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Share-Based Compensation - Valuation Assumptions (Details) - Stock Option [Member]
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Class of Stock [Line Items]    
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Minimum 71.00% 73.00%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate, Maximum 74.00% 76.00%
Fair Value Assumptions, Weighted Average Volatility Rate 35.00% 74.00%
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 1.99% 1.07%
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate, Maximum 2.28% 2.19%
Minimum [Member]    
Class of Stock [Line Items]    
Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term, Minimum 6 years 5 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 10 years