Condensed Statements Of Operations (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Income Statement [Abstract]
Revenue from operations	$ 743,586	$ 616,458	$ 2,066,849	$ 1,745,178
Operating expenses:
Salaries, wages and benefits	363,420	303,853	1,014,910	862,614
Operating supplies and expenses	111,670	96,792	327,881	287,610
General supplies and expenses	21,931	18,311	61,955	53,711
Operating taxes and licenses	21,338	18,155	61,006	53,406
Insurance and claims	10,118	8,395	27,927	23,267
Communications and utilities	6,320	5,726	19,156	17,215
Depreciation and amortization	37,707	32,914	106,920	93,265
Purchased transportation	34,590	28,500	96,883	78,860
Building and office equipment rents	2,880	2,849	7,899	9,136
Miscellaneous expenses, net	7,350	2,887	13,303	4,501
Total operating expenses	617,324	518,382	1,737,840	1,483,585
Operating income	126,262	98,076	329,009	261,593
Non-operating expense (income):
Interest expense	1,463	2,479	5,161	7,282
Interest income	(19)	(45)	(78)	(101)
Other expense (income), net	951	389	1,761	797
Total non-operating expense	2,395	2,823	6,844	7,978
Income before income taxes	123,867	95,253	322,165	253,615
Provision for income taxes	45,958	35,104	124,520	94,658
Net income	$ 77,909	$ 60,149	$ 197,645	$ 158,957
Earnings per share:
Basic	$ 0.90	$ 0.70	$ 2.29	$ 1.84
Diluted	$ 0.90	$ 0.70	$ 2.29	$ 1.84
Weighted average shares outstanding:
Basic	86,164,917	86,164,917	86,164,917	86,164,917
Diluted	86,164,917	86,164,917	86,164,917	86,164,917