Segment Reporting [Abstract] Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] JBG Companies [Member] JBG Companies [Member] JBG Companies [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Net income (loss) attributable to common shareholders Net Income (Loss) Attributable to Parent Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Corporate and other Other General and Administrative Expense Third-party real estate services Management Fee Expense Share-based compensation related to Formation Transaction Allocated Share-based Compensation Expense - Formation Transaction Allocated Share-based Compensation Expense - Formation Transaction Transaction and other costs Business Combination, Acquisition Related Costs Interest expense Interest Expense Loss on extinguishment of debt Gain (Loss) on Extinguishment of Debt Reduction of gain (gain) on bargain purchase Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Bargain Purchase, Reduction Of Gain Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Bargain Purchase, Increase (Decrease) Of Gain Income tax benefit Income Tax Expense (Benefit) Net (income) loss attributable to redeemable noncontrolling interests Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Third-party real estate services, including reimbursements Property Management Fee Revenue Other income Other Income Income (loss) from unconsolidated real estate ventures, net Income (Loss) from Equity Method Investments Interest and other income (loss), net Investment Income, Net Gains (Losses) on Sales of Investment Real Estate Gains (Losses) on Sales of Investment Real Estate Net loss attributable to noncontrolling interests Net Income (Loss) Attributable to Nonredeemable Noncontrolling Interest Consolidated NOI Consolidated NOI Consolidated NOI Equity Method Investments and Joint Ventures [Abstract] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Canadian Pension Plan Investment Board (CPPIB) Canadian Pension Plan Investment Board [Member] Canadian Pension Plan Investment Board [Member] Landmark Landmark [Member] Landmark [Member] CBREI Venture CBREI Venture [Member] CBREI Venture [Member] Berkshire Group [Member] Berkshire Group [Member] Berkshire Group [Member] Brandywine Brandywine [Member] Brandywine [Member] CIM/PacLife [Member] CIM/PacLife [Member] CIM/PacLife JP Morgan JP Morgan [Member] JP Morgan [Member] Other Other Investment [Member] Other Investment [Member] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Ownership Interest Equity Method Investment, Ownership Percentage Total investments in unconsolidated real estate ventures Real Estate Investments, Unconsolidated Real Estate and Other Joint Ventures, Excluding Advances Real Estate Investments, Unconsolidated Real Estate and Other Joint Ventures, Excluding Advances Advances to unconsolidated real estate ventures Real Estate Investments, Unconsolidated Real Estate and Other Joint Ventures, Advances Real Estate Investments, Unconsolidated Real Estate and Other Joint Ventures, Advances Total investments in and advances to unconsolidated real estate ventures Real Estate Investments, Unconsolidated Real Estate and Other Joint Ventures Investments in and Advances to Unconsolidated Real Estate Ventures Equity Method Investments and Joint Ventures Disclosure [Text Block] Statement of Financial Position [Abstract] Preferred shares, par value (in dollars per share) Preferred Stock, Par or Stated Value Per Share Preferred shares, shares authorized Preferred Stock, Shares Authorized Preferred shares, shares issued Preferred Stock, Shares Issued Preferred shares, shares outstanding Preferred Stock, Shares Outstanding Common shares, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common shares, shares authorized Common Stock, Shares Authorized Common shares, shares issued Common Stock, Shares, Issued Common shares, shares outstanding Common Stock, Shares, Outstanding Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Third-Party Real Estate Services Segment Third-Party Real Estate Services Segment [Member] Third-Party Real Estate Services Segment [Member] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Number of reportable segments Number of Reportable Segments Number of operating segments Number of Operating Segments Other assets, net Other Assets Interest Expense [Abstract] Interest Income and Interest Expense Disclosure [Text Block] Interest Income and Interest Expense Disclosure [Text Block] Segment Information Segment Reporting Disclosure [Text Block] Accounting Policies [Abstract] Schedule of Recent Accounting Pronouncements Schedule of New Accounting Pronouncements and Changes in Accounting Principles [Table Text Block] Discontinued Operations and Disposal Groups [Abstract] Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Washington, D.C. [Member] Washington, D.C. [Member] Washington, D.C. [Member] Downtown Silver Spring, MD [Member] Downtown Silver Spring, MD [Member] Downtown Silver Spring, MD [Member] Reston, Virginia [Member] Reston, Virginia [Member] Reston, Virginia [Member] Disposal Group Name [Axis] Disposal Group Name [Axis] Disposal Group Name [Domain] Disposal Group Name [Domain] Summit I and II, Bowen Bldg & Executive Tower [Member] Summit I and II, Bowen Bldg & Executive Tower [Member] Summit I and II, Bowen Bldg & Executive Tower [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event [Member] Subsequent Event [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member] Disposal Group, Held-for-sale or Disposed of by Sale, Not Discontinued Operations [Member] JP Morgan [Member] 1233 20th Street [Member] 1233 20th Street [Member] 1233 20th Street [Member] Falkland Chase-North [Member] Falkland Chase-North [Member] Falkland Chase-North [Member] Summit I & II Land [Member] Summit I & II Land [Member] Summit I & II Land [Member] Summit I and II [Member] Summit I and II [Member] Summit I and II [Member] Bowen Building, Washington DC [Member] Bowen Building, Washington DC [Member] Bowen