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Equity-Based Compensation (Weighted Average Assumptions Used to Measure Fair Value of Stock Options) (Details) - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2015
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]    
Fair Value $ 12.85 $ 7.67
Expected Life (in years) 4 years 4 years
Expected Stock Volatility 35.70% 35.70%
Risk-free Interest Rate 1.70% 1.50%
Expected Dividend Yield 0.00% 0.00%