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Fair Value Measurements (Estimated Fair Value Of Long-Term Debt) (Details) - USD ($)
$ in Thousands
Sep. 30, 2018
Dec. 31, 2017
Debt Instrument [Line Items]    
Long-term debt (excluding capital lease obligations) $ 813,149 $ 597,091
Fair Value, Inputs, Level 2 [Member]    
Debt Instrument [Line Items]    
Long-term debt (excluding capital lease obligations), Fair Value $ 803,977 $ 623,557