Real Estate Investments - Gross Carrying Value of Properties (Details) - USD ($) $ in Thousands		Sep. 30, 2016	Dec. 31, 2015
Property, Plant and Equipment, Gross [Abstract]
Land		$ 488,580	$ 513,268
Tenant improvements		635,783	459,952
Operating properties		3,686,339	3,693,000
Assets held for sale - real estate investments	[1],[2]	16,916	794,588
Total		3,703,255	4,487,588
Building and Improvements [Member]
Property, Plant and Equipment, Gross [Abstract]
Operating properties		$ 2,561,976	$ 2,719,780

[1] As of December 31, 2015, the 58 properties associated with the series of related transactions with Och-Ziff Real Estate were classified as held for sale on the consolidated balance sheets. On February 4, 2016, the Company completed a series of transactions, resulting in the disposition of the properties. See Note 3, “Real Estate Investments,” for further information regarding the disposition. Additionally, as of September 30, 2016, the Company categorized three office properties located on Allendale Road in King of Prussia, Pennsylvania and one property located in Oakland, California known as Oakland Lot B as held for sale in accordance with applicable accounting standards for long lived assets. See Note 3, “Real Estate Investments,” for further information.

[2] As of December 31, 2015, the office property located at 2970 Market Street in Philadelphia, Pennsylvania commonly known as 30th Street Main Post Office (“Cira Square”) was classified as held for sale on the consolidated balance sheets. The Company disposed of its interests in the property on February 5, 2016. See Note 3, "Real Estate Investments," for further information.