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Equity-Based Compensation (PSUs Eligible for Conversion to Cash) (Details) - Performance stock units - USD ($) $ in Thousands | 12 Months Ended
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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 |

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