Investments in Partially Owned Entities - Debt (Details) (USD $) In Thousands, unless otherwise specified					3 Months Ended				3 Months Ended				3 Months Ended						3 Months Ended				3 Months Ended
	Mar. 31, 2014	Dec. 31, 2013	Mar. 31, 2014 Toys R Us [Member]	Dec. 31, 2013 Toys R Us [Member]	Mar. 31, 2014 Toys R Us [Member] Minimum [Member]	Mar. 31, 2014 Toys R Us [Member] Maximum [Member]	Mar. 31, 2014 Alexanders Inc [Member]	Dec. 31, 2013 Alexanders Inc [Member]	Mar. 31, 2014 Alexanders Inc [Member] Minimum [Member]	Mar. 31, 2014 Alexanders Inc [Member] Maximum [Member]	Mar. 31, 2014 Partially owned office buildings [Member]	Dec. 31, 2013 Partially owned office buildings [Member]	Mar. 31, 2014 Partially owned office buildings [Member] Minimum [Member]	Mar. 31, 2014 Partially owned office buildings [Member] Maximum [Member]	Mar. 31, 2014 India real estate ventures [Member] Minimum [Member]	Mar. 31, 2014 India real estate ventures [Member] Maximum [Member]	Mar. 31, 2014 India real estate ventures [Member] Tcg Urban Infrastructure Holdings [Member]	Dec. 31, 2013 India real estate ventures [Member] Tcg Urban Infrastructure Holdings [Member]	Mar. 31, 2014 India real estate ventures [Member] Tcg Urban Infrastructure Holdings [Member] Minimum [Member]	Mar. 31, 2014 India real estate ventures [Member] Tcg Urban Infrastructure Holdings [Member] Maximum [Member]	Mar. 31, 2014 Other equity method investments [Member]	Dec. 31, 2013 Other equity method investments [Member]	Mar. 31, 2014 Other equity method investments [Member] Minimum [Member]	Mar. 31, 2014 Other equity method investments [Member] Maximum [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method ownership percentage			32.60%				32.40%								4.10%	36.50%	25.00%
Maturity, Range, Start					2014				2015				2014						2014				2014
Maturity, Range, End						2021				2021				2023						2022				2023
Debt Instrument, Interest Rate at Period End (in percentage)			7.14%				2.59%				5.74%						13.23%				4.56%
Equity Method Investment Debt Of Partially Owned Entities			$ 4,977,482	$ 5,702,247			$ 1,035,022	$ 1,049,959			$ 3,632,588	$ 3,622,759					$ 202,496	$ 199,021			$ 1,705,703	$ 1,709,509
Equity Method Investment Pro Rata Share Debt Of Partially Owned Entities	$ 3,953,375	$ 4,189,403