Segment and Geographic Information - Summary of Revenue by Geographic Area (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue	$ 212,669	$ 255,136	$ 246,937	$ 229,919	$ 169,393	$ 212,710	$ 197,148	$ 183,715	$ 944,661	$ 762,966	$ 637,063
United States [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue									462,920	386,211	348,066
United Kingdom [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue									119,041	110,213	99,646
All Other Countries [Member]
Revenues from External Customers and Long-Lived Assets [Line Items]
Total revenue									$ 362,700	$ 266,542	$ 189,351