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Summary of Unvested Stock Option Activity (Detail) - $ / shares
shares in Thousands
3 Months Ended
Mar. 31, 2021
Mar. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Granted $ 1.07 $ 0.54
Stock Options    
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]    
Beginning Balance 1,323  
Granted 20  
Vested (18)  
Ending Balance 1,325  
Beginning Balance $ 0.34  
Granted 1.07  
Vested 1.18  
Ending Balance $ 0.34