Related Party Transactions (Details)		12 Months Ended
	Dec. 22, 2014 USD ($)	Dec. 31, 2015 USD ($) $ / ft²	Dec. 31, 2014 USD ($)	Dec. 31, 2013 USD ($)
Management and Development Agreements [Abstract]
Property Management and Development Fee agreement		We pay Vornado an annual management fee equal to the sum of (i) $2,800,000, (ii) 2% of gross revenue from the Rego Park II shopping center, (iii) $0.50 per square foot of the tenant-occupied office and retail space at 731 Lexington Avenue, and (iv) $289,000, escalating at 3% per annum, for managing the common area of 731 Lexington Avenue. Vornado is also entitled to a development fee equal to 6% of development costs, as defined. The payment of development fees for The Alexander apartment tower is due on substantial completion of the construction, as defined.
Leasing Agreement [Abstract]
Leasing service fee payable, description		Vornado also provides us with leasing services for a fee of 3% of rent for the first ten years of a lease term, 2% of rent for the eleventh through the twentieth year of a lease term, and 1% of rent for the twenty-first through thirtieth year of a lease term, subject to the payment of rents by tenants. In the event third-party real estate brokers are used, the fees to Vornado increase by 1% and Vornado is responsible for the fees to the third-party real estate brokers.
Mr. Roth, David Mandelbaum, and Russell B. Wight, Jr.
Related Party Transaction [Line Items]
Ownership Interest in the Company		26.30%
IP & Partners Through Vornado
Related Party Transaction [Line Items]
Ownership Interest in the Company		2.20%
Vornado [Member]
Related Party Transaction [Line Items]
Noncontrolling Interest, Ownership Percentage by Parent		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%
Leasing services fee and commission on asset sale, annual installment, maximum. (in US dollars)	$ 4,000,000
Debt Instrument, Description of Variable Rate Basis	One Year LIBOR
Basis spread over LIBOR	1.00%
Repayment of leasing costs (in US Dollars)	$ 40,353,000
Summary of fees to Vornado
Fees to related party (in US dollars)		$ 11,799,000	$ 11,282,000	$ 7,341,000
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)		$ 289,000
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] | Company Management Fees [Member]
Summary of fees to Vornado
Fees to related party (in US dollars)		$ 2,800,000	2,800,000	2,800,000
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)		$ 2,435,000	3,394,000	0
Fees owed (in US dollars)		$ 5,795,000	3,394,000
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)		$ 2,950,000	1,430,000	1,126,000
Fees owed (in US dollars)		2,473,000
Vornado [Member] | Property Management Fees [Member]
Summary of fees to Vornado
Fees to related party (in US dollars)		3,614,000	3,658,000	$ 3,415,000
Fees owed (in US dollars)		$ 283,000	$ 528,000