Unconsolidated variable interest entities Unconsolidated Properties [Member] Construction-in-progress, consolidated variable interest entities Constructioninprogresofconsolidatedvariableieestentity Construction-in-progress oc consolidated variable interest entity Laurel Laurel [Member] Laurel [Member] Supplemental Cash Flow Information [Abstract] Supplemental Cash Flow Information [Abstract] Maximum partnership percentage required to purchase Option Indexed to Issuer's Equity, Percentage Of Indexed Ownership Interest Option Indexed to Issuer's Equity, Percentage Of Indexed Ownership Interest Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Preferred shares, shares outstanding Preferred Stock, Shares Outstanding Line of credit facility, annual facility fee Line of credit facility, annual facility fee Line of credit facility, annual facility fee Receivable Type [Axis] Receivable Type [Axis] Derivative Liability Derivative liability Derivative Liability Dividends declared to common shareholders Dividends, Common Stock, Cash Security Exchange Name Security Exchange Name Forfeited, Weighted-Average Grant-Date Fair Value (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeitures, Weighted Average Grant Date Fair Value Mortgages payable, consolidated variable interest entities Mortgage Payable From Consolidated Variable Interest Entities Mortgage Payable From Consolidated Variable Interest Entities Mortgages payable balances from variable interest entities, or VIEs, for the periods presented. Exchange [Domain] Exchange [Domain] Weighted-average remaining lease term - operating leases Operating Lease, Weighted Average Remaining Lease Term Linden Square Linden Square [Member] Linden Square [Member] Darien Commons Darien [Member] Darien [Member] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Contractual Obligation [Axis] Contractual Obligation [Axis] Contractual Obligation [Axis] Derivative Instruments Derivatives, Policy [Policy Text Block] Contributions from noncontrolling interests Proceeds from Noncontrolling Interests Operating lease, term Operating Lease, Term Operating Lease, Term Willow Lawn Willow Lawn [Member] Willow Lawn [Member] (Decrease) increase in cash, cash equivalents, and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect Acquired Finite-Lived Intangible Assets [Line Items] Acquired Finite-Lived Intangible Assets [Line Items] Volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Rental Income Operating Lease, Lease Income 2023 Long-Term Debt, Maturity, Year Two 3.25% Senior notes 3.25% Senior notes [Member] 3.25% Senior notes [Member] Other interest income Interest Income, Other Forward Sales Contracts Forward Sales Contracts [Member] Forward Sales Contracts Subsequent Event Type [Domain] Subsequent Event Type [Domain] Cash in excess of the FDIC insured limit Cash, Uninsured Amount Prior Liens SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Prior Lien, Amount Amortization of above market leases, lessor Amortization of Intangible Assets Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Weighted average interest rate before amortization of debt fees LineofCreditFacilityWeightedAverageInterestRateBeforeAmortizationOfDebt Fees Line of credit facility weighted average interest rate, before amortization of debt fees. Issuance of senior notes, net of costs Proceeds from Issuance of Senior Long-term Debt Anti-dilutive issuable shares Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Weighted-average discount rate - operating leases Operating Lease, Weighted Average Discount Rate, Percent Subsidiary, Sale of Stock [Axis] Sale of Stock [Axis] Repayment of mortgages, finance leases, and notes payable Repayment of mortgages, finance leases, and notes payable Repayment of mortgages, finance leases, and notes payable Subsequent Events [Abstract] Subsequent Events [Abstract] Crow Canyon Commons Crow Canyon [Member] Crow Canyon [Member] Number of states in which entity has properties Number of States in which Entity Operates Lessor, Lease, Description [Table] Lessor, Lease, Description [Table] Summary of financial assets/(liabilities) measured at fair value on a recurring basis Fair Value, Liabilities Measured on Recurring Basis [Table Text Block] Finite-Lived Intangible Liabilities By Major Class [Axis] Finite-Lived Intangible Liabilities By Major Class [Axis] Finite-Lived Intangible Liabilities By Major Class [Axis] Below Market Lease Below Market Lease [Member] Below Market Lease [Member] Award Type [Domain] Award Type [Domain] Acquired Lease Assets Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract] Net increase in rental income Amortization of above and below Market Leases Local Phone Number Local Phone Number The Shoppes At Nottingham Square Shoppes At Nottingham Square [Member] Shoppes At Nottingham Square [Member] Troy Troy [Member] Troy [Member] Exercisable at the end of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Marketing Marketing Expense Net proceeds from repayment of mortgage notes receivable Net proceeds from repayment of mortgage notes