Debt Senior Credit Facility (Details) (USD $)			3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Term Loan A	Mar. 31, 2013 Term Loan A2	Mar. 31, 2013 Term Loan A - 3	Mar. 31, 2013 Term Loan B	Mar. 31, 2013 Revolver	Mar. 31, 2013 Term Loan A B A-2 and A-3	Mar. 31, 2013 Letter of Credit	Mar. 31, 2013 Additional Revolver	Apr. 03, 2013 Line of Credit Subsequent Event New Term Loan B BNP Paribas	Apr. 03, 2013 Line of Credit Subsequent Event New Revolver BNP Paribas
Line of Credit Facility [Line Items]
Debt instrument basis spread on variable rate			2.75%	2.75%		2.75%	2.75%				2.50%	2.50%
Debt Instrument, Face Amount			$ 150,000,000	$ 150,000,000	$ 100,000,000	$ 200,000,000
Line of Credit Facility, Maximum Borrowing Capacity											300,000,000	700,000,000
Debt Instrument, Interest Rate Terms			LIBOR plus 2.75%	LIBOR plus 2.75%	LIBOR plus 2.75%	LIBOR plus 2.75% with a LIBOR floor of 1.00%	LIBOR plus 2.75%
Debt Instrument, Maturity Date			Aug. 04, 2015	Aug. 04, 2015	Aug. 04, 2015	Aug. 04, 2016	Aug. 04, 2015
Line of Credit Facility, Remaining Borrowing Capacity							500,000,000
Long-term Debt								556,400,000	61,000,000	439,000,000
Long-term Line of Credit	$ 0	$ 235,000,000
Long-term Debt, Weighted Average Interest Rate	3.20%