Organization and Business (Details)	12 Months Ended
	Dec. 31, 2011
Organization And Business Details [Abstract]
Common limited partnership interest in the Operating Partnership	93.50%
LNR Property [Member]
Real Estate Properties [Line Items]
Equity method ownership percentage	26.20%
JC Penney [Member]
Real Estate Properties [Line Items]
Equity method ownership percentage	11.00%
Real Estate Investment Fund [Member]
Real Estate Properties [Line Items]
Equity method ownership percentage	25.00%
Toys R Us [Member]
Real Estate Properties [Line Items]
Equity method ownership percentage	32.70%
Washington DC Office [Member] | Washington Dc Northern Virginia [Member]
Real Estate Properties [Line Items]
Number Of Real Estate Properties	77
Square Footage Of Real Estate Property	20,500,000
Alexanders Inc [Member]
Real Estate Properties [Line Items]
Equity method ownership percentage	32.40%
Office Properties [Member] | San Francisco [Member] | California Street 555 [Member]
Real Estate Properties [Line Items]
Number Of Real Estate Properties	3
Square Footage Of Real Estate Property	1,800,000
Contolling Interest In Real Estate Properties Percent	70.00%
Office Properties [Member] | New York Office [Member] | Midtown Manhattan [Member]
Real Estate Properties [Line Items]
Number Of Real Estate Properties	30
Square Footage Of Real Estate Property	20,800,000
Office Properties [Member] | Washington DC Office [Member] | Washington Dc Northern Virginia [Member]
Real Estate Properties [Line Items]
Number Of Real Estate Properties	63
Square Footage Of Real Estate Property	17,500,000
Retail Properties [Member] | Northeast States California And Puerto Rico [Member]
Real Estate Properties [Line Items]
Number Of Real Estate Properties	134
Square Footage Of Real Estate Property	24,200,000
Retail Properties [Member] | Manhattan [Member]
Real Estate Properties [Line Items]
Number Of Real Estate Properties	46
Square Footage Of Real Estate Property	2,200,000
Retail Properties [Member] | New York Office [Member] | Manhattan [Member]
Real Estate Properties [Line Items]
Number Of Real Estate Properties	25
Square Footage Of Real Estate Property	1,200,000
Retail Properties [Member] | Retail [Member] | Manhattan [Member]
Real Estate Properties [Line Items]
Number Of Real Estate Properties	21
Square Footage Of Real Estate Property	1,000,000
Merchandise Mart Properties [Member]
Real Estate Properties [Line Items]
Square Footage Of Real Estate Property	5,700,000
Merchandise Mart Properties [Member] | Chicago [Member] | Merchandise Mart Merchandise Mart [Member]
Real Estate Properties [Line Items]
Square Footage Of Real Estate Property	3,500,000
Other Real Estate And Related Investments [Member] | Manhattan [Member] | Hotel Pennsylvania [Member]
Real Estate Properties [Line Items]
Number of Units in Real Estate Property	1,700
Other Real Estate And Related Investments [Member] | Alexanders Inc [Member] | New York City Metropolitan Area [Member]
Real Estate Properties [Line Items]
Number Of Real Estate Properties	7
Other Real Estate And Related Investments [Member] | Alexanders Inc [Member] | New York City Metropolitan Area [Member] | Lexington Avenue 731 [Member]
Real Estate Properties [Line Items]
Square Footage Of Real Estate Property	1,300,000
Residential Properties [Member] | Washington DC Office [Member] | Washington Dc Northern Virginia [Member]
Real Estate Properties [Line Items]
Number Of Real Estate Properties	7
Number of Units in Real Estate Property	2,424