Annual report pursuant to Section 13 and 15(d)

STOCK-BASED COMPENSATION - Assumptions and Activity (Details)

v3.20.4
STOCK-BASED COMPENSATION - Assumptions and Activity (Details)
 12 Months Ended
Dec. 31, 2020
USD ($)
item
$ / shares
shares
Dec. 31, 2019
USD ($)
$ / shares
shares
Dec. 31, 2018
USD ($)
$ / shares
shares
Dec. 31, 2020
USD ($)
$ / shares
shares
Dec. 31, 2019
USD ($)
shares
Stock Based Compensation          
Number of homogenous groups for purposes of determining fair values of options | item 3        
Share-based compensation | $ $ 7,295,000 $ 9,115,000 $ 7,704,000    
Shares Available For Grant          
Outstanding at the end of the period (in shares) 14,218,190        
Additional disclosures          
Shares of common stock available for grant 14,218,190     14,218,190  
Shares reserved for future issuance       27,260,463  
Purchase Plan          
Weighted-average assumptions relating to options granted          
Risk-free interest rate (as a percent) 1.00% 2.70% 2.40%    
Expected term (in years) 1 year 7 months 6 days 1 year 6 months 1 year 3 months 18 days    
Dividend yield (as a percent) 0.00% 0.00% 0.00%    
Expected volatility (as a percent) 62.30% 62.60% 66.20%    
Employee stock option          
Stock Based Compensation          
Contractual term of the option 10 years        
Weighted-average assumptions relating to options granted          
Risk-free interest rate (as a percent) 1.20% 2.40% 2.70%    
Expected term (in years) 6 years 6 months 6 years 6 months 6 years 8 months 12 days    
Dividend yield (as a percent) 0.00% 0.00% 0.00%    
Expected volatility (as a percent) 66.10% 65.50% 65.10%    
Shares Available For Grant          
Outstanding at the beginning of the period (in shares) 16,615,971        
Authorized for grant (in shares) 2,953,519        
Granted (in shares) (8,462,090) (7,457,575) (4,594,225)    
Cancelled (in shares) 3,110,790        
Outstanding at the end of the period (in shares) 14,218,190 16,615,971      
Number of Shares Underlying Options          
Outstanding at the beginning of the period (in shares) 22,670,704        
Granted (in shares) 8,462,090 7,457,575 4,594,225    
Exercised (in shares) (761,541)        
Cancelled (in shares) (3,110,790)        
Outstanding at the end of the period (in shares) 27,260,463 22,670,704      
Vested and expected to vest (in shares)       26,159,213  
Exercisable (in shares)       17,802,873  
Weighted Average Exercise Price          
Outstanding at the beginning of the period (in dollars per share) | $ / shares $ 3.51        
Granted (in dollars per share) | $ / shares 2.32        
Exercised (in dollars per share) | $ / shares 2.26        
Cancelled (in dollars per share) | $ / shares 4.56        
Outstanding at the end of the period (in dollars per share) | $ / shares $ 3.05 $ 3.51      
Vested and expected to vest (in dollars per share) | $ / shares       $ 3.12  
Exercisable (in dollars per share) | $ / shares       $ 3.42  
Weighted Average Remaining Contractual Term (in years)          
Outstanding at the end of the period 6 years 5 months 15 days        
Exercisable 5 years 3 months        
Aggregate Intrinsic Value          
Outstanding at the end of the period (in dollars) | $       $ 23,679,303  
Exercisable | $       $ 12,628,388  
Number of nonvested stock options (in shares)       9,457,590 6,865,971
Intrinsic value of nonvested stock options | $       $ 11,100,000 $ 614,000
Aggregate intrinsic value of options exercised | $ $ 459,000 $ 12,000      
Weighted-average recognition period of unamortized compensation cost 2 years 2 months 12 days 1 year 1 month 6 days      
Number of shares vested 4,386,910 4,442,936      
Weighted-average exercise price for shares vested during the period (in dollars per share) | $ / shares $ 2.41 $ 3.26      
Additional disclosures          
Options cancelled (in shares) 3,110,790        
Options outstanding at the end of the period (in shares) 27,260,463 22,670,704   27,260,463 22,670,704
Grant-date weighted-average fair value (in dollars per share) | $ / shares $ 1.42 $ 1.27 $ 2.66    
Total unrecognized compensation costs | $       $ 11,000,000.0  
Shares of common stock available for grant 14,218,190 16,615,971   14,218,190 16,615,971
Options exercised during the period (in shares) 761,541        
Employee stock option | Consultant          
Stock Based Compensation          
Contractual term of the option 10 years        
Employee stock option | Purchase Plan          
Aggregate Intrinsic Value          
Unrecognized compensation cost related to purchase plan | $       $ 615,000  
Performance shares          
Shares Available For Grant          
Granted (in shares) (1,101,250)        
Number of Shares Underlying Options          
Granted (in shares) 1,101,250        
Performance shares | Vesting upon achievement of corporate performance-based milestones          
Additional disclosures          
Total unrecognized compensation costs | $       $ 1,700,000