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Stock-Based Compensation, Fair Value Assumptions Used (Details) - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Fair value assumptions used in estimating fair value of each option grant [Abstract]    
Expected stock price volatility 92.34% 85.26%
Risk-free interest rate 2.09% 2.73%
Expected life term 6 years 1 month 20 days 6 years 7 days
Expected dividends 0.00% 0.00%
Options granted, weighted average grant date fair value (in dollars per share) $ 4.63 $ 2.58