XML 54 R35.htm IDEA: XBRL DOCUMENT v3.20.4
Summary of Significant Accounting Policies - Property, Plant and Equipment (Details) - USD ($)
$ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Major components of depreciable plant and equipment [Abstract]      
Equipment $ 567,904 $ 521,183  
Transmission and distribution 1,699,953 2,207,051  
Office buildings and other structures 930,203 260,220  
Total depreciable plant and equipment $ 3,198,060 $ 2,988,454  
Estimated Useful Lives of Plant and Equipment [Abstract]      
Depreciation expense as percentage of beginning of year balance of depreciable plant 3.20% 3.80% 3.60%
Capitalized interest costs $ 4,133 $ 4,323 $ 2,856
Equity funds capitalized 1,249    
Administrative and general expense      
Estimated Useful Lives of Plant and Equipment [Abstract]      
Depreciation 2,343 2,869 2,306
Water Plant      
Estimated Useful Lives of Plant and Equipment [Abstract]      
Depreciation $ 86,823 $ 63,785 $ 53,031
Minimum      
Estimated Useful Lives of Plant and Equipment [Abstract]      
Estimated useful life of equipment 5 years    
Estimated useful life of transmission and distribution plant 35 years    
Estimated useful lives of office buildings and other structures 7 years    
Useful life of intangible assets 5 years    
Maximum      
Estimated Useful Lives of Plant and Equipment [Abstract]      
Estimated useful life of equipment 35 years    
Estimated useful life of transmission and distribution plant 75 years    
Estimated useful lives of office buildings and other structures 50 years    
Useful life of intangible assets 70 years