Condensed Consolidated Statement of Earnings (Unaudited) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Operating revenues, excluding fuel surcharge revenues	$ 1,038,940	$ 938,683
Fuel surcharge revenues	252,647	227,239
Total operating revenues	1,291,587	1,165,922
Operating expenses:
Rents and purchased transportation	644,533	556,117
Salaries, wages and employee benefits	263,724	250,044
Fuel and fuel taxes	116,560	120,554
Depreciation and amortization	60,730	56,120
Operating supplies and expenses	44,914	39,811
Insurance and claims	12,770	11,045
General and administrative expenses, net of asset dispositions	10,985	3,995
Operating taxes and licenses	7,513	7,142
Communication and utilities	4,819	4,497
Total operating expenses	1,166,548	1,049,325
Operating income	125,039	116,597
Net interest expense	6,256	6,987
Earnings before income taxes	118,783	109,610
Income taxes	45,434	41,926
Net earnings	$ 73,349	$ 67,684
Weighted average basic shares outstanding (in Shares)	117,553	117,017
Basic earnings per share (in Dollars per share)	$ 0.62	$ 0.58
Weighted average diluted shares outstanding (in Shares)	119,825	119,750
Diluted earnings per share (in Dollars per share)	$ 0.61	$ 0.57
Dividends declared per common share (in Dollars per share)		$ 0.14