Statements Of Consolidated Income (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Income Statement [Abstract]
Revenues	$ 1,398,021	$ 1,404,113	$ 4,115,555	$ 4,216,370
Costs and Expenses
Salaries, wages and employee benefits	541,373	534,011	1,598,770	1,601,105
Purchased transportation	327,691	384,312	1,005,235	1,152,563
Other operating expenses	162,736	145,660	467,550	420,704
Fuel and fuel-related taxes	133,093	136,011	406,052	420,196
Depreciation and amortization	58,911	55,403	172,074	160,687
Purchased labor	38,750	29,956	100,777	84,999
Rents and leases	33,778	29,654	94,764	86,596
Maintenance	34,014	33,893	94,760	98,474
Costs and Expenses	1,330,346	1,348,900	3,939,982	4,025,324
Operating Income	67,675	55,213	175,573	191,046
Other Income (Expense)
Investment income	150	204	473	648
Interest expense	(13,395)	(13,667)	(40,559)	(41,199)
Miscellaneous, net	(1,052)	(592)	(2,485)	(3,218)
Total Other Expense	(14,297)	(14,055)	(42,571)	(43,769)
Income before Income Tax Provision	53,378	41,158	133,002	147,277
Income Tax Provision	22,821	15,854	45,543	54,527
Net Income	$ 30,557	$ 25,304	$ 87,459	$ 92,750
Weighted-Average Common Shares Outstanding
Basic	56,714,423	55,906,636	56,390,621	55,806,937
Diluted	57,362,834	56,463,535	57,065,146	56,432,216
Earnings per Common Share
Basic	$ 0.54	$ 0.45	$ 1.55	$ 1.66
Diluted	$ 0.53	$ 0.45	$ 1.53	$ 1.64