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Partners' Capital, Equity and Incentive Compensation Plans (Summary of Assumptions and Fair Values for Restricted Stock and Options to Purchase Shares of Class A Common Stock Granted) (Details)
9 Months Ended
Sep. 30, 2017
$ / shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Expected dividend yield 3.08%
Minimum  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Fair value of restricted stock granted $ 48.63
Fair value of options granted $ 10.11
Expected volatility 28.00%
Expected risk-free interest rates 2.12%
Maximum  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Fair value of restricted stock granted $ 51.88
Fair value of options granted $ 10.36
Expected risk-free interest rates 2.18%
Class O Units | Minimum  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Expected term (years) 5 years 6 months
Class O Units | Maximum  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Expected term (years) 5 years 10 months 24 days