Statements Of Consolidated Income (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Income Statement [Abstract]
Revenues	$ 1,446,096	$ 1,348,549	$ 2,812,257	$ 2,594,176
Costs and Expenses
Salaries, wages and employee benefits	544,624	508,874	1,067,094	1,000,514
Purchased transportation	400,200	348,526	768,251	665,516
Fuel and fuel-related taxes	140,354	150,110	284,185	286,137
Other operating expenses	138,529	142,018	275,044	272,700
Depreciation and amortization	53,442	50,540	105,284	100,854
Maintenance	32,671	32,509	64,581	61,981
Rents and leases	28,242	28,730	56,942	56,521
Purchased labor	27,891	27,077	55,043	53,092
Total Costs and Expenses	1,365,953	1,288,384	2,676,424	2,497,315
Operating Income	80,143	60,165	135,833	96,861
Other Income (Expense)
Investment income	209	227	444	549
Interest expense	(13,738)	(13,923)	(27,532)	(27,842)
Miscellaneous, net	(1,917)	(1,025)	(2,626)	(2,763)
Total Other Income (Expense)	(15,446)	(14,721)	(29,714)	(30,056)
Income before Income Tax Provision	64,697	45,444	106,119	66,805
Income Tax Provision	22,897	16,022	38,673	30,461
Net Income	$ 41,800	$ 29,422	$ 67,446	$ 36,344
Weighted-Average Common Shares Outstanding
Basic	55,809,358	55,413,243	55,756,540	55,227,528
Diluted	56,439,845	56,136,065	56,377,198	55,939,330
Earnings per Common Share
Basic	$ 0.75	$ 0.53	$ 1.21	$ 0.66
Diluted	$ 0.74	$ 0.52	$ 1.20	$ 0.65