Related Party Transactions (Fees to Vornado) (Details) - Vornado - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Summary of fees to Vornado
Fees to related party	$ 7,039	$ 8,772	$ 14,428
Company management fees
Summary of fees to Vornado
Fees to related party	2,800	2,800	2,800
Development fees
Summary of fees to Vornado
Fees to related party	125	29	194
Leasing fees
Summary of fees to Vornado
Fees to related party	13	1,829	7,401
Property management, cleaning, engineering and security services
Summary of fees to Vornado
Fees to related party	$ 4,101	$ 4,114	$ 4,033