Business Segment Information - Financial Information Regarding Company's Operations by Geographic Area (Detail) - USD ($) $ in Thousands		3 Months Ended				9 Months Ended
		Sep. 30, 2017		Sep. 30, 2016		Sep. 30, 2017		Sep. 30, 2016	Dec. 31, 2016	Dec. 31, 2015
Segment Reporting Information [Line Items]
Total revenues		$ 1,802,166		$ 1,562,394		$ 5,019,577		$ 4,456,030
Net revenues	[1]	599,142		545,259		1,690,380		1,615,445
Operating income		186,895		167,263		501,249		497,953
Identifiable assets at period end		3,068,881		2,794,224		3,068,881		2,794,224	$ 2,790,871
Capital expenditures		34,462		12,659		67,603		39,973
Depreciation and amortization		12,272		11,882		36,241		34,853
Equity		1,981,081		1,853,933		1,981,081		1,853,933	$ 1,847,213	$ 1,694,676
United States Segment
Segment Reporting Information [Line Items]
Total revenues		476,575		423,362		1,354,811		1,248,923
Other North America Segment
Segment Reporting Information [Line Items]
Total revenues		65,544		56,747		187,997		165,527
Latin America Segment
Segment Reporting Information [Line Items]
Total revenues		24,181		21,592		69,747		62,825
North Asia Segment
Segment Reporting Information [Line Items]
Total revenues		686,915		590,622		1,873,393		1,605,343
South Asia Segment
Segment Reporting Information [Line Items]
Total revenues		170,225		154,156		475,163		442,464
Europe Segment
Segment Reporting Information [Line Items]
Total revenues		273,606		228,256		764,596		680,035
Middle East Africa And India Segment
Segment Reporting Information [Line Items]
Total revenues		105,120		87,659		293,870		250,913
Geography Eliminations | United States Segment
Segment Reporting Information [Line Items]
Total revenues		26,888		24,610		79,356		79,617
Geography Eliminations | Other North America Segment
Segment Reporting Information [Line Items]
Total revenues		2,782		2,770		8,246		8,141
Geography Eliminations | Latin America Segment
Segment Reporting Information [Line Items]
Total revenues		3,679		3,724		11,073		11,512
Geography Eliminations | North Asia Segment
Segment Reporting Information [Line Items]
Total revenues		5,253		5,368		15,139		15,849
Geography Eliminations | South Asia Segment
Segment Reporting Information [Line Items]
Total revenues		5,681		6,206		16,520		18,338
Geography Eliminations | Europe Segment
Segment Reporting Information [Line Items]
Total revenues		10,302		9,938		29,288		30,396
Geography Eliminations | Middle East Africa And India Segment
Segment Reporting Information [Line Items]
Total revenues		5,318		5,551		15,316		16,452
Operating Segments | United States Segment
Segment Reporting Information [Line Items]
Total revenues		503,463		447,972		1,434,167		1,328,540
Net revenues	[1]	257,030		229,773		737,842		683,331
Operating income		74,645		69,457		191,256		184,876
Identifiable assets at period end		1,636,293		1,410,287		1,636,293		1,410,287
Capital expenditures		7,398		8,319		19,492		25,234
Depreciation and amortization		7,905		7,566		23,389		22,264
Equity		1,345,266		1,145,293		1,345,266		1,145,293
Operating Segments | Other North America Segment
Segment Reporting Information [Line Items]
Total revenues		68,326		59,517		196,243		173,668
Net revenues	[1]	30,664		30,211		84,630		88,404
Operating income		9,215		6,200		26,583		23,091
Identifiable assets at period end		100,651		95,390		100,651		95,390
Capital expenditures		263		720		1,066		1,476
Depreciation and amortization		405		369		1,163		1,113
Equity		52,212		41,542		52,212		41,542
Operating Segments | Latin America Segment
Segment Reporting Information [Line Items]
Total revenues		27,860		25,316		80,820		74,337
Net revenues	[1]	14,710		14,063		43,634		42,264
Operating income		2,652		3,328		8,349		11,016
Identifiable assets at period end		52,238		56,192		52,238		56,192
Capital expenditures		2,436		139		3,648		941
Depreciation and amortization		310		328		930		869
Equity		25,709		37,765		25,709		37,765
Operating Segments | North Asia Segment
Segment Reporting Information [Line Items]
Total revenues		692,168		595,990		1,888,532		1,621,192
Net revenues	[1]	138,667		124,251		371,459		357,159
Operating income		72,070		59,682		183,515		176,621
Identifiable assets at period end		446,826		480,587		446,826		480,587
Capital expenditures		589		739		2,492		2,502
Depreciation and amortization		1,313		1,404		3,995		4,111
Equity		231,831		293,383		231,831		293,383
Operating Segments | South Asia Segment
Segment Reporting Information [Line Items]
Total revenues		175,906		160,362		491,683		460,802
Net revenues	[1]	41,411		42,711		117,634		128,486
Operating income		11,697		14,045		37,434		48,090
Identifiable assets at period end		143,893		117,333		143,893		117,333
Capital expenditures		390		319		1,172		1,325
Depreciation and amortization		569		594		1,656		1,649
Equity		102,477		87,926		102,477		87,926
Operating Segments | Europe Segment
Segment Reporting Information [Line Items]
Total revenues		283,908		238,194		793,884		710,431
Net revenues	[1]	85,390		74,888		242,244		227,068
Operating income		11,124		7,018		36,189		31,109
Identifiable assets at period end		473,509		388,543		473,509		388,543
Capital expenditures		23,138		2,127		38,717		6,386
Depreciation and amortization		1,309		1,116		3,707		3,402
Equity		139,688		129,989		139,688		129,989
Operating Segments | Middle East Africa And India Segment
Segment Reporting Information [Line Items]
Total revenues		110,438		93,210		309,186		267,365
Net revenues	[1]	29,956		29,363		89,973		88,745
Operating income		5,495		7,534		17,928		23,162
Identifiable assets at period end		212,210		237,104		212,210		237,104
Capital expenditures		248		296		1,016		2,109
Depreciation and amortization		461		505		1,401		1,445
Equity		119,649		150,395		119,649		150,395
Intersegment Eliminations
Segment Reporting Information [Line Items]
Total revenues		(59,903)		(58,167)		(174,938)		(180,305)
Net revenues		1,314	[1]	(1)	[1]	2,964	[1]	(12)
Operating income		(3)		(1)		(5)		(12)
Identifiable assets at period end		3,261		8,788		3,261		8,788
Equity		$ (35,751)		$ (32,360)		$ (35,751)		$ (32,360)

[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.