Summary of Stock Option Activity (Detail) - Employee Stock Option - 2013 Equity Incentive Plan and Inducement Plan	9 Months Ended
	Sep. 30, 2018 $ / shares shares
Shares Subject to Outstanding Stock Options
Beginning balance | shares	6,514,538
Options granted | shares	1,636,628
Options exercised | shares	(516,276)
Options canceled | shares	(434,463)
Ending balance | shares	7,200,427
Weighted-Average Exercise Price Per Share
Beginning balance | $ / shares	$ 31.36
Options granted | $ / shares	44.03
Options exercised | $ / shares	21.48
Options canceled | $ / shares	41.35
Ending balance | $ / shares	$ 34.35