Commitments and Contingencies (Details) (USD $)				3 Months Ended		12 Months Ended		3 Months Ended
	Mar. 31, 2013	Dec. 31, 2012	Mar. 31, 2013 Lexington Avenue Property [Member]	Mar. 31, 2013 Paramus Property [Member] Tenant Occupant [Member] Ikea [Member]	Dec. 31, 2001 Paramus Property [Member] Tenant Occupant [Member] Ikea [Member] acre	Dec. 31, 2021 Paramus Property [Member] Tenant Occupant [Member] Ikea [Member] Scenario, Forecast [Member]	Mar. 31, 2013 Flushing Property [Member]	Mar. 31, 2013 Flushing Property [Member] New World Mall Llc [Member]	Mar. 31, 2013 General Liability [Member]	Mar. 31, 2013 All Risk Property And Rental Value [Member]	Mar. 31, 2013 Terrorism Coverage Including Nbcr [Member]	Mar. 31, 2013 NBCR [Member]
Insurance [Abstract]
Insurance Maximum Coverage Per Incident									$ 300,000,000	$ 1,700,000,000	$ 1,700,000,000
Deductible												275,000
Self Insured Responsibility												15.00%
Federal Government Responsibility												85.00%
Mortgage loans, recourse			75,000,000
Mortgage loan, carrying amount	1,061,953,000	1,065,916,000	320,000,000	68,000,000.00
Flushing Property [Abstract]
Non-refundable purchase deposit							1,875,000
Indemnification Sought by Tenant								50,000,000
Paramus Property [Abstract]
Acres Of Land					30.3
Leases Of Lessor Rental Term Range				40 years
Property purchase option exercisable by lessee						75,000,000.00
Fixed interest rate on the debt				2.90%
Triple-net rent, annual amount				700,000.00
Purchase option exercised, proceeds from sale of land						7,000,000.00
Purchase option exercised, gain on sale of land						60,000,000.00
Purchase option not exercised, amount included in triple net rent over remainder of lease						68,000,000.00
Loan Amortization Period						20 years
Letters Of Credit [Abstract]
Standby letters of credit, issued and outstanding	$ 4,058,000.00