Business Segment Information - Financial Information Regarding Company's Operations by Geographic Area (Detail) - USD ($) $ 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		Dec. 31, 2015
Segment Reporting Information [Line Items]
Total 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]
Operating income										796,563		700,260		670,163
Identifiable assets at year end		3,314,559				3,117,008				3,314,559		3,117,008		2,790,871
Capital expenditures										47,474		95,016		59,316
Depreciation and amortization										54,019		49,310		46,796
Equity		1,987,720				1,994,373				1,987,720		1,994,373		1,847,213		$ 1,694,676
United States Segment
Segment Reporting Information [Line Items]
Total revenues										2,336,681		1,851,395		1,683,006
Other North America Segment
Segment Reporting Information [Line Items]
Total revenues										340,122		256,359		226,561
Latin America Segment
Segment Reporting Information [Line Items]
Total revenues										141,196		97,096		84,665
North Asia Segment
Segment Reporting Information [Line Items]
Total revenues										2,860,876		2,576,971		2,242,670
South Asia Segment
Segment Reporting Information [Line Items]
Total revenues										748,858		661,878		603,980
Europe Segment
Segment Reporting Information [Line Items]
Total revenues										1,268,757		1,072,028		918,561
Middle East Africa And India Segment
Segment Reporting Information [Line Items]
Total revenues										441,875		405,221		338,594
Geography Eliminations | United States Segment
Segment Reporting Information [Line Items]
Total revenues										(143,131)		(111,163)		(106,076)
Geography Eliminations | Other North America Segment
Segment Reporting Information [Line Items]
Total revenues										(15,680)		(11,827)		(10,778)
Geography Eliminations | Latin America Segment
Segment Reporting Information [Line Items]
Total revenues										(15,658)		(14,766)		(15,037)
Geography Eliminations | North Asia Segment
Segment Reporting Information [Line Items]
Total revenues										(25,446)		(21,405)		(21,212)
Geography Eliminations | South Asia Segment
Segment Reporting Information [Line Items]
Total revenues										(29,005)		(22,999)		(24,251)
Geography Eliminations | Europe Segment
Segment Reporting Information [Line Items]
Total revenues										(61,608)		(43,296)		(41,102)
Geography Eliminations | Middle East Africa And India Segment
Segment Reporting Information [Line Items]
Total revenues										(22,196)		(20,848)		(21,876)
Operating Segments | United States Segment
Segment Reporting Information [Line Items]
Total revenues										2,479,812		1,962,558		1,789,082
Net revenues	[1]									1,126,888		1,008,841		918,110
Operating income										310,071		277,821		250,715
Identifiable assets at year end		1,689,950				1,595,140				1,689,950		1,595,140		1,455,722
Capital expenditures										21,732		28,212		39,531
Depreciation and amortization										33,511		32,017		29,939
Equity		1,339,673				1,337,568				1,339,673		1,337,568		1,166,582
Operating Segments | Other North America Segment
Segment Reporting Information [Line Items]
Total revenues										355,802		268,186		237,339
Net revenues	[1]									139,049		119,071		119,492
Operating income										44,099		38,131		32,530
Identifiable assets at year end		161,604				151,181				161,604		151,181		104,804
Capital expenditures										4,259		1,563		1,727
Depreciation and amortization										1,847		1,546		1,479
Equity		72,941				60,705				72,941		60,705		46,448
Operating Segments | Latin America Segment
Segment Reporting Information [Line Items]
Total revenues										156,854		111,862		99,702
Net revenues	[1]									62,813		58,199		56,066
Operating income										8,843		9,964		13,321
Identifiable assets at year end		53,542				55,431				53,542		55,431		49,231
Capital expenditures										1,042		4,612		1,038
Depreciation and amortization										1,508		1,277		1,187
Equity		26,007				26,546				26,007		26,546		27,164
Operating Segments | North Asia Segment
Segment Reporting Information [Line Items]
Total revenues										2,886,322		2,598,376		2,263,882
Net revenues	[1]									570,496		509,235		471,275
Operating income										281,481		248,422		230,777
Identifiable assets at year end		533,071				458,152				533,071		458,152		511,851
Capital expenditures										3,057		3,756		3,889
Depreciation and amortization										5,309		5,326		5,455
Equity		200,371				240,721				200,371		240,721		327,672
Operating Segments | South Asia Segment
Segment Reporting Information [Line Items]
Total revenues										777,863		684,877		628,231
Net revenues	[1]									185,938		163,450		171,033
Operating income										60,882		53,057		64,967
Identifiable assets at year end		152,646				137,279				152,646		137,279		120,300
Capital expenditures										2,182		1,688		3,038
Depreciation and amortization										2,257		2,215		2,177
Equity		100,706				94,516				100,706		94,516		91,983
Operating Segments | Europe Segment
Segment Reporting Information [Line Items]
Total revenues										1,330,365		1,115,324		959,663
Net revenues	[1]									403,416		335,702		304,429
Operating income										65,446		48,491		42,195
Identifiable assets at year end		513,744				501,711				513,744		501,711		351,960
Capital expenditures										10,815		53,954		7,554
Depreciation and amortization										7,727		5,068		4,576
Equity		157,003				142,971				157,003		142,971		108,430
Operating Segments | Middle East Africa And India Segment
Segment Reporting Information [Line Items]
Total revenues										464,071		426,069		360,470
Net revenues	[1]									133,862		121,267		123,335
Operating income										25,731		24,365		35,672
Identifiable assets at year end		206,367				215,495				206,367		215,495		190,902
Capital expenditures										4,387		1,231		2,539
Depreciation and amortization										1,860		1,861		1,983
Equity		123,228				123,600				123,228		123,600		112,633
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenues										(312,724)		(246,304)		(240,332)
Net revenues	[1]									(2,089)		3,424		296
Operating income										10		9		(14)
Identifiable assets at year end		3,635				2,619				3,635		2,619		6,101
Equity		$ (32,209)				$ (32,254)				$ (32,209)		$ (32,254)		$ (33,699)

[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.