Revenue Earning Equipment (Details Textuals) (USD $)	3 Months Ended	9 Months Ended
	Sep. 30, 2012	Sep. 30, 2012	Sep. 30, 2011	Dec. 31, 2011
Revenue Earning Equipment (Textuals) [Abstract]
Cost	$ 9,168,871,000	$ 9,168,871,000		$ 8,512,030,000
Accumulated Depreciation	3,499,462,000	3,499,462,000		3,462,359,000
Effect of change in estimated residual values of revenue earning equipment on pre tax earnings	4,500,000	13,500,000
Sale Leaseback Transaction, Gross Proceeds		130,184,000	0
Assets Held under Capital Leases [Member]
Revenue Earning Equipment (Textuals) [Abstract]
Cost	56,700,000	56,700,000		60,700,000
Accumulated Depreciation	$ 15,500,000	$ 15,500,000		$ 14,400,000