Dispositions - Additional Information (Details)	Sep. 27, 2018 USD ($) ft²	Aug. 09, 2018 USD ($) ft²	May 03, 2017 USD ($) ft²	Dec. 31, 2018 ft²
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Area of office and retail properties | ft²				11,900,000
2099 Pennsylvania Avenue [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Area of office and retail properties | ft²		208,776
Sale agreement amount		$ 219,900,000
Gain on sale of property		$ 35,836,000
425 Eye Street [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Area of office and retail properties | ft²	372,552
Sale agreement amount	$ 157,000,000
Gain on sale of property	$ 1,009,000
Waterview [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Area of office and retail properties | ft²			636,768
Sale agreement amount			$ 460,000,000
Gain on sale of property			$ 110,583,000