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Stock-Based Compensation Plan - Weighted-Average Assumptions (Details)
9 Months Ended
Sep. 30, 2021
Sep. 30, 2020
Stock-Based Compensation Plan    
Risk-free interest rate 1.15% 0.50%
Expected volatility 128.00% 122.00%
Expected term in years 6 years 6 years
Dividend yield 0.00% 0.00%