Revenue from International Customers by Geographic Areas (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 105,056	$ 103,518	$ 216,223	$ 205,878
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	61,239	59,411	116,931	111,323
Geographic revenue percentage	58.00%	57.00%	54.00%	54.00%
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	18,329	22,738	36,467	42,633
Geographic revenue percentage	18.00%	22.00%	17.00%	21.00%
Europe, Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	12,686	10,956	27,244	31,453
Geographic revenue percentage	12.00%	11.00%	13.00%	15.00%
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 12,802	$ 10,413	$ 35,581	$ 20,469
Geographic revenue percentage	12.00%	10.00%	16.00%	10.00%