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Stock-Based Compensation (Summary Of Non-Vested Stock Award Activity Under Incentive Plan) (Details) - $ / shares
shares in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Stock-Based Compensation [Abstract]      
Outstanding, beginning of year, Shares 125 116 70
Outstanding, beginning of year, Grant Date Fair Value $ 606.24 $ 511.88 $ 525.60
Shares granted 127 90 47
Granted, Grant Date Fair Value $ 436.36 $ 509.05 $ 785.32
Vested, Shares (8) (7) (1)
Vested, Grant Date Fair Value $ 454.84 $ 605.83 $ 413.07
Forfeited, Shares (31) (74) 0
Forfeited, Grant Date Fair Value $ 502.46 $ 529.54 $ 534.55
Outstanding, end of year, Shares 213 125 116
Outstanding, end of year, Grant Date Fair Value $ 519.62 $ 606.24 $ 511.88