Segment Information (Parentheticals) (Details) (USD $)	3 Months Ended		6 Months Ended		0 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended			3 Months Ended		6 Months Ended				3 Months Ended	6 Months Ended	3 Months Ended	6 Months Ended	3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended		3 Months Ended		6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Apr. 19, 2013 LNR [Member]	Jun. 30, 2014 New York Segment [Member] Operating Segments [Member]	Jun. 30, 2013 New York Segment [Member] Operating Segments [Member]	Jun. 30, 2014 New York Segment [Member] Operating Segments [Member]	Jun. 30, 2013 New York Segment [Member] Operating Segments [Member]	Jun. 30, 2014 New York Segment [Member] Alexanders Inc [Member] Operating Segments [Member]	Jun. 30, 2013 New York Segment [Member] Alexanders Inc [Member] Operating Segments [Member]	Jun. 30, 2014 New York Segment [Member] Alexanders Inc [Member] Operating Segments [Member]	Jun. 30, 2013 New York Segment [Member] Alexanders Inc [Member] Operating Segments [Member]	Jun. 30, 2014 New York Segment [Member] Hotel Pennsylvania [Member] Operating Segments [Member]	Jun. 30, 2013 New York Segment [Member] Hotel Pennsylvania [Member] Operating Segments [Member]	Jun. 30, 2014 New York Segment [Member] Hotel Pennsylvania [Member] Operating Segments [Member]	Jun. 30, 2013 New York Segment [Member] Hotel Pennsylvania [Member] Operating Segments [Member]	Jun. 30, 2014 New York Segment [Member] Retail Properties [Member] Operating Segments [Member]	Jun. 30, 2013 New York Segment [Member] Retail Properties [Member] Operating Segments [Member]	Jun. 30, 2014 New York Segment [Member] Retail Properties [Member] Operating Segments [Member]	Jun. 30, 2013 New York Segment [Member] Retail Properties [Member] Operating Segments [Member]	Jun. 30, 2014 New York Segment [Member] Office Properties [Member] Operating Segments [Member]	Jun. 30, 2013 New York Segment [Member] Office Properties [Member] Operating Segments [Member]	Jun. 30, 2014 New York Segment [Member] Office Properties [Member] Operating Segments [Member]	Jun. 30, 2013 New York Segment [Member] Office Properties [Member] Operating Segments [Member]	Jun. 30, 2014 Washington DC Segment [Member] Operating Segments [Member]	Jun. 30, 2013 Washington DC Segment [Member] Operating Segments [Member]	Jun. 30, 2014 Washington DC Segment [Member] Operating Segments [Member]	Jun. 30, 2013 Washington DC Segment [Member] Operating Segments [Member]	Jun. 30, 2014 Washington DC Segment [Member] Washington Dc Office Excluding Skyline Properties [Member] Operating Segments [Member]	Jun. 30, 2013 Washington DC Segment [Member] Washington Dc Office Excluding Skyline Properties [Member] Operating Segments [Member]	Jun. 30, 2014 Washington DC Segment [Member] Washington Dc Office Excluding Skyline Properties [Member] Operating Segments [Member]	Jun. 30, 2013 Washington DC Segment [Member] Washington Dc Office Excluding Skyline Properties [Member] Operating Segments [Member]	Jun. 30, 2014 Washington DC Segment [Member] Washington DC Skyline Properties [Member] Operating Segments [Member]	Jun. 30, 2013 Washington DC Segment [Member] Washington DC Skyline Properties [Member] Operating Segments [Member]	Jun. 30, 2014 Washington DC Segment [Member] Washington DC Skyline Properties [Member] Operating Segments [Member]	Jun. 30, 2013 Washington DC Segment [Member] Washington DC Skyline Properties [Member] Operating Segments [Member]	Jun. 30, 2014 Washington DC Segment [Member] Washington Dc Residential Property [Member] Operating Segments [Member]	Jun. 30, 2013 Washington DC Segment [Member] Washington Dc Residential Property [Member] Operating Segments [Member]	Jun. 30, 2014 Washington DC Segment [Member] Washington Dc Residential Property [Member] Operating Segments [Member]	Jun. 30, 2013 Washington DC Segment [Member] Washington Dc Residential Property [Member] Operating Segments [Member]	Jun. 30, 2014 Washington DC Segment [Member] Office Properties [Member] Operating Segments [Member]	Jun. 30, 2013 Washington DC Segment [Member] Office Properties [Member] Operating Segments [Member]	Jun. 30, 2014 Washington DC Segment [Member] Office Properties [Member] Operating Segments [Member]	Jun. 30, 2013 Washington DC Segment [Member] Office Properties [Member] Operating Segments [Member]	Jun. 30, 2014 Retail Properties Segment [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Operating Segments [Member]	Jun. 30, 2014 Retail Properties Segment [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Operating Segments [Member]	Jun. 30, 2014 Retail Properties Segment [Member] Retail Segment Strip Shopping Centers [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Retail Segment Strip Shopping Centers [Member] Operating Segments [Member]	Jun. 30, 2014 Retail Properties Segment [Member] Retail Segment Strip Shopping Centers [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Retail Segment Strip Shopping Centers [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Retail Segment Strip Shopping Centers [Member] Litigation Settlement Income [Member] Operating Segments [Member]	Jun. 30, 2014 Retail Properties Segment [Member] Retail Segment Regional Malls [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Retail Segment Regional Malls [Member] Operating Segments [Member]	Jun. 30, 2014 Retail Properties