Organization, Consolidation and Presentation of Financial Statements [Abstract] Organization and Basis of Presentation and Combination Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Abstract] 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) Other Other Assets, Miscellaneous Total other assets, net Other Assets Business Combinations [Abstract] The Combination Business Combination Disclosure [Text Block] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Commitments and Contingencies Disclosure [Text Block] Noncontrolling Interest [Abstract] Noncontrolling Interest [Table] Noncontrolling Interest [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] OP Units OP Units [Member] OP Units [Member] Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] JBG Smith, LP JBG Smith, LP [Member] JBG Smith, LP [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 Noncontrolling Interest, Ownership Percentage by Parent Segment Reporting [Abstract] Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other Other Assets [Member] Segments [Axis] Segments [Axis] Segments [Domain] Segments [Domain] Third-party real estate services Third-Party Real Estate Services [Member] Third-Party Real Estate Services [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 Total assets Assets 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] Title of Individual [Axis] Title of Individual [Axis] Relationship to Entity [Domain] Relationship to Entity [Domain] Trustee Director [Member] Management Management [Member] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Long-Term Incentive Partnership Units Long-Term Incentive Partnership Units [Member] Long-Term Incentive Partnership Units [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [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] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Equity grants (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Number of independent Trustees Deferred Compensation Arrangement With Individual, Number Of Individuals Deferred Compensation Arrangement With Individual, Number Of Individuals Fair value of awards on grant date Deferred Compensation Arrangement with Individual, Fair Value of Shares Issued Vesting period (in years) Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Share-based compensation expense Share-based Compensation Percentage of vesting rights for each tranche Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage 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 Weighted average grant-fair value (in dollars per unit) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Compensation expense recognition period (in years) Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Expected volatility rate Fair Value Assumptions, Expected Volatility Rate Risk-free interest rate Fair Value Assumptions, Risk Free Interest Rate Expected life (in years) Fair Value Assumptions, Expected Term Vested in period (in units) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited in period (in units) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Schedule of Finite-Lived Intangible Assets [Table] Schedule of Finite-Lived Intangible Assets [Table] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] In-place leases Leases, Acquired-in-Place [Member] Above-market real estate leases Above Market Leases [Member] Below-market ground leases Below Market Leases [Member] Below Market Leases [Member] Option to enter into ground lease Lease Options [Member] Lease Options [Member] Management and leasing contracts Lease Agreements [Member] Other Other Liabilities [Member] Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets [Line Items] Total identified intangibles assets Finite-Lived Intangible Assets, Gross Total accumulated amortization Finite-Lived Intangible Assets, Accumulated Amortization Identified intangible assets, net Finite-Lived Intangible Assets, Net Equity Method Investments and Joint Ventures [Abstract] Investments in Unconsolidated Real Estate Ventures Equity Method Investments and Joint Ventures Disclosure [Text Block] Earnings Per Share [Abstract] Antidilutive securities excluded from computation of earnings per share Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount 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 Variable Interest Entities Variable Interest Entity Disclosure [Text Block] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Mortgages Mortgages [Member] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] 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, net 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 Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan Schedule of Compensation Cost for Share-based Payment Arrangements, Allocation of Share-based Compensation Costs by Plan [Table Text Block] Formation Awards Formation Awards [Member] Formation Awards [Member] Aggregate notional value of shares granted Stock Granted, Value, Share-based Compensation, Gross Weighted average price (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value 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 