Revenue from International Customers by Geographic Areas (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 143,830	$ 101,657	$ 105,056	$ 111,167	$ 115,294	$ 95,503	$ 103,518	$ 102,360	$ 461,710	$ 416,675	$ 336,599
Geographic revenue percentage									100.00%	100.00%	100.00%
U.S.
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue									250,022	216,365	199,863
Geographic revenue percentage									54.00%	52.00%	59.00%
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue									87,135	94,338	59,571
Geographic revenue percentage									19.00%	23.00%	18.00%
Europe, Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue									69,898	70,990	47,050
Geographic revenue percentage									15.00%	17.00%	14.00%
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue									$ 54,655	$ 34,982	$ 30,115
Geographic revenue percentage									12.00%	8.00%	9.00%