Building, Washington DC [Member] Commerce Executive [Member] Commerce Executive [Member] Commerce Executive [Member] Executive Tower [Member] Executive Tower [Member] Executive Tower [Member] Office Segment [Member] Office Segment [Member] Office Segment [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Mortgages payable Mortgages [Member] Revolving credit facility Revolving Credit Facility [Member] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Area of real estate property (in square feet) Area of Real Estate Property Proceeds from Sale of Property Held-for-sale Gross proceeds from sale of real estate Gross proceeds from sale of real estate Proceeds from sale of real estate Proceeds from Sale of Real Estate Held-for-investment Repayments of Secured Debt Repayments of Secured Debt Assets Held-for-sale, Not Part of Disposal Group Assets Held-for-sale, Not Part of Disposal Group Liabilities held for sale Liabilities held for sale Liabilities held for sale Proceeds from Sale of Property Held-for-sale Proceeds from Sale of Property Held-for-sale Subsequent Events [Abstract] Subsequent Event [Table] Subsequent Event [Table] Subsequent Event [Line Items] Subsequent Event [Line Items] Common Stock, Dividends, Per Share, Declared Common Stock, Dividends, Per Share, Declared Related Party Transactions [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] Affiliated Entity [Member] Affiliated Entity [Member] Trustee Director [Member] Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Allocations of centralized corporate costs Allocations Of Centralized Corporate Costs [Member] Allocations Of Centralized Corporate Costs [Member] Financing transactions Financing Transactions [Member] Financing Transactions [Member] Supervise cleaning, engineering and security services Supervisory Services of Properties [Member] Supervisory Services of Properties Separation and Combination transaction Separation And Combination Transaction [Member] Separation And Combination Transaction [Member] Consulting agreement Consulting Agreement [Member] Consulting Agreement [Member] Fees from Legacy JBG Funds Fees from Legacy JBG Funds [Member] Fees from Legacy JBG Funds [Member] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] Vornado Vornado Realty Trust [Member] Vornado Realty Trust [Member] BMS BMS [Member] BMS [Member] Legacy JBG Funds [Member] Legacy JBG Funds [Member] Legacy JBG Funds [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Financing of the Universal Buildings Financing Of The Universal Buildings [Member] Financing Of The Universal Buildings [Member] Note agreement for development of Bartlett Note Agreement For Development Of Bartlett [Member] Note Agreement For Development Of Bartlett [Member] Mortgage loan secured by Bowen Building Mortgage loan secured by Bowen Building [Member] Mortgage loan secured by Bowen Building [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Vornado's revolving credit facility Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] LIBOR London Interbank Offered Rate (LIBOR) [Member] Name of Property [Axis] Name of Property [Axis] Name of Property [Domain] Name of Property [Domain] Universal Buildings, Washington DC Universal Buildings, Washington DC [Member] Universal Buildings, Washington DC [Member] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Allocated amounts included in general and administrative expense Related Party Transaction, Selling, General and Administrative Expenses from Transactions with Related Party Expenses from related parties Related Party Transaction, Expenses from Transactions with Related Party Revenue from related parties Revenue from Related Parties Debt instrument, face amount Debt Instrument, Face Amount Loan to Vornado Origination of Notes Receivable from Related Parties Mortgage loan interest rate Debt Instrument, Basis Spread on Variable Rate Interest Income on loan receivable from Vornado Interest Income, Related Party Repayment of mortgages payable Accrued interest on mortgage loan Debt Instrument, Increase, Accrued Interest Interest expense to Vornado Interest Expense, Related Party Transaction services, initial period (in months) Related Party Transaction, Initial Potential Service Period Related Party Transaction, Initial Potential Service Period Proceeds from credit facility Proceeds from Lines of Credit Related party transaction amount Related Party Transaction, Amounts of Transaction Related party transaction, monthly amount Related Party Transaction, Monthly Transaction Amount Related Party Transaction, Monthly Transaction Amount Liability incurred in connection with the Combination Business Combination, Consideration Transferred, Liabilities Incurred Accounts Receivable, Related Parties Accounts Receivable, Related Parties Statement [Table] Statement [Table] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Statement [Line Items] Statement [Line Items] Interest expense Interest Expense, Debt, Excluding Amortization Amortization of deferred financing costs Amortization of Debt Discount (Premium) Unrealized Gain (Loss) on Derivatives Unrealized Gain (Loss) on Derivatives Derivative, Gain (Loss) on Derivative, Net Derivative, Gain (Loss) on Derivative, Net Capitalized interest Interest Paid, Capitalized, Investing Activities Interest Expense Organization, Consolidation and Presentation of Financial Statements [Abstract] Business Acquisition, Pro Forma Information [Table Text Block] Business Acquisition, Pro Forma Information [Table Text Block] Statement of Cash Flows [Abstract] Temporary Equity, Redemptions of OP Units Temporary Equity, Redemptions of OP Units Temporary Equity, Redemptions of OP Units OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income (loss) Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Adjustments to reconcile net income (loss) to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Share-based compensation expense Share-based Compensation Depreciation and amortization, including