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Equity-Based Compensation - Assumptions Used for Fair Value Measurement (Details)
3 Months Ended
Mar. 31, 2018
Mar. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate 2.72%  
Expected volatility rate 82.40%  
Forfeiture rate 5.00% 5.00%
Expected dividend yield 0.00% 0.00%
Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term 5 years 10 months 24 days 5 years 3 months 18 days
Risk-free interest rate   1.97%
Expected volatility rate   80.80%
Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected term 6 years 6 years 6 months
Risk-free interest rate   2.17%
Expected volatility rate   83.10%
Weighted Average    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-free interest rate   2.07%
Expected volatility rate   81.00%