Share-Based Compensation (Changes in Options Outstanding Under the Plans) (Details) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Weighted average remaining life, Exercisable, in years	4 years 10 months
Share-based Compensation Arrangement by Share-based Payment Award, Options, Other Increases (Decreases) in Period			(14,976)
Share-based Compensation Arrangements by Share-based Payment Award, Options, Other Share Increase (Decrease) in Period, Weighted Average Exercise Price			$ 47.28
Stock Options [Member]
Shares subject to options, Beginning balance	1,313,070	1,592,167	1,962,028
Shares subject to options, Granted	165,113	231,521	220,679
Shares subject to options, Exercised	(410,397)	(447,019)	(575,564)
Shares subject to options, Cancelled	(15,906)	(63,599)
Shares subject to options, Ending balance	1,051,880	1,313,070	1,592,167
Shares subject to options, Exercisable	696,929
Weighted average exercise price, Beginning balance, in dollars per share	$ 39.87	$ 33.91	$ 28.11
Weighted average exercise price, Granted, in dollars per share	71.84	57.91	57.85
Weighted average exercise price, Exercised, in dollars per share	31.54	26.04	22.98
Weighted average exercise price, Cancelled, in dollars per share	60.84	53.40
Weighted average exercise price, Ending Balance, in dollars per share	47.80	$ 39.87	$ 33.91
Weighted average exercise price, Exercisable, in dollars per share	$ 39.46
Aggregate intrinsic value, Outstanding, in USD	$ 33.4
Aggregate intrinsic value, Exercisable, in USD	$ 27.9
Weighted average remaining life, Outstanding, in years	5 years 12 months
Weighted average remaining life, Exercisable, in years	4 years 10 months