amortization of debt issuance costs Depreciation, Depletion and Amortization Deferred rent Straight Line Rent (Income) loss from unconsolidated real estate ventures, net Amortization of above- and below-market lease intangibles, net Amortization Of Acquired Below-Market Lease, Net Of Acquired Above-Market Lease Amortization Of Acquired Below-Market Lease, Net Of Acquired Above-Market Lease Amortization of lease incentives Amortization of Lease Incentives Return on capital from unconsolidated real estate ventures Proceeds from Equity Method Investment, Distribution Gain on sale of real estate Unrealized gain on interest rate swaps and caps Bad debt expense Provision for Doubtful Accounts Other non-cash items Other Noncash Income (Expense) Changes in operating assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Tenant and other receivables Increase (Decrease) in Accounts and Notes Receivable Other assets, net Increase (Decrease) in Other Operating Assets Accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities Other liabilities, net Increase (Decrease) in Other Operating Liabilities Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Development costs, construction in progress and real estate additions Payments to Acquire and Develop Real Estate Cash and restricted cash received in connection with the Combination, net Cash Acquired from Acquisition Proceeds from Sale of Real Estate Proceeds from Sale of Real Estate Acquisition of interests in unconsolidated real estate ventures, net of cash acquired Payments to Acquire Equity Method Investments Distributions of capital from unconsolidated real estate ventures Proceeds from Equity Method Investment, Distribution, Return of Capital Distribution of capital from sale of interest in an unconsolidated real estate venture Proceeds from Sale of Equity Method Investments Investments in and advances to unconsolidated real estate ventures Payments to Acquire Real Estate and Real Estate Joint Ventures Proceeds from Collection of Notes Receivable Proceeds from Collection of Notes Receivable Other investments Payments to Acquire Other Investments Proceeds from repayment of receivable from former parent Repayment of Notes Receivable from Related Parties Net cash provided by investing activities Net Cash Provided by (Used in) Investing Activities FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Contributions from former parent, net Proceeds from Contributions from Affiliates Acquisition of interest in consolidated real estate venture Payments for (Proceeds from) Other Real Estate Partnerships Repayment of borrowings from former parent Repayments of Related Party Debt Proceeds from borrowings from former parent Proceeds from Related Party Debt Capital lease payments Repayments of Long-term Capital Lease Obligations Borrowings under mortgages payable Proceeds from Notes Payable Borrowings under revolving credit facility Borrowings under unsecured term loans Proceeds from Issuance of Unsecured Debt Repayments of mortgages payable Repayments of Notes Payable Repayments of revolving credit facility Repayments of Lines of Credit Debt issuance costs Payments of Debt Issuance Costs Dividends paid to common shareholders Payments of Ordinary Dividends, Common Stock Distributions to redeemable noncontrolling interests Payments of Ordinary Dividends, Noncontrolling Interest Proceeds from Noncontrolling Interests Proceeds from Noncontrolling Interests Distributions to noncontrolling interests Payments to Noncontrolling Interests Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities Net increase in cash and cash equivalents and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Cash and cash equivalents and restricted cash as of the beginning of the period Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Cash and cash equivalents and restricted cash as of the end of the period CASH AND CASH EQUIVALENTS AND RESTRICTED CASH AS OF END OF THE PERIOD: Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Restricted cash Restricted Cash Cash and cash equivalents and restricted cash SUPPLEMENTAL DISCLOSURE OF CASH FLOW AND NON-CASH INFORMATION: Supplemental Cash Flow Information [Abstract] Cash paid for interest (net of capitalized interest of $14,863 and $2,285 in 2018 and 2017) Interest Paid, Excluding Capitalized Interest, Operating Activities Accrued capital expenditures included in accounts payable and accrued expenses Capital Expenditures Incurred but Not yet Paid Write-off of fully depreciated assets Write-Off Of Fully Depreciated Assets, Including Asset Impairment Write-Off Of Fully Depreciated Assets, Including Asset Impairment Deferred interest on mortgages payable (of which $857 in 2018 is included in capitalized interest) Interest Payable Cash receipts from (payments for) income taxes Income Taxes Paid Deconsolidation of 1900 N Street Investments in Joint Ventures Total investments in (A) an entity in which the entity has significant influence, but does not have control, (B) subsidiaries that are not required to be consolidated and are accounted for using the equity and or cost method, and (C) an entity in which the reporting entity shares control of the entity with another party or group. Excludes long-term advances receivable from a party that is affiliated with the reporting entity by means of direct or indirect ownership. Issuance of common limited partnership units at the Separation Temporary Equity, Stock Issued During Period, Value, New Issues Issuance of common shares at the Separation Stock Issued Issuance of common shares in connection with the Combination Stock Issued During Period, Value, Acquisitions Issuance of common limited partnership units in connection with the Combination Noncash or Part Noncash, Issuance of Partnership Units in Business Combination Noncash or Part Noncash, Issuance of Partnership Units in Business Combination Contribution from former parent in connection with the Separation Noncash or Part Noncash