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Financial Instruments And Investments (Long-Term Debt and Short-Term Borrowings - Narratives) (Details) - USD ($)
$ in Thousands
Jun. 30, 2017
Dec. 31, 2016
Financial Instruments and Investments [Line Items]    
Decommissioning Fund Investments $ 271,315 $ 255,708
Nuclear Fuel Financing    
Financial Instruments and Investments [Line Items]    
Line of Credit Facility, Amount Outstanding 38,900 37,600
Working Capital and General Purpose    
Financial Instruments and Investments [Line Items]    
Line of Credit Facility, Amount Outstanding 140,000 44,000
RGRT Senior Notes    
Financial Instruments and Investments [Line Items]    
Long-term Debt, Gross $ 95,000 $ 95,000