Segment [Member] Retail Segment Regional Malls [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Retail Segment Regional Malls [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Retail Segment Regional Malls [Member] Net Gain On Sale Of Real Estate [Member] Operating Segments [Member]	Jun. 30, 2014 Retail Properties Segment [Member] Retail Segment Regional Malls [Member] Impairment Of Development Costs [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Retail San Jose Strip Center [Member] Net Gain On Sale Of Real Estate [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Retail San Jose Strip Center [Member] Net Gain On Sale Of Real Estate [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Retail PA Philadelphia [Member] Net Gain On Sale Of Real Estate [Member] Operating Segments [Member]	Jun. 30, 2013 Retail Properties Segment [Member] Retail PA Philadelphia [Member] Net Gain On Sale Of Real Estate [Member] Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] LNR [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] LNR [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] LNR [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] LNR [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Merchandise Mart Other [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Merchandise Mart Other [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Merchandise Mart Other [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Merchandise Mart Other [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Other Properties 555 California Street [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Other Properties 555 California Street [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Other Properties 555 California Street [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Other Properties 555 California Street [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] India real estate ventures [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] India real estate ventures [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] India real estate ventures [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] India real estate ventures [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Lexington Realty Trust [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Lexington Realty Trust [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Lexington Realty Trust [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Lexington Realty Trust [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Other Investments [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Other Investments [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Other Investments [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Other Investments [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Other EBITDA attributable to identifiable investments [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Other EBITDA attributable to identifiable investments [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Other EBITDA attributable to identifiable investments [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Other EBITDA attributable to identifiable investments [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Corporate General And Administrative Expenses Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Corporate General And Administrative Expenses Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Corporate General And Administrative Expenses Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Corporate General And Administrative Expenses Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Marketable Equity Securities [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Marketable Equity Securities [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Marketable Equity Securities [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Marketable Equity Securities [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Investment Income And Other Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Investment Income And Other Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Investment Income And Other Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Investment Income And Other Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Net Gain On Sale Of Marketable Securities Land Parcels And Residential Condominimums [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Net Gain On Sale Of Marketable Securities Land Parcels And Residential Condominimums [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Net Gain On Sale Of Marketable Securities Land Parcels And Residential Condominimums [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Net Gain On Sale Of Marketable Securities Land Parcels And Residential Condominimums [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Loss On Sale Of J C Penney Common Shares [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Loss On Sale Of J C Penney Common Shares [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Loss On Sale Of J C Penney Common Shares [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Loss On Sale Of J C Penney Common Shares [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Derivative Positions in Marketable Equity Securities [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Derivative