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Stock-Based Compensation - Assumptions for Option Grants Issued (Details)
3 Months Ended 6 Months Ended
Jun. 30, 2021
Jun. 30, 2020
Jun. 30, 2021
Jun. 30, 2020
Share-based Payment Arrangement [Abstract]        
Risk free interest rate 1.12% 0.53% 1.04% 0.62%
Volatility 121.47% 108.08% 121.23% 106.24%
Expected lives (years) 6 years 3 months 6 years 3 months 6 years 2 months 4 days 6 years 1 month 24 days
Expected dividend yield 0.00% 0.00% 0.00% 0.00%