Stock-Based Compensation - Summary of Company's Stock Option Activity and Related Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2018	Dec. 31, 2017
Shares Available for Grant
Shares Available for Grant, Beginning balance	969,783
Shares Available for Grant, Additional options authorized	2,706,158
Shares Available for Grant, Options granted	(182,244)
Shares Available for Grant, Options canceled	35,717
Shares Available for Grant, Ending balance	3,529,414	969,783
Number of Stock Options Outstanding
Number of Stock Options Outstanding, Beginning balance	8,592,747
Number of Stock Options Outstanding, Options granted	182,244
Number of Stock Options Outstanding, Options exercised	(265,647)
Number of Stock Options Outstanding, Options canceled	(35,717)
Number of Stock Options Outstanding, Ending balance	8,473,627	8,592,747
Number of Stock Options Outstanding, Vested and exercisable	5,132,684
Number of Stock Options Outstanding, Vested and expected to vest	8,207,659
Weighted- Average Exercise Price
Weighted- Average Exercise Price, Beginning balance	$ 3.69
Weighted- Average Exercise Price, Options granted	8.16
Weighted- Average Exercise Price, Options exercised	1.42
Weighted- Average Exercise Price, Options canceled	5.62
Weighted- Average Exercise Price, Ending balance	3.85	$ 3.69
Weighted- Average Exercise Price, Vested and exercisable	2.87
Weighted- Average Exercise Price, Vested and expected to vest	$ 3.80
Weighted- Average Remaining Contractual Life (Years)
Options Outstanding, Weighted- Average Remaining Contractual Life (Years)	7 years 4 months 24 days	7 years 4 months 24 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 3 months 19 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value	$ 22,906	$ 47,864
Aggregate Intrinsic Value, Vested and exercisable	18,702
Aggregate Intrinsic Value, Vested and expected to vest	$ 22,557