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Employee Benefit Plans (Unrealized Gain Loss On Trading Securities Held In Rabbi Trust) (Details) - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Employee Benefit Plans [Abstract]      
Unrealized gains (losses) on trading securities held in rabbi trust $ 1,520 $ 586 $ (571)