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Stock-Based Incentive Compensation Plans (Summary of activity for stock appreciation rights plan) (Details) - Non-employee Stock Appreciation Rights [Member]
 12 Months Ended
Dec. 31, 2018
$ / shares
shares
Summary of activity for stock options [Roll Forward]  
Outstanding as of beginning of year (in shares) | shares 162,188
Granted - original (in shares) | shares 14,692
Exercised (includes shares tendered) (in shares) | shares (39,661)
Forfeited or expired (in shares) | shares (7,212)
Outstanding as of end of year (in shares) | shares 130,007
Vested or expected to vest as of end of year (in shares) | shares 124,916 [1]
Exercisable as of end of year (in shares) | shares 84,783
Summary of activity for stock options, additional disclosures [Abstract]  
Weighted average exercise price as of beginning of year (in dollars per share) | $ / shares $ 50.22
Weighted average exercise price granted - original (in dollars per share) | $ / shares 78.41
Weighted average exercise price exercised (includes shares tendered) (in dollars per share) | $ / shares 44.55
Weighted average exercise price forfeited or expired (in dollars per share) | $ / shares 54.82
Weighted average exercise price outstanding as of end of year (in dollars per share) | $ / shares 54.88
Weighted average exercise price vested or expected to vest as of end of year (in dollars per share) | $ / shares 54.75 [1]
Weighted average exercise price exercisable as of end of year (in dollars per share) | $ / shares $ 52.55
Weighted average remaining contractual term outstanding as of end of year (in years) 2 years 1 month 6 days
Weighted average remaining contractual term vested or expected to vest as of end of year (in years) 2 years 22 days [1]
Weighted average remaining contractual term exercisable as of end of year (in years) 1 year 7 months 6 days
[1] Includes estimated forfeitures.