Summary of Stock Option Activity (Detail) - Employee Stock Option - 2013 Equity Incentive Plan and Inducement Plan	3 Months Ended
	Mar. 31, 2018 $ / shares shares
Shares Subject to Outstanding Stock Options
Beginning balance | shares	6,514,538
Options granted | shares	1,144,976
Options exercised | shares	(185,664)
Options canceled | shares	(180,117)
Ending balance | shares	7,293,733
Weighted-Average Exercise Price Per Share
Beginning balance | $ / shares	$ 31.36
Options granted | $ / shares	47.83
Options exercised | $ / shares	22.30
Options canceled | $ / shares	37.37
Ending balance | $ / shares	$ 34.03