Organization and Basis of Presentation - Narrative (Details)	Sep. 30, 2020 ft² property building
Real Estate Properties [Line Items]
Number of Real Estate Properties	64
Under-construction assets
Real Estate Properties [Line Items]
Number of Real Estate Properties	2
Near-term Development
Real Estate Properties [Line Items]
Number of Real Estate Properties	10
Area of real estate property (in square feet) | ft²	5,600,000
Future Development
Real Estate Properties [Line Items]
Number of Real Estate Properties	28
Area of real estate property (in square feet) | ft²	14,200,000
Commercial Real Estate
Real Estate Properties [Line Items]
Number of Real Estate Properties	43
Area of real estate property (in square feet) | ft²	13,300,000
Multifamily
Real Estate Properties [Line Items]
Number of Real Estate Properties	21
Number of Units in Real Estate Property | building	7,800
Multifamily | Under-construction assets
Real Estate Properties [Line Items]
Number of Real Estate Properties	1
Number of Units in Real Estate Property | building	322
Wholly Owned Properties | Future Development
Real Estate Properties [Line Items]
Area of real estate property (in square feet) | ft²	11,500,000
Wholly Owned Properties | Commercial Real Estate
Real Estate Properties [Line Items]
Area of real estate property (in square feet) | ft²	11,200,000
Wholly Owned Properties | Commercial Real Estate | Under-construction assets
Real Estate Properties [Line Items]
Number of Real Estate Properties	1
Area of real estate property (in square feet) | ft²	274,000
Wholly Owned Properties | Multifamily
Real Estate Properties [Line Items]
Number of Units in Real Estate Property | building	5,999
Wholly Owned Properties | Multifamily | Under-construction assets
Real Estate Properties [Line Items]
Number of Units in Real Estate Property | ft²	161
JBG Smith, LP
Real Estate Properties [Line Items]
Ownership interest by parent	90.40%