Property Acquisitions - Schedule of Fair Value of Equity Interest Immediately Before Acquisition Date (Details) - USD ($) $ in Thousands			1 Months Ended
	Nov. 30, 2015	Apr. 30, 2014	Dec. 31, 2015	May. 31, 2014
600 Lexington Avenue
Property Acquisitions
Contract purchase price	$ 284,000		$ 277,268
Net consideration funded by us at closing, excluding consideration financed by debt	(79,085)		(79,085)
Debt assumed	(112,795)		(112,795)
Fair value of retained equity interest	92,120
Equity and/or debt investment held	(54,575)		(54,575)
Other	2,533
Purchase price fair value adjustment	$ 40,078		$ 40,100
388-390 Greenwich Street
Property Acquisitions
Contract purchase price		$ 1,585,000		$ 1,584,868
Net consideration funded by us at closing, excluding consideration financed by debt		(208,614)		(208,614)
Debt assumed		(1,162,379)		(1,162,379)
Fair value of retained equity interest		214,007
Equity and/or debt investment held		(148,025)		(148,025)
Other		5,464
Purchase price fair value adjustment		$ 71,446		$ 71,400