Stock-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2011 Y plan	Dec. 31, 2010	Dec. 31, 2009
Stock-based compensation
Number of stock incentive plans	3
Total unrecognized compensation cost related to the unvested awards	$ 10.6
Total weighted average remaining term of unrecognized compensation costs (in years)	2.4
Compensation cost recognized in selling, general and administrative expenses	5.3	4.7	4.9
ISOs | Class A
Stock-based compensation
Minimum exercise price as percentage of fair market value of common stock on grant date	100.00%
NSOs | Class A
Stock-based compensation
Minimum exercise price as percentage of fair market value of common stock on grant date	50.00%
2004 Stock Incentive Plan
Stock-based compensation
Number of stock-based compensation plans available for grant of new equity awards	1
2004 Stock Incentive Plan | Class A
Stock-based compensation
Shares authorized for future grants of new equity awards	1,596,082
2004 Stock Incentive Plan | Stock options
Stock-based compensation
Period over which options become exercisable (in years)	4 years
Percentage of stock options becoming exercisable per year	25.00%
Expiration period (in years)	P10Y
Total unrecognized compensation cost related to the unvested awards	4.9
Total weighted average remaining term of unrecognized compensation costs (in years)	3.0
Compensation cost recognized in selling, general and administrative expenses	1.6	1.7	1.7
Summary of stock option activity and related information
Outstanding at beginning of year (in shares)	1,303,000	1,300,000	1,216,000
Granted (in shares)	295,000	282,000	214,000
Cancelled/Forfeitures (in shares)	(78,000)	(94,000)	(101,000)
Exercised (in shares)	(248,000)	(185,000)	(29,000)
Outstanding at end of year (in shares)	1,272,000	1,303,000	1,300,000
Exercisable at end of year (in shares)	745,000	769,000	882,000
Weighted Average Exercise Price
Outstanding at beginning of year (in dollars per share)	$ 29.00	$ 26.25	$ 26.07
Granted (in dollars per share)	$ 29.39	$ 33.65	$ 26.34
Cancelled/Forfeitures (in dollars per share)	$ 30.38	$ 23.33	$ 27.63
Exercised (in dollars per share)	$ 21.68	$ 19.69	$ 14.23
Outstanding at end of year (in dollars per share)	$ 30.43	$ 29.00	$ 26.25
Exercisable at end of year (in dollars per share)	$ 30.61	$ 27.56	$ 24.98
Weighted Average Intrinsic Value
Outstanding at end of year (in dollars per share)	$ 3.78
Exercisable at end of year (in dollars per share)	$ 3.60
Aggregate intrinsic values of exercisable options (in dollars)	2.7
Total intrinsic value of options exercised	3.9	2.7	0.3
Fair value assumptions
Expected life (in years)	6.0	6.0	6.0
Expected stock price volatility (as a percent)	40.90%	41.30%	41.20%
Expected dividend yield (as a percent)	1.50%	1.30%	1.70%
Risk-free interest rate (as a percent)	1.60%	1.90%	2.80%
Estimated forfeiture rate (as a percent)	6.75%	6.75%	6.75%
Weighted average grant-date fair value of stock options (in dollars per share)	$ 10.19	$ 12.36	$ 9.70
Additional stock compensation expense	2.2
2004 Stock Incentive Plan | Stock options | Class A
Weighted Average Intrinsic Value
Company's closing Common Stock price (in dollars per share)	$ 34.21
2004 Stock Incentive Plan | Restricted stock
Stock-based compensation
Maximum vesting period (in years)	P3Y
Vesting rate per year for maximum vesting period	0.3333
Total unrecognized compensation cost related to the unvested awards	3.8
Total weighted average remaining term of unrecognized compensation costs (in years)	2.2
Compensation cost recognized in selling, general and administrative expenses	2.4	1.8	2.0
Fair value assumptions
Estimated forfeiture rate (as a percent)	9.00%	9.75%	5.20%
Weighted average grant-date fair value (in dollars per share)	$ 29.51	$ 33.65	$ 26.21
Additional stock compensation expense	0.8
2004 Stock Incentive Plan | Restricted stock | Class A
Weighted Average Intrinsic Value
Company's closing Common Stock price (in dollars per share)	$ 34.21
Prior stock incentive plan | Stock options
Stock-based compensation
Period over which options become exercisable (in years)	5 years
Percentage of stock options becoming exercisable per year	20.00%
Expiration period (in years)	P10Y
Management Stock Purchase Plan | Class A
Stock-based compensation
Shares authorized for future grants of new equity awards	2,000,000
Number of common shares for each unit of award held	1
Exercise price as percentage of fair market value of common stock on grant date	67.00%
Management Stock Purchase Plan | Restricted stock units (RSUs)
Stock-based compensation
Total unrecognized compensation cost related to the unvested awards	1.9
Total weighted average remaining term of unrecognized compensation costs (in years)	1.7
Compensation cost recognized in selling, general and administrative expenses	$ 1.3	$ 1.2	$ 1.2
Fair value assumptions
Expected life (in years)	3.0	3.0	3.0
Expected stock price volatility (as a percent)	44.90%	45.60%	45.00%
Expected dividend yield (as a percent)	1.20%	1.50%	2.20%
Risk-free interest rate (as a percent)	1.20%	1.50%	1.40%
Estimated forfeiture rate (as a percent)	6.30%	6.30%	5.20%
Weighted average grant-date fair value (in dollars per share)	$ 16.25	$ 12.81	$ 8.14
Management Stock Purchase Plan | Restricted stock units (RSUs) | Class A
Weighted Average Intrinsic Value
Company's closing Common Stock price (in dollars per share)	$ 34.21