receivable Net proceeds from repayment of mortgage notes receivable Preferred shares, authorized 15,000,000 shares, $.01 par: Preferred Stock, Value, Issued Above market leases Finite-lived Intangible Assets Acquired CocoWalk CocoWalk [Member] CocoWalk Distributions declared to noncontrolling interests, excluding amounts attributable to redeemable noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Above Market Leases Above Market Leases [Member] Tower Shops Tower Shops January 19 2011 [Member] Tower Shops 1/19/11 [Member] Square footage of real estate property Area of Real Estate Property Carrying Amount of Mortgages Balance at beginning of year Balance at end of year SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate Andorra Andorra Shopping Center [Member] Andorra Shopping Center [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Shares withheld for employee taxes (in shares) Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation COMPREHENSIVE INCOME Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Financing cash flows for finance leases Finance Lease, Principal Payments Return of capital, common shares Common shares, return of capital Common shares, return of capital Fixed interest rate of derivative instrument Fixed interest rate of derivative instrument Derivative, Fixed Interest Rate Net income available for common shareholders Earnings Per Share, Basic Amount reclassified from other comprehensive income to interest expense Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net No Trading Symbol Flag No Trading Symbol Flag Minimum percentage of taxable income distributed to shareholders Minimum Percentage Of Taxable Income Distributed To Shareholders Minimum percentage of taxable income distributed to shareholders. New York Stock Exchange, Inc. NEW YORK STOCK EXCHANGE, INC. [Member] Unvested at the beginning of year (in shares) Unvested at the end of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number At The Market Equity Program At The Market Equity Program [Member] At The Market Equity Program [Member] 2022 Long-Term Debt, Maturity, Year One Charge related to the buyout of a lease Gain (Loss) on Termination of Lease Purchase price of real estate acquisition Purchase price of fee interest in real estate Purchase price of fee interest in real estate Portion at Fair Value Measurement Fair Value Measurement [Domain] EARNINGS PER COMMON SHARE, DILUTED Earnings Per Share, Diluted [Abstract] Freedom Plaza Jordan Downs Plaza [Member] Jordan Downs Plaza [Member] Other, net Other Noncash Income (Expense) Bell Gardens Bell Gardens [Member] Bell Gardens [Member] Mortgages payable, net (including $335,301 and $413,681 of consolidated variable interest entities, respectively) Mortgages payable Secured Debt Restricted cash Restricted Cash and Cash Equivalents Depositary Shares Depository Shares [Member] Depository Shares [Member] Georgetowne Shopping Center Georgetowne Shopping Center [Member] Georgetowne Shopping Center Entity Voluntary Filers Entity Voluntary Filers Third Street Promenade Third Street Promenade [Member] Third Street Promenade [Member] Plan Name [Axis] Plan Name [Axis] Long-term Debt Long-term Debt Level 1 Fair Value, Inputs, Level 1 [Member] INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities [Abstract] Entity Listings, Exchange [Axis] Entity Listings, Exchange [Axis] Commissions Commissions [Member] Commissions [Member] Entity Small Business Entity Small Business Preferred Units, Class [Domain] Preferred Units, Class [Domain] Scenario [Axis] Scenario [Axis] Decrease (increase) in accounts receivable, net Increase (Decrease) in Accounts and Other Receivables Prepaid expenses and other assets prepaid expenses and other assets [Member] prepaid expenses and other assets Accumulated Dividends in Excess of Net Income Accumulated Distributions in Excess of Net Income [Member] Option By Type [Domain] Option By Type [Domain] Option By Type [Domain] Savings and Retirement Plans [Abstract] Savings and Retirement Plans [Abstract] Savings and Retirement Plans [Abstract] Interest Rate Swap Interest Rate Swap [Member] Mortgages payable and notes payable Mortgages Payable And Notes Payable [Member] Mortgages Payable And Notes Payable [Member] Montrose Crossing Montrose Crossing [Member] Montrose Crossing [Member] Entity Interactive Data Current Entity Interactive Data Current Thereafter Long-Term Debt, Maturity, after Year Five 2025 Finite-Lived Intangible Asset, Expected Amortization, Year Four Amortization of above market leases, lessee Amortization Of Intangible Liability Amortization Of Intangible Liability Increase (decrease) in security deposits and other liabilities Increase Decrease In Security Deposits And Other Liabilities The net change in Security Deposits And Other Liabilities which includes security deposits, deferred revenue and prepaid rent. Also includes liabilities not individually reported in the financial statements, or not separately disclosed in notes. Below Market Leases, Lessee BelowMarketLeasesLessee [Member] Below Market Leases, Lessee