Related Party Transactions (Fees to Vornado) (Details) - Vornado - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Summary of fees to Vornado
Fees to related party	$ 12,630	$ 7,039	$ 8,772
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	29	125	29
Leasing fees
Summary of fees to Vornado
Fees to related party	4,786	13	1,829
Property management, cleaning, engineering and security services
Summary of fees to Vornado
Fees to related party	$ 5,015	$ 4,101	$ 4,114