Summary of Unaudited Results of Operations for Each Quarter (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended									12 Months Ended
	Dec. 31, 2012		Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Total revenues:
Transportation	$ 2,585,930	[1]	$ 2,445,883	$ 2,476,805	$ 2,176,797	$ 2,200,258	$ 2,280,208	$ 2,269,036	$ 1,991,022	$ 9,685,415	$ 8,740,524	$ 7,575,659
Sourcing	379,479	[1]	418,377	462,597	359,730	352,744	399,220	423,536	360,028	1,620,183	1,535,528	1,643,174
Payment Services	5,467	[1]	16,149	16,312	15,587	15,282	15,500	15,090	14,422	53,515	60,294	55,472
Total revenues	2,970,876	[1]	2,880,409	2,955,714	2,552,114	2,568,284	2,694,928	2,707,662	2,365,472	11,359,113	10,336,346	9,274,305
Costs and expenses:
Purchased transportation and related services	2,176,789	[1]	2,063,109	2,107,799	1,809,581	1,841,586	1,905,731	1,901,189	1,648,102	8,157,278	7,296,608	6,302,530
Purchased products sourced for resale	348,936	[1]	384,630	422,392	327,787	325,313	366,131	388,607	327,029	1,483,745	1,407,080	1,503,797
Purchased payment services	519	[1]	0	0	0					519	0	0
Personnel expenses	226,042	[1]	179,342	177,184	183,438	164,062	178,117	178,945	175,109	766,006	696,233	632,064
Other selling, general, and administrative expenses	84,986	[1]	66,071	63,425	61,763	65,368	60,984	58,826	58,517	276,245	243,695	213,054
Total costs and expenses	2,837,272	[1]	2,693,152	2,770,800	2,382,569	2,396,329	2,510,963	2,527,567	2,208,757	10,683,793	9,643,616	8,651,445
Income from operations	133,604	[1]	187,257	184,914	169,545	171,955	183,965	180,095	156,715	675,320	692,730	622,860
Net income	$ 256,392	[1]	$ 116,330	$ 114,582	$ 106,500	$ 109,214	$ 114,347	$ 111,023	$ 97,028	$ 593,804	$ 431,612	$ 387,026
Basic net income per share (in dollars per share)	$ 1.59	[1]	$ 0.72	$ 0.71	$ 0.65	$ 0.67	$ 0.70	$ 0.67	$ 0.59	$ 3.68	$ 2.63	$ 2.35
Diluted net income per share (in dollars per share)	$ 1.58	[1]	$ 0.72	$ 0.71	$ 0.65	$ 0.67	$ 0.70	$ 0.67	$ 0.59	$ 3.67	$ 2.62	$ 2.33
Basic weighted average shares outstanding	160,880	[1]	160,782	161,887	162,693	162,919	163,948	164,607	165,124	161,557	164,114	164,909
Dilutive effect of outstanding stock awards	919	[1]	221	313	330	906	523	587	640	389	627	1,063
Diluted weighted average shares outstanding	161,799	[1]	161,003	162,200	163,023	163,825	164,471	165,194	165,764	161,946	164,741	165,972
Market price range of common stock:
High (in dollars per share)	$ 64.14	[1]	$ 61.97	$ 67.31	$ 71.76	$ 76.76	$ 82.61	$ 81.53	$ 82.05
Low (in dollars per share)	$ 57.16	[1]	$ 50.81	$ 55.35	$ 62.84	$ 63.21	$ 62.30	$ 73.30	$ 70.32

[1] The quarter ended December 31, 2012 is not comparable to the previous periods shown in this footnote due to certain significant charges or credits related to our recent acquisitions and divestitures.