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	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected volatility	33.00%	33.00%
Minimum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock granted	$ 35.81	$ 35.81
Fair value of options granted	$ 8.00	$ 8.00
Expected term (years)	5 years 6 months	5 years 6 months
Expected dividend yield	3.40%	3.40%
Expected risk-free interest rates	1.67%	1.67%
Maximum [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Fair value of restricted stock granted	$ 37.69	$ 37.69
Fair value of options granted	$ 8.77	$ 8.77
Expected term (years)	6 years 1 month 6 days	6 years 1 month 6 days
Expected dividend yield		3.57%
Expected risk-free interest rates	1.94%	1.94%