Stock-Based Compensation (Stock Option Activity) (Details) (Stock Options, USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2015
Stock Options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding, beginning of period (in shares)	618,115
Options, granted (in shares)	117,511
Options, exercised (in shares)	(194,648)
Options, outstanding, end of period (in shares)	540,978
Options, vested and expected to vest (in shares)	499,627
Options, exercisable (in shares)	327,100
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price [Roll Forward]
Weighted average exercise price, beginning of period (per share)	$ 53.10
Weighted average exercise price, granted (per share)	$ 113.72
Weighted average exercise price, exercised (per share)	$ 42.16
Weighted average exercise price, end of period (per share)	$ 70.21
Weighted average exercise price, vested and expected to vest (per share)	$ 67.67
Weighted average exercise price, exercisable (per share)	$ 51.83
Weighted average remaining contractual term (in years)	7 years 5 months 15 days
Weighted average remaining contractual term, vested and expected to vest (in years)	7 years 4 months 28 days
Weighted average remaining contractual term, exercisable (in years)	6 years 4 months 19 days
Options, outstanding, intrinsic value	$ 20.7
Options, vested and expected to vest, intrinsic value	20.3
Options, vested and expected to vest, exercisable	$ 18.0