Organization (Segment spinoff) (Details) - Subsequent Event - Spin off - Washington DC ft² in Thousands, $ in Thousands	1 Months Ended
	Jul. 17, 2017 USD ($) ft² ApartmentUnits property Unit
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations
Disposal Group Including Discontinued Operation Cash | $	$ 275,000
Pro rata basis of distribution	1:2
Office
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations
Number of real estate properties | property	37
Net rentable area | ft²	11,100
Multi family
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations
Number of real estate properties | property	5
Number Of Units | ApartmentUnits	3,133
Other Property
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations
Number of real estate properties | property	5
Net rentable area | ft²	406
Future development assets
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations
Number of development assets | Unit	18
Square Footage Of Real Estate Property | ft²	10,400