Statements of Consolidated Income (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Statement [Abstract]
Revenues	$ 5,473,356	$ 5,580,247	$ 5,289,953
Salaries, wages and employee benefits	2,143,036	2,125,104	2,027,870
Purchased transportation	1,323,005	1,531,319	1,381,267
Other operating expenses	634,107	567,810	553,692
Fuel and fuel-related taxes	532,958	553,301	566,026
Depreciation and amortization	230,751	216,215	202,647
Purchased labor	148,165	113,619	113,929
Rents and leases	129,325	115,954	116,415
Maintenance	123,056	128,084	130,179
Gain from purchase-price adjustment	0	0	(10,000)
Costs and Expenses	5,264,403	5,351,406	5,082,025
Operating Income	208,953	228,841	207,928
Investment income	621	831	920
Interest expense	(53,339)	(54,777)	(55,589)
Miscellaneous, net	(1,870)	(3,941)	(5,187)
Other Income (Expense)	(54,588)	(57,887)	(59,856)
Income before income tax provision	154,365	170,954	148,072
Income Tax Provision	55,212	66,408	59,629
Net Income	$ 99,153	$ 104,546	$ 88,443
Weighted-Average Common Shares Outstanding
Basic	56,511,563	55,837,574	55,388,297
Diluted	57,240,588	56,485,987	56,101,903
Earnings per Common Share
Basic	$ 1.75	$ 1.87	$ 1.60
Diluted	$ 1.73	$ 1.85	$ 1.58