Real Estate Investments - Summary of Office Properties Sold (Parenthetical) (Details) - Office Properties [Member] $ in Millions		3 Months Ended		6 Months Ended
	Feb. 04, 2016 property	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)	Jun. 30, 2016 property
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Number of Properties Sold				61
196/198 Van Buren Street (Herndon Metro Plaza I&II) [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment on assets held for sale | $		$ 7.4
Number of Properties Sold				2
Och Ziff Portfolio [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Provision for impairment on assets held for sale | $			$ 45.4
Number of Properties Sold	58			58	[1]

[1] Exhibit 99.2 to the Company’s Current Report on Form 8-K filed on February 10, 2016 contains a complete list of the 58 properties disposed of in the transactions with Och-Ziff Capital Management. See Note 4, "Investment in Unconsolidated Real Estate Ventures," for further details of the transactions.