Stock-Based Compensation - Summary of Company's Stock Option Activity and Related Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Shares Available for Grant
Shares Available for Grant, Beginning balance	2,168,391
Shares Available for Grant, Additional authorized	1,743,247
Shares Available for Grant, Granted	(2,986,244)
Shares Available for Grant, Cancelled	100,411
Shares Available for Grant, RSUs granted	(56,022)
Shares Available for Grant, Ending balance	969,783	2,168,391
Number of Stock Options Outstanding
Number of Stock Options Outstanding, Beginning balance	6,127,291
Number of Stock Options Outstanding, Granted	2,986,244
Number of Stock Options Outstanding, Exercised	(420,377)
Number of Stock Options Outstanding, Cancelled	(100,411)
Number of Stock Options Outstanding, Ending balance	8,592,747	6,127,291
Number of Stock Options Outstanding, Vested and exercisable	5,011,207
Number of Stock Options Outstanding, Vested and expected to vest	8,303,413
Weighted- Average Exercise Price
Weighted- Average Exercise Price, Beginning balance	$ 2.60
Weighted- Average Exercise Price, Granted	5.65
Weighted- Average Exercise Price, Exercised	1.58
Weighted- Average Exercise Price, Cancelled	3.95
Weighted- Average Exercise Price, Ending balance	3.69	$ 2.60
Weighted- Average Exercise Price, Vested and exercisable	2.65
Weighted- Average Exercise Price, Vested and expected to vest	$ 3.64
Weighted- Average Remaining Contractual Life (Years)
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	7 years 4 months 24 days	7 years 3 months 19 days
Weighted- Average Remaining Contractual Life (Years), Vested and exercisable	6 years 6 months
Weighted- Average Remaining Contractual Life (Years), Vested and expected to vest	7 years 4 months 24 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 47,864	$ 7,800
Aggregate Intrinsic Value, Vested and exercisable	33,130
Aggregate Intrinsic Value, Vested and expected to vest	$ 46,655