Condensed Statements Of Operations (USD $) In Thousands, except Share data	3 Months Ended		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Condensed Statements Of Operations [Abstract]
Revenue from operations	$ 494,475	$ 395,981	$ 1,397,409	$ 1,082,026
Operating expenses:
Salaries, wages and benefits	247,157	213,380	708,031	590,441
Operating supplies and expenses	91,421	62,746	264,751	175,020
General supplies and expenses	12,648	11,136	37,415	31,151
Operating taxes and licenses	16,128	14,360	47,547	41,071
Insurance and claims	8,154	7,204	22,875	18,838
Communications and utilities	4,518	3,820	13,501	11,263
Depreciation and amortization	23,396	19,396	66,530	60,500
Purchased transportation	16,628	15,026	47,696	36,825
Building and office equipment rents	3,412	3,719	10,299	11,768
Miscellaneous expenses, net	2,819	1,810	8,004	5,379
Total operating expenses	426,281	352,597	1,226,649	982,256
Operating income	68,194	43,384	170,760	99,770
Non-operating expense (income):
Interest expense	3,397	2,964	10,737	9,663
Interest income	(3)	(37)	(36)	(142)
Other expense (income), net	1,678	(178)	622	924
Total non-operating expense	5,072	2,749	11,323	10,445
Income before income taxes	63,122	40,635	159,437	89,325
Provision for income taxes	24,491	16,254	59,850	35,730
Net income	$ 38,631	$ 24,381	$ 99,587	$ 53,595
Earnings per share:
Basic	$ 0.67	$ 0.44	$ 1.75	$ 0.96
Diluted	$ 0.67	$ 0.44	$ 1.75	$ 0.96
Weighted average shares outstanding:
Basic	57,443,324	55,926,984	57,047,539	55,927,003
Diluted	57,443,324	55,926,984	57,047,539	55,927,003