Employee Savings Plan (Details) (USD $) In Millions, except Share data, unless otherwise specified	1 Months Ended	3 Months Ended		12 Months Ended
	Feb. 15, 2013	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Compensation and Retirement Disclosure [Abstract]
Employer contribution expense to 401(k) Savings Plan				$ 6.3	$ 4.1	$ 3.2
Common Stock contributed to the Savings Plan (in shares)	38,877	63,937	91,761