Statements Of Consolidated Income (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Income Statement [Abstract]
Revenues	$ 1,381,370	$ 1,446,096	$ 2,717,534	$ 2,812,257
Costs and Expenses
Salaries, wages and employee benefits	539,556	544,624	1,057,397	1,067,094
Purchased transportation	329,021	400,200	677,544	768,251
Other operating expenses	147,117	138,529	304,814	275,044
Fuel and fuel-related taxes	135,547	140,354	272,959	284,185
Depreciation and amortization	57,235	53,442	113,163	105,284
Purchased labor	31,414	32,671	60,746	64,581
Rents and leases	34,045	27,891	62,027	55,043
Maintenance	31,136	28,242	60,986	56,942
Total Costs and Expenses	1,305,071	1,365,953	2,609,636	2,676,424
Operating Income	76,299	80,143	107,898	135,833
Other Income (Expense)
Investment income	159	209	323	444
Interest expense	(13,659)	(13,738)	(27,164)	(27,532)
Miscellaneous, net	50	(1,917)	(1,433)	(2,626)
Total Other Expense	(13,450)	(15,446)	(28,274)	(29,714)
Income before Income Tax Provision	62,849	64,697	79,624	106,119
Income Tax Provision	19,952	22,897	22,722	38,673
Net Income	$ 42,897	$ 41,800	$ 56,902	$ 67,446
Weighted-Average Common Shares Outstanding
Basic	56,354,017	55,809,358	56,226,038	55,756,540
Diluted	56,960,738	56,439,845	56,860,095	56,377,198
Earnings per Common Share
Basic	$ 0.76	$ 0.75	$ 1.01	$ 1.21
Diluted	$ 0.75	$ 0.74	$ 1.00	$ 1.20