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
Stock-based compensation
Total unrecognized compensation cost related to the unvested awards	$ 20.2
Total weighted average remaining term of unrecognized compensation costs	1 year 10 months 24 days
Compensation cost recognized	8.6	9.6	6.6
Selling, general and administrative expenses
Stock-based compensation
Compensation cost recognized	8.0
Performance Shares
Stock-based compensation
Vesting period	3 years
Total unrecognized compensation cost related to the unvested awards	5.0
Total weighted average remaining term of unrecognized compensation costs	2 years
Compensation cost recognized	0.7
Fair value assumptions
Weighted average grant-date fair value (in dollars per share)	$ 57.02
Performance Shares | Class A
Weighted Average Intrinsic Value
Company's closing Common Stock price (in dollars per share)	$ 63.44
Performance Shares | Class A | Minimum
Stock-based compensation
Percentage of stock options becoming exercisable	0.00%
Performance Shares | Class A | Maximum
Stock-based compensation
Percentage of stock options becoming exercisable	200.00%
Second Amended and Restated 2004 Stock Incentive Plan
Stock-based compensation
Number of stock incentive plans	1
Second Amended and Restated 2004 Stock Incentive Plan | Class A
Stock-based compensation
Shares authorized	1,706,591
Second Amended and Restated 2004 Stock Incentive Plan | Stock options
Stock-based compensation
Vesting period	4 years
Percentage of stock options becoming exercisable	25.00%
Expiration period	10 years
Total unrecognized compensation cost related to the unvested awards	5.6
Total weighted average remaining term of unrecognized compensation costs	2 years 2 months 12 days
Compensation cost recognized	2.6	3.8	2.7
Summary of stock option activity and related information
Outstanding at beginning of year (in shares)	1,029,000	1,064,000	1,272,000
Granted (in shares)	114,000	379,000	415,000
Cancelled/Forfeitures (in shares)	(306,000)	(53,000)	(33,000)
Exercised (in shares)	(342,000)	(361,000)	(590,000)
Outstanding at end of year (in shares)	495,000	1,029,000	1,064,000
Exercisable at end of year (in shares)	128,000	249,000	360,000
Weighted Average Exercise Price
Outstanding at beginning of year (in dollars per share)	$ 41.66	$ 33.37	$ 30.43
Granted (in dollars per share)	$ 57.58	$ 54.78	$ 37.67
Cancelled/Forfeitures (in dollars per share)	$ 44.19	$ 36.97	$ 31.18
Exercised (in dollars per share)	$ 36.48	$ 31.73	$ 30.19
Outstanding at end of year (in dollars per share)	$ 47.34	$ 41.66	$ 33.37
Exercisable at end of year (in dollars per share)	$ 40.04	$ 32.35	$ 30.91
Weighted Average Intrinsic Value
Outstanding at end of year (in dollars per share)	$ 16.10
Exercisable at end of year (in dollars per share)	$ 23.40
Aggregate intrinsic values of exercisable options (in dollars)	3.0
Total intrinsic value of options exercised	8.2	7.4	5.7
Fair value assumptions
Expected life	6 years	6 years	6 years
Expected stock price volatility (as a percent)	37.50%	40.30%	41.20%
Expected dividend yield (as a percent)	1.00%	1.00%	1.20%
Risk-free interest rate (as a percent)	1.90%	1.70%	0.90%
Weighted average grant-date fair value of stock options (in dollars per share)	$ 20.04	$ 20.30	$ 13.49
Second Amended and Restated 2004 Stock Incentive Plan | Stock options | Class A
Stock-based compensation
Minimum exercise price as percentage of fair market value of common stock on grant date	100.00%
Weighted Average Intrinsic Value
Company's closing Common Stock price (in dollars per share)	$ 63.44
Second Amended and Restated 2004 Stock Incentive Plan | Stock options | Grants in 2014
Stock-based compensation
Expiration period	3 years
Vesting rate per year for maximum vesting period	0.33
Second Amended and Restated 2004 Stock Incentive Plan | Restricted stock | Maximum
Stock-based compensation
Vesting period	3 years
Vesting rate per year for maximum vesting period	0.33
Second Amended and Restated 2004 Stock Incentive Plan | Restricted stock | Grants in 2014 | Maximum
Stock-based compensation
Vesting period	2 years
Percentage of stock options becoming exercisable	50.00%
Second Amended and Restated 2004 Stock Incentive Plan | Deferred shares
Stock-based compensation
Vesting period	3 years
Vesting rate per year for maximum vesting period	0.33
Second Amended and Restated 2004 Stock Incentive Plan | Deferred shares | Grants in 2014
Stock-based compensation
Vesting period	2 years
Percentage of stock options becoming exercisable	50.00%
Management Stock Purchase Plan | Class A
Stock-based compensation
Shares available for future grants of new equity awards	913,526
Shares authorized	2,000,000
Exercise price as percentage of fair market value of common stock on grant date	67.00%
Management Stock Purchase Plan | Restricted stock | Class A
Weighted Average Intrinsic Value
Company's closing Common Stock price (in dollars per share)	$ 63.44
Management Stock Purchase Plan | Restricted stock units (RSUs)
Stock-based compensation
Total unrecognized compensation cost related to the unvested awards	0.6
Total weighted average remaining term of unrecognized compensation costs	1 year 4 months 24 days
Compensation cost recognized	$ 0.5	$ 0.7	$ 0.8
Fair value assumptions
Expected life	3 years	3 years	3 years
Expected stock price volatility (as a percent)	31.20%	34.10%	38.30%
Expected dividend yield (as a percent)	0.90%	0.90%	1.10%
Risk-free interest rate (as a percent)	0.70%	0.40%	0.40%
Weighted average grant-date fair value (in dollars per share)	$ 22.57	$ 18.05	$ 15.68
Management Stock Purchase Plan | Restricted stock units (RSUs) | Minimum
Stock-based compensation
Vesting period	3 years