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Stock-Based Compensation - Schedule of Assumptions Used in Estimation of Fair Value of the Share-based Payment Awards on the Grant Date (Details) - Options
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Dec. 31, 2016
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Risk-free interest rate 2.20%    
Risk-free interest rate, minimum   1.60% 1.00%
Risk-free interest rate, maximum   1.80% 2.10%
Volatility 109.50%    
Volatility, minimum   70.20% 61.40%
Volatility, maximum   101.50% 65.00%
Expected life (years) 4 years 4 years  
Dividend yield 0.00% 0.00% 0.00%
Minimum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected life (years)     3 years
Maximum      
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]      
Expected life (years)     5 years