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Stockholders' Equity - Schedule of Fair Value of Award Granted Using Black-Scholes Option Pricing Model (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 life (years)   6 years    
Risk-free interest rate   0.40%    
Volatility   84.00%    
Dividend rate 0.00% 0.00% 0.00% 0.00%
Minimum [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expected life (years)     5 years 6 months 5 years 6 months
Risk-free interest rate     0.60% 0.40%
Volatility     91.00% 64.00%
Maximum [Member]        
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]        
Expected life (years)     6 years 6 years
Risk-free interest rate     1.00% 0.50%
Volatility     108.00% 84.00%