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Summary of Significant Accounting Policies - Property, Plant and Equipment and Intangible Assets (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2022
Dec. 31, 2021
Dec. 31, 2020
Major components of depreciable plant and equipment [Abstract]      
Equipment $ 652,723 $ 598,285  
Transmission and distribution plant 2,649,476 1,802,008  
Office buildings and other structures 359,086 981,615  
Total depreciable plant and equipment $ 3,661,285 $ 3,381,908  
Useful Lives      
Depreciation expense as percentage of beginning of year balance of depreciable plant 3.30% 3.20% 3.20%
Capitalized interest costs $ 4,703 $ 4,422 $ 4,133
Equity funds capitalized 1,551 1,926 1,249
Water Plant      
Useful Lives      
Depreciation $ 99,413 $ 91,906 $ 86,823
Minimum      
Useful Lives      
Equipment 5 years    
Transmission and distribution plant 35 years    
Office buildings and other structures 7 years    
Useful life of intangible assets 5 years    
Maximum      
Useful Lives      
Equipment 35 years    
Transmission and distribution plant 75 years    
Office buildings and other structures 50 years    
Useful life of intangible assets 70 years