Dividend yield rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Income Statement [Abstract] REVENUE Revenues [Abstract] Property rentals Operating Leases, Income Statement, Lease Revenue Tenant reimbursements Tenant Reimbursements Third-party real estate services, including reimbursements Management Fees Revenue Other income Other Income Total revenue Revenues EXPENSES Costs and Expenses [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Property operating Cost of Other Property Operating Expense Real estate taxes Real Estate Tax Expense General and administrative: General and Administrative Expense [Abstract] 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 Transaction and other costs Business Combination, Acquisition Related Costs Total operating expenses Operating Expenses OPERATING (LOSS) INCOME Operating Income (Loss) (Loss) income from unconsolidated real estate ventures Income (Loss) from Equity Method Investments Interest and other (loss) income, net Investment Income, Net Interest expense Interest Expense Loss on extinguishment of debt Gain (Loss) on Extinguishment of Debt Gain on bargain purchase Business Combination, Bargain Purchase, Gain Recognized, Amount (LOSS) INCOME BEFORE INCOME TAX EXPENSE Income (Loss) from Continuing Operations before Income Taxes, Noncontrolling Interest Income tax benefit (expense) Income Tax Expense (Benefit) NET (LOSS) INCOME Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net loss attributable to redeemable noncontrolling interests Net Income (Loss) Attributable to Redeemable Noncontrolling Interest NET (LOSS) INCOME ATTRIBUTABLE TO JBG SMITH PROPERTIES Net Income (Loss) Attributable to Parent 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 Weighted Average Number of Shares Outstanding, Basic and Diluted Schedule of Business Acquisitions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] JBG Companies JBG Companies [Member] JBG Companies [Member] Business Acquisition [Line Items] Business Acquisition [Line Items] Net income (loss) attributable to JBG SMITH Properties Interest expense Loss on extinguishment of debt Income tax (benefit) expense NOI Income (Loss) from Continuing Operations, Net of Tax, Attributable to Noncontrolling Interest Accounting Policies [Abstract] Use of Estimates Use of Estimates, Policy [Policy Text Block] Business Combinations Business Combinations Policy [Policy Text Block] Real Estate Real Estate, Policy [Policy Text Block] Real Estate Held for Sale Real Estate Held for Development and Sale, Policy [Policy Text Block] Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Restricted Cash Cash and Cash Equivalents, Restricted Cash and Cash Equivalents, Policy [Policy Text Block] Allowance for Doubtful Accounts Receivables, Trade and Other Accounts Receivable, Allowance for Doubtful Accounts, Policy [Policy Text Block] Investments in and Advances to Real Estate Ventures Consolidation, Variable Interest Entity, Policy [Policy Text Block] Intangibles Intangible Assets, Finite-Lived, Policy [Policy Text Block] Deferred Costs Deferred Charges, Policy [Policy Text Block] Noncontrolling Interests Consolidation, Policy [Policy Text Block] Derivatives Financial Instruments and Hedge Accounting Derivatives, Methods of Accounting, Hedging Derivatives [Policy Text Block] Fair Value of Assets and Liabilities Fair Value Measurement, Policy [Policy Text Block] Revenue Recognition Revenue Recognition, Policy [Policy Text Block] Third-Party Real Estate Services Expenses Third-Party Real Estate Services Expenses [Policy Text Block] Third-Party Real Estate Services Expenses [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] (Loss) Earnings Per Share Earnings Per Share, Policy [Policy Text Block] Share-based Compensation Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Subsequent Events [Abstract] Subsequent Event [Table] Subsequent Event [Table] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] LIBOR London Interbank Offered Rate (LIBOR) [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] 1235 South Clark 1235 South Clark [Member] 1235 South Clark [Member] 220 20th Stree 220 20th Street [Member] 220 20th Street [Member] RTC West RTC West [Member] RTC West [Member] 800 North Glebe Road 800 North Glebe Road [Member] 800 North Glebe Road [Member] Atlantic Plumbing Atlantic Plumbing [Member] Atlantic Plumbing [Member] Line of credit Line of Credit [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Tranche A-1 Term Loan Tranche A-1 Term Loan Credit Facility [Member] Tranche A-1 Term Loan Credit Facility [Member] Subsequent Event [Line Items] Subsequent Event [Line Items] Debt Long-term Debt Term Debt Instrument, Term Mortgage loan interest rate Debt Instrument, Basis Spread on Variable Rate Interest Rate Debt Instrument, Interest Rate, Stated Percentage Proceeds from debt Proceeds from Issuance of Secured Debt Repayment of mortgages payable Repayments of Secured Debt Remaining available Line of Credit Facility, Remaining Borrowing Capacity Repayments of borrowings Repayments of Long-term Debt