Quarterly Results (Unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017		Dec. 31, 2016		Dec. 31, 2015
Selected Quarterly Financial Information [Abstract]
Revenues	$ 1,901,371	$ 1,802,166	$ 1,672,279	$ 1,545,132	$ 1,642,007	$ 1,562,394	$ 1,475,164	$ 1,418,472	$ 6,920,948		$ 6,098,037		$ 6,616,632
Net revenues	628,809	599,142	563,633	527,605	548,591	545,259	553,117	517,069	2,319,189	[1]	2,164,036	[1]	2,187,777	[1]
Net earnings	167,455	120,606	108,755	93,567	111,098	107,949	116,439	97,047	490,383		432,533		459,497
Net earnings attributable to shareholders	$ 166,967	$ 120,263	$ 108,851	$ 93,264	$ 110,590	$ 107,581	$ 116,052	$ 96,584	$ 489,345		$ 430,807		$ 457,223
Diluted earnings attributable to shareholders per share	$ 0.92	$ 0.66	$ 0.60	$ 0.51	$ 0.61	$ 0.59	$ 0.63	$ 0.53	$ 2.69		$ 2.36		$ 2.40
Basic earnings attributable to shareholders per share	$ 0.94	$ 0.67	$ 0.60	$ 0.52	$ 0.61	$ 0.59	$ 0.64	$ 0.53	$ 2.73		$ 2.38		$ 2.42

[1] Net revenues are a non-GAAP measure calculated as revenues less directly related operating expenses attributable to the Company's principal services. The Company's management believes that net revenues are a better measure than total revenues when evaluating the Company's operating segment performance since total revenues earned as a freight consolidator include the carriers' charges for carrying the shipment, whereas revenues earned in other capacities include primarily the commissions and fees earned by the Company. Net revenue is one of the Company's primary operational and financial measures and demonstrates the Company's ability to concentrate and leverage purchasing power through effective consolidation of shipments from customers utilizing a variety of transportation carriers and optimal routings.