Corporate Indebtedness (Details 3) - USD ($)	1 Months Ended	9 Months Ended
	Jun. 30, 2005	Sep. 30, 2015
Scheduled Amortization and Principal Repayments
Remaining 2015		$ 8,716,000
2016		693,487,000
2017		1,141,400,000
2018		330,462,000
2019		1,031,726,000
Thereafter		6,951,908,000
Total amortization of debt and principal repayments		$ 10,157,699,000
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
Remaining 2015		$ 0
2016		0
2017		0
2018		0
2019		0
Thereafter		100,000,000
Total amortization of debt and principal repayments		100,000,000
Mortgages and other loans payable
Scheduled Amortization
Remaining 2015		7,716,000
2016		47,360,000
2017		61,063,000
2018		64,462,000
2019		70,409,000
Thereafter		200,403,000
Total amortization of debt		451,413,000
Principal Repayments and Joint Venture Debt
Remaining 2015		1,000,000
2016		390,819,000
2017		725,329,000
2018		16,000,000
2019		28,317,000
Thereafter		5,252,505,000
Total principal repayments		6,413,970,000
2012 Credit Facility
Scheduled Amortization and Principal Repayments
Remaining 2015		0
2016		0
2017		0
2018		0
2019		0
Thereafter		949,000,000
Total amortization of debt and principal repayments		949,000,000
Unsecured Term Loan
Scheduled Amortization and Principal Repayments
Remaining 2015		0
2016		0
2017		0
2018		0
2019		933,000,000
Thereafter		0
Total amortization of debt and principal repayments		933,000,000
Senior Unsecured Notes
Scheduled Amortization and Principal Repayments
Remaining 2015		0
2016		255,308,000
2017		355,008,000
2018		250,000,000
2019		0
Thereafter		450,000,000
Total amortization of debt and principal repayments		1,310,316,000
Joint venture
Principal Repayments and Joint Venture Debt
Remaining 2015		2,961,000
2016		534,036,000
2017		580,044,000
2018		2,196,000
2019		104,687,000
Thereafter		474,942,000
Total principal repayments		$ 1,698,866,000
LIBOR | Trust Preferred Securities
Debt Instrument [Line Items]
Interest rate added to base rate (as a percent)		1.25%
LIBOR | Unsecured Term Loan
Debt Instrument [Line Items]
Interest rate added to base rate (as a percent)		1.40%