Share-Based Compensation - Summary of Share Based Compensation Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Granted, Weighted-Average Grant-Date Fair Value (in dollars per share)	$ 79.96	$ 54.52	$ 96.52
SARs and Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Outstanding at Beginning, Number (in shares)	1,124
Granted, Number (in shares)	254
Exercised or converted, Number (in shares)	(210)
Forfeited or expired, Number (in shares)	(36)
Outstanding at Ending, Number (in shares)	1,132	1,124
Vested or expected to vest at End, Number (in shares)	1,118
Exercisable or convertible at End, Number (in shares)	623
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Abstract]
Outstanding at Beginning, Weighted-Average Exercise Price (in dollars per share)	$ 56.79
Granted, Weighted-Average Exercise Price (in dollars per share)	74.91
Exercised or converted, Weighted-Average Exercise Price (in dollars per share)	44.08
Forfeited or expired, Weighted-Average Exercise Price (in dollars per share)	71.02
Outstanding at End, Weighted-Average Exercise Price (in dollars per share)	62.75	$ 56.79
Vested or expected to vest at End, Weighted-Average Exercise Price	62.65
Exercisable or convertible at End, Weighted-Average Exercise Price	$ 58.57
Outstanding at End, Weighted-Average Remaining Contractual Term	6 years 10 months 18 days
Vested or expected to vest at End, Weighted-Average Remaining Contractual Term	6 years 9 months 18 days
Exercisable or convertible at End, Weighted-Average Remaining Contractual Term	5 years 7 months 2 days
Outstanding at End, Aggregate Intrinsic Value	$ 16,327
Vested or expected to vest at End, Aggregate Intrinsic Value	16,234
Exercisable or convertible at End, Aggregate Intrinsic Value	$ 11,585
Restricted Shares and Units [Member]
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward]
Outstanding at Beginning, Number (in shares)	454
Granted, Number (in shares)	222
Exercised or converted, Number (in shares)	(145)
Forfeited or expired, Number (in shares)	(35)
Outstanding at End, Number (in shares)	496	454
Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract]
Outstanding at Beginning, Weighted-Average Grant-Date Fair Value (in dollars per share)	$ 69.55
Granted, Weighted-Average Grant-Date Fair Value (in dollars per share)	79.96
Exercised or converted, Weighted-Average Grant-Date Fair Value (in dollars per share)	71.27
Forfeited or expired, Weighted-Average Grant-Date Fair Value (in dollars per share)	75.56
Outstanding at End, Weighted-Average Grant-Date Fair Value (in dollars per share)	$ 78.03	$ 69.55