Unsecured term loan, net Derivative, Notional Amount Debt instrument, face amount Debt Instrument, Face Amount Dividends declared (in dollars per share) Common Stock, Dividends, Per Share, Declared Combined balance sheet information: Equity Method Investment, Summarized Financial Information, Liabilities and Equity [Abstract] Total assets Equity Method Investment, Summarized Financial Information, Assets Total liabilities Equity Method Investment, Summarized Financial Information, Liabilities Noncontrolling interests Equity Method Investment, Summarized Financial Information, Noncontrolling Interest Total equity Equity Method Investment, Summarized Financial Information, Equity Excluding Noncontrolling Interests Combined income statement information: Equity Method Investment, Summarized Financial Information, Gross Profit (Loss) [Abstract] Total revenue Equity Method Investment, Summarized Financial Information, Revenue Net (loss) income Equity Method Investment, Summarized Financial Information, Net Income (Loss) Debt Disclosure [Abstract] Summary of Mortgages Payable Schedule of Long-term Debt Instruments [Table Text Block] Schedule of Maturities of Debt Outstanding Schedule of Maturities of Long-term Debt [Table Text Block] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Eliminations Consolidation, Eliminations [Member] Office Office Segment [Member] Office Segment [Member] Multifamily Multifamily segment [Member] Multifamily segment [Member] Other Other Segments [Member] Real estate, at cost Real Estate Investment Property, at Cost Investments in and advances to unconsolidated real estate ventures Real Estate Investments, Unconsolidated Real Estate and Other Joint Ventures Weighted average number of shares outstanding - basic and diluted Receivables [Abstract] Tenants Accounts Receivable, Gross Other Other Receivables Allowance for doubtful accounts Allowance for Doubtful Accounts, Premiums and Other Receivables Total tenant and other receivables, net Accounts and Notes Receivable, Net Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] Property Operating Expenses Property Operating Expenses [Member] Property Operating Expenses [Member] Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Bad debt expense Provision for Doubtful Accounts Total unrecognized compensation expense Employee Service Share-based Compensation, Nonvested Awards, Compensation Not yet Recognized, Share-based Awards Other than Options Contributions to the 401(k) Plan Defined Contribution Plan, Employer Discretionary Contribution Amount Fair Value Disclosures [Abstract] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Derivative Instrument [Axis] Derivative Instrument [Axis] Derivative Contract [Domain] Derivative Contract [Domain] Interest rate swap and caps Interest Rate Cap [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] Net unrealized gain (loss) on interest rate swaps and caps Unrealized Gain (Loss) on Derivatives Business Combination, Consideration Transferred [Abstract] Common shares and OP Units Business Combination, Consideration Transferred, Equity Interests Issued and Issuable Cash Payments to Acquire Businesses, Gross Total consideration paid Business Combination, Consideration Transferred Fair value of assets acquired and liabilities assumed: Business Combination, Recognized Identifiable Assets Acquired, Goodwill, and Liabilities Assumed, Less Noncontrolling Interest [Abstract] Land and improvements Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Land Building and improvements Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Buildings Construction in progress, including land Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Construction in Progress, Gross, Including Land Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Construction in Progress, Gross, Including Land Leasehold improvements and equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Leasehold Improvements and Equipment Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Leasehold Improvements and Equipment Cash Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Cash and Equivalents Restricted cash Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Restricted Cash Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Restricted Cash Investments in and advances to unconsolidated real estate ventures Business Combination, Recognized Identifiable Assets acquired and Liabilities Assumed, Real Estate Investments, Unconsolidated Real Estate and Other Joint Ventures Business Combination, Recognized Identifiable Assets acquired and Liabilities Assumed, Real Estate Investments, Unconsolidated Real Estate and Other Joint Ventures Identified intangible assets Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Assets, Other than Goodwill Notes receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Notes Receivable Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Notes Receivable Identified intangible liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Liabilities Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Intangible