Summary of Stock Option Activity (Detail) - Employee Stock Option - 2013 and 2017 Equity Incentive Plan	9 Months Ended
	Sep. 30, 2017 $ / shares shares
Shares Subject to Outstanding Stock Options
Beginning balance | shares	5,817,116
Options granted | shares	1,813,300
Options exercised | shares	(1,008,791)
Options canceled | shares	(200,522)
Ending balance | shares	6,421,103
Weighted-Average Exercise Price Per Share
Beginning balance | $ / shares	$ 25.26
Options granted | $ / shares	38.68
Options exercised | $ / shares	15.37
Options canceled | $ / shares	35.48
Ending balance | $ / shares	$ 30.28