Positions in Marketable Equity Securities [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Derivative Positions in Marketable Equity Securities [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Derivative Positions in Marketable Equity Securities [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Acquisition Costs [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Acquisition Costs [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Acquisition Costs [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Acquisition Costs [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Severance Costs [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Severance Costs [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Severance Costs [Member] Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Severance Costs [Member] Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Income before net realized / unrealized gains [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Income before net realized / unrealized gains [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Income before net realized / unrealized gains [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Income before net realized / unrealized gains [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Net realized gains on exited investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Net realized gains on exited investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Net realized gains on exited investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Net realized gains on exited investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Previously recorded unrealized gains on exited investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Previously recorded unrealized gains on exited investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Previously recorded unrealized gains on exited investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Previously recorded unrealized gains on exited investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Net unrealized gains on held investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Net unrealized gains on held investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Net unrealized gains on held investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Net unrealized gains on held investments [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Carried Interest [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Carried Interest [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Carried Interest [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Carried Interest [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Our Total Share Of Real Estate Fund [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Our Total Share Of Real Estate Fund [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2014 Other Segment [Member] Our Total Share Of Real Estate Fund [Member] Real Estate Fund Other Non-Operating Segments [Member]	Jun. 30, 2013 Other Segment [Member] Our Total Share Of Real Estate Fund [Member] Real Estate Fund Other Non-Operating Segments [Member]
Segment Reporting Information [Line Items]
Earnings Before Interest, Taxes, Depreciation, and Amortization	$ 454,101,000	$ 506,617,000	$ 927,800,000	$ 1,227,982,000		$ 251,329,000	$ 235,723,000	$ 485,127,000	$ 453,260,000	$ 10,271,000	$ 10,213,000	$ 20,701,000	$ 20,754,000	$ 10,278,000	$ 10,094,000	$ 9,572,000	$ 10,412,000	$ 67,947,000	$ 57,230,000	$ 134,142,000	$ 117,612,000	$ 162,833,000	$ 158,186,000	$ 320,712,000	$ 304,482,000	$ 84,894,000	$ 84,778,000	$ 168,981,000	$ 171,022,000	$ 67,057,000	$ 66,136,000	$ 134,314,000	$ 133,243,000	$ 7,073,000	$ 7,543,000	$ 13,572,000	$ 15,705,000	$ 10,764,000	$ 11,099,000	$ 21,095,000	$ 22,074,000	$ 74,130,000	$ 73,679,000	$ 147,886,000	$ 148,948,000	$ 54,180,000	$ 118,406,000	$ 89,460,000	$ 440,732,000	$ 40,056,000	$ 101,529,000	$ 81,377,000	$ 204,890,000	$ 59,599,000	$ 14,124,000	$ 16,877,000	$ 8,083,000	$ 235,842,000	$ 202,275,000	$ 20,000,000	$ 32,169,000	$ 32,169,000	$ 33,058,000	$ 33,058,000	$ 58,509,000	$ 58,656,000	$ 93,646,000	$ 11,953,000	$ 0	$ 0	$ 0	$ 20,443,000	$ 22,454,000	$ 22,453,000	$ 41,541,000	$ 39,307,000	$ 11,506,000	$ 11,022,000	$ 23,572,000	$ 21,651,000	$ 99,000	$ 2,254,000	$ 1,923,000	$ 4,013,000	$ 0	$ 0	$ 0	$ 6,931,000	$ 4,288,000	$ 5,760,000	$ 9,207,000	$ 8,877,000	$ 76,677,000	$ 61,600,000	$ 121,872,000	$ 128,357,000	$ (23,022,000)	$ (24,831,000)	$ (49,004,000)	$ (47,587,000)	$ 0	$ 0	$ 0	$ (39,487,000)	$ 8,032,000	$ 16,709,000	$ 16,105,000	$ 28,045,000	$ 905,000	$ 1,005,000	$ 10,540,000	$ 1,005,000	$ 0	$ 0	$ 0	$ (36,800,000)	$ 0	$ 9,065,000	$ 0	$ (13,475,000)	$ (4,083,000)	$ (3,350,000)	$ (5,867,000)	$ (3,951,000)	$ 0	$ (1,542,000)	$ 0	$ (4,154,000)	$ 2,191,000	$ 1,643,000	$ 4,617,000	$ 3,651,000	$ 18,767,000	$ 0	$ 18,767,000	$ 0	$ (8,841,000)	$ 0	$ (5,597,000)	$ 0	$ 14,339,000	$ 8,398,000	$ 14,637,000	$ 11,777,000	$ 11,874,000	$ 10,070,000	$ 13,205,000	$ 11,707,000	$ 38,330,000	$ 20,111,000	$ 45,629,000	$ 27,135,000
Sales Of Real Estate					1,053,000,000
Mark-to-market of investments in our deferred compensation plan	$ 2,380,000	$ 2,492,000	$ 6,780,000	$ 5,938,000																																																																																													$ 2,380,000	$ 2,492,000	$ 6,780,000	$ 5,938,000