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Select Balance Sheet Information - Schedule of Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
Jun. 30, 2023
Dec. 31, 2022
Property, Plant and Equipment [Line Items]    
Property, Plant and Equipment, net of accumulated depreciation $ 2,316,246 $ 2,212,717
Electric Plant    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 3,074,852 2,958,311
Less Accumulated Depreciation and Amortization 888,374 859,988
Property, Plant and Equipment, net of accumulated depreciation 2,186,478 2,098,323
Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 332,055 309,098
Less Accumulated Depreciation and Amortization 202,287 194,704
Property, Plant and Equipment, net of accumulated depreciation 129,768 114,394
Electric Plant in Service | Electric Plant    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 2,933,603 2,844,379
Construction Work in Progress | Electric Plant    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 141,249 113,932
Construction Work in Progress | Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross 34,147 15,170
Nonelectric Property, Plant and Equipment in Service | Nonelectric Property, Plant and Equipment    
Property, Plant and Equipment [Line Items]    
Property, plant and equipment, gross $ 297,908 $ 293,928