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Stock-Based Compensation (Stock Option Valuation Assumptions) (Details) - $ / shares
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Common stock closing price $ 0.21  
Common Stock Options [Member]    
Expected term (in years) 6 years 7 days  
Expected dividend yield 0.00% 0.00%
Minimum [Member] | Common Stock Options [Member]    
Risk-free interest rate 2.74% 1.27%
Expected volatility 121.00% 117.00%
Expected term (in years)   2 years
Maximum [Member] | Common Stock Options [Member]    
Risk-free interest rate 2.99% 2.36%
Expected volatility 126.00% 144.00%
Expected term (in years)   9 years 1 month 6 days