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Fair Value of Financial Instruments - Additional Information (Details) - USD ($)
1 Months Ended 9 Months Ended 12 Months Ended
Jul. 01, 2020
Dec. 31, 2019
Aug. 31, 2019
Sep. 30, 2020
Sep. 30, 2019
Dec. 31, 2019
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]            
Fair value assets transfers from level 1 to level 2       $ 0    
Fair value assets transfers from level 2 to level 1       0    
Fair value liabilities transfers from level 1 to level 2       0    
Fair value liabilities transfers from level 2 to level 1       0    
Impairments           $ 0
Realized gain or loss on available-for-sale securities       0    
Proceeds from issuance of convertible preferred stock         $ 5,986,000  
Preferred stock purchase right liability   $ 1,478,000   41,600,000   $ 1,478,000
Fair value of preferred stock purchase right liability percentage   90.00% 90.00%      
Fair value of preferred stock purchase right liability discount rate   1.60% 1.80%      
Fair value of preferred stock purchase right liability outstanding term   9 months 18 days 1 year 1 month 6 days      
Series B Convertible Preferred Stock            
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]            
Temporary equity, shares issued 27,066,206          
Proceeds from issuance of convertible preferred stock $ 64,400,000          
Short-term Investments            
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]            
Accrued interest receivable       300,000    
Quoted Prices in Active Markets for Identical Assets (Level 1) | Money Market Funds            
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]            
Investments       186,300,000    
Significant Other Observable Inputs (Level 2) | Short-term Investments            
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]            
Marketable securities       $ 141,200,000