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Summary of Stock Option, Restricted Stock Award, and Restricted Stock Unit Activity (Detail) - USD ($)
$ / shares in Units, $ in Thousands
 12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Options and restricted stock available for grant, Beginning Balance 11,566,000  
Options and restricted stock available for grant, increase to pool   2,214,000
Options granted (760,000)  
Options cancelled 1,472,000  
Options expired 477,000  
Options forfeited 133,000  
Options and restricted stock available for grant, Ending Balance 14,563,000 11,566,000
Options exercisable at December 31, 2020 1,934,000  
Number of shares, Beginning Balance 4,782,000  
Options granted, Shares 760,000  
Options cancelled, Shares (1,472,000)  
Options expired, Shares (477,000)  
Options forfeited, Shares (133,000)  
Number of shares, Ending Balance 3,460,000 4,782,000
Weighted average exercise price, Beginning Balance $ 4.80  
Options granted, Weighted average exercise price 2.29  
Options cancelled, Weighted average exercise price 5.81  
Options expired, Weighted average exercise price 5.12  
Options forfeited, Weighted average exercise price 3.48  
Weighted average exercise price, Ending Balance 3.82 $ 4.80
Options exercisable at December 31, 2020 $ 4.51  
Weighted average remaining contractual term 6 years 6 months 5 years 9 months 25 days
Weighted average remaining contractual term, Options exercisable at December 31, 2019 5 years 1 month 6 days  
Aggregate intrinsic value, Outstanding $ 27 $ 1,585
Restricted Stock    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Restricted stock granted (560,000)  
Restricted stock forfeited 21,000