Stock Based Compensation - Summary of Stock Option Activity (Detail) - Employee Stock Option - 2013 Equity Incentive Plan and Inducement Plan	6 Months Ended
	Jun. 30, 2019 $ / shares shares
Shares Subject to Outstanding Stock Options
Beginning balance | shares	7,507,690
Options granted | shares	1,716,643
Options exercised | shares	(632,254)
Options canceled | shares	(678,423)
Ending balance | shares	7,913,656
Weighted-Average Exercise Price Per Share
Beginning balance | $ / shares	$ 33.25
Options granted | $ / shares	27.71
Options exercised | $ / shares	20.79
Options canceled | $ / shares	39.19
Ending balance | $ / shares	$ 32.54