Dispositions - Additional Information (Details)	Sep. 26, 2019 USD ($) ft²	Sep. 27, 2018 USD ($) ft²	Aug. 09, 2018 USD ($) ft²	Dec. 31, 2019 ft²
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Area of office and retail properties | ft²				13,100,000
Liberty Place [Member]
Income Statement Balance Sheet And Additional Disclosures By Disposal Groups Including Discontinued Operations [Line Items]
Area of office and retail properties | ft²	172,000
Sale agreement amount	$ 154,500,000
Gain on sale of property	$ 1,140,000
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			209,000
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		373,000
Sale agreement amount		$ 157,000,000
Gain on sale of property		$ 1,009,000