Investments in Partially Owned Entities - Debt (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Equity Method Investment Pro Rata Share Debt Of Partially Owned Entities	$ 4,189,403	$ 29,443,128
Equity Method Investment Prorata Share Debt Of Partially Owned Entities Excluding Our Pro Rata Share Of Lnr Liabilities Related To Cmbs And Cdo		3,998,929
Toys R Us [Member]
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Equity method ownership percentage	32.60%
Maturity, Range, Start	2014
Maturity, Range, End	2021
Debt Instrument, Interest Rate at Period End (in percentage)	6.56%
Equity Method Investment Debt Of Partially Owned Entities	5,702,247	5,683,733
Alexanders Inc [Member]
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Equity method ownership percentage	32.40%
Maturity, Range, Start	2014
Maturity, Range, End	2018
Debt Instrument, Interest Rate at Period End (in percentage)	3.83%
Equity Method Investment Debt Of Partially Owned Entities	1,049,959	1,065,916
Lexington Realty Trust [Member]
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Equity Method Investment Debt Of Partially Owned Entities	0	1,994,179
LNR [Member]
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Equity Method Investment Debt Of Partially Owned Entities	0	97,521,521
LNR [Member] | LNR mortgage notes payable [Member]
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Equity Method Investment Debt Of Partially Owned Entities	0	309,787
LNR [Member] | Liabilities Of Consolidated CMBS And CDO Trusts [Member]
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Equity Method Investment Debt Of Partially Owned Entities	0	97,211,734
Partially owned office buildings [Member]
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Maturity, Range, Start	2014
Maturity, Range, End	2023
Debt Instrument, Interest Rate at Period End (in percentage)	5.74%
Equity Method Investment Debt Of Partially Owned Entities	3,622,759	2,731,893
India real estate ventures [Member] | Minimum [Member]
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Equity method ownership percentage	4.10%
India real estate ventures [Member] | Maximum [Member]
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Equity method ownership percentage	36.50%
India real estate ventures [Member] | Tcg Urban Infrastructure Holdings [Member]
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Equity method ownership percentage	25.00%
Maturity, Range, Start	2014
Maturity, Range, End	2022
Debt Instrument, Interest Rate at Period End (in percentage)	13.50%
Equity Method Investment Debt Of Partially Owned Entities	199,021	236,579
Other equity method investments [Member]
Schedule Of Long Term Debt Equity Method Investments [Line Items]
Maturity, Range, Start	2014
Maturity, Range, End	2023
Debt Instrument, Interest Rate at Period End (in percentage)	4.56%
Equity Method Investment Debt Of Partially Owned Entities	$ 1,709,509	$ 1,150,543