Revenue from International Customers by Geographic Areas (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 117,315	$ 105,056	$ 233,561	$ 216,223
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	62,313	61,239	130,455	116,931
Geographic revenue percentage	53.00%	58.00%	56.00%	54.00%
United Kingdom
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	21,228	18,329	36,667	36,467
Geographic revenue percentage	18.00%	18.00%	16.00%	17.00%
Europe, Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	21,279	14,930	41,264	32,215
Geographic revenue percentage	18.00%	14.00%	17.00%	15.00%
Other
Revenues from External Customers and Long-Lived Assets [Line Items]
Geographic revenue	$ 12,495	$ 10,558	$ 25,175	$ 30,610
Geographic revenue percentage	11.00%	10.00%	11.00%	14.00%