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Stock-Based Compensation - Summary of Stock-Based Compensation Expense (Detail) - Employees And Non Employees - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Total stock-based compensation expense $ 975 $ 663 $ 3,694 $ 2,793 $ 470
Research and Development          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Total stock-based compensation expense 400 277 1,542 1,236 246
General and Administrative          
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]          
Total stock-based compensation expense $ 575 $ 386 $ 2,152 $ 1,557 $ 224