Mortgages Payable (Details) (USD $)	Sep. 30, 2012	Dec. 31, 2011
Mortgage Loans on Real Estate [Line Items]
Mortgages Payable	$ 1,069,776,000	$ 1,080,932,000
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%
Mortgages Payable	78,246,000	78,246,000
Percentage of cash mortgage collateralized	100.00%
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%
Mortgages Payable	272,901,000	274,796,000
Basis spread over LIBOR	1.85%
Lexington Avenue Property [Member]
Mortgage Loans on Real Estate [Line Items]
Mortgages Payable	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%
Mortgages Payable	330,629,000	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%
Mortgages Payable	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] | Mortgages [Member] | Secured [Member]
Mortgage Loans on Real Estate [Line Items]
Debt Instrument Maturity Date String	2018-10
Interest rate	2.90%
Mortgages Payable	$ 68,000,000	$ 68,000,000