Liabilities Mortgages payable assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Long-term Debt Capital lease obligations assumed Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Capital Lease Obligation Deferred tax liability Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Deferred Tax Liabilities, Current Other liabilities acquired, net Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Current Liabilities, Other Noncontrolling interests in consolidated subsidiaries Business Combination, Acquisition of Less than 100 Percent, Noncontrolling Interest, Fair Value Net assets acquired Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Net Repayment of notes receivable Proceeds from Collection of Notes Receivable Ground leases that qualify as capital leases Capital Leased Assets, Number of Units Land parcel purchase price Payments to Acquire Land Line of Credit Facility [Table] Line of Credit Facility [Table] Revolving credit facility Revolving Credit Facility [Member] Line of Credit Facility [Line Items] Line of Credit Facility [Line Items] Unsecured term loan, net Long-term Line of Credit Unamortized deferred financing costs and premium/discount, net Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Proceeds from lines of credit Proceeds from Lines of Credit Leases [Abstract] 2017 Operating Leases, Future Minimum Payments Receivable, Remainder of Fiscal Year 2018 Operating Leases, Future Minimum Payments Receivable, Current 2019 Operating Leases, Future Minimum Payments Receivable, in Two Years 2020 Operating Leases, Future Minimum Payments Receivable, in Three Years 2021 Operating Leases, Future Minimum Payments Receivable, in Four Years 2022 Operating Leases, Future Minimum Payments Receivable, in Five Years Thereafter Operating Leases, Future Minimum Payments Receivable Other Liabilities Disclosure [Abstract] Other Liabilities, Net Other Liabilities Disclosure [Text Block] Debt Debt Disclosure [Text Block] 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 Interest rate on payable to Vornado Related Party Transaction, Rate Variable rate amount Long-term Debt, Percentage Bearing Variable Interest, Amount Fixed rate amount Long-term Debt, Percentage Bearing Fixed Interest, Amount Mortgages payable Long-term Debt, Gross Mortgages payable, net Payable to former parent Due to Related Parties Proceeds from Vornado's revolving credit facility Schedule of Future Minimum Rental Income Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Statement of Cash Flows [Abstract] OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Net (loss) income Adjustments to reconcile net (loss) income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation and amortization, including amortization of debt issuance costs Depreciation, Depletion and Amortization Deferred rent Straight Line Rent Loss from unconsolidated real estate ventures 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 Return on capital from unconsolidated real estate ventures Proceeds from Equity Method Investment, Distribution Gain on bargain purchase Unrealized gain on interest rate swaps 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 received in connection with the Combination Cash Acquired from Acquisition Restricted cash Increase (Decrease) in Restricted Cash Investments in and advances to unconsolidated real estate ventures Payments to Acquire Real Estate and Real Estate Joint Ventures 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 (used in) 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 Repayment of borrowings from former parent Repayments of Related Party Debt Capital lease payments Repayments of Long-term Capital Lease Obligations Proceeds from borrowings from former parent Proceeds from Related Party Debt Proceeds from borrowings Proceeds from Issuance of Long-term Debt Repayments of borrowings Debt issuance costs Payments of Debt Issuance Costs Contributions from noncontrolling interests Proceeds from Noncontrolling Interests Distributions to noncontrolling interests Payments to Noncontrolling Interests Net cash provided by financing activities Net Cash Provided by (Used in) Financing Activities Net increase (decrease) in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of the period Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents at end of the period SUPPLEMENTAL DISCLOSURE OF CASH FLOW AND NON-CASH INFORMATION: Supplemental Cash Flow Information [Abstract] Transfer of mortgage payable to former parent Transfer Mortgage Payable Cash paid for interest (net of capitalized interest of $2,285 and $3,690 in 2017 and 2016, respectively) Interest Paid, Net 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 Cash payments for income taxes Income Taxes Paid Non-cash transactions related to the Formation Transaction: Noncash Transactions [Abstract] Noncash Transactions [Abstract] 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 During Period, Value, New Issues 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 Adjustment to record redeemable noncontrolling interest at redemption value Temporary