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Financial Instruments And Investments (Long-Term Debt And Short-Term Borrowings - Narratives) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2016
Dec. 31, 2015
May 01, 2005
Financial Instruments and Investments [Line Items]      
Interest Rate Cash Flow Hedge Loss to be Reclassified During Next 12 Months, Net $ 500    
Decommissioning Fund Investments 255,708 $ 239,035  
Accounting Standards Update 2015-03 [Member]      
Financial Instruments and Investments [Line Items]      
Amounts previously reported, reclassified 11,600    
Nuclear Fuel Financing      
Financial Instruments and Investments [Line Items]      
Line of Credit Facility, Amount Outstanding 37,600 33,700  
Working Capital and General Purpose      
Financial Instruments and Investments [Line Items]      
Line of Credit Facility, Amount Outstanding $ 44,000 $ 108,000  
Senior Notes | 6.00% Senior Notes, Net of Discount, due 2035      
Financial Instruments and Investments [Line Items]      
Debt Instrument, Interest Rate, Stated Percentage 6.00% 6.00% 6.00%
RGRT Senior Notes      
Financial Instruments and Investments [Line Items]      
Long-term Debt, Gross $ 95,000 $ 95,000