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Summary of Stock Option (Detail) - $ / shares
 9 Months Ended 12 Months Ended
Sep. 30, 2021
Dec. 31, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]    
Number of shares, Beginning Balance 3,460  
Options granted, Shares 527  
Options forfeited, Shares (159)  
Options expired, Shares (227)  
Options exercised, Shares (69)  
Number of shares, Ending Balance 3,532 3,460
Weighted average exercise price, Beginning Balance $ 3.82  
Options granted, Weighted average exercise price 2.46  
Options forfeited, Weighted average exercise price 3.35  
Options expired, Weighted average exercise price 4.97  
Options exercised, Weighted average exercise price 2.64  
Weighted average exercise price, Ending Balance $ 3.59 $ 3.82
Weighted average remaining contractual term, End of the period 6 years 7 days 6 years 6 months