Related Party Transactions (Fees to Vornado) (Details) - Vornado - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Summary of fees to Vornado
Fees to related party (in US dollars)	$ 14,428	$ 11,799	$ 11,282
Company management fees
Summary of fees to Vornado
Fees to related party (in US dollars)	2,800	2,800	2,800
Development fees
Summary of fees to Vornado
Fees to related party (in US dollars)	194	2,435	3,394
Leasing Fees
Summary of fees to Vornado
Fees to related party (in US dollars)	7,401	2,950	1,430
Property Management Fees
Summary of fees to Vornado
Fees to related party (in US dollars)	$ 4,033	$ 3,614	$ 3,658