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Commitments and Contingencies - Additional Information (Detail) - USD ($)
$ in Thousands
3 Months Ended 12 Months Ended
Mar. 31, 2019
Mar. 31, 2018
Dec. 31, 2020
Dec. 31, 2019
Contingencies And Commitments [Line Items]        
Research and development expense [1] $ 33,822 $ 19,519    
Research Agreements [Member]        
Contingencies And Commitments [Line Items]        
Research and development expense 1,700      
Research Agreements [Member] | Scenario Forecast [Member]        
Contingencies And Commitments [Line Items]        
Research and development expense     $ 1,900 $ 2,100
Manufacturing Agreements [Member] | Prepaid Expenses [Member]        
Contingencies And Commitments [Line Items]        
Upfront payment recorded as prepaid expense 4,000      
Letter of Credit [Member]        
Contingencies And Commitments [Line Items]        
Letters of credit secured by cash held in restricted depository account $ 3,200      
[1] Including the following research and development expense with a related party, see Notes 6 & 11: