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Select Balance Sheet Information - Schedule of Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
Mar. 31, 2025
Dec. 31, 2024
Property, Plant and Equipment [Line Items]    
Property, Plant and Equipment, net of accumulated depreciation $ 2,709,311 $ 2,692,460
Electric Plant    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 3,442,403 3,412,833
Less Accumulated Depreciation and Amortization 911,470 899,049
Property, Plant and Equipment, net of accumulated depreciation 2,530,933 2,513,784
Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 408,410 403,101
Less Accumulated Depreciation and Amortization 230,032 224,425
Property, Plant and Equipment, net of accumulated depreciation 178,378 178,676
Electric Plant in Service | Electric Plant    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 3,214,984 3,180,943
Construction Work in Progress | Electric Plant    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 227,419 231,890
Construction Work in Progress | Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 15,830 40,536
Nonelectric Property, Plant and Equipment in Service | Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 392,580 $ 362,565