Segment Information - Schedule of Geographical Areas of Which Company Operates (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
Segment Reporting Information [Line Items]
Revenues	$ 237,099	$ 235,558	$ 156,121	$ 144,586	$ 143,903	$ 145,218	$ 141,246	$ 126,410	$ 773,364	$ 556,777	$ 448,746
United States [Member]
Segment Reporting Information [Line Items]
Revenues									677,873	556,777	448,746
United Kingdom [Member]
Segment Reporting Information [Line Items]
Revenues									$ 95,491