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Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Details) - Employees And Non Employees - USD ($)
$ in Thousands
3 Months Ended 9 Months Ended
Sep. 30, 2019
Sep. 30, 2018
Sep. 30, 2019
Sep. 30, 2018
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Total stock-based compensation expense $ 1,202 $ 629 $ 2,808 $ 2,212
Research and Development        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Total stock-based compensation expense 633 229 1,409 955
General and Administrative        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Total stock-based compensation expense $ 569 $ 400 $ 1,399 $ 1,257