Statements Of Consolidated Income (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Statements Of Consolidated Income [Abstract]
Revenues	$ 1,366,161	$ 1,245,627
Costs and Expenses
Salaries, wages and employee benefits	522,470	491,640
Purchased transportation	368,051	316,990
Fuel and fuel-related taxes	143,831	136,027
Other operating expenses	136,515	130,682
Depreciation and amortization	51,842	50,314
Maintenance	31,910	29,472
Rents and leases	28,700	27,791
Purchased labor	27,152	26,015
Total Costs and Expenses	1,310,471	1,208,931
Operating Income	55,690	36,696
Other Income (Expense)
Investment income	235	322
Interest expense	(13,794)	(13,919)
Miscellaneous, net	(709)	(1,738)
Total Other Income (Expense)	(14,268)	(15,335)
Income before Income Tax Provision	41,422	21,361
Income Tax Provision	15,776	14,439
Net Income	$ 25,646	$ 6,922
Weighted-Average Common Shares Outstanding
Basic	55,703,722	55,039,751
Diluted	56,257,783	55,725,230
Earnings per Common Share
Basic	$ 0.46	$ 0.13
Diluted	$ 0.46	$ 0.12