Consolidated Statements of Earnings (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Operating revenues, excluding fuel surcharge revenues	$ 4,058,165	$ 3,677,679	$ 3,277,218
Fuel surcharge revenues	996,815	849,163	516,267
Total operating revenues	5,054,980	4,526,842	3,793,485
Operating expenses:
Rents and purchased transportation	2,485,635	2,122,811	1,711,204
Salaries, wages and employee benefits	1,037,526	1,001,953	911,028
Fuel and fuel taxes	465,874	463,597	343,700
Depreciation and amortization	229,166	213,943	197,062
Operating supplies and expenses	178,610	160,425	152,500
Insurance and claims	53,832	44,929	48,280
General and administrative expenses, net of asset dispositions	27,231	28,900	37,017
Operating taxes and licenses	29,461	27,871	26,895
Communication and utilities	17,445	18,180	18,174
Total operating expenses	4,524,780	4,082,609	3,445,860
Operating income	530,200	444,233	347,625
Interest income	1	8	75
Interest expense	25,560	28,508	28,006
Earnings before income taxes	504,641	415,733	319,694
Income taxes	194,287	158,727	120,077
Net earnings	$ 310,354	$ 257,006	$ 199,617
Weighted average basic shares outstanding (in Shares)	117,572	119,158	124,712
Basic earnings per share (in Dollars per share)	$ 2.64	$ 2.16	$ 1.60
Weighted average diluted shares outstanding (in Shares)	120,022	121,922	127,767
Diluted earnings per share (in Dollars per share)	$ 2.59	$ 2.11	$ 1.56
Dividends declared per common share (in Dollars per share)	$ 0.71	$ 0.52	$ 0.48