Stock Option Plan - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Shares Available for Grant
Options outstanding, beginning balance	405,893	301,971	79,722
Additional shares reserved under plan	611,272	416,666	416,666
Options granted	(405,624)	(366,909)	(211,500)
Options forfeited	3,666	54,165	17,083
Options outstanding, ending balance	615,207	405,893	301,971
Shares Subject to Outstanding Options
Options outstanding, beginning balance	458,234	336,513	209,527
Options granted	405,624	366,909	211,500
Options forfeited	(7,395)	(54,165)	(17,083)
Options exercised	(31,333)	(191,023)	(67,431)
Options outstanding, ending balance	825,130	458,234	336,513
Vested and expected to vest	766,402	430,730	279,505
Exercisable	303,162	232,827	92,833
Weighted-Average Exercise Price Per Share
Options outstanding, beginning balance	$ 6.26	$ 0.91	$ 0.63
Options granted	16.06	8.80	1.12
Options forfeited	6.62	3.70	0.71
Options exercised	1.11	2.45	0.70
Options outstanding, ending balance	11.27	6.26	0.91
Vested and expected	10.95	6.16	0.88
Exercisable	$ 7.32	$ 4.27	$ 0.54
Weighted- Average Remaining Contractual Term (in years)
Options outstanding	8 years 6 months 15 days
Vested and expected	8 years 5 months 27 days	8 years 9 months 18 days	8 years 4 months 21 days
Exercisable	7 years 6 months 11 days	8 years 4 months 17 days	6 years 5 months 9 days
Aggregate Intrinsic Value
Options outstanding	$ 12,994
Vested and expected to vest	12,314	$ 5,102	$ 1,996
Exercisable	$ 5,974	$ 3,196	$ 694