Revenue from International Clients by Geographic Areas (Detail) - USD ($) $ in Thousands		3 Months Ended		6 Months Ended
		Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue		$ 197,980	$ 188,996	$ 421,227	$ 367,854
Geographic revenue percentage		100.00%	100.00%	100.00%	100.00%
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue		$ 118,447	$ 103,547	$ 256,056	$ 196,775
Geographic revenue percentage		60.00%	55.00%	60.00%	53.00%
Other Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue		$ 12,086	$ 15,983	$ 21,577	$ 41,542
Geographic revenue percentage		6.00%	8.00%	5.00%	12.00%
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue		$ 19,228	$ 31,336	$ 49,418	$ 55,691
Geographic revenue percentage		10.00%	17.00%	12.00%	15.00%
Other EMEA
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	[1]	$ 27,395	$ 22,391	$ 49,241	$ 43,658
Geographic revenue percentage	[1]	13.00%	12.00%	12.00%	12.00%
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue		$ 20,824	$ 15,739	$ 44,935	$ 30,188
Geographic revenue percentage		11.00%	8.00%	11.00%	8.00%

[1] Includes Europe, the Middle East and Africa, but excludes the United Kingdom.