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, 2020	Dec. 31, 2019	Dec. 31, 2018
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of TSR units granted	79.18	54.64
Expected term (years)	5 years 6 months	5 years 6 months
Expected volatility	27.00%	28.00%	28.00%
Expected dividend yield			4.82%
Minimum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock granted	$ 56.84	$ 42.01	$ 34.03
Fair value of options granted	$ 9.35	$ 7.56	$ 5.55
Expected term (years)			5 years 6 months
Expected dividend yield	3.31%	3.89%
Expected risk-free interest rates	0.61%	2.33%	2.69%
Maximum
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock granted	$ 65.96	$ 51.25	$ 54.01
Fair value of options granted		$ 8.28	$ 5.64
Expected term (years)			6 years
Expected dividend yield		4.19%
Expected risk-free interest rates		2.56%	2.73%