Condensed Statements Of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Income Statement [Abstract]
Revenue from operations	$ 532,575	$ 497,140
Operating expenses:
Salaries, wages and benefits	270,800	257,989
Operating supplies and expenses	95,703	94,216
General supplies and expenses	17,761	14,152
Operating taxes and licenses	17,269	16,356
Insurance and claims	7,270	7,683
Communications and utilities	5,721	4,854
Depreciation and amortization	29,834	25,544
Purchased transportation	17,498	16,231
Building and office equipment rents	3,178	3,268
Miscellaneous expenses, net	1,597	2,629
Total operating expenses	466,631	442,922
Operating income	65,944	54,218
Non-operating expense (income):
Interest expense	2,400	3,219
Interest income	(14)	(52)
Other expense (income), net	74	(346)
Total non-operating expense	2,460	2,821
Income before income taxes	63,484	51,397
Provision for income taxes	22,931	20,302
Net income	$ 40,553	$ 31,095
Earnings per share:
Basic	$ 0.47	$ 0.36
Diluted	$ 0.47	$ 0.36
Weighted average shares outstanding:
Basic	86,164,917	86,164,986
Diluted	86,164,917	86,164,986