Quarterly report pursuant to Section 13 or 15(d)

Stockholders' Equity (Narrative) (Details)

v3.21.2
Stockholders' Equity (Narrative) (Details) - USD ($)
3 Months Ended 6 Months Ended
Aug. 29, 2020
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Dec. 31, 2020
Aug. 27, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock-based compensation expense       $ 8,123,000 $ 7,148,000    
Stock options, unrecognized compensation expense   $ 0   0      
Stock-based compensation expense   $ 4,350,000 $ 3,748,000 $ 8,123,000 7,148,000    
Outstanding warrants   4,505,621   4,505,621   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     $ 4,400,000
Research and Development Expense [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock-based compensation expense   800,000 900,000 2,000,000.0 1,800,000    
General and Administrative Expense [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock-based compensation expense   $ 3,600,000 2,900,000 $ 6,100,000 5,400,000    
Employee Stock Option [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Predetermined fair value percentage during offering period   85.00%   85.00%      
Shares purchased in connection with the ESPP offering       636,408      
Number of shares available for future issuance   363,592   363,592      
Stock-based compensation expense   $ 35,000 25,000        
Restricted Stock Awards and Restricted Stock Units [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Unrecognized compensation expense for awards other than options   23,500,000 17,100,000 $ 23,500,000 $ 17,100,000    
Share-based compensation, period for recognition of expense       3 years 2 months 12 days 4 years    
Restricted Stock [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares Granted       2,330,678      
Weighted average grant price, Granted       $ 3.17      
Restricted Stock Units (RSUs) [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Number of shares Granted       1,112,666      
Weighted average grant price, Granted       $ 4.13      
Warrants [Member]              
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]              
Stock-based compensation expense   $ 0 $ 65,000 $ 0 $ 65,000