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Financial Instruments And Investments (Long-Term Debt and Short-Term Borrowings - Narratives) (Details) - USD ($)
$ in Thousands
Mar. 31, 2019
Feb. 01, 2019
Dec. 31, 2018
Financial Instruments and Investments [Line Items]      
Decommissioning Fund Investments $ 298,338   $ 276,905
Nuclear Fuel Financing      
Financial Instruments and Investments [Line Items]      
Line of Credit Facility, Amount Outstanding 30,000   26,200
Working Capital and General Purpose      
Financial Instruments and Investments [Line Items]      
Line of Credit Facility, Amount Outstanding 173,000   23,000
RGRT Senior Notes      
Financial Instruments and Investments [Line Items]      
Long-term Debt, Gross $ 110,000   $ 110,000
7.25% 2009 Series A Refunding Bonds, due 2040 | Pollution Control Bonds      
Financial Instruments and Investments [Line Items]      
Debt Instrument, Repurchased Face Amount   $ 63,500  
Debt Instrument, Interest Rate, Stated Percentage   7.25%