Condensed Consolidated Statement of Earnings (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Operating revenues, excluding fuel surcharge revenues	$ 1,046,769	$ 947,381	$ 2,990,971	$ 2,703,670
Fuel surcharge revenues	249,023	223,889	725,873	618,235
Total operating revenues	1,295,792	1,171,270	3,716,844	3,321,905
Operating expenses:
Rents and purchased transportation	646,049	552,509	1,818,890	1,542,901
Salaries, wages and employee benefits	260,911	255,982	766,820	743,470
Fuel and fuel taxes	114,694	117,779	348,332	347,030
Depreciation and amortization	57,773	54,404	170,120	158,312
Operating supplies and expenses	48,281	43,164	133,632	120,789
Insurance and claims	13,745	11,042	37,385	32,531
General and administrative expenses, net of asset dispositions	9,369	6,114	19,718	20,511
Operating taxes and licenses	7,451	7,095	21,916	20,626
Communication and utilities	4,467	4,501	13,166	13,789
Total operating expenses	1,162,740	1,052,590	3,329,979	2,999,959
Operating income	133,052	118,680	386,865	321,946
Net interest expense	6,346	7,145	20,263	22,286
Earnings before income taxes	126,706	111,535	366,602	299,660
Income taxes	48,465	42,885	140,225	115,219
Net earnings	$ 78,241	$ 68,650	$ 226,377	$ 184,441
Weighted average basic shares outstanding (in Shares)	118,131	118,627	117,461	119,940
Basic earnings per share (in Dollars per share)	$ 0.66	$ 0.58	$ 1.93	$ 1.54
Weighted average diluted shares outstanding (in Shares)	120,281	121,126	120,022	122,784
Diluted earnings per share (in Dollars per share)	$ 0.65	$ 0.57	$ 1.89	$ 1.50
Dividends declared per common share (in Dollars per share)	$ 0.14	$ 0.13	$ 0.42	$ 0.39