Stock-based Compensation Stock-based Compensation (Details textual) (USD $) In Millions, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Share-based Compensation [Abstract]
Unrecognized stock-based compensation costs, net of estimated forfeitures	$ 55.3		$ 55.3
Weighted average period of unrecognized stock-based compensation costs, net of estimated forfeitures	2 years 2 months
Cash received from the exercise of stock options	0.6	0.8	1.7	1.7
Related tax benefit realized from the exercise of the stock options	$ (0.3)	$ (1.0)	$ (0.1)	$ (0.7)
Time-vested restricted stock unit [Member]
Statement [Line Items]
Restricted stock units granted			1,088,000	978,000
Weighted average grant date fair value per share			$ 23.43	$ 21.68
Market-based restricted stock unit
Statement [Line Items]
Restricted stock units granted			7,000	795,000
Weighted average grant date fair value per share			$ 15.87	$ 11.73
Vesting period for market-based RSUs			3 years
Employee Stock
Statement [Line Items]
Weighted average grant date fair value per share	$ 5.25	$ 5.02	$ 5.25	$ 5.02
Number of common stock shares issued			125,000
Shares of common stock reserved for future issuance under all of the stock incentive plans	3,728,000		3,728,000