Commitments and Contingencies (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Commitments and Contingencies( Details) [Abstract]
Rental expense	$ 235,600,000	$ 230,300,000	$ 221,900,000
Future Minimum Rental Payment under Operating Leases (Table Details) [Abstract]
Operating lease payments, total	573,563,000
Guarantor Obligations [Line Items]
Maximum financing amount	50,000,000
Amount outstanding	24,900,000
Investment in Equipment under Capital Leases (Table Details) [Abstract]
Equipment under capital lease	0	2,773,000
Accumulated amortization	0	(2,689,000)
Equipment under capital lease, net	0	84,000
Citibank [Member]
Guarantor Obligations [Line Items]
Maximum financing amount	30,000,000
Texas Capital Bank [Member]
Guarantor Obligations [Line Items]
Maximum financing amount	$ 20,000,000