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Mortgages Payable (Details) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011 | Dec. 31, 2010
Mortgage Loans on Real Estate [Line Items] |  |  |
Balance | $ 1,065,916,000 | $ 1,080,932,000 |
Proceeds from Issuance of Long-term Debt | 0 | 593,000,000 | 34,828,000
Net carrying value of real estate collaterizing the debt | 746,867,000 |  |
Repayments of Long-term Debt [Abstract] |  |  |
2013 | 94,203,000 |  |
2014 | 317,179,000 |  |
2015 | 323,193,000 |  |
2016 | 3,440,000 |  |
2017 | 3,707,000 |  |
Thereafter | 324,194,000 |  |
Rego Park 1 Shopping [Member] | Mortgages [Member] | Secured [Member] |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Debt Instrument Maturity Date String | 2013-03 |  |
Interest rate | 0.50% |  |
Balance | 78,246,000 | 78,246,000 |
Rego Park 2 Property [Member] | Mortgages [Member] | Secured [Member] |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Debt Instrument Maturity Date String | 2018-11 |  |
Interest rate | 2.06% |  |
Balance | 272,245,000 | 274,796,000 |
Basis spread over LIBOR | 1.85% |  |
Lexington Avenue Property [Member] |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Balance | 320,000,000 |  |
Mortgage Loan Converted To Recourse | 75,000,000 |  |
Lexington Avenue Property [Member] | Mortgages [Member] | Secured [Member] | Office Space [Member] |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Debt Instrument Maturity Date String | 2014-02 |  |
Interest rate | 5.33% |  |
Balance | 327,425,000 | 339,890,000 |
Lexington Avenue Property [Member] | Mortgages [Member] | Secured [Member] | Retail Space [Member] |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Debt Instrument Maturity Date String | 2015-07 |  |
Interest rate | 4.93% |  |
Balance | 320,000,000 | 320,000,000 |
Lexington Avenue Property [Member] | Mortgages [Member] | Secured [Member] | Retail Space [Member] | Maximum [Member] |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Mortgage Loan Converted To Recourse | 75,000,000 |  |
Paramus Property [Member] |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Interest rate | 2.90% |  |
Balance | 68,000,000.00 |  |
Paramus Property [Member] | Mortgages [Member] | Secured [Member] |  |  |
Mortgage Loans on Real Estate [Line Items] |  |  |
Debt Instrument Maturity Date String | 2018-10 |  |
Interest rate | 2.90% |  |
Balance | $ 68,000,000 | $ 68,000,000 |

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