Revenue from International Clients by Geographic Areas (Detail) - USD ($) $ in Thousands		3 Months Ended
		Mar. 31, 2016	Mar. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue		$ 178,858	$ 153,918
Geographic revenue percentage		100.00%	100.00%
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue		$ 93,228	$ 90,164
Geographic revenue percentage		52.00%	59.00%
Other Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue		$ 25,559	$ 12,296
Geographic revenue percentage		14.00%	8.00%
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue		$ 24,355	$ 20,227
Geographic revenue percentage		14.00%	13.00%
Other EMEA
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	[1]	$ 21,267	$ 18,869
Geographic revenue percentage	[1]	12.00%	12.00%
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue		$ 14,449	$ 12,362
Geographic revenue percentage		8.00%	8.00%

[1] Includes Europe, other than the United Kingdom, the Middle East and Africa ("Other EMEA").