Statements Of Consolidated Income (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Income Statement [Abstract]
Revenues	$ 1,404,113	$ 1,377,079	$ 4,216,370	$ 3,971,255
Costs and Expenses
Salaries, wages and employee benefits	534,011	516,083	1,601,105	1,516,597
Purchased transportation	384,312	365,306	1,152,563	1,030,822
Other operating expenses	145,660	145,298	420,704	417,998
Fuel and fuel-related taxes	136,011	142,185	420,196	428,322
Depreciation and amortization	55,403	50,814	160,687	151,668
Maintenance	33,893	35,711	98,474	97,692
Rents and leases	29,654	30,423	86,596	86,944
Purchased labor	29,956	30,134	84,999	83,226
Total Costs and Expenses	1,348,900	1,315,954	4,025,324	3,813,269
Operating Income	55,213	61,125	191,046	157,986
Other Income (Expense)
Investment income	204	163	648	712
Interest expense	(13,667)	(13,909)	(41,199)	(41,751)
Miscellaneous, net	(592)	227	(3,218)	(2,536)
Total Other Income (Expense)	(14,055)	(13,519)	(43,769)	(43,575)
Income before Income Tax Provision	41,158	47,606	147,277	114,411
Income Tax Provision	15,854	18,478	54,527	48,939
Net Income	$ 25,304	$ 29,128	$ 92,750	$ 65,472
Weighted-Average Common Shares Outstanding
Basic	55,906,636	55,535,074	55,806,937	55,331,170
Diluted	56,463,535	56,117,334	56,432,216	56,054,059
Earnings per Common Share
Basic	$ 0.45	$ 0.52	$ 1.66	$ 1.18
Diluted	$ 0.45	$ 0.52	$ 1.64	$ 1.17