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Equity-based Awards, Restricted Unit Awards (Details) - Restricted Common Unit Awards [Member] - USD ($)
$ / shares in Units, $ in Millions
 3 Months Ended 6 Months Ended
Jun. 30, 2016
Jun. 30, 2015
Jun. 30, 2016
Jun. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Vesting rate of restricted common unit awards (in hundredths) 25.00%   25.00%  
Summary of awards activity, equity instruments other than options [Roll Forward]        
Beginning of period (in units)     1,960,520  
Vested (in units)     (1,188,428)  
Forfeited (in units)     (30,474)  
End of period (in units) 741,618   741,618  
Restricted units outstanding, weighted-average grant date fair value [Roll Forward]        
Weighted-average grant date fair value per unit, at beginning of period (in dollars per unit) [1]     $ 27.88  
Vested weighted-average grant date fair value per unit (in dollars per unit) [1]     27.42  
Forfeited weighted-average grant date fair value per unit (in dollars per unit) [1]     28.44  
Weighted-average grant date fair value per unit, at end of period (in dollars per unit) [1] $ 28.59   $ 28.59  
Summary of awards activity, equity instruments other than options, additional disclosures [Abstract]        
Cash distributions paid to restricted common unitholders $ 0.3 $ 0.9 $ 1.1 $ 2.4
Total intrinsic value of our restricted common unit awards that vested during period 0.5 $ 3.0 27.3 $ 65.4
Unrecognized Compensation Expense [Abstract]        
Unrecognized compensation cost 3.2   3.2  
Enterprise [Member]        
Unrecognized Compensation Expense [Abstract]        
Unrecognized compensation cost $ 2.4   $ 2.4  
[1] Determined by dividing the aggregate grant date fair value of awards (before an allowance for forfeitures) by the number of awards issued.