Statement of Consolidated Income (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Statement [Abstract]
Revenues	$ 5,580,247	$ 5,289,953	$ 4,952,000
Salaries, wages and employee benefits	2,125,104	2,026,739	2,024,606
Purchased transportation	1,531,319	1,381,267	1,265,848
Other operating expenses	567,810	552,842	547,095
Fuel and fuel-related taxes	553,301	566,026	464,997
Depreciation and amortization	216,215	202,647	192,502
Maintenance	128,084	130,179	123,864
Rents and leases	115,954	116,415	117,312
Purchased labor	113,619	113,929	113,435
Loss (Gain) from asset impairments and purchase-price adjustment	0	(10,000)	19,181
Restructuring charges	0	1,981	4,990
Costs and Expenses	5,351,406	5,082,025	4,873,830
Operating Income	228,841	207,928	78,170
Investment income	831	920	1,327
Interest expense	(54,777)	(55,589)	(59,015)
Miscellaneous, net	(3,941)	(5,187)	(3,925)
Other Income (Expense)	(57,887)	(59,856)	(61,613)
Income before Income Tax Provision	170,954	148,072	16,557
Income Tax Provision	66,408	59,629	12,572
Net Income	$ 104,546	$ 88,443	$ 3,985
Weighted-Average Common Shares Outstanding
Basic	55,837,574	55,388,297	52,507,320
Diluted	56,485,987	56,101,903	53,169,299
Earnings per Common Share
Basic	$ 1.87	$ 1.60	$ 0.08
Diluted	$ 1.85	$ 1.58	$ 0.07