Summary of Stock Option Activity (Detail)	12 Months Ended
	Dec. 31, 2016 $ / shares shares
Shares Subject to Outstanding Stock Options
Ending balance | shares	5,817,116
Weighted-Average Exercise Price Per Share
Ending balance | $ / shares	$ 25.26
Employee Stock Option
Shares Subject to Outstanding Stock Options
Beginning balance | shares	4,731,483
Options granted | shares	1,649,836
Options exercised | shares	(54,045)
Options canceled | shares	(510,158)
Ending balance | shares	5,817,116
Weighted-Average Exercise Price Per Share
Beginning balance | $ / shares	$ 24.19
Options granted | $ / shares	29.03
Options exercised | $ / shares	7.42
Options canceled | $ / shares	29.45
Ending balance | $ / shares	$ 25.26