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Stock-Based Compensation - Schedule of Estimated Grant-date Fair Values of Stock-based Awards Using Black-Scholes Option Pricing Model Assumptions (Detail)
3 Months Ended 9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Sep. 30, 2021
Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected volatility, Minimum 82.00% 88.00% 82.00% 88.00%
Expected volatility, Maximum 83.00% 89.00% 85.00% 90.00%
Risk-free interest rate, Minimum 0.80% 0.30% 0.50% 0.30%
Risk-free interest rate, Maximum 1.20% 0.50% 1.20% 1.20%
Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected term (in years) 6 years 5 years 6 months 5 years 3 months 18 days 5 years 3 months 18 days
Maximum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected term (in years) 6 years 1 month 6 days 7 years 7 years 7 years