Stock Based Compensation - Summary of PSO Activities (Detail) - Performance Stock Options (PSOs) - 2013 Equity Incentive Plan	3 Months Ended
	Mar. 31, 2020 $ / shares shares
Shares Subject to Outstanding PSOs
Beginning balance (in shares) | shares	552,010
Options granted (in shares) | shares	575,625
Options exercised (in shares) | shares	(2,293)
Options canceled (in shares) | shares	(430,799)
Ending balance (in shares) | shares	694,543
Weighted-Average Exercise Price Per Share
Beginning balance (in dollars per share) | $ / shares	$ 31.43
Options granted (in dollars per share) | $ / shares	12.79
Options exercised (in dollars per share) | $ / shares	23.76
Options canceled (in dollars per share) | $ / shares	33.29
Ending balance (in dollars per share) | $ / shares	$ 14.85