Shareholders' Equity (Deficit) (Details) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Equity [Abstract]
Authorized shares	300,000,000	300,000,000
Par value of common stock (in dollars per share)	$ 0.01	$ 0.01
Shares reserved for issuance of stock options	10,100,000
Proceeds from stock options exercised	$ 32.1	$ 12.1	$ 10.4
Common stock activity roll forward
Common stock outstanding at the beginning of the period (in shares)	73,886,050	73,120,357
Stock options exercised (in shares)	1,679,359	765,693	837,039
Common stock outstanding at the end of the period (in shares)	75,565,409	73,886,050	73,120,357