Equity, Accretion to Redemption Value 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 (Loss) Earnings Per Share Earnings Per Share [Text Block] Composition of Other Liabilities, Net Other Liabilities [Table Text Block] Finite-lived Intangible Liabilities Amortization Expense Finite-lived Intangible Liabilities Amortization Expense [Table Text Block] Finite-lived Intangible Liabilities Amortization Expense [Table Text Block] Schedule of Finite-Lived Intangible Liabilities, Future Amortization Expense Schedule of Finite-Lived Intangible Liabilities, Future Amortization Expense [Table Text Block] Schedule of Finite-Lived Intangible Liabilities, Future Amortization Expense [Table 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] OP Units Common Limited Partnership Units [Member] Common Limited Partnership Units [Member] OPP Units Out-Performance Award Units [Member] Out-Performance Award Units [Member] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] Transaction and other costs Acquisition-related Costs [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] Near-Term Development Near-Term Development [Member] Near-Term Development [Member] Future Development Future Development [Member] Future Development [Member] 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] Number of real estate properties Number of Real Estate Properties Number of building units Number of Units in Real Estate Property Area of real estate property (in square feet) Area of Real Estate Property Severance and transaction bonus expense Business Acquisition, Transaction Costs Investment banking fees Fees and Commissions Legal fees Legal Fees Accounting fees Professional Fees Number of unrelated owners Number Of Unrelated Owners Number Of Unrelated Owners Number of owners turned employees Number Of Former Owners Turned Employees Number Of Former Owners Turned Employees Number of owners turned board of trustee members Number Of Former Owners Turned Board Members Number Of Former Owners Turned Board Members Revenue of JBG included in statement of operations Business Combination, Pro Forma Information, Revenue of Acquiree since Acquisition Date, Actual Net loss of JBG included in statement of operations Business Combination, Pro Forma Information, Earnings or Loss of Acquiree since Acquisition Date, Actual Segment Information Segment Reporting Disclosure [Text Block] Total rental revenue Revenue, Net Total rental expense Operating Leases, Rent Expense 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 Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Schedule of Antidilutive Securities Excluded from Computation of Earnings Per Share [Table Text Block] Landmark Landmark [Member] Landmark [Member] CBREI Venture CBREI Venture [Member] CBREI Venture [Member] Canadian Pension Plan Investment Board Canadian Pension Plan Investment Board [Member] Canadian Pension Plan Investment Board [Member] Brandywine Brandywine [Member] Brandywine [Member] Berkshire Group Berkshire Group [Member] Berkshire Group [Member] MRP Realty MRP Realty [Member] MRP Realty [Member] JP Morgan JP Morgan [Member] JP Morgan [Member] Other Other Investment [Member] Other Investment [Member] 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 Investment Balance Tranche A-2 Term Loan Tranche A-2 Term Loan Credit Facility [Member] Tranche A-2 Term Loan Credit Facility [Member] Net carrying value of real estate collateralizing the mortgages payable Debt Instrument, Collateral Amount Mortgages payable assumed 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 Basis spread on variable rate Fees and expenses on debt Debt Instrument, Fee Amount Summary of Other Assets, net Deferred Costs, Capitalized, Prepaid, and Other Assets Disclosure [Table Text Block] Summary of Identified Intangible Assets, Net Schedule of Finite-Lived Intangible Assets [Table Text Block] Summary of Amortization Expense Finite-lived Intangible Assets Amortization Expense [Table Text Block] Schedule of Estimated Amortization of Identified Intangible Assets Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Statement of Financial Position [Abstract] 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 Less accumulated depreciation Real Estate Investment Property, Accumulated Depreciation Real estate, net Real Estate Investment Property, Net Cash and cash equivalents Restricted cash Restricted Cash Tenant and other receivables, net Deferred rent receivable, net Deferred Rent Receivables, Net Receivable from former parent Due from Related Parties Other assets, net TOTAL ASSETS LIABILITIES, REDEEMABLE NONCONTROLLING INTERESTS AND EQUITY Liabilities and Equity [Abstract] Liabilities: Liabilities [Abstract] Mortgages payable, net Secured Debt Revolving credit facility Unsecured term loan, net Unsecured Debt Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities Other liabilities, net Other Liabilities Total liabilities Liabilities Commitments and Contingencies Commitments and Contingencies Redeemable noncontrolling interests Redeemable Noncontrolling Interest, Equity, Carrying Amount 