Summary of Stock Option Activity (Detail) - Employee Stock Option - 2013 Equity Incentive Plan and Inducement Plan	3 Months Ended
	Mar. 31, 2019 $ / shares shares
Shares Subject to Outstanding Stock Options
Beginning balance | shares	7,507,690
Options granted | shares	1,557,406
Options exercised | shares	(424,589)
Options canceled | shares	(309,175)
Ending balance | shares	8,331,332
Weighted-Average Exercise Price Per Share
Beginning balance | $ / shares	$ 33.25
Options granted | $ / shares	27.53
Options exercised | $ / shares	17.84
Options canceled | $ / shares	38.31
Ending balance | $ / shares	$ 32.78