Segment Information - Reconciliation of Adjusted EBITDA to Net Income (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Segment Reporting [Abstract]
Adjusted EBITDA	$ 104,422	$ 107,059	$ 326,601	$ 288,169
Depreciation	(7,634)	(5,037)	(20,834)	(14,033)
Amortization of intangible assets	(1,443)	(1,310)	(4,182)	(4,909)
Stock-based compensation	(11,651)	(8,463)	(35,470)	(19,923)
Other expense, net	(71)	(1,439)	(8,154)	(10,619)
Provision for income taxes	(27,741)	(31,275)	(72,792)	(77,814)
Net income	$ 55,882	$ 59,535	$ 185,169	$ 160,871