Notes and Mortgages Payable (Details) (USD $)	Jun. 30, 2012	Dec. 31, 2011
Mortgage Loans on Real Estate [Line Items]
Balance	$ 1,323,532,000	$ 1,330,932,000
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%
Balance	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	2.10%
Balance	273,544,000	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	333,742,000	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
Mortgage Loan Converted To Recourse	75,000
Kings Plaza Regional Shopping Center [Member] | Mortgages [Member] | Secured [Member]
Mortgage Loans on Real Estate [Line Items]
Debt Instrument Maturity Date String	2016-06
Interest rate	1.94%
Balance	250,000,000	250,000,000
Basis spread over LIBOR	1.70%
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