Revenue Recognition - Narrative (Details) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Dec. 31, 2022 USD ($) unit	Sep. 30, 2023 USD ($)	Sep. 30, 2022 USD ($)	Sep. 30, 2023 USD ($) member service	Sep. 30, 2022 USD ($)
Revenue Recognition
Number of electric distribution cooperative members | member				38
Number of services provided | service				2
Member energy requirements supplied(1)		67.00%	68.00%	67.00%	62.00%
Margins for interest ratio				1.10
Targeted margins for interest ratio				1.14
Refund liability	$ 28,471	$ 10,300	$ 9,022	$ 10,300	$ 9,022
Operating revenues		500,776	704,265	1,279,618	1,657,835
Washington County Power | Natural Gas Processing Plant
Revenue Recognition
Number of generating units acquired | unit	2
Members
Revenue Recognition
Operating revenues		471,488	627,130	1,224,637	1,523,361
Receivables from contracts	$ 187,401	165,919		165,919
Non-Members
Revenue Recognition
Operating revenues		29,288	77,135	54,981	134,474
Capacity revenues | Members
Revenue Recognition
Operating revenues		287,067	243,860	763,294	728,992
Capacity revenues | Non-Members
Revenue Recognition
Operating revenues		8,583	0	12,970	0
Energy revenues | Members
Revenue Recognition
Operating revenues		184,421	383,270	461,343	794,369
Energy revenues | Non-Members
Revenue Recognition
Operating revenues		20,705	$ 77,135	42,011	$ 134,474
Sale of Bobby C. Smith Jr. Deferring Members' Output
Revenue Recognition
Receivables from contracts	8,787	6,038		6,038
Transactions with Affiliated Companies and Investment Income
Revenue Recognition
Receivables from contracts	$ 13,834	$ 44,745		$ 44,745