Debt Narrative (Details) (USD $)	3 Months Ended			0 Months Ended										0 Months Ended
	Mar. 31, 2013		Mar. 31, 2012	Dec. 18, 2012 Credit Agreement	Mar. 31, 2013 Credit Agreement		Mar. 16, 2012 Line of Credit Credit Agreement	Mar. 16, 2012 Line of Credit Credit Agreement	Mar. 16, 2012 Line of Credit Credit Agreement Minimum	Mar. 16, 2012 Line of Credit Credit Agreement Maximum	Mar. 16, 2012 Line of Credit Senior Secured Term Loan Facility with interest payable at various dates at floating rates (2.20% at March 31, 2013) payable through 2017	Mar. 16, 2012 Line of Credit Senior Secured Term Loan Facility with interest payable at various dates at floating rates (2.20% at March 31, 2013) payable through 2017 Minimum	Mar. 16, 2012 Line of Credit Senior Secured Term Loan Facility with interest payable at various dates at floating rates (2.20% at March 31, 2013) payable through 2017 Maximum	Mar. 16, 2012 Line of Credit Senior Secured Term Loan Payable Through 2014 - A Senior Secured Term Loan Payable Through 2014 - B	Mar. 16, 2012 Term Loan Facility Senior Secured Term Loan Facility with interest payable at various dates at floating rates (2.20% at March 31, 2013) payable through 2017
Credit Agreement
Line of Credit Facility, Maximum Borrowing Capacity	$ 1,041,400,000			$ 300,000,000	$ 1,000,000,000		$ 2,000,000,000.0	$ 1,000,000,000.0							$ 1,000,000,000.0
Credit facility, Variable rate, Spread over LIBOR							2.00%	2.00%	1.75%	2.75%	2.00%	1.75%	2.75%
Line of Credit Facility, Amount Outstanding	416,400,000				378,500,000
Undrawn capacity	598,100,000	[1]			594,600,000	[1]
Gains (losses) on modification or extinguishment of Debt	0		(8,900,000)											(8,900,000)
Gains (Losses) on Restructuring of Debt				2,100,000
Unamortized Debt Issuance Expense				$ 3,100,000

[1] In accordance with its debt agreements, the Company’s availability under its Revolving Credit Facility has been reduced by the amount of standby letters of credit issued of $26.9 million as of March 31, 2013. These letters of credit are used primarily as security against its self-insurance obligations and workers’ compensation obligations. These letters of credit expire at various dates through 2013 unless extended.