Subsequent Events (Details) - Subsequent Event [Member] ft² in Thousands	Jul. 31, 2015 USD ($) ft² RenewalOptions shares	Jul. 28, 2015 USD ($) ft²
New York 100 West 33rd Street [Member]
Schedule Of Equity Method Investments [Line Items]
Notes And Loans Payable Refinanced Amount (in US Dollars) | $		$ 580,000,000
Square Footage Of Real Estate Property		1,100
Debt Instrument, Description of Variable Rate Basis		LIBOR
Spread Over LIBOR (in percentage)		1.65%
Debt Instrument Maturity		July 2020
Net proceeds from refinancing of loan | $		$ 242,000,000
New York 100 West 33rd Street [Member] | Office [Member]
Schedule Of Equity Method Investments [Line Items]
Square Footage Of Real Estate Property		851
New York 100 West 33rd Street [Member] | Manhattan Mall [Member]
Schedule Of Equity Method Investments [Line Items]
Square Footage Of Real Estate Property		256
New York 260 11th Avenue [Member]
Schedule Of Equity Method Investments [Line Items]
Area Of Property For Parking Lot And Air Rights (in sqft)	10
Area Of Land	44
Lease expiration term	99 years
Purchase Options, Land | $	$ 110,000,000
Annual ground rent | $	$ 3,900,000
Inflation Rate Agreement For Calculating Annual Ground Rent And Purchase Price Option	annual ground rent and the purchase option price escalate annually at the lesser of 1.5% or CPI
Operating partnership units issued | shares	813,900
Operating Partnership Units Value | $	$ 80,000,000
New York 260 11th Avenue [Member] | Office [Member]
Schedule Of Equity Method Investments [Line Items]
Square Footage Of Real Estate Property	235
Number Of Market Renewal Options | RenewalOptions	2
Term Of Market Renewal Options	5 years
Lease Expiration Date	2021