Contributions from Former Parent Noncash or Part Noncash Contributions from Former Parent Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Time-Based LTIP Units Time-Based Long-Term Incentive Partnership Units [Member] Time-Based Long-Term Incentive Partnership Units [Member] Performance-Based LTIP Units Performance Shares [Member] LTIP Units Long-Term Incentive Partnership Units [Member] Long-Term Incentive Partnership Units [Member] Other Equity Awards Other Equity Awards [Member] Other Equity Awards [Member] Share-based compensation expense - other Share-Based Compensation, Other [Member] Share-Based Compensation, Other [Member] Formation Awards Formation Awards [Member] Formation Awards [Member] LTIP and OP Units (1) Long-Term Incentive Partnership Units And Time-Based Long-Term Incentive Partnership Units [Member] Long-Term Incentive Partnership Units And Time-Based Long-Term Incentive Partnership Units [Member] Share-based compensation related to Formation Transaction Share-Based Compensation Related To Formation Transaction [Member] Share-Based Compensation Related To Formation Transaction [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based compensation related to Formation Transaction Allocated Share-based Compensation Expense Allocated Share-based Compensation Expense, Before Capitalization Allocated Share-based Compensation Expense, Before Capitalization Allocated Share-based Compensation Expense, Before Capitalization Less amount capitalized Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount Share-based compensation expense Share-based Compensation Arrangement by Share-based Payment Award, Compensation Cost Total unrecognized compensation expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options Compensation expense recognition period (in years) Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract] Other Assets, Net Other Assets Disclosure [Text Block] Other Liabilities Disclosure [Abstract] Composition of Other Liabilities, Net Other Liabilities [Table Text Block] Statement of Stockholders' Equity [Abstract] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Common Shares Common Stock [Member] Additional Paid-In Capital Additional Paid-in Capital [Member] Accumulated Deficit Retained Earnings [Member] Accumulated Other Comprehensive Income AOCI Including Portion Attributable to Noncontrolling Interest [Member] Former Parent Equity Former Parent Equity [Member] Former Parent Equity [Member] Noncontrolling Interests in Consolidated Subsidiaries Noncontrolling Interest [Member] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Balance at beginning of period Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Balance at beginning of period (in shares) Net loss attributable to common shareholders Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Common Shares Issued During Period in Connection with Redemption of OP Units Common Shares Issued During Period in Connection with Redemption of OP Units Common Shares Issued During Period in Connection with Redemption of OP Units Dividends Dividends Deferred compensation shares and options, net Stock Issued During Period, Value, Employee Benefit Plan Contributions from former parent, net Stockholders' Equity Note, Spinoff Transaction Stock Repurchased During Period, Value Stock Repurchased During Period, Value Stock Issued During Period, Shares, New Issues Stock Issued During Period, Shares, New Issues Stock Issued During Period, Value, New Issues Stock Issued During Period, Value, New Issues Stock Issued During Period, Shares, Acquisitions Stock Issued During Period, Shares, Acquisitions Noncontrolling Interest, Increase from Business Combination Noncontrolling Interest, Increase from Business Combination Distributions to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Noncontrolling Interest, Contributions Noncontrolling Interest, Contributions Noncontrolling Interest, Contributions Redeemable noncontrolling interest redemption value adjustment and other comprehensive income allocation Noncontrolling Interest, Change in Redemption Value Other comprehensive income Other Comprehensive Income (Loss), Net of Tax Stockholders' Equity, Other Stockholders' Equity, Other Balance at end of period (in shares) Balance at end of period Noncontrolling Interest [Abstract] Redeemable Noncontrolling Interests Temporary Equity Disclosure [Text Block] Temporary Equity Disclosure [Text Block] Income Statement [Abstract] REVENUE Revenues [Abstract] Property rentals Operating Leases, Income Statement, Lease Revenue Reimbursements from Tenants Reimbursements from Tenants Tenants Reimbursements Total revenue Revenues EXPENSES Costs and Expenses [Abstract] Property operating Cost of Other Property Operating Expense Real estate taxes Real Estate Tax Expense General and administrative: General and Administrative Expense [Abstract] Operating Expenses Operating Expenses OPERATING INCOME (LOSS) Operating Income (Loss) Interest expense Loss on extinguishment of debt Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Bargain Purchase, Reduction Of Gain INCOME (LOSS) BEFORE INCOME TAX BENEFIT Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income tax benefit NET INCOME (LOSS) Net (income) loss attributable to redeemable noncontrolling interests NET INCOME (LOSS) ATTRIBUTABLE TO COMMON SHAREHOLDERS EARNINGS (LOSS) PER COMMON SHARE: Earnings Per Share [Abstract] Basic (in dollars per share) Earnings Per Share, Basic Diluted (in dollars per share) Earnings Per Share, Diluted WEIGHTED AVERAGE NUMBER OF COMMON SHARES OUTSTANDING - basic and diluted (in shares) Weighted Average Number of Shares Outstanding, Basic and Diluted Weighted Average Number of Shares Outstanding, Diluted Weighted Average Number of Shares Outstanding, Diluted Net loss attributable to noncontrolling interests Net income (loss) attributable to common shareholders Distributions to participating securities Undistributed Earnings (Loss) Allocated to Participating