Stock Based Compensation - Summary of Stock Option Activity (Detail) - Employee Stock Option - 2013 Equity Incentive Plan and Inducement Plan	9 Months Ended
	Sep. 30, 2019 $ / shares shares
Shares Subject to Outstanding Stock Options
Beginning balance (in shares) | shares	7,507,690
Options granted (in shares) | shares	1,962,744
Options exercised (in shares) | shares	(821,489)
Options canceled (in shares) | shares	(996,552)
Ending balance (in shares) | shares	7,652,393
Weighted-Average Exercise Price Per Share
Beginning balance (in dollars per share) | $ / shares	$ 33.25
Options granted (in dollars per share) | $ / shares	27.65
Options exercised (in dollars per share) | $ / shares	21.68
Options canceled (in dollars per share) | $ / shares	38.69
Ending balance (in dollars per share) | $ / shares	$ 32.35