Schedule of minimum future commercial property rentals from noncancelable operating leases Lessor, Operating Lease, Payment to be Received, Fiscal Year Maturity [Table Text Block] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Comprehensive income attributable to noncontrolling interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Material unrecognized tax benefits Unrecognized Tax Benefits Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Cumulative Effect on Retained Earnings Cumulativeimpacttoaccumulateddividendsinexcessofnetincome Cumulative impact to accumulated dividends in excess of net income Entity Address, State or Province Entity Address, State or Province Colorado Blvd Colorado Blvd [Member] Colorado Blvd [Member] 2022 Lessor, Operating Lease, Payment to be Received, Year One Graham Park Plaza Graham Park [Member] Graham Park 3.5% Senior Note [Member] 3.5% Senior Note [Member] 3.5% Senior Note Receivable [Domain] Receivable [Domain] Management fees and costs Management Fee Expense Decrease of operating lease liability Increase (Decrease) in Operating Lease Liability General and administrative General and Administrative Expense Beginning balance (in shares) Ending balance (in shares) Shares, Outstanding Exercisable at the end of the year, Weighted-Average Exercise Price (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Exercise Price 2026 Below Market Lease, Amortization Income, Year Five Operating real estate, consolidated variable interest entities Operating Real Estate From Consolidated Variable Interest Entities Operating real estate balances from variable interest entities, or VIEs, for the periods presented. Accounting Policies [Abstract] Accounting Policies [Abstract] Del Mar Village Del Mar Village [Member] Del Mar Village [Member] Outstanding at the end of year, Weighted-Average Remaining Contractual Term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Remaining Contractual Term Contractual obligations Contractual Obligation Derivative Instrument Derivative Instrument [Axis] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Abstract] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Abstract] Operating lease liabilities Operating Lease, Liability Redeemable noncontrolling interests Beginning balance Ending balance Redeemable Noncontrolling Interest, Equity, Carrying Amount Document Transition Report Document Transition Report Real estate taxes Real Estate Tax Expense Common shares of beneficial interest, $.01 par, 100,000,000 shares authorized, 78,603,305 and 76,727,394 shares issued and outstanding, respectively Common Stock, Value, Issued SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Abstract] SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Abstract] Weighted-average discount rate - finance leases Finance Lease, Weighted Average Discount Rate, Percent Number of condominium units sold Number of condominium units sold Number of condominium units sold Weighted-average period for recognition Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition Unvested at the beginning of year, Weighted-Average Grant-Date Fair Value (in dollars per share) Unvested at the end of year, Weighted-Average Grant-Date Fair Value (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Weighted Average Grant Date Fair Value Mount Vernon/South Valley/7770 Richmond Hwy, Mount Vernon Plaza Mount Vernon [Member] Mount Vernon [Member] Lancaster Lancaster [Member] Lancaster [Member] Conversion and redemption of OP units Conversion And Redemption Of Operating Partnership Units Increase (Decrease) in noncontrolling interest as a result of redeeming, purchasing and/or converting to common stock the interests of Operating Partnership Units. Finance Lease, amortization of right-of-use assets Finance Lease, Right-of-Use Asset, Amortization ICFR Auditor Attestation Flag ICFR Auditor Attestation Flag Summary of weighted average assumptions used to value options granted Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Recourse Status [Domain] Recourse Status [Domain] Co-Registrant [Axis] Legal Entity [Axis] Distributions to and redemptions of noncontrolling interests PaymentsOfDividendsAndRedemptionsMinorityInterest The cash outflow for the return on capital for noncontrolled interest in the entity and cash outflow during the period for redemptions of noncontrolling interests. DownREIT operating partnership units issued with acquisition ValueofdownREITOperatingPartnershipUnitsIssuedinConnectionwithBusinessAcquisition Value of downREIT Operating Partnership Units Issued in Connection with Business Acquisition Preferred Units by Name [Axis] Preferred Units by Name [Axis] Class of Stock [Axis] Class of Stock [Axis] Total interest costs incurred Interest Costs Incurred Option By Type [Axis] Option By Type [Axis] Option By Type [Axis] Thereafter Finance Lease, Liability, to be Paid, after Year Five Maximum amount of borrowings outstanding Line of Credit Facility, Maximum Amount Outstanding During Period Lawrence Park Lawrence Park [Member] Lawrence Park [Member] Dividends