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Stock-Based Compensation - Weighted Average Assumptions and Grant Date Fair Value (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Weighted-average assumptions and grant date fair value    
Expected volatility (as a percent) 121.10%  
Risk free interest rate (as a percent) 1.90%  
Expected volatility (as a percent), minimum   153.70%
Expected volatility (as a percent), maximum   168.50%
Risk free interest rate (as a percent), minimum   1.19%
Risk free interest rate (as a percent), maximum   2.18%
Dividend yield 0.00% 0.00%
Expected life in years 6 years 6 years
Weighted average grant date fair value $ 2.25 $ 2.12