Stock-Based Compensation (Stock Option Activity) (Details) - Stock Options $ / shares in Units, $ in Millions	3 Months Ended	9 Months Ended
	Sep. 30, 2019 USD ($) $ / shares shares	Sep. 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		(188,489)
Options, expired (in shares) | shares	(37,005)
Options, forfeited (in shares) | shares		(85,526)
Options, outstanding, end of period (in shares) | shares	1,261,520	1,261,520
Options, vested and expected to vest (in shares) | shares	1,169,198	1,169,198
Options, exercisable (in shares) | shares	578,235	578,235
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		57.43
Weighted average exercise price, expired (per share) | $ / shares	$ 93.06
Weighted average exercise price, forfeited (per share) | $ / shares		70.70
Weighted average exercise price, end of period (per share) | $ / shares	66.45	66.45
Weighted average exercise price, vested and expected to vest (per share) | $ / shares	67.19	67.19
Weighted average exercise price, exercisable (per share) | $ / shares	$ 77.25	$ 77.25
Weighted average remaining contractual term (in years)		6 years 1 month 6 days
Weighted average remaining contractual term, vested and expected to vest (in years)		6 years
Weighted average remaining contractual term, exercisable (in years)		3 years 8 months 12 days
Options, outstanding, intrinsic value | $	$ 18.0	$ 18.0
Options, vested and expected to vest, intrinsic value | $	16.0	16.0
Options, vested and expected to vest, exercisable | $	$ 4.0	$ 4.0