Stock-Based Compensation Expense - Summary of Stock Option Activity (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	6 Months Ended
	Jun. 30, 2013
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Outstanding, Shares	3,559
Granted, Shares	823
Exercised, Shares	(710)
Forfeited or expired, Shares	(122)
Outstanding, Shares	3,550
Exercisable, Shares	1,309
Options vested or expected to vest, Shares	3,139
Outstanding, Weighted-Average Exercise Price	$ 25.56
Granted, Weighted-Average Exercise Price	$ 42.12
Exercised, Weighted-Average Exercise Price	$ 22.88
Forfeited or expired, Weighted-Average Exercise Price	$ 32.53
Outstanding, Weighted-Average Exercise Price	$ 29.70
Exercisable, Weighted-Average Exercise Price	$ 23.03
Options vested or expected to vest, Weighted-Average Exercise Price	$ 28.93
Outstanding, Weighted-Average Remaining Contractual Term (in years)	7 years 4 months 24 days
Exercisable, Weighted-Average Remaining Contractual Term (in years)	5 years 9 months 18 days
Options vested or expected to vest, Weighted-Average Remaining Contractual Term (in years)	7 years 3 months 18 days
Outstanding, Aggregate Intrinsic Value	$ 55,132
Exercisable, Aggregate Intrinsic Value	29,075
Options vested or expected to vest, Aggregate Intrinsic Value	$ 51,172