Principal Accounting Policies (Narrative) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2013 Buildings [Member]	Dec. 31, 2013 Software and Software Development Costs [Member]	Dec. 31, 2012 Software and Software Development Costs [Member]	Dec. 31, 2011 Software and Software Development Costs [Member]	Dec. 31, 2013 Minimum [Member] Revenue Equipment [Member]	Dec. 31, 2013 Minimum [Member] Other equipment [Member]	Dec. 31, 2013 Minimum [Member] Software and Software Development Costs [Member]	Dec. 31, 2013 Maximum [Member] Revenue Equipment [Member]	Dec. 31, 2013 Maximum [Member] Other equipment [Member]	Dec. 31, 2013 Maximum [Member] Software and Software Development Costs [Member]	Dec. 31, 2014 Salvage Value [Member]	Dec. 31, 2013 Salvage Value [Member]
Principal Accounting Policies [Line Items]
Reporting Segments	3
Unearned revenue	$ 12,100,000	$ 16,900,000
Deferred setup costs	9,900,000	15,200,000
Cash and Cash Equivalents, Fair Value Disclosure	441,199,000	378,266,000
Variable-rate demand notes		3,200,000
Property, plant and equipment, estimated useful lives, years				P25Y
Property, plant and equipment, useful lives, years								4 years	3 years	3 years	14 years	10 years	7 years
Depreciation expense	221,200,000	204,900,000	191,400,000
Amortization expense related to capitalized software					7,200,000	8,300,000	7,900,000
Accumulated amortization expense related to capitalized software					158,700,000	155,900,000
Book overdrafts	40,800,000	43,000,000
Liability related to assumed claims	59,200,000	65,000,000
Receivable from the re-insurance pool	38,100,000	39,600,000
Operating income from reinsurance pool	$ (2,200,000)	$ 2,500,000	$ 4,400,000
Change in Accounting Estimate, Financial Effect														7.3	1.3