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Equity-based Compensation - Long-Term Incentive Awards Narrative (Details) - Equity Plan [Member] - USD ($)
$ in Millions
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
General and Administrative Expense [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense     $ 0.1
Long Term Incentive Target Awards [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Vesting period 3 years    
Unrecognized compensation expense $ 6.1    
Weighted-average remaining term (years) 1 year 8 months 12 days    
Awards canceled during period (in shares) 671,712    
Long Term Incentive Target Awards [Member] | General and Administrative Expense [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Compensation expense $ 7.4 $ 4.6 $ 1.9