Summary of Stock Option Activity (Detail) - Employee Stock Option	9 Months Ended
	Sep. 30, 2016 $ / shares shares
Shares Subject to Outstanding Stock Options
Beginning balance | shares	4,731,483
Options granted | shares	1,586,286
Options exercised | shares	(53,255)
Options canceled | shares	(376,365)
Ending balance | shares	5,888,149
Weighted-Average Exercise Price Per Share
Beginning balance | $ / shares	$ 24.19
Options granted | $ / shares	29.37
Options exercised | $ / shares	7.34
Options canceled | $ / shares	29.66
Ending balance | $ / shares	$ 25.39