Segment Information (Parentheticals) (Details) (USD $) | 3 Months Ended | 0 Months Ended | 3 Months Ended |
Mar. 31, 2014 | Mar. 31, 2013 | Apr. 19, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 | Mar. 31, 2014 | Mar. 31, 2013 |
LNR [Member] | New York Segment [Member] | New York Segment [Member] | New York Segment [Member] | New York Segment [Member] | New York Segment [Member] | New York Segment [Member] | New York Segment [Member] | New York Segment [Member] | New York Segment [Member] | New York Segment [Member] | Washington DC Segment [Member] | Washington DC Segment [Member] | Washington DC Segment [Member] | Washington DC Segment [Member] | Washington DC Segment [Member] | Washington DC Segment [Member] | Washington DC Segment [Member] | Washington DC Segment [Member] | Washington DC Segment [Member] | Washington DC Segment [Member] | Retail Properties Segment [Member] | Retail Properties Segment [Member] | Retail Properties Segment [Member] | Retail Properties Segment [Member] | Retail Properties Segment [Member] | Retail Properties Segment [Member] | Retail Properties Segment [Member] | Retail Properties Segment [Member] | Retail Properties Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] | Other Segment [Member] |
| Operating Segments [Member] | Operating Segments [Member] | Alexanders Inc [Member] | Alexanders Inc [Member] | Hotel Pennsylvania [Member] | Hotel Pennsylvania [Member] | Retail Properties [Member] | Retail Properties [Member] | Office Properties [Member] | Office Properties [Member] | Operating Segments [Member] | Operating Segments [Member] | Washington Dc Office Excluding Skyline Properties [Member] | Washington Dc Office Excluding Skyline Properties [Member] | Washington DC Skyline Properties [Member] | Washington DC Skyline Properties [Member] | Washington Dc Residential Property [Member] | Washington Dc Residential Property [Member] | Office Properties [Member] | Office Properties [Member] | Operating Segments [Member] | Operating Segments [Member] | Retail Segment Strip Shopping Centers [Member] | Retail Segment Strip Shopping Centers [Member] | Retail Segment Strip Shopping Centers [Member] | Retail Segment Regional Malls [Member] | Retail Segment Regional Malls [Member] | Retail Segment Regional Malls [Member] | Retail Segment Regional Malls [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | LNR [Member] | Merchandise Mart Other [Member] | Merchandise Mart Other [Member] | Other Properties 555 California Street [Member] | Other Properties 555 California Street [Member] | India real estate ventures [Member] | India real estate ventures [Member] | Lexington Realty Trust [Member] | Other Investments [Member] | Other Investments [Member] | Other EBITDA attributable to identifiable investments [Member] | Other EBITDA attributable to identifiable investments [Member] | Corporate General And Administrative Expenses Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] | Corporate General And Administrative Expenses Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] | Marketable Equity Securities [Member] | Investment Income And Other Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] | Investment Income And Other Excluding Mark To Market Of Deferred Compensation Plan Assets And Offsetting Liability [Member] | Net Gain On Sale Of Marketable Securities Land Parcels And Residential Condominimums [Member] | Loss On Sale Of J C Penney Common Shares [Member] | Derivative Positions in Marketable Equity Securities [Member] | Acquisition Costs [Member] | Acquisition Costs [Member] | Severance Costs [Member] | Income before net realized / unrealized gains (Operations) [Member] | Income before net realized / unrealized gains (Operations) [Member] | Carried Interest [Member] | Carried Interest [Member] | Unrealized Gain From Mark To Market [Member] | Unrealized Gain From Mark To Market [Member] | Our Total Share Of Real Estate Fund [Member] | Our Total Share Of Real Estate Fund [Member] |
| | | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | | | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | Operating Segments [Member] | | | Operating Segments [Member] | Operating Segments [Member] | Litigation Settlement Income [Member] | Operating Segments [Member] | Operating Segments [Member] | Net Gain On Sale Of Real Estate [Member] | Impairment Of Development Costs [Member] | | | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Real Estate Fund [Member] | Real Estate Fund [Member] | Real Estate Fund [Member] | Real Estate Fund [Member] | Real Estate Fund [Member] | Real Estate Fund [Member] | Real Estate Fund [Member] | Real Estate Fund [Member] |
| | | | | | | | | | | | | | | | | | | | | | | | | Operating Segments [Member] | | | Operating Segments [Member] | Operating Segments [Member] | | | | | | | | | | | | | | | | | | | | | | | | | | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] | Other Non-Operating Segments [Member] |
Segment Reporting Information [Line Items] | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |
Earnings Before Interest, Taxes, Depreciation, and Amortization | $473,699,000 | $721,365,000 | ' | $233,798,000 | $217,537,000 | $10,430,000 | $10,541,000 | ($706,000) | $318,000 | $66,195,000 | $60,382,000 | $157,879,000 | $146,296,000 | $84,087,000 | $86,244,000 | $67,257,000 | $67,107,000 | $6,499,000 | $8,162,000 | $10,331,000 | $10,975,000 | $73,756,000 | $75,269,000 | $35,280,000 | $322,326,000 | $41,321,000 | $103,361,000 | $59,599,000 | ($6,041,000) | $218,965,000 | $202,275,000 | $20,000,000 | $35,137,000 | ($46,703,000) | $20,443,000 | $19,087,000 | $16,854,000 | $12,066,000 | $10,629,000 | $1,824,000 | $1,759,000 | $6,931,000 | $4,919,000 | $3,117,000 | $45,195,000 | $66,757,000 | ($25,982,000) | ($22,756,000) | ($39,487,000) | $8,073,000 | $11,336,000 | $9,635,000 | ($36,800,000) | ($22,540,000) | ($1,784,000) | ($601,000) | ($2,612,000) | $1,982,000 | $1,462,000 | $1,775,000 | $2,183,000 | $3,542,000 | $3,379,000 | $7,299,000 | $7,024,000 |
Sales Of Real Estate | ' | ' | $1,053,000,000 | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' | ' |