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Stock-Based Awards - Summary of Stock-Based Compensation Expense Related to Stock Options and Restricted Common Stock (Detail) - USD ($)
$ in Thousands
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Total stock-based compensation expense $ 710 $ 2,076
Research and Development [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Total stock-based compensation expense (144) 960
General and Administrative [Member]    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Total stock-based compensation expense $ 854 $ 1,116