Stock Compensation Plans - Outstanding and Exercisable Stock Options (Details) - USD ($) $ / shares in Units, $ in Millions	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Options Vested or Expected to Vest
Number of Options (in shares)	530,462
Weighted-Average Remaining Contractual Life	6 years 3 months 6 days
Weighted-Average Exercise Price (in dollars per share)	$ 38.35
Aggregate Intrinsic Value	$ 25.0
Options Exercisable
Number of Options (in shares)	336,336
Weighted-Average Exercise Price (in dollars per share)	$ 27.94
Aggregate Intrinsic Value	$ 19.3
Closing market price for common stock (in dollars per share)	$ 85.20
Intrinsic value, exercises in the period	$ 4.7	$ 5.5	$ 12.7
$7.41 — $19.42 | Stock Options
Exercise Price
Exercise price, low end of range (in dollars per share)	$ 7.41
Exercise price, high end of range (in dollars per share)	$ 19.42
Options Vested or Expected to Vest
Number of Options (in shares)	65,095
Weighted-Average Remaining Contractual Life	3 years 1 month 6 days
Weighted-Average Exercise Price (in dollars per share)	$ 13.15
Aggregate Intrinsic Value	$ 4.7
Options Exercisable
Number of Options (in shares)	65,095
Weighted-Average Exercise Price (in dollars per share)	$ 13.15
Aggregate Intrinsic Value	$ 4.7
$21.13 — $32.84 | Stock Options
Exercise Price
Exercise price, low end of range (in dollars per share)	$ 21.13
Exercise price, high end of range (in dollars per share)	$ 32.84
Options Vested or Expected to Vest
Number of Options (in shares)	202,695
Weighted-Average Remaining Contractual Life	5 years 2 months 6 days
Weighted-Average Exercise Price (in dollars per share)	$ 25.67
Aggregate Intrinsic Value	$ 12.1
Options Exercisable
Number of Options (in shares)	202,695
Weighted-Average Exercise Price (in dollars per share)	$ 25.67
Aggregate Intrinsic Value	$ 12.1
$32.87 — $42.82 | Stock Options
Exercise Price
Exercise price, low end of range (in dollars per share)	$ 32.87
Exercise price, high end of range (in dollars per share)	$ 42.82
Options Vested or Expected to Vest
Number of Options (in shares)	66,550
Weighted-Average Remaining Contractual Life	6 years 4 months 16 days
Weighted-Average Exercise Price (in dollars per share)	$ 42.26
Aggregate Intrinsic Value	$ 2.9
Options Exercisable
Number of Options (in shares)	39,699
Weighted-Average Exercise Price (in dollars per share)	$ 41.88
Aggregate Intrinsic Value	$ 1.7
$50.60 — $59.72 | Stock Options
Exercise Price
Exercise price, low end of range (in dollars per share)	$ 50.60
Exercise price, high end of range (in dollars per share)	$ 59.72
Options Vested or Expected to Vest
Number of Options (in shares)	192,553
Weighted-Average Remaining Contractual Life	8 years 6 months 20 days
Weighted-Average Exercise Price (in dollars per share)	$ 58.45
Aggregate Intrinsic Value	$ 5.2
Options Exercisable
Number of Options (in shares)	28,847
Weighted-Average Exercise Price (in dollars per share)	$ 58.09
Aggregate Intrinsic Value	$ 0.8
$60.55 | Stock Options
Exercise Price
Exercise price, low end of range (in dollars per share)	$ 60.55
Options Vested or Expected to Vest
Number of Options (in shares)	3,569
Weighted-Average Remaining Contractual Life	9 years 2 months 6 days
Weighted-Average Exercise Price (in dollars per share)	$ 60.56
Aggregate Intrinsic Value	$ 0.1
Options Exercisable
Number of Options (in shares)	0
Weighted-Average Exercise Price (in dollars per share)	$ 60.56
Aggregate Intrinsic Value	$ 0.0