Commitments and Contingencies (Details)			9 Months Ended	12 Months Ended
	Oct. 15, 2015 USD ($)	Jun. 24, 2014 USD ($) Fires	Sep. 30, 2015 USD ($)	Dec. 31, 2021 USD ($)	Jan. 01, 2016	Dec. 31, 2014 USD ($)	Dec. 31, 2001 a
Paramus Property [Abstract]
Mortgages payable			$ 1,060,408,000			$ 1,032,780,000
Letters Of Credit [Abstract]
Standby letters of credit, outstanding			2,074,000
Kings Plaza Regional Shopping Center [Member] | Subsequent Event [Member]
Loss Contingency [Abstract]
Loss Contingency, claim value	$ 20,300,000
Paramus Property [Member] | Tenant Occupant [Member] | Ikea [Member]
Paramus Property [Abstract]
Area Of Land (in acre) | a							30.3
Mortgages payable			$ 68,000,000
Fixed interest rate on the debt (in percentage)			2.90%
Debt Instrument Maturity Date String			October 2018
Triple-net rent, annual amount			$ 700,000
Paramus Property [Member] | Tenant Occupant [Member] | Ikea [Member] | Scenario Forecast [Member]
Paramus Property [Abstract]
Property purchase option exercisable be leasee with purchase option in 2021				$ 75,000,000
Purchase option exercised, net cash proceeds from sale of land				7,000,000
Purchase option excercised, gain on sale of land				60,000,000
Purchase option not excercised amount included in triple net rent over remainder of lease				$ 68,000,000
Loan Amortization Period				20 years
Rego Park I [Member] | Sears [Member]
Loss Contingency [Abstract]
Number Of Fires | Fires		2
Rego Park I [Member] | Sears [Member] | Minimum [Member]
Loss Contingency [Abstract]
Loss Contingency, claim value		$ 4,000,000
Rego Park I [Member] | Sears [Member] | Minimum [Member] | Estimated Future Damages [Member]
Loss Contingency [Abstract]
Loss Contingency, claim value		$ 25,000,000
General Liability [Member]
Insurance [Abstract]
Insurance Maximum Coverage Per Incident			300,000,000
All Risk Property And Rental Value [Member]
Insurance [Abstract]
Insurance Maximum Coverage Per Incident			1,700,000,000
Terrorism Coverage Including Nbcr [Member]
Insurance [Abstract]
Insurance Maximum Coverage Per Incident			1,700,000,000
Insurance Maximum Coverage In Aggregate			$ 1,700,000,000
NBCR [Member]
Insurance [Abstract]
Insurance Coverage End Date			December 2020
Deductible			$ 275,000
Self Insured Responsibility (in percentage)			15.00%
Federal Government Responsibility (in percentage)			85.00%
NBCR [Member] | Scenario Forecast [Member]
Insurance [Abstract]
Self Insured Responsibility (in percentage)					16.00%
Federal Government Responsibility (in percentage)					84.00%