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Stock-Based Compensation (Shares Authorized Under Stock Option Plans By Exercise Price Range) (Details) - Directors Plan
12 Months Ended
Dec. 31, 2017
$ / shares
shares
$31.30 - $41.21  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Minimum Limit $ 31.30
Maximum limit $ 41.21
Outstanding and exercisable options, number of shares | shares 38,500
Outstanding and exercisable options weighted average remaining contractual life, years 1 year 10 months 12 days
Outstanding and exercisable options, weighted average exercise price $ 37.58
$53.81 - $73.26  
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]  
Minimum Limit 53.81
Maximum limit $ 73.26
Outstanding and exercisable options, number of shares | shares 49,000
Outstanding and exercisable options weighted average remaining contractual life, years 2 years 1 month 15 days
Outstanding and exercisable options, weighted average exercise price $ 62.15