Acquisition, Disposals and Assets Held for Sale Dispositions and Assets Held for Sale (Details) $ in Thousands	1 Months Ended	3 Months Ended		12 Months Ended
	Jan. 31, 2020 USD ($)	Sep. 30, 2019 USD ($)	Mar. 31, 2019 USD ($)	Dec. 31, 2019 USD ($) ft²	Dec. 31, 2018 USD ($) ft²	Dec. 31, 2017 USD ($)
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Property Held-for-sale					$ 427,400
Gain on sale of real estate				$ (104,991)	(52,183)	$ 0
Assets held for sale				168,412	78,981
Liabilities related to assets held for sale				$ 0	$ 3,717
Commerce Executive/Commerce Metro Land [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of real estate			$ (39,000)
Prudential Global Investment Management (PGIM) [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in square feet) | ft²				552,000
Equity Method Investment, Ownership Percentage Sold				50.00%
1600 K Street [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of real estate		$ (8,100)
Central Place Tower [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Gain on sale of real estate				$ (53,400)
Commerce Executive / Commerce Metro Land, 1600 K Street [Domain]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in square feet) | ft²				479,799
Proceeds from Sale of Property Held-for-sale				$ 165,350
Proceeds from sale of real estate				164,815
Gain on sale of real estate				$ (51,635)
Reston, Virginia [Member] | Commerce Executive/Commerce Metro Land [Member] | Commercial Segment [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in square feet) | ft²				388,562	388,562
Proceeds from Sale of Property Held-for-sale				$ 114,950
Proceeds from sale of real estate				117,676
Gain on sale of real estate				(39,033)
Assets held for sale					$ 78,981
Liabilities related to assets held for sale					$ 3,717
Proceeds from Sale of Real Estate Held-for-Investment, Reimbursements				$ 4,000
Washington, D.C. [Member] | 1600 K Street [Member] | Commercial Segment [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in square feet) | ft²				82,653
Proceeds from Sale of Property Held-for-sale				$ 43,000
Proceeds from sale of real estate				40,134
Gain on sale of real estate				$ (8,088)
Vienna, Virginia [Member] | Vienna Retail [Member] | Commercial Segment [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in square feet) | ft²				8,584
Proceeds from Sale of Property Held-for-sale				$ 7,400
Proceeds from sale of real estate				7,005
Gain on sale of real estate				(4,514)
National Landing, Virginia [Member] | Pen Place - Land Parcel [Member] | Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale				73,895
Liabilities related to assets held for sale				0
National Landing, Virginia [Member] | Metropolitan Park [Member] | Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Assets held for sale				94,517
Liabilities related to assets held for sale				$ 0
National Landing, Virginia [Member] | Penn Place and Met 6, 7 and 8 [Member] | Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Property Held-for-sale			$ 293,900
Future Development
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in square feet) | ft²				21,900,000
Future Development | Commerce Executive/Commerce Metro Land [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in square feet) | ft²				894,000
Future Development | Penn Place and Met 6, 7 and 8 [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Area of real estate property (in square feet) | ft²				4,100,000
Subsequent Event [Member] | Metropolitan Park [Member]
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Proceeds from Sale of Property Held-for-sale	$ 155,000
Subsequent Event [Member] | National Landing, Virginia [Member] | Metropolitan Park [Member] | Other
Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items]
Increase Over Previously Disclosed Contract Price	$ 11,000