Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - 2018 Equity Inducement Plan and 2016 Employee Stock Purchase Plan - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 6,220	$ 4,876	$ 4,046
Non-Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	36		234
Research and Development | Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	2,168	1,828	1,440
Research and Development | Non-Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	36		234
General and Administrative | Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 4,052	$ 3,048	$ 2,606