Revenue from International Clients by Geographic Areas (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 137,631	$ 122,011	$ 421,080	$ 355,572
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	77,792	59,034	230,220	189,489
Geographic revenue percentage	57.00%	49.00%	55.00%	53.00%
Other Americas
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	12,195	4,208	21,499	14,419
Geographic revenue percentage	9.00%	3.00%	5.00%	4.00%
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	19,098	22,115	72,655	58,782
Geographic revenue percentage	14.00%	18.00%	17.00%	17.00%
Other EMEA
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	15,910	24,910	66,218	66,538
Geographic revenue percentage	11.00%	20.00%	16.00%	19.00%
Asia Pacific
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 12,636	$ 11,744	$ 30,488	$ 26,344
Geographic revenue percentage	9.00%	10.00%	7.00%	7.00%