Summary of Stock Option Activity (Detail) - Employee Stock Option - 2013 and 2017 Equity Incentive Plan	12 Months Ended
	Dec. 31, 2018 $ / shares shares
Shares Subject to Outstanding Stock Options
Beginning balance | shares	6,514,538
Options granted | shares	2,452,738
Options exercised | shares	(699,974)
Options canceled | shares	(759,612)
Ending balance | shares	7,507,690
Weighted-Average Exercise Price Per Share
Beginning balance | $ / shares	$ 31.36
Options granted | $ / shares	36.36
Options exercised | $ / shares	16.92
Options canceled | $ / shares	42.12
Ending balance | $ / shares	$ 33.25