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Investments in Unconsolidated Real Estate Ventures - Narrative (Details) $ in Millions	1 Months Ended	3 Months Ended			9 Months Ended
	Apr. 30, 2021 USD ($) ft² item	Sep. 30, 2021 USD ($)	Jun. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)	Sep. 30, 2021 USD ($)	Sep. 30, 2020 USD ($)
J.P. Morgan Global Alternatives ("J.P. Morgan")
Schedule of Equity Method Investments [Line Items]
Ownership interest (as percent)		50.00%			50.00%
J.P. Morgan Global Alternatives ("J.P. Morgan") | Potomac Yard Mixed Use Development
Schedule of Equity Method Investments [Line Items]
Number of real estate ventures | item	2
Ownership interest (as percent)	50.00%
Area of real estate property | ft²	2,000,000.0
Gain from contribution to real estate ventures	$ 11.3
Real estate venture promote interest paid			$ 17.5
J.P. Morgan Global Alternatives ("J.P. Morgan") | Potomac Yard Mixed Use Development | Non-employee Trustees and Certain Executives
Schedule of Equity Method Investments [Line Items]
Real estate venture promote interest paid			$ 4.2
J.P. Morgan Global Alternatives ("J.P. Morgan") | Potomac Yard Landbay G
Schedule of Equity Method Investments [Line Items]
Area of real estate property | ft²	700,000
J.P. Morgan Global Alternatives ("J.P. Morgan") | Institutional Investor | Potomac Yard Landbay F
Schedule of Equity Method Investments [Line Items]
Area of real estate property | ft²	1,300,000
Landmark | Courthouse Metro
Schedule of Equity Method Investments [Line Items]
Ownership interest (as percent)		18.00%			18.00%
Investments in Unconsolidated Real Estate Ventures
Schedule of Equity Method Investments [Line Items]
Property management fee revenue		$ 5.9		$ 6.3	$ 17.8	$ 19.3

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Gain (loss) from cash and land contribution to a real estate venture.

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The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

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