Mortgages Payable - Schedule of mortgages payable (Details) - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2017	Dec. 31, 2016
Debt Instrument [Line Items]
Mortgages payable, net	$ 1,376,077	$ 1,165,014
Payable to Vornado Realty Trust	$ 289,904	283,232
Mortgages
Debt Instrument [Line Items]
Variable interest rate	2.77%
Fixed interest rate	5.52%
Interest rate on payable to Vornado	3.70%
Variable rate amount	$ 767,291	547,291
Fixed rate amount	613,637	620,327
Mortgages payable	1,380,928	1,167,618
Unamortized deferred financing costs and premium/discount, net	(4,851)	(2,604)
Mortgages payable, net	1,376,077	1,165,014
Payable to Vornado Realty Trust	$ 289,904	$ 283,232