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, 2018	Dec. 31, 2017	Dec. 31, 2016
Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 4,046	$ 2,492	$ 1,221
Non-Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	234
Research and Development | Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	1,440	961	389
Research and Development | Non-Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	234
General and Administrative | Employees
Employee Service Share Based Compensation Allocation of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 2,606	$ 1,531	$ 832