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Share-Based Compensation - Assumptions (Details) - Stock Option
12 Months Ended
Dec. 31, 2018
Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Risk-Free interest rate, minimum 2.24% 1.87%
Risk-Free interest rate, maximum 2.96% 2.15%
Expected dividend yield 0.00% 0.00%
Expected stock price volatility, minimum 27.80% 70.24%
Expected stock price volatility, maximum 23.36% 71.43%
Discount for lack of marketability 9.35% 17.72%
Minimum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life of options 5 years 5 years
Maximum    
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]    
Expected life of options 6 years 2 months 30 days 6 years 2 months 30 days