General form of registration statement for all companies including face-amount certificate companies

CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY - Restricted Stock Agreements (Details)

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CONVERTIBLE PREFERRED STOCK AND STOCKHOLDERS' EQUITY - Restricted Stock Agreements (Details) - USD ($)
$ / shares in Units, $ in Thousands
 9 Months Ended 12 Months Ended
Sep. 30, 2020
Sep. 30, 2019
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Vesting of restricted Common Stock $ 6 $ 6 $ 8 $ 8  
Weighted-average remaining contractual term (in years) 7 years 10 months 6 days   7 years 10 months 2 days 8 years 2 months 16 days  
Restricted stock          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Shares issued         27,850,000
Share price         $ 0.0001
Percentage of shares on which right to repurchase lapses         20.00%
Percentage of shares per month on which right to repurchase lapses         1.67%
Right to repurchase expiry term         4 years
Vesting of restricted Common Stock (in shares)     497,290    
Vesting of restricted Common Stock     $ 2,000    
Vesting period     4 years    
Weighted-average remaining contractual term (in years) 8 months 12 days   8 months 12 days