Revenue from International Clients by Geographic Areas (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 122,011	$ 101,657	$ 355,572	$ 317,880
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	59,034	56,475	189,489	173,406
Geographic revenue percentage	49.00%	56.00%	53.00%	55.00%
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	22,115	18,862	58,782	55,329
Geographic revenue percentage	18.00%	18.00%	17.00%	17.00%
Europe, Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	24,748	12,836	66,012	45,051
Geographic revenue percentage	20.00%	13.00%	18.00%	14.00%
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 16,114	$ 13,484	$ 41,289	$ 44,094
Geographic revenue percentage	13.00%	13.00%	12.00%	14.00%