Related Party Transactions (Details) ft² in Thousands, $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended
	Mar. 31, 2016 USD ($)	Sep. 30, 2016 USD ($) ft²	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) ft² $ / ft²	Sep. 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				$ 1,990
Leasing Fees [Member]
Summary of fees to Vornado
Management, property management, cleaning, leasing and security fees owed						$ 8,916
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				$ 2,800
Leasing Agreement [Abstract]
Asset Sale Commission Threshold				$ 50,000
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		$ 1,788	$ 2,076	$ 12,629	$ 7,316
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				$ 297
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	$ 5,784
Vornado [Member] | Company Management Fees [Member]
Summary of fees to Vornado
Fees to related party		$ 700	700	$ 2,100	2,100
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		44	517	$ 163	2,176
Management, property management, cleaning, leasing and security fees owed		92		$ 92			$ 5,795
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		106	21	$ 7,397	419
Management, property management, cleaning, leasing and security fees owed		426		426		$ 1,716	2,473
Vornado [Member] | Property Management Fees [Member]
Summary of fees to Vornado
Fees to related party		938	$ 838	2,969	$ 2,621
Management, property management, cleaning, leasing and security fees owed		$ 379		$ 379			$ 283