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 and 117,957 shares issued and outstanding at September 30, 2017 Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital Accumulated deficit Retained Earnings (Accumulated Deficit) Former parent equity Stockholders' Equity Attributable to Parent Noncontrolling interests in consolidated subsidiaries Stockholders' Equity Attributable to Noncontrolling Interest Total equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest TOTAL LIABILITIES, REDEEMABLE NONCONTROLLING INTERESTS AND EQUITY Liabilities and Equity Other Equity Awards Other Equity Awards [Member] Other Equity Awards [Member] Share-based compensation expense - other Allocated Share-based Compensation Expense, Other Allocated Share-based Compensation Expense, Other Total share-based compensation expense Allocated Share-based Compensation Expense, Before Capitalization Allocated Share-based Compensation Expense, Before Capitalization Share-based compensation expense Temporary Equity, Share-based Compensation Temporary Equity, Share-based Compensation Less amount capitalized Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount Net share-based compensation expense Allocated Share-based Compensation Expense, Net of Tax Portion of consideration attributable to performance of future services Business Combination, Contingent Consideration, Liability Fair value of common shares and OP Units issued in consideration Business Acquisition, Equity Interest Issued or Issuable, Value Assigned Total identified intangible asset amortization Amortization of Intangible Assets Outstanding common shares and common limited partnership units prior to the Combination Common Stock, Shares, Outstanding Exchange ratio Business Acquisition, Equity Interest Issued or Issuable, Exchange Ratio Business Acquisition, Equity Interest Issued or Issuable, Exchange Ratio Price per share/unit Business Acquisition, Equity Interest Issued or Issuable, Value Assigned per Share Business Acquisition, Equity Interest Issued or Issuable, Value Assigned per Share Fair value adjustment to OP Units due to transfer restrictions Business Acquisition, Equity Interest Issued or Issuable, Fair Value Adjustment Business Acquisition, Equity Interest Issued or Issuable, Fair Value Adjustment Portion of consideration attributable to performance of future services Capitalized interest Interest Paid, Capitalized Fair Value Measurements Fair Value Disclosures [Text Block] Schedule of Recognized Identified Assets Acquired and Liabilities Assumed Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Schedule of Business Acquisitions by Acquisition, Equity Interest Issued or Issuable Schedule of Business Acquisitions by Acquisition, Equity Interest Issued or Issuable [Table Text Block] Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination Schedule of Finite-Lived Intangible Assets Acquired as Part of Business Combination [Table Text Block] Schedule of Indefinite-lived Intangible Assets Acquired as Part of Business Combination Schedule of Indefinite-lived Intangible Assets Acquired as Part of Business Combination [Table Text Block] Business Acquisition, Pro Forma Information Business Acquisition, Pro Forma Information [Table Text Block] Building and improvements Building and Building Improvements [Member] Management and leasing contracts Management and Leasing Contracts [Member] Management and Leasing Contracts [Member] Building and improvements Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Buildings and Improvements Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Buildings and Improvements Tenant improvements Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Tenant Improvements Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Tenant Improvements Total building and improvements Leasehold improvements Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Leasehold Improvements Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Leasehold Improvements Useful life (in years) Finite-Lived Intangible Asset, Useful Life Identified intangible assets Finite-lived Intangible Assets Acquired Weighted average amortization period (in years) Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Below-market real estate leases 2017 Long-term Debt, Maturities, Principal Outstanding, Remainder of Fiscal Year Long-term Debt, Maturities, Principal Outstanding, Remainder of Fiscal Year 2018 Long-term Debt, Maturities, Principal Outstanding in Year Two Long-term Debt, Maturities, Principal Outstanding in Year Two 2019 Long-term Debt, Maturities, Principal Outstanding in Year Three Long-term Debt, Maturities, Principal Outstanding in Year Three 2020 Long-term Debt, Maturities, Principal Outstanding in Year Four Long-term Debt, Maturities, Principal Outstanding in Year Four 2021 Long-term Debt, Maturities, Principal Outstanding in Year Five Long-term Debt, Maturities, Principal Outstanding in Year Five 2022 Long-term Debt, Maturities, Principal Outstanding in Year Six Long-term Debt, Maturities, Principal Outstanding in Year Six Thereafter Long-term