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Stock-Based Compensation - Assumptions Used in Determining Fair Value of Stock Options (Details) - $ / shares
6 Months Ended
Jun. 30, 2022
Jun. 30, 2021
Stock-Based Compensation    
Options to purchase common stock granted to employees and directors 660,700 833,500
Average risk free interest rate 2.30% 0.40%
Dividend rate 0.00% 0.00%
Expected lives (years) 4 years 3 years 7 months 6 days
Expected volatility 102.00% 87.00%
Weighted average exercise price (per share) $ 0.53 $ 3.66