Corporate Indebtedness (Junior Subordinated Deferrable Interest Debentures and Principal Maturities)(Details) - USD ($)	1 Months Ended	12 Months Ended
	Jun. 30, 2005	Dec. 31, 2016
Scheduled Amortization and Principal Repayments
2017		$ 1,326,860,000
2018		603,926,000
2019		1,241,916,000
2020		970,231,000
2021		93,696,000
Thereafter		2,332,083,000
Total amortization of debt and principal repayments		6,568,712,000
Joint Venture Debt
Principal Repayments and Joint Venture Debt
2017		574,327,000
2018		48,253,000
2019		555,545,000
2020		31,183,000
2021		222,452,000
Thereafter		1,311,022,000
Total principal repayments		$ 2,742,782,000
Trust Preferred Securities
Debt Instrument [Line Items]
Proceeds from Issuance of Debt	$ 100,000,000.0
Coupon Rate (as a percent)		5.61%
Number of Years from Issuance of Debt for which Fixed Rate of Interest will be in Force		10 years
Scheduled Amortization and Principal Repayments
2017		$ 0
2018		0
2019		0
2020		0
2021		0
Thereafter		100,000,000
Total amortization of debt and principal repayments		$ 100,000,000
Trust Preferred Securities | LIBOR
Debt Instrument [Line Items]
Interest rate added to base rate (as a percent)		1.25%
Mortgages and other loans payable
Scheduled Amortization
2017		$ 51,531,000
2018		54,371,000
2019		58,916,000
2020		40,700,000
2021		29,666,000
Thereafter		86,275,000
Total amortization of debt		321,459,000
Principal Repayments and Joint Venture Debt
2017		930,329,000
2018		299,555,000
2019		0
2020		679,531,000
2021		64,030,000
Thereafter		1,845,808,000
Total principal repayments		3,819,253,000
Revolving Credit Facility
Scheduled Amortization and Principal Repayments
2017		0
2018		0
2019		0
2020		0
2021		0
Thereafter		0
Total amortization of debt and principal repayments		0
Unsecured Term Loan
Scheduled Amortization and Principal Repayments
2017		0
2018		0
2019		1,183,000,000
2020		0
2021		0
Thereafter		0
Total amortization of debt and principal repayments		$ 1,183,000,000
Unsecured Term Loan | LIBOR
Debt Instrument [Line Items]
Interest rate added to base rate (as a percent)		1.40%
Senior Unsecured Notes
Scheduled Amortization and Principal Repayments
2017		$ 345,000,000
2018		250,000,000
2019		0
2020		250,000,000
2021		0
Thereafter		300,000,000
Total amortization of debt and principal repayments		$ 1,145,000,000