Debt, Maturities, Principal Outstanding, Thereafter Long-term Debt, Maturities, Principal Outstanding, Thereafter Total Long-term Debt, Maturities, Principal Outstanding Long-term Debt, Maturities, Principal Outstanding Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] 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 Accumulated Distributions in Excess of Net Income [Member] Former Parent Equity Former Parent Equity [Member] Former Parent Equity [Member] Noncontrolling Interests in Consolidated Subsidiaries Noncontrolling Interest [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] BALANCE (beginning of period) Common shares outstanding (in shares) Deferred compensation shares and options, net Stock Issued During Period, Value, Employee Benefit Plan Contributions from Vornado Realty Trust, net Stockholders' Equity Note, Spinoff Transaction Issuance of common limited partnership units to Vornado Realty Trust at the separation Stock Repurchased During Period, Value Issuance of common shares to former parent at the Separation (in shares) Stock Issued During Period, Shares, New Issues Issuance of common shares in connection with the Combination (in shares) Stock Issued During Period, Shares, Acquisitions Noncontrolling interests acquired in connection with the Combination Noncontrolling Interest, Increase from Business Combination Distributions to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Contributions from noncontrolling interests Noncontrolling Interest, Contributions Noncontrolling Interest, Contributions Adjustment to record redeemable noncontrolling interest at redemption value Noncontrolling Interest, Change in Redemption Value Common shares outstanding (in shares) BALANCE, (end of period) Other Assets, Net Other Assets Disclosure [Text Block] 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 Summary of Significant Accounting Policies Significant Accounting Policies [Text Block] Total revenue Business Acquisition, Pro Forma Revenue Net income (loss) attributable to JBG SMITH Properties Business Acquisition, Pro Forma Net Income (Loss) Earnings (loss) per common share: Basic Business Acquisition, Pro Forma Earnings Per Share, Basic Earnings (loss) per common share: Diluted Business Acquisition, Pro Forma Earnings Per Share, Diluted Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Omnibus Share Plan, 2017 Omnibus Share Plan, 2017 [Member] Omnibus Share Plan, 2017 [Member] Number of shares authorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Number of shares available for issuance Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Available for Grant Segment information Schedule of Segment Reporting Information, by Segment [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 2017 Capital Leases, Future Minimum Payments, Remainder of Fiscal Year 2018 Capital Leases, Future Minimum Payments Due, Next Twelve Months 2019 Capital Leases, Future Minimum Payments Due in Two Years 2020 Capital Leases, Future Minimum Payments Due in Three Years 2021 Capital Leases, Future Minimum Payments Due in Four Years 2022 Capital Leases, Future Minimum Payments Due in Five Years Thereafter Capital Leases, Future Minimum Payments Due Thereafter Total Capital Leases, Future Minimum Payments Due Redeemable Noncontrolling Interests Redeemable Noncontrolling Interest [Table Text Block] 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 Nuclear, biological, chemical, and radiological terrorism insurance limit Nuclear, Biological, Chemical, and Radiological Terrorism Insurance Limit, Per Occurrence and in Aggregate Nuclear, Biological, Chemical, and Radiological Terrorism Insurance Limit, Per Occurrence and in Aggregate Additional capital funding committed amount Other Commitment Schedule of Real Estate Properties [Table] Schedule of Real Estate Properties [Table] Consolidated Properties Consolidated Properties [Member] Unconsolidated Properties Unconsolidated Properties [Member] Real Estate Properties [Line Items] Real Estate Properties [Line Items] Purchase obligation Purchase Obligation Principal payment guarantees Principal Payment Guarantees Principal Payment Guarantees Schedule of Other Liabilities [Table] Schedule of Other Liabilities [Table] Schedule of Other Liabilities [Table] Liability Class [Axis] Liability Class [Axis] Fair Value by Liability Class [Domain] Fair Value by Liability Class [Domain] Schedule of Other Liabilities [Line Items] Schedule of Other Liabilities [Line Items] [Line Items] for Schedule of Other Liabilities [Table] Lease intangible liabilities amortization Amortization of Intangible Liabilities Amortization of Intangible Liabilities 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 assumptions 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 Deferred tax liability Deferred Tax Liabilities, Net Other Other Sundry Liabilities Total other liabilities, net 2018 Below Market Lease, Amortization Income, Next Twelve Months 2019 Below Market Lease, Amortization Income, Year Two 2020 Below Market Lease, Amortization Income, Year Three 2021 Below Market Lease, Amortization