Limited Partners Capital Account, Units Split, Conversion Ratio

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Percentage Of Outstanding Common Shares Distributed

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Area of a real estate property.

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Number of shares of equity interests issued or issuable to acquire entity.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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The number of limited partner units issued.

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The number of limited partner units outstanding.

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The parent entity's interest in net assets of the subsidiary, expressed as a percentage.

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The number of real estate properties owned as of the balance sheet date.

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The number of units in a real estate property owned as of the balance sheet date.

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The amount of a reclassification adjustment made to prior period financial statement amounts.

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Ratio applied to the conversion of stock split, for example but not limited to, one share converted to two or two shares converted to one.

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Organization and Basis of Presentation and Combination - Narrative (Details) $ in Millions				3 Months Ended	9 Months Ended	12 Months Ended
	Jul. 18, 2017 ft² building_unit properties shares	Jul. 17, 2017 shares	Jul. 07, 2017	Sep. 30, 2016 USD ($)	Sep. 30, 2016 USD ($)	Dec. 31, 2016 USD ($)	Sep. 30, 2017 ft² building_unit property properties shares
Real Estate Properties [Line Items]
Common stock issued (in shares) \| shares		94,700,000					117,957,000
Common limited partnership units (in shares) \| shares		5,800,000
Outstanding common shares and common limited partnership units prior to the Combination \| shares	118,000,000						117,957,000
Common limited partnership units outstanding (in shares) \| shares	19,800,000
Number of real estate properties \| properties							69
Prior period reclassification adjustment \| $				$ 2.0		$ 6.0
Other
Real Estate Properties [Line Items]
Prior period reclassification adjustment \| $						$ 4.0
General and Administrative Expense
Real Estate Properties [Line Items]
Prior period reclassification adjustment \| $				$ 4.8	$ 14.3
Asset under Construction
Real Estate Properties [Line Items]
Number of real estate properties \| properties							9
Near-Term Development
Real Estate Properties [Line Items]
Number of real estate properties \| properties							1
Future Development
Real Estate Properties [Line Items]
Number of real estate properties \| properties							42
Area of real estate property (in square feet)							21,300,000
Office Building
Real Estate Properties [Line Items]
Number of real estate properties \| properties							51
Area of real estate property (in square feet)							13,700,000
Office Building \| Asset under Construction
Real Estate Properties [Line Items]
Number of real estate properties \| properties							4
Area of real estate property (in square feet)							1,300,000
Multifamily
Real Estate Properties [Line Items]
Number of real estate properties \| properties							14
Number of building units \| building_unit							6,016
Multifamily \| Asset under Construction
Real Estate Properties [Line Items]
Number of real estate properties \| properties							4
Number of building units \| building_unit							1,334
Multifamily \| Near-Term Development
Real Estate Properties [Line Items]
Number of building units \| building_unit							433
Other Property
Real Estate Properties [Line Items]
Number of real estate properties \| properties							4
Area of real estate property (in square feet)							765,000
Other Property \| Near-Term Development
Real Estate Properties [Line Items]
Number of real estate properties \| property							1
Area of real estate property (in square feet)							41,100
Wholly Owned Properties \| Future Development
Real Estate Properties [Line Items]
Area of real estate property (in square feet)							17,600,000
Wholly Owned Properties \| Office Building
Real Estate Properties [Line Items]
Area of real estate property (in square feet)							11,800,000
Wholly Owned Properties \| Office Building \| Asset under Construction
Real Estate Properties [Line Items]
Area of real estate property (in square feet)							1,200,000
Wholly Owned Properties \| Multifamily
Real Estate Properties [Line Items]
Number of building units \| building_unit							4,232
Wholly Owned Properties \| Multifamily \| Asset under Construction
Real Estate Properties [Line Items]
Number of building units \| building_unit							1,149
Wholly Owned Properties \| Multifamily \| Near-Term Development
Real Estate Properties [Line Items]
Number of building units \| building_unit							303
Wholly Owned Properties \| Other Property
Real Estate Properties [Line Items]
Area of real estate property (in square feet)							348,000
Wholly Owned Properties \| Other Property \| Near-Term Development
Real Estate Properties [Line Items]
Area of real estate property (in square feet)							4,100
JBG Smith, LP
Real Estate Properties [Line Items]
Ownership interest	85.60%						85.60%
JBG Companies
Real Estate Properties [Line Items]
Common shares and OP Units issued in consideration \| shares	37,164,000
Outstanding common shares and common limited partnership units prior to the Combination \| shares		100,571,000
Number of real estate properties \| properties	30
JBG Companies \| Asset under Construction
Real Estate Properties [Line Items]
Number of real estate properties \| properties	11
Area of real estate property (in square feet)	2,500,000
JBG Companies \| Near-Term Development
Real Estate Properties [Line Items]
Number of real estate properties \| properties	2
Area of real estate property (in square feet)	401,000
JBG Companies \| Future Development
Real Estate Properties [Line Items]
Number of real estate properties \| properties	26
Area of real estate property (in square feet)	11,700,000
JBG Companies \| Office Building
Real Estate Properties [Line Items]
Number of real estate properties \| properties	19
Area of real estate property (in square feet)	3,600,000
JBG Companies \| Multifamily
Real Estate Properties [Line Items]
Number of real estate properties \| properties	9
Number of building units \| building_unit	2,883
JBG Companies \| Other Property
Real Estate Properties [Line Items]
Number of real estate properties \| properties	2
Area of real estate property (in square feet)	490,000
JBG Companies \| Wholly Owned Properties \| Asset under Construction
Real Estate Properties [Line Items]
Area of real estate property (in square feet)	2,200,000
JBG Companies \| Wholly Owned Properties \| Near-Term Development
Real Estate Properties [Line Items]
Area of real estate property (in square feet)	242,000
JBG Companies \| Wholly Owned Properties \| Future Development
Real Estate Properties [Line Items]
Area of real estate property (in square feet)	8,500,000
JBG Companies \| Wholly Owned Properties \| Office Building
Real Estate Properties [Line Items]
Area of real estate property (in square feet)	2,300,000
JBG Companies \| Wholly Owned Properties \| Multifamily
Real Estate Properties [Line Items]
Number of building units \| building_unit	1,099
JBG Companies \| Wholly Owned Properties \| Other Property
Real Estate Properties [Line Items]
Area of real estate property (in square feet)	73,000
JBG Companies \| Common Shares
Real Estate Properties [Line Items]
Common shares and OP Units issued in consideration \| shares	23,300,000
JBG Companies \| Partnership units
Real Estate Properties [Line Items]
Common shares and OP Units issued in consideration \| shares	13,900,000
Affiliate \| Vornado
Real Estate Properties [Line Items]
Percentage of common shares distributed		100.00%
Spinoff ratio			0.5
Limited Partners spinoff ratio			0.5