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Equity-Based Compensation (PSUs Eligible for Conversion to Cash) (Details) - Performance stock units - USD ($)
$ in Thousands
12 Months Ended
Dec. 31, 2017
Dec. 31, 2016
Dec. 31, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Number of units (in shares)   128,000 219,000
Grant date fair value   $ 3,100 $ 4,039
Equity Based Compensation Percent Of Targeted Performance Stock Units Earned 200.00% 200.00%  
Units vested (in shares) 256,000 438,000