Investments in Partially Owned Entities (Details) (USD $)	3 Months Ended
	Mar. 31, 2014	Feb. 01, 2014	Mar. 31, 2013	Feb. 02, 2013	Dec. 31, 2013	Nov. 02, 2013
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	$ 1,979,000		$ 22,525,000
Toys R Us [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Investments in partially owned entities excluding our share of other comprehensive income	80,062,000				80,062,000
Equity method ownership percentage	32.60%
Carrying amount of investments in partially owned entities	75,932,000				83,224,000
Non-cash impairment charges	355,953,000
Condensed Financial Information For Equity Method Investments [Abstract]
Assets		10,400,000,000				11,756,000,000
Liabilities		9,018,000,000				10,437,000,000
Noncontrolling interests		78,000,000				75,000,000
Equity		1,304,000,000				1,244,000,000
Total revenue		5,267,000,000		5,770,000,000
Net income attributable to investee		82,500,000		241,000,000
Equity Method Investment, Difference Excess Of Underlying Equity Over Carrying Amount	349,759,000
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	1,847,000		1,759,000
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	75,196,000		78,542,000
Toys R Us [Member] | Management Fees [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	1,847,000		1,759,000
Toys R Us [Member] | Impairment Loss [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Non-cash impairment charges	75,196,000
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	(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%
Carrying amount of investments in partially owned entities	167,124,000				167,785,000
Fees owed by Alexander's under management agreements	42,492,000
Excess of investee's carrying amount over equity in net assets	41,873,000
Condensed Financial Information For Equity Method Investments [Abstract]
Assets	1,452,000,000				1,458,000,000
Liabilities	1,118,000,000				1,124,000,000
Equity	334,000,000				334,000,000
Total revenue	49,000,000		49,000,000
Net income attributable to investee	15,000,000		14,000,000
Other Financial Data For Equity Method Investments [Abstract]
Ownership common shares, investee (in shares)	1,654,068
Income Loss From Equity Method Investments	6,385,000		6,076,000
Sale price, per share (in dollars per share)	$ 360.99
Equity Method Investment Market Value	597,102,000
Excess of investee's fair value over carrying amount	429,978,000
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	4,759,000		4,589,000
Alexanders Inc [Member] | Management Leasing And Development Fees [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	1,626,000		1,487,000
Lexington Realty Trust [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	0		(979,000)
LNR [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	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		45,962,000
LNR [Member] | Impairment Loss [Member]
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	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	88,563,000				88,467,000
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	(137,000)		(767,000)
India real estate ventures [Member] | Minimum [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Equity method ownership percentage	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%
Partially owned office buildings [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Carrying amount of investments in partially owned entities	628,881,000				621,294,000
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	(2,395,000)		(582,000)
Other equity method investments [Member]
Equity Method Investments And Income From Equity Method Investments [Abstract]
Carrying amount of investments in partially owned entities	284,428,000				288,897,000
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	(3,721,000)		(1,713,000)
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	1,168,996,000				1,166,443,000
Other Financial Data For Equity Method Investments [Abstract]
Income Loss From Equity Method Investments	$ 132,000		$ 20,766,000