Quarterly Results (Unaudited) (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Selected Quarterly Financial Information [Abstract]
Revenues	$ 2,235,597	$ 2,090,947	$ 1,957,559	$ 1,854,262	$ 1,901,371	$ 1,802,166	$ 1,672,279	$ 1,545,132	$ 8,138,365		$ 6,920,948		$ 6,098,037
Net revenues	680,675	661,314	642,546	635,838	628,809	599,142	563,633	527,605	2,620,373	[1]	2,319,189	[1]	2,164,036	[1]
Net earnings	179,577	163,067	140,946	136,200	167,455	120,606	108,755	93,567	619,790		490,383		432,533
Net earnings attributable to shareholders	$ 179,210	$ 162,692	$ 140,605	$ 135,692	$ 166,967	$ 120,263	$ 108,851	$ 93,264	$ 618,199		$ 489,345		$ 430,807
Diluted earnings attributable to shareholders per share	$ 1.02	$ 0.92	$ 0.79	$ 0.76	$ 0.92	$ 0.66	$ 0.60	$ 0.51	$ 3.48		$ 2.69		$ 2.36
Basic earnings attributable to shareholders per share	$ 1.04	$ 0.94	$ 0.80	$ 0.77	$ 0.94	$ 0.67	$ 0.60	$ 0.52	$ 3.55		$ 2.73		$ 2.38

[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.