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Stockholders' Equity (Stock Option Grants Weighted Average Assumptions) (Details) - Employee Stock Option [Member]
12 Months Ended
Dec. 31, 2020
Dec. 31, 2019
Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility     81.00%
Risk free interest rate     2.60%
Expected dividend yield 0.00% 0.00% 0.00%
Expected life (in years) 5 years 5 years 5 years
Minimum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility 101.00% 89.00%  
Risk free interest rate 0.31% 1.55%  
Maximum [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected volatility 104.00% 100.00%  
Risk free interest rate 1.67% 2.85%