Revenue from International Clients by Geographic Areas (Detail) - USD ($) $ in Thousands		3 Months Ended												12 Months Ended
		Dec. 31, 2016	[1]	Sep. 30, 2016	[1]	Jun. 30, 2016	[1]	Mar. 31, 2016	[1]	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue		$ 199,610		$ 182,802		$ 188,996		$ 178,858		$ 204,355	$ 162,403	$ 162,019	$ 153,918	$ 750,266	$ 682,695	$ 590,004
Geographic revenue percentage														100.00%	100.00%	100.00%
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue														$ 430,562	$ 379,936	$ 327,154
Geographic revenue percentage														57.00%	56.00%	55.00%
Other Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue														$ 59,160	$ 57,892	$ 32,642
Geographic revenue percentage														8.00%	8.00%	6.00%
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue														$ 101,733	$ 96,314	$ 93,923
Geographic revenue percentage														14.00%	14.00%	16.00%
Other EMEA
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	[2]													$ 92,540	$ 87,240	$ 87,050
Geographic revenue percentage	[2]													12.00%	13.00%	15.00%
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue														$ 66,271	$ 61,313	$ 49,235
Geographic revenue percentage														9.00%	9.00%	8.00%

[1] The Company elected to early adopt ASU 2016-09 in the fourth quarter of 2016, which requires, among other things, excess tax benefits to be recorded as a reduction of the provision for income taxes in the consolidated statement of operations, whereas they were previously recognized in equity. The Company is required to reflect any adoption adjustments as of January 1, 2016, the beginning of the annual period that includes the period of adoption. As such, certain information above includes the impact of the ASU 2016-09 adoption. See Note 2 "Significant Accounting Policies-New accounting pronouncements" for additional information related to this adoption.

[2] Includes Europe, the Middle East and Africa, but excludes the United Kingdom ("Other EMEA").