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Equity-Based Compensation - PSU awards (Details)
$ / shares in Units, $ in Millions
3 Months Ended
Mar. 31, 2018
USD ($)
$ / shares
shares
Performance share unit awards  
Number of units  
Total granted and unvested at the beginning of the period (in shares) | shares 1,283,843
Vested (in shares) | shares (41,666)
Forfeited (in shares) | shares (12,186)
Total awarded and unvested at the end of the period (in shares) | shares 1,229,991
Weighted average grant date fair value  
Total granted and unvested at the beginning of the period (in dollars per share) | $ / shares $ 28.29
Vested (in dollars per share) | $ / shares 27.38
Forfeited (in dollars per share) | $ / shares 29.83
Total awarded and unvested at the end of the period (in dollars per share) | $ / shares $ 28.30
Additional disclosures  
Additional equity compensation to be recognized over the remaining period | $ $ 15.1
Weighted average period for recognizing unrecognized stock-based compensation expense 1 year 8 months 12 days
Price target performance share unit awards  
Number of successive days closing stock price must achieve specific thresholds for PSUs to vest per schedule 10 days
Vesting period 3 years
Price target performance share unit awards | Vesting before first anniversary | Maximum  
Number of PSUs that may vest, as a percent 0.00%
Price target performance share unit awards | Vesting before the second anniversary | Maximum  
Number of PSUs that may vest, as a percent 33.33%
Price target performance share unit awards | Vesting before the third anniversary | Maximum  
Number of PSUs that may vest, as a percent 66.67%
TSR performance share unit awards  
Vesting period 3 years
TSR performance share unit awards | Maximum  
Number of PSUs that may be earned as compared to the number of PSUs granted, as a percent 200.00%
TSR performance share unit awards | Minimum  
Number of PSUs that may be earned as compared to the number of PSUs granted, as a percent 0.00%