Stock Based Compensation - Summary of PSO Activities (Detail) - Performance Stock Options (PSOs) - 2013 Equity Incentive Plan	9 Months Ended
	Sep. 30, 2019 $ / shares shares
Shares Subject to Outstanding PSOs
Beginning balance (in shares) | shares	143,335
Options granted (in shares) | shares	490,986
Options exercised (in shares) | shares	(31,667)
Options canceled (in shares) | shares	(24,187)
Ending balance (in shares) | shares	578,467
Weighted-Average Exercise Price Per Share
Beginning balance (in dollars per share) | $ / shares	$ 23.76
Options granted (in dollars per share) | $ / shares	33.29
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	$ 31.45