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Fair Value Measurements (Estimated Fair Value Of Long-Term Debt) (Details) - USD ($)
$ in Thousands
Dec. 31, 2020
Dec. 31, 2019
Debt Instrument [Line Items]    
Long-term debt, Carrying Amount $ 598,848 $ 642,941
Level 2    
Debt Instrument [Line Items]    
Long-term debt, Fair Value $ 648,671 $ 677,253