Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity (Narrative) (Details)

v3.21.1
Stockholders' Equity (Narrative) (Details) - USD ($)
3 Months Ended
Aug. 29, 2020
Mar. 31, 2021
Mar. 31, 2020
Dec. 31, 2020
Aug. 27, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock-based compensation expense   $ 3,773,000 $ 3,400,000    
Stock options, unrecognized compensation expense   0      
Stock-based compensation expense   $ 3,773,000 3,400,000    
Outstanding warrants   4,530,621   4,590,621  
Oaktree Note [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Percentage of market price of common stock for additional warrants 95.00%        
Warrants expiration date Aug. 27, 2030        
Fair value assumptions, expected term 10 years        
Fair value assumptions, expected volatility rate 0.868%        
Fair value assumptions, risk free interest rate 0.74%        
Fair value assumptions, expected return $ 4,800,000        
Warrants, fair value   $ 4,400,000     $ 4,400,000
Research and Development Expense [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock-based compensation expense   1,200,000 900,000    
General and Administrative Expense [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Stock-based compensation expense   $ 2,600,000 2,500,000    
Employee Stock Option [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Predetermined fair value percentage during offering period   85.00%      
Shares purchased in connection with the ESPP offering   577,301      
Number of shares available for future issuance   422,699      
Stock-based compensation expense   $ 34,000 18,000    
Restricted Stock Awards and Restricted Stock Units [Member]          
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]          
Number of shares Granted   2,330,678      
Unrecognized compensation expense for awards other than options   $ 21,800,000 $ 17,900,000    
Weighted average grant price, Granted   $ 3.17      
Share-based compensation, period for recognition of expense   3 years 7 months 6 days 4 years 2 months 12 days