Revenue from International Customers by Geographic Areas (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 101,657	$ 95,503	$ 317,880	$ 301,381
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	56,475	49,166	173,406	160,489
Geographic revenue percentage	56.00%	51.00%	55.00%	53.00%
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	18,862	17,822	55,329	60,455
Geographic revenue percentage	18.00%	19.00%	17.00%	20.00%
Europe, Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	12,836	19,515	45,051	52,884
Geographic revenue percentage	13.00%	21.00%	14.00%	18.00%
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 13,484	$ 9,000	$ 44,094	$ 27,553
Geographic revenue percentage	13.00%	9.00%	14.00%	9.00%