Corporate Indebtedness (Junior Subordinated Deferrable Interest Debentures and Principal Maturities)(Details) - USD ($)	1 Months Ended	6 Months Ended
	Jun. 30, 2005	Jun. 30, 2017
Scheduled Amortization and Principal Repayments
Remaining 2017		$ 320,626,000
2018		604,298,000
2019		1,242,618,000
2020		1,170,958,000
2021		30,418,000
Thereafter		3,066,470,000
Total amortization of debt and principal repayments		6,435,388,000
Joint Venture Debt
Principal Repayments and Joint Venture Debt
Remaining 2017		78,752,000
2018		285,924,000
2019		555,574,000
2020		320,914,000
2021		332,892,000
Thereafter		1,350,672,000
Total principal repayments		2,924,728,000
Trust Preferred Securities
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 100,000,000.0
Scheduled Amortization and Principal Repayments
Remaining 2017		0
2018		0
2019		0
2020		0
2021		0
Thereafter		100,000,000
Total amortization of debt and principal repayments		100,000,000
Mortgages and other loans payable
Scheduled Amortization
Remaining 2017		25,659,000
2018		54,938,000
2019		59,618,000
2020		41,427,000
2021		30,418,000
Thereafter		90,533,000
Total amortization of debt		302,593,000
Principal Repayments and Joint Venture Debt
Remaining 2017		0
2018		299,360,000
2019		0
2020		679,531,000
2021		0
Thereafter		2,575,937,000
Total principal repayments		3,554,828,000
Revolving Credit Facility
Scheduled Amortization and Principal Repayments
Remaining 2017		0
2018		0
2019		0
2020		200,000,000
2021		0
Thereafter		0
Total amortization of debt and principal repayments		200,000,000
Unsecured Term Loan
Scheduled Amortization and Principal Repayments
Remaining 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
Senior Unsecured Notes
Scheduled Amortization and Principal Repayments
Remaining 2017		294,967,000
2018		250,000,000
2019		0
2020		250,000,000
2021		0
Thereafter		300,000,000
Total amortization of debt and principal repayments		$ 1,094,967,000
LIBOR | Trust Preferred Securities
Debt Instrument [Line Items]
Interest rate added to base rate (as a percent)		1.25%
Effective interest rate (as a percent)		2.38%
LIBOR | Unsecured Term Loan
Debt Instrument [Line Items]
Interest rate added to base rate (as a percent)		1.40%