Stock-Based Compensation - Summary of Stock Option Activity and Related Information (Details) - USD ($) $ / shares in Units, $ in Thousands	6 Months Ended	12 Months Ended
	Jun. 30, 2019	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Options, Balance	405,683
Options Outstanding, Options, Granted	188,550
Options Outstanding, Options, Cancelled	(5,496)
Options Outstanding, Options, Balance	588,737	405,683
Options Outstanding, Options, Exercisable	376,922
Options Outstanding, Weighted-Average Exercise Price, Balance	$ 9.69
Options Outstanding, Weighted-Average Exercise Price, Granted	4.96
Options Outstanding, Weighted-Average Exercise Price, Canceled	13.01
Options Outstanding, Weighted-Average Exercise Price, Balance	8.15	$ 9.69
Options Outstanding, Weighted-Average Exercise Price, Exercisable	$ 9.36
Options Outstanding Weighted-Average Remaining Contractual Life (Years), Balance	7 years 2 months 12 days	6 years 6 months
Options Outstanding Weighted-Average Remaining Contractual Life (Years), Exercisable	5 years 10 months 24 days
Options Outstanding, Aggregate Intrinsic Value, Balance	$ 211
Options Outstanding, Aggregate Intrinsic Value, Exercisable	$ 1