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Stock-Based Compensation, Assumptions Used to Value Stock Options Granted (Details) - $ / shares
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Stock-Based Compensation [Abstract]        
Options granted (in shares) 1,391,130   1,658,930  
Assumptions Used in Determining Fair Value of Stock Options Granted [Abstract]        
Volatility 100.63% 97.13% 100.59% 97.00%
Risk-free interest rate 0.79% 0.34% 0.72% 0.38%
Expected term 6 years 4 months 17 days 6 years 25 days 6 years 3 months 10 days 6 years 25 days
Dividend rate 0.00% 0.00% 0.00% 0.00%
Fair value of option on grant date (in dollars per share) $ 7.28 $ 1.11 $ 6.39 $ 1.11