Regulatory Assets and Liabilities (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2024	Dec. 31, 2023
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 1,138,527	$ 1,131,489
Total Regulatory Liabilities	652,043	706,320
Net Regulatory Assets	486,484	425,169
Accumulated retirement costs for other obligations
Regulatory Assets and Liabilities
Total Regulatory Liabilities	23,134	25,992
Deferral of effects on net margin - Hawk Road Energy Facility | Hawk Road Energy Facility
Regulatory Assets and Liabilities
Total Regulatory Liabilities	15,712	16,020
Deferral of effects on net margin - Hawk Road Energy Facility | BC Smith Energy Facility
Regulatory Assets and Liabilities
Total Regulatory Liabilities	0	546
Major maintenance reserve
Regulatory Assets and Liabilities
Total Regulatory Liabilities	79,627	120,547
Deferred debt service adder
Regulatory Assets and Liabilities
Total Regulatory Liabilities	178,591	170,466
Asset retirement obligations
Regulatory Assets and Liabilities
Total Regulatory Liabilities	78,809	47,217
Revenue deferral plan
Regulatory Assets and Liabilities
Total Regulatory Liabilities	$ 252,103	308,507
Amortization period, regulatory liability	5 years
Natural gas hedges
Regulatory Assets and Liabilities
Total Regulatory Liabilities	$ 22,090	13,445
Other regulatory liabilities
Regulatory Assets and Liabilities
Total Regulatory Liabilities	$ 1,977	3,580
Other regulatory liabilities | Maximum
Regulatory Assets and Liabilities
Amortization period, regulatory liability	3 years
Premium and loss on reacquired debt
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 23,532	25,476
Premium and loss on reacquired debt | Maximum
Regulatory Assets and Liabilities
Amortization period, other regulatory assets	20 years
Amortization of financing leases
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 26,739	28,780
Outage costs
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 29,776	30,040
Coal-fired maintenance outage costs | Maximum
Regulatory Assets and Liabilities
Amortization period, other regulatory assets	60 months
Nuclear refueling outage costs | Maximum
Regulatory Assets and Liabilities
Amortization period, other regulatory assets	24 months
Nuclear refueling outage costs | Minimum
Regulatory Assets and Liabilities
Amortization period, other regulatory assets	18 months
Asset retirement obligations | Ashpond and other
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 334,240	343,523
Depreciation expense | Plant Vogtle
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 33,414	34,125
Operating license expected extension period for Plant Vogtle	20 years
Operating license period	40 years
Depreciation expense | Plant Wansley
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 325,483	335,884
Deferred charges related to Vogtle Units No. 3 and No. 4 training costs | Vogtle Units No. 3 & No. 4
Regulatory Assets and Liabilities
Total Regulatory Assets	55,008	55,159
Interest rate options cost
Regulatory Assets and Liabilities
Total Regulatory Assets	133,859	137,463
Deferral of effects on net margin - Smith Energy Facility | TA Smith Energy Facility
Regulatory Assets and Liabilities
Total Regulatory Assets	127,813	130,786
Deferral of effects on net margin - Smith Energy Facility | BC Smith Energy Facility
Regulatory Assets and Liabilities
Total Regulatory Assets	18,406	1,817
Other regulatory assets
Regulatory Assets and Liabilities
Total Regulatory Assets	$ 30,257	$ 8,436
Other regulatory assets | Maximum
Regulatory Assets and Liabilities
Amortization period, other regulatory assets	30 years