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Share-Based Compensation - Valuation Assumptions (Details) - Stock Option [Member]
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Class of Stock [Line Items]    
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Minimum 68.00% 71.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Maximum 73.00% 74.00%
Fair Value Assumptions, Weighted Average Volatility Rate 72.00% 35.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate 0.00% 0.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Minimum 2.35% 1.99%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Maximum 2.96% 2.28%
Minimum [Member]    
Class of Stock [Line Items]    
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term, Minimum 5 years 6 months 6 years
Maximum [Member]    
Class of Stock [Line Items]    
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term, Minimum 6 years 6 years