Summary of Stock Option Activity (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Stock Option Shares
Grants outstanding at beginning of the period	6,515,976	5,216,203	4,190,367
Granted	1,285,051	2,830,078	1,694,560
Exercised	(1,056,821)	(816,696)	(86,007)
Cancelled	(1,307,255)	(713,609)	(582,717)
Grants outstanding at end of the period	5,436,951	6,515,976	5,216,203
Grants exercisable at end of the period	2,942,624	2,617,167	2,019,514
Grants vested and expected to vest at end of the period	5,116,409	5,908,213	4,462,100
Weighted Average Exercise Price
Grants outstanding at beginning of the period	$ 23.91	$ 24.45	$ 23.46
Granted	14.89	20.28	25.67
Exercised	18.31	12.26	11.40
Cancelled	24.61	26.78	22.79
Grants outstanding at end of the period	22.70	23.91	24.45
Grants exercisable at end of the period	24.42	23.85	18.69
Grants vested and expected to vest at end of the period	$ 22.83	$ 23.94	$ 23.27
Aggregate Intrinsic Value
Outstanding at end of year	$ 38,660
Exercisable at end of year	17,483
Vested and expected to vest	$ 35,955
Weighted Average Remaining Contractual Life (Years)
Outstanding at end of year	7 years 4 months 28 days
Exercisable at end of year	6 years 5 months 12 days
Vested and expected to vest	7 years 3 months 29 days