Stockholders' Equity - Summary of Stock Option Activity (Detail) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) $ / shares shares
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options outstanding at December 31, 2017, Number of Shares | shares	8,287,456
Options granted, Number of Shares | shares	3,115,078
Options exercised, Number of Shares | shares	(2,028,328)
Options canceled, Number of Shares | shares	(648,114)
Options outstanding at December 31, 2018, Number of Shares | shares	8,726,092
Options vested and expected to vest at December 31, 2018, Number of Shares | shares	8,726,092
Options exercisable at December 31, 2018, Number of Shares | shares	3,699,150
Options outstanding, Weighted-Average Exercise per Share Price, Beginning Balance | $ / shares	$ 7.77
Options granted, Weighted-Average Exercise per Share Price | $ / shares	17.78
Options exercised, Weighted-Average Exercise per Share Price | $ / shares	7.12
Options canceled, Weighted-Average Exercise per Share Price | $ / shares	11.15
Options outstanding, Weighted-Average Exercise per Share Price, Ending Balance | $ / shares	11.23
Options vested and expected to vest at December 31, 2018, Weighted-Average Exercise Per Share Price | $ / shares	11.23
Options exercisable at December 31, 2018, Weighted-Average Exercise per Share Price | $ / shares	$ 8.91
Options outstanding at December, 31, 2018, Weighted Average Remaining Contractual Term	7 years 4 months 6 days
Options vested and expected to vest at December, 31, 2018, Weighted Average Remaining Contractual Term	7 years 4 months 6 days
Options exercisable at December, 31, 2018, Weighted Average Remaining Contractual Term	5 years 4 months 20 days
Options outstanding at December 31, 2018, Aggregate Intrinsic Value | $	$ 24,468
Options vested and expected to vest at December 31, 2018, Aggregate Intrinsic Value | $	24,468
Options exercisable at December 31, 2018, Aggregate Intrinsic Value | $	$ 12,702