Corporate Indebtedness - Junior Subordinated Deferrable Interest Debentures and Principal Maturities (Details) - USD ($)	1 Months Ended	12 Months Ended
	Jun. 30, 2005	Dec. 31, 2018
Principal Repayments and Joint Venture Debt
2019		$ 33,741,000
2020		576,640,000
2021		501,505,000
2022		1,008,017,000
2023		1,922,851,000
Thereafter		1,545,405,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		$ 5,588,159,000
Trust Preferred Securities
Debt Instrument [Line Items]
Proceeds from issuance of debt	$ 100,000,000.0
Trust Preferred Securities | LIBOR
Debt Instrument [Line Items]
Interest rate added to base rate (as a percent)		1.25%
Joint venture
Principal Repayments and Joint Venture Debt
2019		$ 115,295,000
2020		278,791,000
2021		518,371,000
2022		220,810,000
2023		277,996,000
Thereafter		2,430,198,000
Repayments of principal		3,841,461,000
Joint venture | Trust Preferred Securities
Principal Repayments and Joint Venture Debt
2019		0
2020		0
2021		0
2022		0
2023		0
Thereafter		100,000,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		100,000,000
Joint venture | Mortgages and other loans payable
Scheduled Amortization
2019		6,241,000
2020		11,117,000
2021		11,636,000
2022		9,429,000
2023		7,301,000
Thereafter		9,290,000
Principal Repayments and Joint Venture Debt
2019		27,500,000
2020		315,523,000
2021		139,869,000
2022		198,588,000
2023		115,550,000
Thereafter		1,136,115,000
Future Amortization of Debt		55,014,000
Repayments of principal		1,933,145,000
Joint venture | Revolving Credit Facility
Principal Repayments and Joint Venture Debt
2019		0
2020		0
2021		0
2022		0
2023		500,000,000
Thereafter		0
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		500,000,000
Joint venture | Unsecured Term Loans
Principal Repayments and Joint Venture Debt
2019		0
2020		0
2021		0
2022		0
2023		1,300,000,000
Thereafter		200,000,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		1,500,000,000
Joint venture | Senior Unsecured Notes
Principal Repayments and Joint Venture Debt
2019		0
2020		250,000,000
2021		350,000,000
2022		800,000,000
2023		0
Thereafter		100,000,000
Scheduled Amortization and Principal Repayments
Total fixed rate and floating rate debt		$ 1,500,000,000