Stock Based Compensation (Details 2) (USD $) In Millions, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Weighted-Average Grant Date Fair Value per Share
Stock based compensation expense	$ 51.8	$ 33.5	$ 39.5
Restricted Stock Units
Summary of restricted stock award activity
Outstanding at beginning of year (in shares)	515,468	687,308	568,504
Granted and fully vested (in shares)	50,853	76,608	118,804
Issued (in shares)		(248,448)
Outstanding at the end of the period (in shares)	566,321	515,468	687,308
Weighted-Average Grant Date Fair Value per Share
Outstanding at the beginning of the period (in dollars per share)	$ 9.10	$ 7.88	$ 7.34
Granted and fully vested (in dollars per share)	$ 27.53	$ 18.28	$ 10.44
Issued (in dollars per share)		$ 8.56
Outstanding at the end of the period (in dollars per share)	$ 10.75	$ 9.10	$ 7.88
Aggregate intrinsic value	22.0
Stock based compensation expense	$ 1.4	$ 1.4	$ 1.2