Summary of Stock Option Activity (Detail) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Stock Option Shares
Grants outstanding at beginning of the period	4,190,367	2,522,522
Granted	1,185,265	242,320
Exercised	(48,579)	(64,390)
Canceled or expired	(53,715)	(5,774)
Grants outstanding at end of the period	5,273,338	2,694,678
Grants exercisable at end of the period	1,180,245	656,805
Weighted Average Exercise Price
Grants outstanding at Beginning of the period	$ 23.46	$ 11.76
Granted	$ 26.83	$ 28.76
Exercised	$ 10.39	$ 8.97
Canceled or expired	$ 30.26	$ 14.83
Grants outstanding at end of the period	$ 24.27	$ 13.35
Grants exercisable at end of the period	$ 12.85	$ 12.36