Share-Based Compensation (Details) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Share-Based Compensation [Abstract]
Shares available for future grants	13,100,000		13,100,000
Total compensation expense related to share-based compensation	$ 6.6	$ 3.4	$ 12.3	$ 10.8
Stock Options [Member]
Share-based Compensation, Shares Authorized under Stock Option Plans, Exercise Price Range [Line Items]
Fair value of options at grant date			$ 14.46
Risk-free interest rate (in hundredths)			0.81%
Expected price volatility (in hundredths)			55.90%
Expected dividend yield (in hundredths)			0.26%
Expected life in years			5 years
Options Outstanding [RollForward]
Outstanding at December 31, 2011 (in shares)			2,003,694
Granted (in shares)			291,143
Exercised (in shares)			(313,342)
Forfeited (in shares)			0
Outstanding at June 30, 2012 (in shares)	1,981,495		1,981,495
Options Excercisable (in shares)	1,500,192		1,500,192
Unvested Options (in shares)	481,303		481,303
Weighted-Average Price [Abstract]
Weighted-Average Price, beginning (in dollars per share)			$ 21.23
Weighted-Average Price, Granted (in dollars per share)			$ 30.83
Weighted-Average Price, Exercised (in dollars per share)			$ 8.15
Weighted-Average Price, Forfeited (in dollars per share)			$ 0
Weighted-Average Price, Ending (in dollars per share)	$ 24.71		$ 24.71
Weighted-Average Price, Options Excercisable	$ 22.19		$ 22.19
Weighted-Average Price, Unvested Options	$ 32.56		$ 32.56
Weighted-Average Remaining Contractual Term, Outstanding			3 years 7 months 6 days
Aggregate Intrinsic Value, Outstanding	12.5		12.5
Weighted-Average Remaining Contractual Term, Options Excercisable			2 years 9 months 18 days
Aggregate Intrinsic Value, Options Excercisable	12.3		12.3
Weighted-Average Remaining Contractual Term, Unvested Options			6 years 1 month 6 days
Aggregate Intrinsic Value, Unvested Options	0.2		0.2
Intrinsic value of options exercised			6.9	2.6
Unrecognized compensation cost	4.6		4.6
Weighted-average period for recognition of compensation costs			2 years 4 months 24 days
Restricted Stock [Member]
Weighted-Average Price [Abstract]
Weighted-Average Price, beginning balance (in dollars per share)			$ 32.80
Weighted-Average Price, Granted (in dollars per share)			$ 30.74	$ 39.14
Weighted-Average Price, Vested (in dollars per share)			$ 32.31
Weighted-Average Price, Forfeited (in dollars per share)			$ 32.71
Weighted-Average Price, Ending Balance (in dollars per share)	$ 31.88		$ 31.88
Unrecognized compensation cost	25.3		25.3
Weighted-average period for recognition of compensation costs			2 years 4 months 24 days
Total fair value of stock that vested			12.6	9.9
Restricted Shares Outstanding [Roll Forward]
Balance, beginning (in shares)			1,099,752
Granted (in shares)			706,221
Vested (in shares)			(397,204)
Forfeited (in shares)			(49,209)
Balance, Ending (in shares)	1,359,560		1,359,560
Restricted Stock [Member] | Maximum [Member]
Weighted-Average Price [Abstract]
Vesting period (in years)			4 years
Restricted Stock [Member] | Minimum [Member]
Weighted-Average Price [Abstract]
Vesting period (in years)			3 years
Performance Share Units [Member]
Weighted-Average Price [Abstract]
Weighted-Average Price, beginning balance (in dollars per share)			$ 39.07
Weighted-Average Price, Granted (in dollars per share)			$ 30.90	$ 39.07
Weighted-Average Price, Vested (in dollars per share)			$ 0
Weighted-Average Price, Forfeited (in dollars per share)			$ 39.07
Weighted-Average Price, Ending Balance (in dollars per share)	$ 34.11		$ 34.11
Unrecognized compensation cost	$ 5.3		$ 5.3
Weighted-average period for recognition of compensation costs			2 years 4 months 24 days
Restricted Shares Outstanding [Roll Forward]
Balance, beginning (in shares)			115,274
Granted (in shares)			171,954
Vested (in shares)			0
Forfeited (in shares)			(4,148)
Balance, Ending (in shares)	283,080		283,080