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Stock-Based Compensation - Assumptions for Share Based Awards (Details) - TSR Performance Share Awards - $ / shares
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Liability      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Expected dividend yield 0.00% 0.00% 0.00%
Stock price volatility, minimum rate 29.10% 40.40% 33.50%
Stock price volatility, maximum rate 36.70% 43.00% 37.50%
Risk free rate of return, minimum rate 1.80% 0.90% 0.70%
Risk free rate of return, maximum rate 1.90% 1.20% 1.10%
Stockholders' Equity      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value per performance share award granted during the period $ 19.85 $ 18.57 $ 19.29
Stock price volatility 37.80% 34.40% 32.30%
Risk free rate of return 1.40% 0.90% 1.00%
Expected dividend yield 0.00% 0.00% 0.30%
Minimum | Liability      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value per performance share award granted during the period $ 13.23 $ 5.59 $ 2.49
Maximum | Liability      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Fair value per performance share award granted during the period $ 21.64 $ 7.10 $ 6.39