Securities, Basic Net income (loss) available to common shareholders — basic and diluted Net Income (Loss) Available to Common Stockholders, Basic Weighted average number of common shares outstanding — basic and diluted (1) Earnings (loss) per common share: Earnings Per Share, Diluted [Abstract] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Elimination of Intersegment Activity Consolidation, Eliminations [Member] Office Multifamily Multifamily segment [Member] Multifamily segment [Member] Other Other Segments [Member] Total rental revenue Rental Revenue Rental Revenue Total rental expense Operating Leases, Rent Expense Consolidated NOI Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Measurement Input Type [Axis] Measurement Input Type [Axis] Measurement Input Type [Domain] Measurement Input Type [Domain] Measurement Input, Expected Dividend Rate [Member] Measurement Input, Expected Dividend Rate [Member] Measurement Input, Price Volatility [Member] Measurement Input, Price Volatility [Member] Measurement Input, Risk Free Interest Rate [Member] Measurement Input, Risk Free Interest Rate [Member] Vesting [Axis] Vesting [Axis] Vesting [Domain] Vesting [Domain] Vesting Period One Share-based Compensation Award, Tranche One [Member] Vesting Period Two Share-based Compensation Award, Tranche Two [Member] Equity grants (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vesting period Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Percentage of vesting rights for each tranche Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Fair value of awards on grant date Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued Fair value of awards on grant date (in dollars per unit) Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued, Per Unit Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued, Per Unit Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Dividend yield rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Weighted Average Grant-Date Fair Value Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value [Abstract] Granted (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Basis of Accounting [Text Block] Basis of Accounting [Text Block] Business Combinations Policy [Policy Text Block] Business Combinations Policy [Policy Text Block] Use of Estimates, Policy [Policy Text Block] Use of Estimates, Policy [Policy Text Block] New Accounting Pronouncements, Policy [Policy Text Block] New Accounting Pronouncements, Policy [Policy Text Block] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table] Antidilutive Securities [Axis] Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Antidilutive Securities, Name [Domain] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive securities excluded from computation of earnings per share (in shares) Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Other Liabilities, Net Other Liabilities Disclosure [Text Block] Earnings (Loss) Per Common Share Earnings Per Share [Text Block] Measurement Input, Expected Term [Member] Measurement Input, Expected Term [Member] Title of Individual [Axis] Title of Individual [Axis] Relationship to Entity [Domain] Relationship to Entity [Domain] LTIP and Time-Based LTIPs Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Additional Disclosures [Abstract] Number of installments Share-Based Compensation Arrangement By Share-Based Payment Award, Award Vesting Rights, Number Of Installments Share-Based Compensation Arrangement By Share-Based Payment Award, Award Vesting Rights, Number Of Installments Expected life (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Share-Based Payments and Employee Benefits Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Document And Entity Information [Abstract] Document and entity information. Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Current Reporting Status Entity Current Reporting Status Entity Public Float Entity Public Float Entity Emerging Growth Company Entity Emerging Growth Company Entity Small Business Entity Small Business Mergers, Acquisitions and Dispositions Disclosures [Text Block] Mergers, Acquisitions and Dispositions Disclosures [Text Block] Debt Disclosure [Abstract] Line of Credit Facility [Table] Line of Credit Facility [Table] Line of credit Line of Credit [Member] Tranche A-1 Term Loan Tranche A-1 Term Loan Credit Facility [Member] Tranche A-1 Term Loan Credit Facility [Member] Tranche A-2 Term Loan Credit Facility [Member] Tranche A-2 Term Loan Credit Facility [Member] Tranche A-2 Term Loan Credit Facility [Member] Tranche A-1 and A-2 Loans [Member] Tranche A-1 and A-2 Loans [Member] Tranche A-1 and A-2 Loans [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Interest Rate (1) Debt Instrument, Interest Rate, Stated Percentage Debt, gross Long-term Debt, Gross Unamortized deferred financing costs, net Debt Issuance Costs, Net Debt, net Long-term Debt Letters of credit Letters of Credit Outstanding, Amount Debt Issuance Costs, Line of Credit Arrangements, Net Debt Issuance Costs, Line of Credit Arrangements, Net Repayments of Lines of Credit Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Deferred leasing costs Deferred Costs, Leasing, Gross Accumulated amortization Deferred Costs, Leasing, Accumulated Amortization Deferred leasing costs, net Deferred Costs, Leasing, Net Prepaid expenses Prepaid Expense Identified intangible assets, net Intangible Assets, Net (Excluding Goodwill) Deferred financing costs on credit facility, net Deposits Deposit Assets Derivative Instruments in Hedges, Assets, at Fair Value Derivative Instruments in Hedges, Assets, at Fair Value Other Other Assets, Miscellaneous Total other assets, net Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Debt Instrument [Line Items] Debt Instrument [Line Items] Variable interest rate Long-term Debt, Percentage Bearing Variable Interest, Percentage Rate Fixed interest rate Long-term Debt, Percentage Bearing Fixed Interest, Percentage Rate Variable