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Stock-Based Compensation - Summary of Stock-Based Compensation Activity (Detail) - 2008 Plan, 2015 Plan and 2018 Plan [Member] - USD ($)
$ / shares in Units, $ in Thousands
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Options Outstanding, Shares Available for Grant    
Shares Available for Grant, Beginning balance 51,514  
Shares Available for Grant, Awards authorized 4,887,187  
Shares Available for Grant, Granted (4,074,939)  
Shares Available for Grant, forfeited/cancelled 254,034  
Shares Available for Grant, Ending balance 1,117,796 51,514
Options Outstanding, Number of Shares Outstanding    
Number of Shares Outstanding, Beginning balance 326,023  
Number of Shares Outstanding, Options granted 4,074,939  
Number of Shares Outstanding, Options forfeited/cancelled (254,034)  
Number of Shares Outstanding, Ending balance 4,146,928 326,023
Number of Shares Outstanding, Exercisable 466,879  
Number of Shares Outstanding, Vested and expected to vest 3,594,690  
Options Outstanding, Weighted-Average Exercise Price Per Share    
Weighted-Average Exercise Price Per Share, Beginning balance $ 102.56  
Weighted-Average Exercise Price Per Share, Options granted 12.88  
Weighted-Average Exercise Price Per Share, Options forfeited/cancelled 20.73  
Weighted-Average Exercise Price Per Share, Ending balance 19.45 $ 102.56
Weighted-Average Exercise Price Per Share, Exercisable 65.48  
Weighted-Average Exercise Price Per Share, Vested and expected to vest $ 20.57  
Options Outstanding, Weighted-Average Remaining Contractual Term (Years)    
Weighted-Average Remaining Contractual Term (Years) 8 years 10 months 2 days 7 years 5 months 12 days
Weighted-Average Remaining Contractual Term (Year), Exercisable 3 years 10 months 24 days  
Weighted-Average Remaining Contractual Term (Year), Vested and expected to vest 8 years 8 months 15 days  
Options Outstanding, Aggregate Intrinsic Value of Outstanding Options    
Aggregate Intrinsic Value of Outstanding Options $ 12,227 $ 11
Aggregate Intrinsic Value of Outstanding Options, Exercisable 555  
Aggregate Intrinsic Value of Outstanding Options, Vested and expected to vest $ 10,084