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Stock-Based Compensation - Fair Value Assumptions (Details) - PRSU
12 Months Ended
Dec. 31, 2017
$ / shares
shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Shares issued | shares 6,089
Expected Term in Years 2 years 10 months 6 days
Expected Dividend Yield (as a percent) 0.00%
Weighted-Average Fair Value (in usd per share) | $ / shares $ 24.39
Correlation Coefficient Rate 75.93%
Volatility Rate 21.80%
Weighted Average  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Weighted-Average Risk Free Interest Rate 1.40%
Peer Company  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Volatility Rate, Minimum 17.80%
Volatility Rate, Maximum 63.10%
Peer Company | Minimum  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Correlation Coefficient Rate 8.24%
Peer Company | Maximum  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Correlation Coefficient Rate 89.79%