Debt Obligations - Narrative (Details) (USD $)	Dec. 31, 2012	Feb. 29, 2012	Dec. 31, 2011	Dec. 31, 2012 Term Loan Due August 2013	Mar. 25, 2012 Term Loan Due June 2012	Dec. 31, 2012 Term Loan Due March 2012	Feb. 29, 2012 Term Loan Due March 2012	Dec. 31, 2012 Revolver 2012
Debt Instrument
Long term debt, face amount		$ 455,000,000		$ 250,000,000	$ 465,000,000		$ 455,000,000
Debt Instrument, Fair Value Disclosure	1,810,000,000		2,130,000,000
Long term debt, amount outstanding	$ 1,760,000,000		$ 1,970,000,000		$ 342,000,000
Debt Covenant, Cross Default Feature, Minimum Amount						5
Debt, Weighted Average Interest Rate								1.84%