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Common Stock (Schedule of significant assumptions) (Details)
12 Months Ended
Dec. 31, 2019
Time-Vested Options  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Risk-free interest rate 1.81%
Expected volatility of common stock 73.59%
Expected life of options in years 5 years
Dividend yield 0.00%
Vesting period in years 5 years
Performance-Based Options  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Risk-free interest rate 1.84%
Expected volatility of common stock 71.57%
Expected life of options in years 7 years
Dividend yield 0.00%
Vesting period in years 7 years