Condensed Consolidated Statements of Earnings (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Operating revenues, excluding fuel surcharge revenues	$ 1,165,965	$ 1,046,769	$ 3,325,070	$ 2,990,971
Fuel surcharge revenues	269,885	249,023	785,225	725,873
Total operating revenues	1,435,850	1,295,792	4,110,295	3,716,844
Operating expenses:
Rents and purchased transportation	724,417	646,049	2,062,745	1,818,890
Salaries, wages and employee benefits	289,789	260,911	835,765	766,820
Fuel and fuel taxes	114,147	114,694	340,987	348,332
Depreciation and amortization	64,291	57,773	187,304	170,120
Operating supplies and expenses	55,378	48,281	149,918	133,632
Insurance and claims	13,878	13,745	38,759	37,385
General and administrative expenses, net of asset dispositions	10,172	9,369	33,581	19,718
Operating taxes and licenses	8,168	7,451	23,723	21,916
Communication and utilities	4,881	4,467	14,338	13,166
Total operating expenses	1,285,121	1,162,740	3,687,120	3,329,979
Operating income	150,729	133,052	423,175	386,865
Net interest expense	5,835	6,346	18,320	20,263
Earnings before income taxes	144,894	126,706	404,855	366,602
Income taxes	55,422	48,465	154,337	140,225
Net earnings	$ 89,472	$ 78,241	$ 250,518	$ 226,377
Weighted average basic shares outstanding (in Shares)	117,723	118,131	117,472	117,461
Basic earnings per share (in Dollars per share)	$ 0.76	$ 0.66	$ 2.13	$ 1.93
Weighted average diluted shares outstanding (in Shares)	119,357	120,281	119,552	120,022
Diluted earnings per share (in Dollars per share)	$ 0.75	$ 0.65	$ 2.10	$ 1.89
Dividends declared per common share (in Dollars per share)	$ 0.15	$ 0.14	$ 0.30	$ 0.42