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Incentive Plan (Summary of Long-Term Incentive Units) (Details) - USD ($)
$ / shares in Units, $ in Millions
3 Months Ended
Mar. 31, 2017
Mar. 31, 2016
Dec. 31, 2016
Units      
Granted (shares) 55,324    
Weighted-Average Grant Date Fair Value      
Award vesting period 4 years    
Long-Term Incentive Units      
Units      
Unvested beginning of period (shares) 128,822    
Granted (shares) 55,324    
Vested (shares) (41,558)    
Unvested end of period (shares) 142,588    
Weighted-Average Grant Date Fair Value      
Unvested, beginning of period ($ per share) $ 66.58    
Granted ($ per share) 107.98    
Vested ($ per share) 60.83    
Unvested, end of period ($ per share) $ 84.32    
Award vesting period 4 years    
Share/unit compensation expense $ 0.7 $ 1.0  
Capitalized expense related to construction and leasing activities 0.4 $ 0.5  
Unearned compensation $ 10.5   $ 5.6
Unearned compensation, period of recognition (in years) 3 years 18 days