Business Segment Information - Financial Information Regarding Company's Operations by Geographic Area (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		$ 2,020,051	$ 1,854,262
Net revenues	[1]	654,114	635,838
Operating income		187,601	192,818
Identifiable assets at period end		3,642,912	3,212,481	$ 3,314,559
Capital expenditures		9,435	13,796
Depreciation and amortization		13,393	13,922
Equity		2,125,434	1,982,266	$ 1,987,720	$ 1,994,373
United States Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		681,424	534,869
Other North America Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		85,103	76,525
Latin America Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		35,949	32,722
North Asia Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		617,000	630,572
South Asia Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		171,930	168,600
Europe Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		320,049	305,792
Middle East Africa And India Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		108,596	105,182
Geography Eliminations | United States Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		(21,640)	28,881
Geography Eliminations | Other North America Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		6,307	3,562
Geography Eliminations | Latin America Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		(1,770)	3,387
Geography Eliminations | North Asia Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		15,853	6,017
Geography Eliminations | South Asia Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		5,249	6,550
Geography Eliminations | Europe Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		(7,359)	14,188
Geography Eliminations | Middle East Africa And India Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		4,079	5,355
Operating Segments | United States Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		659,784	563,750
Net revenues	[1]	292,429	277,185
Operating income		74,013	69,648
Identifiable assets at period end		1,906,278	1,558,181
Capital expenditures		6,915	3,171
Depreciation and amortization		8,222	8,765
Equity		1,401,450	1,247,522
Operating Segments | Other North America Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		91,410	80,087
Net revenues	[1]	35,169	30,447
Operating income		10,960	9,018
Identifiable assets at period end		175,034	165,368
Capital expenditures		228	1,528
Depreciation and amortization		467	398
Equity		82,170	68,050
Operating Segments | Latin America Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		34,179	36,109
Net revenues	[1]	15,063	14,745
Operating income		2,636	2,370
Identifiable assets at period end		71,168	55,036
Capital expenditures		93	505
Depreciation and amortization		432	368
Equity		28,581	27,226
Operating Segments | North Asia Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		632,853	636,589
Net revenues	[1]	134,207	137,208
Operating income		65,780	69,923
Identifiable assets at period end		511,589	542,965
Capital expenditures		344	784
Depreciation and amortization		1,407	1,376
Equity		238,518	278,651
Operating Segments | South Asia Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		177,179	175,150
Net revenues	[1]	47,369	44,406
Operating income		15,907	15,132
Identifiable assets at period end		174,512	153,411
Capital expenditures		176	329
Depreciation and amortization		536	583
Equity		114,290	105,642
Operating Segments | Europe Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		312,690	319,980
Net revenues	[1]	96,795	98,635
Operating income		13,952	19,278
Identifiable assets at period end		579,924	533,012
Capital expenditures		982	7,191
Depreciation and amortization		1,831	1,976
Equity		165,718	160,038
Operating Segments | Middle East Africa And India Segment
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		112,675	110,537
Net revenues	[1]	33,172	33,201
Operating income		4,361	7,438
Identifiable assets at period end		234,195	208,173
Capital expenditures		697	288
Depreciation and amortization		498	456
Equity		126,953	128,487
Intersegment Eliminations
Segment Reporting Information [Line Items]
Revenue from Contract with Customer, Excluding Assessed Tax		(719)	(67,940)
Net revenues	[1]	(90)	11
Operating income		(8)	11
Identifiable assets at period end		(9,788)	(3,665)
Equity		$ (32,246)	$ (33,350)

[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.