Revenue Recognition - Narrative (Details)	1 Months Ended	3 Months Ended		12 Months Ended
	Dec. 31, 2022 unit	Mar. 31, 2024 USD ($) member service	Mar. 31, 2023 USD ($)	Dec. 31, 2018	Dec. 31, 2023 USD ($)
Revenue Recognition
Number of electric distribution cooperative members | member		38
Number of services provided | service		2
Margins for interest ratio		1.10
Targeted margins for interest ratio		1.14
Refund liability		$ 0			$ 34,266,000
Vogtle New Units
Revenue Recognition
Refund liability		279,467,000
Cumulative recovery of financing costs		369,102,000
Rate management program, additional collection period				5 years
Rate management program, billing period				5 years
Amounts billed under additional rate management program		30,409,000	$ 15,713,000
Vogtle Units No. 3 & No. 4
Revenue Recognition
Amounts billed under rate management program			$ 1,761,000
Cumulative recovery of financing costs		135,693,000
Washington County Power | Natural Gas Processing Plant
Revenue Recognition
Number of generating units acquired | unit	2
Sales to members
Revenue Recognition
Receivables from contracts		147,851,000			170,901,000
Sale of Bobby C. Smith Jr. Deferring Members' Output
Revenue Recognition
Receivables from contracts		$ 32,563,000			$ 30,883,000