rate amount Long-term Debt, Percentage Bearing Variable Interest, Amount Fixed rate amount Long-term Debt, Percentage Bearing Fixed Interest, Amount Unamortized deferred financing costs and premium/ discount, net Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Summary of Share-Based Compensation Expense Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] Business Combinations [Abstract] JBG Companies Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Lease Liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Lease Liabilities Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Lease Liabilities Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Real Estate Investments, Unconsolidated Real Estate And Other Joint Ventures Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Real Estate Investments, Unconsolidated Real Estate And Other Joint Ventures Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Real Estate Investments, Unconsolidated Real Estate And Other Joint Ventures Total revenue Business Acquisition, Pro Forma Revenue Net loss attributable to common shareholders Business Acquisition, Pro Forma Net Income (Loss) Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Current Liabilities, Other Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Current Liabilities, Other Business Combination, Provisional Information, Initial Accounting Incomplete, Adjustment, Current Liabilities, Other Schedule of Real Estate Properties [Table] Schedule of Real Estate Properties [Table] JBG Smith, LP JBG Smith, LP [Member] JBG Smith, LP [Member] Equity Interest Type [Axis] Equity Interest Type [Axis] Equity Interest Issued or Issuable, Type [Domain] Equity Interest Issued or Issuable, Type [Domain] Real Estate Property Ownership [Axis] Real Estate Property Ownership [Axis] Real Estate Properties [Domain] Real Estate Properties [Domain] Wholly Owned Properties Wholly Owned Properties [Member] Real Estate, Type of Property [Axis] Real Estate, Type of Property [Axis] Real Estate [Domain] Real Estate [Domain] Office Building Office Building [Member] Multifamily Multifamily [Member] Other Property Other Property [Member] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Asset under Construction Asset under Construction [Member] Future Development Future Development [Member] Future Development [Member] Real Estate Properties [Line Items] Real Estate Properties [Line Items] Ownership interest by parent Noncontrolling Interest, Ownership Percentage by Parent Number of real estate properties Number of Real Estate Properties Number of building units Number of Units in Real Estate Property Schedule of Other Liabilities [Table] Schedule of Other Liabilities [Table] Schedule of Other Liabilities [Table] Schedule of Other Liabilities [Line Items] Schedule of Other Liabilities [Line Items] [Line Items] for Schedule of Other Liabilities [Table] Lease intangible liabilities Below Market Lease, Gross Accumulated amortization Below Market Lease, Accumulated Amortization Lease intangible liabilities, net Below Market Lease, Net Prepaid rent Advance Rent Lease assumption liabilities and accrued tenant incentives Lease Assumptions Liabilities And Accrued Tenant Incentives Lease Assumptions Liabilities And Accrued Tenant Incentives Capital lease obligation Capital Lease Obligations Security deposits Security Deposit Liability Ground lease deferred rent payable Deferred Rent Credit Net deferred tax liability Deferred Income Tax Liabilities, Net Dividends payable Dividends Payable Other Other Sundry Liabilities Total other liabilities, net Other Liabilities Redeemable Noncontrolling Interests Redeemable Noncontrolling Interest [Table Text Block] Net carrying value of real estate collateralizing the mortgages payable Debt Instrument, Collateral Amount Derivative, notional amount Derivative, Notional Amount Derivatives Entered Into, Notional Value Derivatives Entered Into, Notional Value Derivatives Entered Into, Notional Value Credit facility, maximum borrowing capacity Line of Credit Facility, Maximum Borrowing Capacity Number of debt extension options Debt Instrument, Number Of Term Extension Options Debt Instrument, Number Of Term Extension Options Debt extension option period (in months) Debt Instrument, Extension Option, Term Debt Instrument, Extension Option, Term Debt, gross Basis spread on variable rate Organization and Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Debt Debt Disclosure [Text Block] Noncontrolling Interest [Table] Noncontrolling Interest [Table] Minimum Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] OP Units OP Units [Member] OP Units [Member] Consolidated Real Estate Venture Consolidated Real Estate Venture [Member] Consolidated Real Estate Venture [Member] Noncontrolling Interest [Line Items] Noncontrolling Interest [Line Items] Common shares and OP Units issued in consideration Business Acquisition, Equity Interest Issued or Issuable, Number of Shares Ownership interest by parent, threshold for capital contributions to cease Noncontrolling Interest, Capital Contribution Threshold, Ownership Percentage by Parent Noncontrolling Interest, Capital Contribution Threshold, Ownership Percentage by Parent Redemption period Redeemable Noncontrolling Interest, Redemption Period Redeemable Noncontrolling Interest, Redemption Period Segment information Schedule of Segment Reporting Information, by Segment [Table Text Block] Fair Value Disclosures [Abstract] Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis Schedule of Fair Value, Assets and Liabilities Measured on Recurring Basis [Table Text Block] Schedule of Financial Instruments and Liabilities as Reflected on Balance Sheet Fair Value, by Balance Sheet Grouping [Table Text Block] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Variable Interest Entities Variable Interest Entity Disclosure [Text Block] Subsequent Events Subsequent Events [Text Block] Fair Value Measurements Fair Value Disclosures [Text