Investments in Partially Owned Entities (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2014	May 03, 2014	Jun. 30, 2013	May 04, 2013	Jun. 30, 2014	May 03, 2014	Jun. 30, 2013	May 04, 2013	Dec. 31, 2013	Nov. 02, 2013
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	$ (53,742,000)		$ (35,389,000)		$ (51,763,000)		$ (12,864,000)
Toys R Us [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Equity method ownership percentage	32.60%				32.60%
Carrying amount of investments in partially owned entities	26,309,000				26,309,000				83,224,000
Non-cash impairment charges					355,953,000
Condensed Financial Information For Equity Method Investments [Abstract]
Assets		10,358,000,000				10,358,000,000				11,756,000,000
Liabilities		9,130,000,000				9,130,000,000				10,437,000,000
Noncontrolling interests		83,000,000				83,000,000				75,000,000
Equity		1,145,000,000				1,145,000,000				1,244,000,000
Total revenue		2,479,000,000		2,408,000,000		7,746,000,000		8,178,000,000
Net income attributable to investee		(194,000,000)		(119,000,000)		(111,000,000)		122,000,000
Equity Method Investment, Difference Excess Of Underlying Equity Over Carrying Amount	347,337,000				347,337,000
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	(57,591,000)		(36,861,000)		(55,744,000)		(35,102,000)
Toys R Us [Member] | Equity In Net Income After Income Taxes [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	(59,530,000)		(38,708,000)		15,666,000		39,834,000
Toys R Us [Member] | Management Fees [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	1,939,000		1,847,000		3,786,000		3,606,000
Toys R Us [Member] | Impairment Loss [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	0		0		(75,196,000)		(78,542,000)
Alexanders Inc [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Equity method ownership percentage	32.40%				32.40%
Carrying amount of investments in partially owned entities	167,004,000				167,004,000				167,785,000
Fees owed by Alexander's under management agreements	42,489,000				42,489,000
Excess of investee's carrying amount over equity in net assets	41,569,000				41,569,000
Condensed Financial Information For Equity Method Investments [Abstract]
Assets	1,450,000,000				1,450,000,000				1,458,000,000
Liabilities	1,113,000,000				1,113,000,000				1,124,000,000
Equity	337,000,000				337,000,000				334,000,000
Total revenue	50,000,000		47,000,000		99,000,000		96,000,000
Net income attributable to investee	17,000,000		13,000,000		32,000,000		27,000,000
Other Financial Data For Equity Method Investments [Abstract]
Ownership common shares, investee (in shares)	1,654,068				1,654,068
Income Loss From Equity Method Investments	6,894,000		5,751,000		13,279,000		11,827,000
Sale price, per share (in dollars per share)	$ 369.47				$ 369.47
Equity Method Investment Market Value	611,128,000				611,128,000
Excess of investee's fair value over carrying amount	444,124,000				444,124,000
Alexanders Inc [Member] | Equity In Net Income After Income Taxes [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	5,272,000		4,077,000		10,031,000		8,486,000
Alexanders Inc [Member] | Management Leasing And Development Fees [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	1,622,000		1,674,000		3,248,000		3,341,000
Lexington Realty Trust [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	0		0		0		(979,000)
LNR [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	0		0		0		18,731,000
LNR [Member] | Equity In Net Income After Income Taxes [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	0		0		0		45,962,000
LNR [Member] | Impairment Loss [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	0		0		0		(27,231,000)
India real estate ventures [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Carrying amount of investments in partially owned entities	87,859,000				87,859,000				88,467,000
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	(2,041,000)		(414,000)		(2,178,000)		(1,181,000)
India real estate ventures [Member] | Minimum [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Equity method ownership percentage	4.10%				4.10%
India real estate ventures [Member] | Maximum [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Equity method ownership percentage	36.50%				36.50%
Partially owned office buildings [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Carrying amount of investments in partially owned entities	725,483,000				725,483,000				621,294,000
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	990,000		(1,042,000)		(1,405,000)		(1,624,000)
Other equity method investments [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Carrying amount of investments in partially owned entities	287,024,000				287,024,000				288,897,000
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	(1,994,000)		(2,823,000)		(5,715,000)		(4,536,000)
All Equity Method Investees Excluding Toys [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Carrying amount of investments in partially owned entities	1,267,370,000				1,267,370,000				1,166,443,000
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	$ 3,849,000		$ 1,472,000		$ 3,981,000		$ 22,238,000