Income Taxes - Summary of Components of Deferred Tax Assets and Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Deferred Tax Assets, Gross [Abstract]
Allowance for doubtful accounts	$ 11,279	$ 17,220
Accrued vacation and bonus	23,896	38,596
Deferred rent	8,491	12,034
Share-based compensation	15,108	24,783
Notes receivable from employees	12,879	21,010
State net operating loss carryforward and credits	3,586	4,169
Foreign net operating loss carryforward	12,075	12,437
Future foreign tax credit asset and foreign tax credit carryforward	7,403	2,545
Deferred compensation	2,688	3,084
Other, net	7,159	5,284
Total deferred tax assets	104,564	141,162
Deferred tax liabilities
Revenue recognition	(7,227)	(11,590)
Property, equipment and capitalized software	(2,308)	(6,527)
Goodwill and other intangible asset amortization	(190,638)	(273,990)
Total deferred tax liabilities	(200,173)	(292,107)
Foreign withholding tax	(1,035)	0
Valuation allowance	(21,621)	(18,900)
Net deferred tax liabilities	$ (118,265)	$ (169,845)