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Stock Award Plans - Fair Value of Employee Stock Options Assumptions (Detail)
12 Months Ended
Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Risk free interest rate, minimum 0.39%
Risk free interest rate, maximum 1.52%
Volatility, minimum 93.83%
Volatility, maximum 94.25%
Minimum  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Expected lives 5 years 8 months 1 day
Maximum  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Expected lives 7 years