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Share-Based Compensation - Weighted-average Assumptions (Details) - Options to purchase common stock - $ / shares
3 Months Ended
Mar. 31, 2020
Mar. 31, 2019
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected stock price volatility 75.20% 74.20%
Risk free interest rate 1.70% 2.50%
Expected life of options (years) 5 years 8 months 1 day 5 years 8 months 4 days
Expected annual dividend per share (in dollars per share) $ 0 $ 0