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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, 2020
Sep. 30, 2019
Sep. 30, 2020
Sep. 30, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected volatility, Minimum 88.00% 91.00% 88.00% 90.00%
Expected volatility, Maximum 89.00%   90.00% 94.00%
Risk-free interest rate, Minimum 0.30% 1.60% 0.30% 1.60%
Risk-free interest rate, Maximum 0.50%   1.20% 2.60%
Minimum [Member]        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Expected term (in years) 5 years 6 months 6 years 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) 7 years 6 years 1 month 6 days 7 years 6 years 10 months 24 days