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Notes and Mortgages Payable (Details) (USD $) | 12 Months Ended |  |  | 0 Months Ended |  |  | 12 Months Ended |  |  | 12 Months Ended |  | 0 Months Ended |  |  |  | 0 Months Ended |  |
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Dec. 31, 2011 | Dec. 31, 2010 | Dec. 31, 2009 | Dec. 31, 2011 Rego Park 1 Shopping [Member] Mortgages [Member] Secured [Member] | Dec. 31, 2010 Rego Park 1 Shopping [Member] Mortgages [Member] Secured [Member] | Nov. 30, 2011 Rego Park 2 Property [Member] Mortgages [Member] Secured [Member] | Dec. 31, 2011 Rego Park 2 Property [Member] Mortgages [Member] Secured [Member] | Dec. 31, 2010 Rego Park 2 Property [Member] Mortgages [Member] Secured [Member] | Dec. 31, 2011 Lexington Avenue Property [Member] | Dec. 31, 2011 Lexington Avenue Property [Member] Mortgages [Member] Secured [Member] Office Space [Member] | Dec. 31, 2010 Lexington Avenue Property [Member] Mortgages [Member] Secured [Member] Office Space [Member] | Dec. 31, 2011 Lexington Avenue Property [Member] Mortgages [Member] Secured [Member] Retail Space [Member] | Dec. 31, 2010 Lexington Avenue Property [Member] Mortgages [Member] Secured [Member] Retail Space [Member] | Jun. 10, 2011 Kings Plaza Regional Shopping Center [Member] Mortgages [Member] Secured [Member] | Dec. 31, 2011 Kings Plaza Regional Shopping Center [Member] Mortgages [Member] Secured [Member] | Dec. 31, 2010 Kings Plaza Regional Shopping Center [Member] Mortgages [Member] Secured [Member] | Dec. 31, 2011 Paramus Property [Member] | Oct. 05, 2011 Paramus Property [Member] Mortgages [Member] Secured [Member] | Dec. 31, 2011 Paramus Property [Member] Mortgages [Member] Secured [Member] | Dec. 31, 2010 Paramus Property [Member] Mortgages [Member] Secured [Member]
Mortgage Loans on Real Estate [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Instrument Maturity Date String |  |  |  | 2012-03 |  |  | 2018-11 |  |  | 2014-02 |  | 2015-07 |  |  | 2016-06 |  |  |  | 2018-10 |
Interest rate |  |  |  | 0.75% |  |  | 2.15% |  |  | 5.33% |  | 4.93% |  |  | 2.24% |  | 2.90% |  | 2.90% |
Balance | $ 1,330,932,000 | $ 1,246,411,000 |  | $ 78,246,000 | $ 78,246,000 |  | $ 274,796,000 | $ 277,200,000 | $ 320,000,000 | $ 339,890,000 | $ 351,751,000 | $ 320,000,000 | $ 320,000,000 |  | $ 250,000,000 | $ 151,214,000 | $ 68,000,000.00 |  | $ 68,000,000 | $ 68,000,000
Basis spread over LIBOR |  |  |  |  |  | 1.85% |  |  |  |  |  |  |  | 1.70% |  |  |  |  |  |
Mortgage Loan Converted To Recourse |  |  |  |  |  |  |  |  | 75,000,000 |  |  | 75,000,000 |  |  |  |  |  |  |  |
Proceeds from Issuance of Long-term Debt | 593,000,000 | 34,828,000 | 162,961,000 |  |  | 275,000,000 |  |  |  |  |  |  |  | 250,000,000 |  |  |  |  |  |
Proceeds from (Repayments of) Debt |  |  |  |  |  |  |  |  |  |  |  |  |  | 95,000,000 |  |  |  |  |  |
Debt amortization period |  |  |  |  |  | 30 years |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt Term |  |  |  |  |  | 7 years |  |  |  |  |  |  |  | 5 years |  |  |  | 7 years |  |
Net carrying value of real estate collaterizing the debt | 873,911,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Repayments of Long-term Debt [Abstract] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2012 | 93,262,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2013 | 15,957,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2014 | 317,179,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2015 | 323,192,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
2016 | 253,440,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Thereafter | $ 327,902,000 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |

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