Commitments and Contingencies (Details) ft² in Thousands		6 Months Ended	12 Months Ended
	Jun. 24, 2014 USD ($) Fires	Jun. 30, 2015 USD ($) ft² aptunits	Dec. 31, 2021 USD ($)	Jan. 01, 2016	Dec. 31, 2014 USD ($)	Dec. 31, 2001 a
Commitments And Contingencies Disclosure [Line Items]
Mortgages payable		$ 1,031,213,000			$ 1,032,780,000
Rego Park 2 Property [Abstract]
Development and construction in progress		105,544,000			$ 75,289,000
Letters Of Credit [Abstract]
Standby letters of credit, issued and outstanding		2,074,000
Lexington Avenue Property [Member] | Retail Space [Member]
Commitments And Contingencies Disclosure [Line Items]
Mortgages payable		320,000,000
Insurance [Abstract]
Mortgage loan, recourse		75,000,000
Paramus Property [Member] | Tenant Occupant [Member] | Ikea [Member]
Commitments And Contingencies Disclosure [Line Items]
Mortgages payable		$ 68,000,000
Paramus Property [Abstract]
Area Of Land (in acre) | a						30.3
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, Damages Sought, Value	$ 4,000,000
Rego Park I [Member] | Sears [Member] | Minimum [Member] | Estimated Future Damages [Member]
Loss Contingency [Abstract]
Loss Contingency, Damages Sought, Value	$ 25,000,000
Rego Park II [Member] | Apartment Tower [Member] | Property Under Development [Member]
Rego Park 2 Property [Abstract]
Number of units in apartment tower (in units) | aptunits		312
Area of property (in square feet) | ft²		255
Estimated Date Of Completion		2015
Estimated Budgeted Cost		$ 125,000,000
Development and construction in progress		103,307,000
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%