Stockholders' Equity - Summary of Stock-Based Compensation Expense (Details) - 2016 Equity Incentive Plans and Employee Stock Purchase Plan - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,245	$ 996	$ 2,326	$ 1,831
Research and Development
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	464	390	866	713
General and Administrative
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 781	$ 606	$ 1,460	$ 1,118