Stock-Based Compensation (Stock Option Activity) (Details) - Stock Options $ / shares in Units, $ in Millions	9 Months Ended
	Sep. 30, 2015 USD ($) $ / shares shares
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options, outstanding, beginning of period (in shares) | shares	618,115
Options, granted (in shares) | shares	133,814
Options, exercised (in shares) | shares	(198,221)
Options, forfeited (in shares) | shares	(26,386)
Options, outstanding, end of period (in shares) | shares	527,322
Options, vested and expected to vest (in shares) | shares	502,780
Options, exercisable (in shares) | shares	330,734
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)	111.54
Weighted average exercise price, exercised (per share)	42.51
Weighted average exercise price, forfeited (per share)	100.45
Weighted average exercise price, end of period (per share)	69.55
Weighted average exercise price, vested and expected to vest (per share)	67.97
Weighted average exercise price, exercisable (per share)	$ 52.71
Weighted average remaining contractual term (in years)	6 years 10 months 6 days
Weighted average remaining contractual term, vested and expected to vest (in years)	6 years 8 months 27 days
Weighted average remaining contractual term, exercisable (in years)	5 years 7 months 12 days
Options, outstanding, intrinsic value | $	$ 14.5
Options, vested and expected to vest, intrinsic value | $	14.4
Options, vested and expected to vest, exercisable | $	$ 13.4