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Incentive Plan (Summary of Long-Term Incentive Units) (Details) - $ / shares
12 Months Ended
Dec. 31, 2019
Dec. 31, 2018
Dec. 31, 2017
Units      
Granted (shares) 120,368 128,986 73,449
Weighted-Average Grant Date Fair Value      
Award vesting period 4 years    
Long-term incentive units      
Units      
Unvested beginning of period (shares) 162,186    
Granted (shares) 120,368    
Vested (shares) (55,039)    
Cancelled or expired (shares) (19,228)    
Unvested end of period (shares) 208,287 162,186  
Weighted-Average Grant Date Fair Value      
Unvested, beginning of period (in dollars per share) $ 100.59    
Granted (in dollars per share) 116.22 $ 101.86 $ 109.71
Vested (in dollars per share) 100.33    
Cancelled or expired (in dollars per share) 97.32    
Unvested, end of period (in dollars per share) $ 110.00 100.59  
Long-term incentive units | Minimum      
Weighted-Average Grant Date Fair Value      
Award vesting period 2 years    
Long-term incentive units | Maximum      
Weighted-Average Grant Date Fair Value      
Award vesting period 4 years    
Market performance-based awards      
Units      
Vested (shares) (696,379)    
Weighted-Average Grant Date Fair Value      
Granted (in dollars per share) $ 114.97 $ 119.29 $ 111.06
Class D Units      
Units      
Vested (shares) (2,509,963)