Organization and Basis of Presentation - Narrative (Details) ft² in Millions, $ in Billions	Sep. 30, 2021 USD ($) ft² property item
Real Estate Properties [Line Items]
Number of Real Estate Properties | property	63
Near-term Development
Real Estate Properties [Line Items]
Number of Real Estate Properties | property	11
Area of real estate property | ft²	5.3
Future Development
Real Estate Properties [Line Items]
Number of Real Estate Properties | property	25
Area of real estate property | ft²	14.3
Commercial Real Estate
Real Estate Properties [Line Items]
Number of Real Estate Properties | property	42
Area of real estate property | ft²	13.1
Multifamily
Real Estate Properties [Line Items]
Number of Real Estate Properties | property	21
Number of Units in Real Estate Property | item	7,776
Multifamily | Under-construction assets
Real Estate Properties [Line Items]
Number of Real Estate Properties | property	1
Number of Units in Real Estate Property | item	808
Wholly Owned Properties | Near-term Development
Real Estate Properties [Line Items]
Area of real estate property | ft²	5.0
Wholly Owned Properties | Future Development
Real Estate Properties [Line Items]
Area of real estate property | ft²	11.6
Wholly Owned Properties | Commercial Real Estate
Real Estate Properties [Line Items]
Area of real estate property | ft²	11.3
Wholly Owned Properties | Multifamily
Real Estate Properties [Line Items]
Number of Units in Real Estate Property | item	6,125
Wholly Owned Properties | Multifamily | Under-construction assets
Real Estate Properties [Line Items]
Number of Units in Real Estate Property | item	808
Virginia Tech
Real Estate Properties [Line Items]
Under-construction property value developed by Virginia Tech | $	$ 1
JBG Smith, LP
Real Estate Properties [Line Items]
Ownership interest by parent	90.80%