Stock-Based Compensation - Summary of Stock Options Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended		12 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Dec. 31, 2018
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Options Outstanding, Number of Options, Shares, Beginning Balance	1,867,747
Options Outstanding, Number of Options, Granted, Shares	195,975	0
Options Outstanding, Number of Options, Exercised, Shares	(487)
Options Outstanding, Number of Options, Cancelled, Shares	(165,622)
Options Outstanding, Number of Options, Shares, Ending Balance	1,897,613		1,867,747
Options Outstanding, Number of Options Exercisable, Shares, as of September 30, 2019	218,096
Options Outstanding, Number of Options, Vested and expected to vest, Shares as of September 30, 2019	1,954,263
Options Outstanding, Weighted Average Exercise Price, Beginning Balance	$ 9.01
Options Outstanding, Weighted Average Exercise Price, Granted	9.49
Options Outstanding, Weighted Average Exercise Price, Exercised	4.14
Options Outstanding, Weighted Average Exercise Price, Cancelled	8.76
Options Outstanding, Weighted Average Exercise Price, Ending Balance	9.10		$ 9.01
Options Outstanding, Weighted Average Exercise Price, Exercisable as of September 30, 2019	6.31
Options Outstanding, Weighted Average Exercise Price, Vested and expected to vest as of September 30, 2019	$ 9.13
Options Outstanding, Weighted Average Remaining Contractual Life (Years)	9 years 7 days		9 years 7 months 21 days
Options Outstanding, Weighted Average Remaining Contractual Life (Years), Exercisable as of September 30, 2019	7 years 6 months 18 days
Options Outstanding, Weighted Average Remaining Contractual Life (Years), Vested and expected to vest as of September 30, 2019	8 years 9 months
Options Outstanding, Aggregate Intrinsic Value	$ 498,451		$ 19,573,295
Options Outstanding, Aggregate Intrinsic Value, Exercised	1,630
Options Outstanding, Aggregate Intrinsic Value, Exercisable as of September 30, 2019	359,753
Options Outstanding, Aggregate Intrinsic Value, Vested and expected to vest as of September 30, 2019	$ 498,451