Stock-Based Compensation (Stock Option Activity) (Details) - Stock Options $ / shares in Units, $ in Millions	6 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares
Shares
Options, outstanding, beginning of period (in shares) | shares	1,439,708
Options, granted (in shares) | shares	132,832
Options, exercised (in shares) | shares	(118,991)
Options, forfeited (in shares) | shares	(77,952)
Options, outstanding, end of period (in shares) | shares	1,375,597
Options, vested and expected to vest (in shares) | shares	1,263,536
Options, exercisable (in shares) | shares	684,738
Weighted Average Exercise Price
Weighted average exercise price, beginning of period (per share) | $ / shares	$ 63.21
Weighted average exercise price, granted (per share) | $ / shares	98.97
Weighted average exercise price, exercised (per share) | $ / shares	58.32
Weighted average exercise price, forfeited (per share) | $ / shares	69.54
Weighted average exercise price, end of period (per share) | $ / shares	66.72
Weighted average exercise price, vested and expected to vest (per share) | $ / shares	67.54
Weighted average exercise price, exercisable (per share) | $ / shares	$ 75.93
Weighted average remaining contractual term (in years)	6 years
Weighted average remaining contractual term, vested and expected to vest (in years)	5 years 8 months 12 days
Weighted average remaining contractual term, exercisable (in years)	3 years 4 months 24 days
Options, outstanding, intrinsic value | $	$ 41.3
Options, vested and expected to vest, intrinsic value | $	36.9
Options, vested and expected to vest, exercisable | $	$ 14.7