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) - $ / shares	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of TSR units granted	54.64
Expected term (years)	5 years 6 months
Expected volatility	28.00%	28.00%	28.00%
Expected dividend yield		4.82%	3.08%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock granted	$ 42.01	$ 34.03	$ 48.63
Fair value of options granted	$ 7.56	$ 5.55	$ 10.11
Expected term (years)		5 years 6 months	5 years 6 months
Expected dividend yield	3.89%
Expected risk-free interest rates	2.33%	2.69%	2.12%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock granted	$ 51.25	$ 54.01	$ 51.88
Fair value of options granted	$ 8.28	$ 5.64	$ 10.36
Expected term (years)		6 years	5 years 10 months 24 days
Expected dividend yield	4.19%
Expected risk-free interest rates	2.56%	2.73%	2.18%