Related Party Transactions (Details) ft² in Thousands	1 Months Ended	3 Months Ended		6 Months Ended
	Mar. 31, 2016 USD ($)	Jun. 30, 2016 USD ($) ft²	Jun. 30, 2015 USD ($)	Jun. 30, 2016 USD ($) ft² $ / ft²	Jun. 30, 2015 USD ($)	Jan. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Rego Park II [Member] | Retail Space [Member] | Toys R Us [Member]
Other Agreements [Abstract]
Area of property (in square feet) | ft²		47		47
Rent related to leased space				$ 1,309,000
Leasing Fees [Member]
Summary of fees to Vornado
Fees owed (in US dollars)						$ 8,916,000
Vornado [Member]
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent		32.40%		32.40%
Management and Development Agreements [Abstract]
Management Fee Agreement Value (in US dollars)				$ 2,800,000
Leasing Agreement [Abstract]
Asset Sale Commission Threshold (in US dollars)				$ 50,000,000
Percentage Commissions On Sale Of Assets Under Fifty Million				3.00%
Percentage Commissions On Sale Of Assets Over Fifty Million				1.00%
Summary of fees to Vornado
Fees to related party (In US dollars)		$ 2,523,000	$ 2,464,000	$ 10,840,000	$ 5,240,000
Vornado [Member] | Toys R Us [Member]
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent		32.50%		32.50%
Vornado [Member] | 731 Lexington Avenue [Member] | Office And Retail Space [Member]
Management and Development Agreements [Abstract]
Property Management Fee Agreement Price Per Square Foot | $ / ft²				0.5
Vornado [Member] | 731 Lexington Avenue [Member] | Common Area [Member]
Management and Development Agreements [Abstract]
Property Management Fee Agreement Value (in US dollars)				$ 297,000
Property Management Fee Escalation Percentage Per Annum				3.00%
Vornado [Member] | Rego Park II [Member] | Retail Space [Member]
Management and Development Agreements [Abstract]
Property Management Fee Agreement Percentage Of Income				2.00%
Vornado [Member] | Alexander Apartment Tower [Member]
Summary of fees to Vornado
Development Fees Paid (In US Dollars)	$ 5,784,000
Vornado [Member] | Company Management Fees [Member]
Summary of fees to Vornado
Fees to related party (In US dollars)		$ 700,000	700,000	$ 1,400,000	1,400,000
Vornado [Member] | Development fees [Member]
Management and Development Agreements [Abstract]
Development fee as percentage of development costs				6.00%
Summary of fees to Vornado
Fees to related party (In US dollars)		75,000	895,000	$ 119,000	1,659,000
Fees owed (in US dollars)		74,000		$ 74,000			$ 5,795,000
Vornado [Member] | Leasing Fees [Member]
Leasing Agreement [Abstract]
Lease Fee Percentage Of Rent One To Ten Years				3.00%
Lease Fee Percentage Of Rent Eleven To Twenty Years				2.00%
Lease Fee Percentage Of Rent Twenty First To Thirty Years				1.00%
Percentage Increase Lease Fee If Broker Used				1.00%
Summary of fees to Vornado
Fees to related party (In US dollars)		833,000	16,000	$ 7,291,000	398,000
Fees owed (in US dollars)		831,000		831,000		$ 1,716,000	2,473,000
Vornado [Member] | Property Management Fees [Member]
Summary of fees to Vornado
Fees to related party (In US dollars)		915,000	$ 853,000	2,030,000	$ 1,783,000
Fees owed (in US dollars)		$ 318,000		$ 318,000			$ 283,000