Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Stock Option Shares
Grants outstanding at beginning of the period	5,216,203	4,190,367	2,522,522
Granted	2,830,078	1,694,560	2,283,719
Exercised	(816,696)	(86,007)	(241,056)
Canceled or expired	(713,609)	(582,717)	(371,818)
Grants outstanding at end of the period	6,515,976	5,216,203	4,190,367
Grants exercisable at end of the period	2,617,167	2,019,514	1,051,329
Grants vested and expected to vest at end of the period	5,908,213	4,462,100	3,467,069
Weighted Average Exercise Price
Grants outstanding at beginning of the period	$ 24.45	$ 23.46	$ 11.76
Granted	20.28	25.67	34.18
Exercised	12.26	11.40	11.31
Canceled or expired	26.78	22.79	16.83
Grants outstanding at end of the period	23.91	24.45	23.46
Grants exercisable at end of the period	23.85	18.69	11.91
Grants vested and expected to vest at end of the period	$ 23.94	$ 23.27	$ 21.50
Aggregate Intrinsic Value
Outstanding at end of year	$ 96,102
Exercisable at end of year	38,916
Vested and expected to vest	$ 87,029
Weighted Average Remaining Contractual Life (Years)
Outstanding at end of year	7 years 1 month 28 days
Exercisable at end of year	5 years 7 months 6 days
Vested and expected to vest	7 years 1 month 28 days