Real Estate - Schedule of Acquisitions (Details) $ in Thousands	3 Months Ended
Sep. 30, 2017 USD ($) ft²	Dec. 31, 2016 USD ($)
Real Estate [Line Items]
Contract Purchase Price	$ 2,830,144	$ 2,685,403
Watergate 600 [Member]
Real Estate [Line Items]
Net Rentable Square Feet \| ft²	293,000
Contract Purchase Price	$ 135,000

Amount of real estate investment property which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(d))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Name:	us-gaap_RealEstateInvestmentPropertyAtCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant