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Stock-Based Compensation - Assumptions (Details) - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Stock options      
Assumptions      
Unrecognized stock-based compensation expense $ 40.4    
Period for recognition 2 years 8 months 12 days    
Employee and Consultant Options | Employees and directors      
Assumptions      
Expected volatility 60.00% 73.80% 77.50%
Expected option term (in years) 6 years 3 months 6 years 3 months 6 years 3 months
Risk free interest rate 1.50% 2.00% 2.90%