Stock-Based Compensation - Summary of Stock Option Activity (Details) - Options Issued and Outstanding $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019 USD ($) $ / shares shares	Dec. 31, 2018 $ / shares shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Outstanding, beginning, Shares Available for Grant	1,350,582
Shares reserved for issuance, Shares Available for Grant	1,122,213
Options granted, Shares Available for Grant	(1,049,524)
Options cancelled, Shares Available for Grant	77,900
Outstanding, ending, Shares Available for Grant	1,501,171	1,350,582
Outstanding, beginning, Number of Options	1,122,677
Options granted, Number of Options	1,049,524
Options exercised, Number of Options	(7,029)
Options cancelled, Number of Options	(77,900)
Outstanding, ending, Number of Options	2,087,272	1,122,677
Exercisable, Number of Options	274,954
Vested and expected to vest, Number of Options	2,087,272
Outstanding, beginning, Weighted-Average Exercise Price per Option | $ / shares	$ 11.63
Options granted, Weighted-Average Exercise Price per Option | $ / shares	8.30
Options exercised, Weighted-Average Exercise Price per Option | $ / shares	0.79
Options cancelled, Weighted-Average Exercise Price per Option | $ / shares	10.52
Outstanding, ending, Weighted-Average Exercise Price per Option | $ / shares	10.04	$ 11.63
Exercisable, Weighted-Average Exercise Price per Option | $ / shares	11.19
Vested and expected to vest, Weighted-Average Exercise Price per Option | $ / shares	$ 10.04
Outstanding, beginning, Weighted-Average Remaining Contract Term	9 years 2 months 23 days	9 years 2 months 19 days
Exercisable, Weighted-Average Remaining Contract Term	8 years 6 months 3 days
Vested and expected to vest, Weighted-Average Remaining Contract Term	9 years 2 months 23 days
Outstanding, ending, Aggregate Intrinsic Value | $	$ 3,167
Exercisable, Aggregate Intrinsic Value | $	457
Vested and expected to vest, Aggregate Intrinsic Value | $	$ 3,167