Investments in Partially Owned Entities (512 West 22nd Street) (Details) ft² in Thousands, $ in Thousands	Nov. 24, 2015 USD ($) Extensions	Jun. 24, 2015 USD ($) ft²	Dec. 31, 2015 USD ($)	Dec. 31, 2014 USD ($)
Schedule Of Equity Method Investments [Line Items]
Notes And Loans Payable			$ 9,513,713	$ 8,187,843
512 West 22nd Street [Member]
Schedule Of Equity Method Investments [Line Items]
Debt Instrument Maturity	November 2019
Number Of Extensions Available | Extensions	2
Length Of Extension Available	6 months
Debt Instrument, Description of Variable Rate Basis	LIBOR
Spread Over LIBOR (in percentage)	2.65%
Interest Rate, End of Period (in percentage)			3.07%
512 West 22nd Street [Member] | Office Building [Member]
Schedule Of Equity Method Investments [Line Items]
Equity method ownership percentage		55.00%
Square Footage Of Real Estate Property | ft²		173
Estimated Development Cost		$ 235,000
Project Start Date		Fourth Quarter of 2015
Estimated Project Completion Date		2018
512 West 22nd Street [Member] | Vornado Realty Trust [Member]
Schedule Of Equity Method Investments [Line Items]
Notes And Loans Payable			$ 24,240
512 West 22nd Street [Member] | Joint Venture [Member]
Schedule Of Equity Method Investments [Line Items]
Notes And Loans Payable	$ 126,000		$ 44,072