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Selected Balance Sheet Data Balance Sheet Related Disclosures, Inventories (Details) - USD ($)
$ in Thousands
Jun. 30, 2020
Dec. 31, 2019
Public Utilities, Inventory [Line Items]    
Inventory, Net $ 154,100 $ 192,000
Materials and supplies    
Public Utilities, Inventory [Line Items]    
Inventories 62,800 62,600
Fuel    
Public Utilities, Inventory [Line Items]    
Inventories 67,200 77,100
Natural gas    
Public Utilities, Inventory [Line Items]    
Inventories $ 24,100 $ 52,300