Block] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] 1900 N Street 1900 N Street [Member] 1900 N Street [Member] 1101 17th Street [Member] 1101 17th Street [Member] 1101 17th Street [Member] Long-term Purchase Commitment, Amount Long-term Purchase Commitment, Amount Payments to Acquire Interest in Joint Venture Payments to Acquire Interest in Joint Venture Equity Method Investment, Ownership Percentage After Funding Of Contributions Equity Method Investment, Ownership Percentage After Funding Of Contributions Equity Method Investment, Ownership Percentage After Funding Of Contributions Equity Method Investment, Realized Gain (Loss) on Disposal Equity Method Investment, Realized Gain (Loss) on Disposal Net unrealized gain on derivative designated as cash flow hedge Other Comprehensive Income (Loss), Derivatives Qualifying as Hedges, Net of Tax Gain expected to be reclassified into interest expense within the next 12 months Cash Flow Hedge Gain (Loss) to be Reclassified within Twelve Months Temporary Equity Increase (Decrease) in Temporary Equity [Roll Forward] Beginning Balance Redeemable Noncontrolling Interest, Equity, Carrying Amount Fair value of OP Unit redemptions OP Units issued in connection with the Combination (1) Temporary Equity, Stock Issued During Period, Value, Acquisitions Temporary Equity, Stock Issued During Period, Value, Acquisitions Net income (loss) attributable to redeemable noncontrolling interests Temporary Equity, Net Income Other comprehensive income Temporary Equity, Other Comprehensive Income (Loss) Temporary Equity, Other Comprehensive Income (Loss) Contributions (distributions) Temporary Equity, Contributions (Distributions) Temporary Equity, Contributions (Distributions) Share-based compensation expense Temporary Equity, Share-based Compensation Temporary Equity, Share-based Compensation Adjustment to redemption value Temporary Equity, Carrying Amount, Period Increase (Decrease) Ending Balance Business Combination, Contingent Consideration, Liability Business Combination, Contingent Consideration, Liability Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Capitalization of internal leasing costs - QTD Deferred Costs, Internal Leasing, Net Deferred Costs, Internal Leasing, Net Contractual Obligation Ground lease contractual obligation Ground lease contractual obligation Combined balance sheet information: Equity Method Investment, Summarized Financial Information, Liabilities and Equity [Abstract] Real estate, net Equity Method Investment, Summarized Financial Information, Assets, Real Estate Investment Property, Net Equity Method Investment, Summarized Financial Information, Assets, Real Estate Investment Property, Net Other assets, net Equity Method Investment, Summarized Financial Information, Assets, Other Equity Method Investment, Summarized Financial Information, Assets, Other Total assets Equity Method Investment, Summarized Financial Information, Assets Mortgages payable, net Equity Method Investment, Summarized Financial Information, Liabilities, Secured Debt Equity Method Investment, Summarized Financial Information, Liabilities, Secured Debt Other liabilities, net Equity Method Investment, Summarized Financial Information, Liabilities, Other Equity Method Investment, Summarized Financial Information, Liabilities, Other Total liabilities Equity Method Investment, Summarized Financial Information, Liabilities Total equity Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests Total liabilities and equity Equity Method Investment, Summarized Financial Information, Liabilities and Equity Combined income statement information: Equity Method Investment, Summarized Financial Information, Gross Profit (Loss) [Abstract] Total revenue Equity Method Investment, Summarized Financial Information, Revenue Operating income Equity Method Investment, Summarized Financial Information, Operating Income (Loss) Equity Method Investment, Summarized Financial Information, Operating Income (Loss) Net loss Equity Method Investment, Summarized Financial Information, Net Income (Loss) Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Other Assets, Net Other Assets [Member] Other Liabilities, Net Other Liabilities [Member] Hedging Designation [Axis] Hedging Designation [Axis] Hedging Designation [Domain] Hedging Designation [Domain] Designated as Hedging Instrument Designated as Hedging Instrument [Member] Not Designated as Hedging Instrument Not Designated as Hedging Instrument [Member] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Interest rate swap and caps Interest Rate Swap [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Recurring Fair Value, Measurements, Recurring [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Classified as assets in Other assets, net Derivative Asset Classified as liabilities in Other liabilities, net Derivative Liability Consolidated Properties Consolidated Properties [Member] Unconsolidated Properties Unconsolidated Properties [Member] General liability insurance limit General Liability Insurance Coverage Limit, Per Occurrence General Liability Insurance Coverage Limit, Per Occurrence Property and rental value insurance coverage limit Property and Rental Value Insurance Coverage Limit Property and Rental Value Insurance Coverage Limit Terrorist acts insurance coverage limit Terrorist Acts Insurance Coverage Limit, Per Occurrence Terrorist Acts Insurance Coverage Limit, Per Occurrence Purchase obligation Purchase Obligation Commitment amortization period Commitment Amortization Period Commitment Amortization Period Principal payment guarantees Guarantor Obligations, Maximum Exposure, Undiscounted Additional capital funding committed amount Other Commitment Composition of Investments Equity Method Investments [Table Text Block] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Variable Interest Entities [Axis] Variable Interest Entities [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Not Primary Beneficiary Variable Interest