v3.25.1
Regulatory Assets and Liabilities (Details) - USD ($)
$ in Thousands
 3 Months Ended
Mar. 31, 2025
Dec. 31, 2024
Regulatory Assets and Liabilities    
Total Regulatory Assets $ 1,106,060 $ 1,103,633
Total Regulatory Liabilities 662,088 661,592
Net Regulatory Assets 443,972 442,041
Accumulated retirement costs for other obligations    
Regulatory Assets and Liabilities    
Total Regulatory Liabilities 23,808 29,975
Deferral of effects on net margin - Hawk Road Energy Facility | Hawk Road Energy Facility    
Regulatory Assets and Liabilities    
Total Regulatory Liabilities 15,250 15,404
Major maintenance reserve    
Regulatory Assets and Liabilities    
Total Regulatory Liabilities 99,196 99,987
Deferred debt service adder    
Regulatory Assets and Liabilities    
Total Regulatory Liabilities 190,629 186,757
Asset retirement obligations    
Regulatory Assets and Liabilities    
Total Regulatory Liabilities 97,064 102,858
Revenue deferral plan    
Regulatory Assets and Liabilities    
Total Regulatory Liabilities $ 175,811 197,373
Amortization period, regulatory liability 5 years  
Natural gas hedges    
Regulatory Assets and Liabilities    
Total Regulatory Liabilities $ 59,792 28,624
Other regulatory liabilities    
Regulatory Assets and Liabilities    
Total Regulatory Liabilities $ 538 614
Other regulatory liabilities | Maximum    
Regulatory Assets and Liabilities    
Amortization period, regulatory liability 2 years  
Premium and loss on reacquired debt    
Regulatory Assets and Liabilities    
Total Regulatory Assets $ 20,978 21,587
Premium and loss on reacquired debt | Maximum    
Regulatory Assets and Liabilities    
Amortization period, other regulatory assets 19 years  
Amortization of financing leases    
Regulatory Assets and Liabilities    
Total Regulatory Assets $ 23,413 24,699
Outage costs    
Regulatory Assets and Liabilities    
Total Regulatory Assets $ 58,799 45,749
Coal-fired maintenance outage costs | Maximum    
Regulatory Assets and Liabilities    
Amortization period, other regulatory assets 60 months  
Nuclear refueling outage costs | Minimum    
Regulatory Assets and Liabilities    
Amortization period, other regulatory assets 18 months  
Nuclear refueling outage costs | Maximum    
Regulatory Assets and Liabilities    
Amortization period, other regulatory assets 24 months  
Asset retirement obligations | Ashpond and other    
Regulatory Assets and Liabilities    
Total Regulatory Assets $ 262,791 268,074
Depreciation expense | Plant Vogtle    
Regulatory Assets and Liabilities    
Total Regulatory Assets $ 32,346 32,702
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 $ 331,912 337,181
Deferred charges related to Vogtle Units No. 3 and No. 4 training costs | Deferred charges related to Vogtle Units    
Regulatory Assets and Liabilities    
Total Regulatory Assets 54,314 54,545
Interest rate options cost    
Regulatory Assets and Liabilities    
Total Regulatory Assets 128,755 130,456
Deferral of effects on net margin | BC Smith Energy Facility    
Regulatory Assets and Liabilities    
Total Regulatory Assets 29,169 27,841
Deferral of effects on net margin | TA Smith Energy Facility    
Regulatory Assets and Liabilities    
Total Regulatory Assets 123,354 124,840
Inventory Adjustments | TA Smith Energy Facility    
Regulatory Assets and Liabilities    
Total Regulatory Assets 14,467 14,723
Other regulatory assets    
Regulatory Assets and Liabilities    
Total Regulatory Assets $ 25,762 $ 21,236
Other regulatory assets | Maximum    
Regulatory Assets and Liabilities    
Amortization period, other regulatory assets 29 years