Income, Year Four 2022 Below Market Lease, Amortization Income, Year Five 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] 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] Mortgages payable Debt Instrument, Fair Value Disclosure Redeemable Noncontrolling Interests Temporary Equity Disclosure [Text Block] Temporary Equity Disclosure [Text Block] Tenant and Other Receivables, Net Loans, Notes, Trade and Other Receivables Disclosure [Text Block] 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] Affiliate Affiliated Entity [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 Legacy JBG Funds [Member] Legacy JBG Funds [Member] 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] Vornado's revolving credit facility 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] Bowen Building, Washington DC Bowen Building, Washington DC [Member] Bowen Building, Washington DC [Member] Related Party Transaction [Line Items] Related Party Transaction [Line Items] Related party transaction amount Related Party Transaction, Amounts of Transaction Service charges Related Party Transaction, Expenses from Transactions with Related Party Service revenue Revenue from Related Parties Loan to Vornado Origination of Notes Receivable from Related Parties Interest Income on loan receivable from Vornado Interest Income, Related Party Amount outstanding on note agreements with Vornado Notes Payable, Related Parties Interest expense to Vornado Interest Expense, Related Party Repayment of mortgage loan Accrued interest on mortgage loan Debt Instrument, Increase, Accrued Interest Related party transaction, monthly amount Related Party Transaction, Monthly Transaction Amount Related Party Transaction, Monthly Transaction Amount Transaction services, initial period (in months) Related Party Transaction, Initial Potential Service Period Related Party Transaction, Initial Potential Service Period Liability incurred in connection with the Combination Business Combination, Consideration Transferred, Liabilities Incurred Real estate service revenue Real Estate Revenue, Net Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [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] 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] Classified as liabilities in Other liabilities, net Derivative Liability Equity Interest Type [Axis] Equity Interest Type [Axis] Equity Interest Issued or Issuable, Type [Domain] Equity Interest Issued or Issuable, Type [Domain] Partnership units Partnership Interest [Member] General and Administrative Expense General and Administrative Expense [Member] Percentage of common shares distributed Percentage Of Outstanding Common Shares Distributed Percentage Of Outstanding Common Shares Distributed Spinoff ratio Stockholders' Equity Note, Stock Split, Conversion Ratio Limited Partners spinoff ratio Limited Partners Capital Account, Units Split, Conversion Ratio Limited Partners Capital Account, Units Split, Conversion Ratio Common stock issued (in shares) Common limited partnership units (in shares) Limited Partners' Capital Account, Units Issued Common limited partnership units outstanding (in shares) Limited Partners' Capital Account, Units Outstanding Prior period reclassification adjustment Prior Period Reclassification Adjustment Future Minimum Rental Income Lessor, Operating Leases [Text Block] Temporary Equity Increase (Decrease) in Temporary Equity [Roll Forward] Beginning Balance OP Units issued Net loss attributable to redeemable noncontrolling interests Temporary Equity, Net Income Ending Balance Share-Based Payments and Employee Benefits Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Subsequent Events Subsequent Events [Text Block] 2018 Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months 2019 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2020 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Five Schedule of U.S Governmental Revenue Schedule of Revenue by Major Customers by Reporting Segments [Table Text Block] Composition of Investments Equity Method Investments [Table Text Block] Disaggregation of Revenue [Table] Disaggregation of Revenue [Table] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] U.S. federal government U.S Federal Government [Member] U.S Federal Government [Member] Concentration Risk Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] U.S. federal government Government Contracts Concentration Risk [Member] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Office segment revenue Sales Revenue, Segment [Member] Total revenue Sales Revenue, Net [Member] Disaggregation of Revenue [Line Items] Disaggregation of Revenue [Line Items] Revenues Percentage of revenue Concentration Risk, Percentage Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Estimated useful lives (in years) Property, Plant and Equipment, Useful Life Transactions With Vornado and JBG Legacy Funds Related Party Transactions Disclosure [Text Block] Schedule of Tenants and Other Receivables, Net Schedule of Accounts, Notes, Loans and Financing Receivable [Table Text Block]