Entity, Not Primary Beneficiary [Member] Variable Interest Entity, Primary Beneficiary Variable Interest Entity, Primary Beneficiary [Member] Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Assets Variable Interest Entity, Nonconsolidated, Carrying Amount, Assets Liabilities Variable Interest Entity, Nonconsolidated, Carrying Amount, Liabilities Number of Real Estate Properties Capitalized interest Interest Costs Capitalized Interest Costs Capitalized - Mortgages Payable Deferred Interest Interest Costs Capitalized - Mortgages Payable Deferred Interest ASSETS Assets [Abstract] Real estate, at cost: Real Estate Investment Property, at Cost [Abstract] Land and improvements Land and Land Improvements Buildings and improvements Investment Building and Building Improvements Construction in progress, including land Development in Process Real estate, at cost Real Estate Investment Property, at Cost Less accumulated depreciation Real Estate Investment Property, Accumulated Depreciation Real estate, net Real Estate Investment Property, Net Cash and cash equivalents Restricted cash Tenant and other receivables, net Accounts and Notes Receivable, Net Deferred rent receivable, net Deferred Rent Receivables, Net Investments in and advances to unconsolidated real estate ventures TOTAL ASSETS Assets LIABILITIES, REDEEMABLE NONCONTROLLING INTERESTS AND EQUITY Liabilities and Equity [Abstract] Liabilities: Liabilities [Abstract] Mortgages payable, net Secured Debt Revolving credit facility Long-term Line of Credit Unsecured term loans, net Unsecured Debt Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities Other liabilities, net Total liabilities Liabilities Commitments and Contingencies Commitments and Contingencies Redeemable noncontrolling interests Shareholders' equity: Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Preferred shares, $0.01 par value - 200,000 shares authorized, none issued Preferred Stock, Value, Issued Common shares, $0.01 par value - 500,000 shares authorized; 120,917 and 117,955 shares issued and outstanding as of September 30, 2018 and December 31, 2017 Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Accumulated deficit Retained Earnings (Accumulated Deficit) Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Shareholders' equity / Former parent equity Stockholders' Equity Attributable to Parent Noncontrolling interests in consolidated subsidiaries Stockholders' Equity Attributable to Noncontrolling Interest Total equity TOTAL LIABILITIES, REDEEMABLE NONCONTROLLING INTERESTS AND EQUITY Liabilities and Equity Statement of Comprehensive Income [Abstract] NET INCOME (LOSS) Other Comprehensive Income (Loss), Net of Tax [Abstract] Other Comprehensive Income (Loss), Net of Tax [Abstract] Change in fair value of derivative financial instruments Other Comprehensive Income (Loss), Unrealized Gain (Loss) on Derivatives Arising During Period, Net of Tax Reclassification of net loss on derivative financial instruments from accumulated other comprehensive income into interest expense Other Comprehensive Income (Loss), Reclassification Adjustment from AOCI on Derivatives, Net of Tax Other comprehensive income COMPREHENSIVE INCOME (LOSS) Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Other comprehensive income attributable to redeemable noncontrolling interests Comprehensive Income (Loss), Net Of Tax, Attributable To Redeemable Noncontrolling Interest Comprehensive Income (Loss), Net Of Tax, Attributable To Redeemable Noncontrolling Interest Net loss attributable to noncontrolling interests Comprehensive Income (Loss), Net Of Tax, Attributable To Nonredeemable Noncontrolling Interest Comprehensive Income (Loss), Net Of Tax, Attributable To Nonredeemable Noncontrolling Interest COMPREHENSIVE INCOME (LOSS) ATTRIBUTABLE TO JBG SMITH PROPERTIES Comprehensive Income (Loss), Net of Tax, Attributable to Parent Transactions with Vornado and Related Parties Related Party Transactions Disclosure [Text Block] LTIP Units [Member] LTIP Units [Member] LTIP Units [Member] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Summary of Other Assets, net Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Table Text Block] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Financial Instrument [Axis] Financial Instrument [Axis] Financial Instruments [Domain] Financial Instruments [Domain] Unsecured term loans Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Carrying Amount Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Financial liabilities: Financial Instruments, Financial Liabilities, Balance Sheet Groupings [Abstract] Financial liabilities Debt Instrument, Fair Value Disclosure Real estate, at cost Total assets (1) Summary of Debt Schedule of Long-term Debt Instruments [Table Text Block] Variable rate, weighted average interest rate Equity Method Investment, Long Term Debt, Percentage Bearing Variable Interest, Percentage Rate Equity Method Investment, Long Term Debt, Percentage Bearing Variable Interest, Percentage Rate Variable rate Equity Method Investment, Long Term Debt, Bearing Variable, Amount Equity Method Investment, Long Term Debt, Bearing Variable, Amount Fixed rate, weighted average interest rate Equity Method Investment, Long Term Debt, Percentage Bearing Fixed Interest, Percentage Rate Equity Method Investment, Long Term Debt, Percentage Bearing Fixed Interest, Percentage Rate Fixed rate Equity Method Investment, Long Term Debt, Bearing Fixed, Amount Equity Method Investment, Long Term Debt, Bearing Fixed, Amount Unconsolidated real estate ventures - mortgages payable Equity Method Investment, Long Term Debt Equity Method Investment, Long Term Debt Unamortized deferred financing costs Equity Method Investment, Unamortized Deferred Financing Costs Equity Method Investment, Unamortized Deferred Financing Costs Unconsolidated real estate ventures - mortgages payable, net Equity Method Investment, Long Term Debt, Net Equity Method Investment, Long Term Debt, Net