Properties Held for Sale and Property Dispositions (Details) $ in Millions		1 Months Ended
	May 09, 2018 USD ($)	Jan. 31, 2018 USD ($) ft²	Mar. 31, 2018 USD ($) ft²
Properties Sold [Abstract]
Approximate Square Feet | ft²			32,449,593
International Drive 1-6
Properties Sold [Abstract]
Sales Price			$ 55.0
115-117 Stevens Avenue
Properties Sold [Abstract]
Sales Price			$ 12.0
600 Lexington Ave
Properties Sold [Abstract]
Approximate Square Feet | ft²		303,515
Sales Price		$ 305.0
Gain on Sale (Loss)		$ 23.8
Subsequent Event | 635 Madison Avenue
Properties Sold [Abstract]
Sales Price	$ 151.0
Charge expected to be recorded	$ 14.0