234,357	507,168	494,977
Energy revenues Market-based rates	9,803	4,390	17,255	7,875
Demand revenues Market-based rates	2,689	559	3,974	1,100
Total Market-based rates revenues	12,492	4,949	21,229	8,975
Total Member distribution cooperatives revenues	259,231	239,306	528,397	503,952
Energy revenues	2,861	12,185	4,207	23,452
Renewable energy credits	519	2,649	1,491	2,649
Total Non-members revenues	3,380	14,834	5,698	26,101
Total Operating revenues	$ 262,611	$ 254,140	$ 534,095	$ 530,053
Type Of Revenue Extensible List	us-gaap:ElectricityMember	us-gaap:ElectricityMember	us-gaap:ElectricityMember	us-gaap:ElectricityMember