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Assumptions Used in Estimating Fair Value of Stock Options Granted (Detail) - $ / shares
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award Fair Value Assumptions And Methodology [Abstract]        
Expected term (years)   5 years 6 months 6 years 1 month 6 days 5 years 6 months
Volatility 103.00% 110.00% 103.00%
Annual dividend per share  
Risk-free interest rate 0.36% 0.69% 0.37%