Stock-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Term of stock options granted under Plan	10 years
Vesting period, generally, for stock options granted under the plan	3 years
Share based compensation costs	$ 3.1	$ 2.8	$ 2.0
Tax benefit of share-based compensation	1.2	1.1	0.8
Forfeiture rate assumed (in hundredths)	7.13%	7.50%	7.31%
Weighted average grant date fair value for stock options granted (in dollars per share)	$ 22.89	$ 15.83	$ 10.74
Weighted average grant date fair value for stock options vested (in dollars per share)	$ 13.59	$ 10.29	$ 8.57
Total intrinsic value of stock options exercised	13.0	10.0	3.3
Stock Options [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected life (years)	6 years 6 months	6 years 10 months 24 days	6 years 10 months 24 days
Interest rate (in hundredths)	2.16%	1.22%	1.36%
Volatility (in hundredths)	37.15%	37.82%	31.26%
Expected dividend yield (in hundredths)	0.34%	0.48%	0.31%
Stock Options [Roll Forward]
Balance, beginning of year (in shares)	1,131,415
Granted (in shares)	173,068
Exercised (in shares)	(323,636)
Forfeited/canceled (in shares)	(29,768)
Balance, end of year (in shares)	951,079	1,131,415
Exercisable, end of year (in shares)	631,487
Weighted Average Exercise Price Per Share [Abstract]
Balance, beginning of year (in dollars per share)	$ 32.42
Granted (in dollars per share)	$ 58.25
Exercised (in dollars per share)	$ 30.57
Forfeited/canceled (in dollars per share)	$ 41.88
Balance, end of year (in dollars per share)	$ 37.46	$ 32.42
Exercisable, end of year (in dollars per share)	$ 31.55
Weighted Average Remaining Contractual Life [Abstract]
Outstanding options, end of year (in years)	6 years 8 months 1 day
Exercisable options, end of year (in years)	5 years 9 months
Aggregate Intrinsic Value [Abstract]
Outstanding options, end of year	30.40
Exercisable options, end of year	23.90
Closing stock price on last business day of the period (in dollars per share)	$ 69.45
Weighted average intrinsic value of options exercised (in dollars per share)	$ 40.17	$ 20.03	$ 10.11
Unrecognized stock-based compensation expense	2.7
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized	3 years
Restricted Stock [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share based compensation costs	4.9	3.9	3.4
Stock Options [Roll Forward]
Exercised (in shares)	61,621	61,981	102,424
Forfeited/canceled (in shares)	55,038	48,332	89,386
Aggregate Intrinsic Value [Abstract]
Unrecognized stock-based compensation expense	4.7
Weighted average period over which unrecognized stock-based compensation expense is expected to be recognized	3 years
Restricted Stock [Roll Forward]
Balance, beginning of year (in shares)	185,572	183,660	252,024
Granted (in shares)	106,116	112,225	123,446
Vested (in shares)	(61,621)
Canceled (in shares)	(55,038)
Balance, end of year (in shares)	175,029	185,572	183,660
Weighted Average Grant Date Fair Value [Abstract]
Balance, beginning of year (in dollars per share)	$ 37.65	$ 31.25	$ 27.21
Granted (in dollars per share)	$ 58.94	$ 41.44	$ 32.04
Vested (in dollars per share)	$ 36.51	$ 28.09	$ 25.90
Canceled (in dollars per share)	$ 38.73	$ 31.59	$ 27.08
Balance, end of year (in dollars per share)	$ 50.56	$ 37.65	$ 31.25
Reversals of compensation expense related to restricted stock forfeitures	$ 2.1	$ 0.1	$ 0
Nonvested Stock Options [Member]
Stock Options [Roll Forward]
Balance, beginning of year (in shares)	373,401
Granted (in shares)	173,068
Vested (in shares)	(197,109)
Forfeited/canceled (in shares)	(29,768)
Balance, end of year (in shares)	319,592
Weighted Average Exercise Price Per Share [Abstract]
Balance, beginning of year (in dollars per share)	$ 38.01
Granted (in dollars per share)	$ 58.25
Vested (in dollars per share)	$ 37.17
Forfeited/canceled (in dollars per share)	$ 41.88
Balance, end of year (in dollars per share)	$ 49.13