declared to common shareholders (in dollars per share) Dividends declared to common shareholders Common Stock, Dividends, Per Share, Declared Entity [Domain] Entity [Domain] Options Share-based Payment Arrangement, Option [Member] Purchase price of partners interest Payments to Acquire Interest in Joint Venture Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Wildwood Wildwood [Member] Wildwood [Member] Stock Issuance Costs by Type [Domain] Stock Issuance Costs by Type [Domain] [Domain] for Stock Issuance Costs by Type [Axis] Notes Payable Notes Payable, Other Payables [Member] Variable Rate [Axis] Variable Rate [Axis] Weighted-average remaining lease term - finance leases Finance Lease, Weighted Average Remaining Lease Term Purchase of noncontrolling interest Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Document Fiscal Year Focus Document Fiscal Year Focus Real Estate and Accumulated Depreciation, by Property [Table] SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, by Property [Table] Variable Rate [Domain] Variable Rate [Domain] Additional Paid-in Capital Additional Paid-in Capital [Member] Repayments of Debt Repayments of Debt Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Common shares, paid Common Stock, Dividends, Per Share, Cash Paid Collectibility Adjustment Collectibility Adjustment Collecitbility adjustments recognized during the period. Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Sylmar Towne Center Sylmar Towne Center [Member] Sylmar Town Center Minor Improvements, Furniture and Equipment Minor Improvements, Furniture and Equipment [Member] Minor Improvements, Furniture and Equipment [Member] Equity Method Investment, Nonconsolidated Investee [Axis] Equity Method Investment, Nonconsolidated Investee [Axis] THE AVENUE at White Marsh THE AVENUE at White Marsh, Due 2021 [Member] THE AVENUE at White Marsh, Due 2021 [Member] Entity Information [Line Items] Entity Information [Line Items] COMPONENTS OF RENTAL EXPENSE Operating Leases Revenue And Expense Text Block [Text Block] The principal components of rental income and/or rental expense recognized for the period. Other Assets Other Assets [Member] Mortgage receivable, net of valuation allowances Financing Receivable, after Allowance for Credit Loss Fair value of long-term debt Long-term Debt, Fair Value Plaza Del Mercado Plaza Del Mercado [Member] Plaza Del Mercado Member Two In Plaza El Segundo Member Two In Plaza El Segundo [Member] Member Two In Plaza El Segundo [Member] Real Estate Properties [Domain] Real Estate Properties [Domain] Maximum Maximum [Member] Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement [Abstract] Contractual Obligation [Domain] Contractual Obligation [Domain] Contractual Obligation [Domain] Initial cost to company, Buildings and Improvements SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Initial Cost of Building and Improvements Change in redemption value Temporary Equity, Other Changes Award Type [Axis] Award Type [Axis] FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities [Abstract] Minimum annual payments Lessee, Operating Lease, Liability, Maturity [Table Text Block] Common Shares Of Beneficial Interest Common Shares Of Beneficial Interest [Member] Common Shares Of Beneficial Interest [Member] Total shareholders’ equity of the Trust Stockholders' Equity Attributable to Parent 401(k) Maximum annual contribution per employee Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount Pan Am Shopping Center Pan Am Shopping Center [Member] Pan Am Shopping Center [Member] City Area Code City Area Code Increase in accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities Exercisable at the end of year, Aggregate Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items] Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items] Schedule of supplemental disclosures related to the Consolidated Statements Of Cash Flows Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] January 1, 2020 adoption of new accounting standard January 1, 2020 adoption of new accounting standard January 1, 2020 adoption of new accounting standard East Bay Bridge East Bay Bridge [Member] EastBayBridge [Member] Redemption and retirement of senior notes Repayments of Senior Debt Number of leases Number Of Leases Number Of Leases ACQUIRED IN-PLACE LEASES Intangible Assets Disclosure [Text Block] Mortgage loans assumed with acquisition Noncash or Part Noncash Acquisition, Debt Assumed Estimated useful lives Property, Plant and Equipment, Useful Life Estimated maximum liability upon exercise of the put option Estimated Liability Upon Exercise Of Option Estimated Liability Upon Exercise Of Option Other liabilities and deferred credits Deferred Credits and Other Liabilities Utilities Utilities Operating Expense Payments of ordinary dividends, common stock Common Stock, Ordinary Dividends, Per Share, Cash Paid Common Stock, Ordinary Dividends, Per Share, Cash Paid Shares issued under dividend reinvestment plan (in shares) Stock Issued During Period, Shares, Dividend Reinvestment Plan Accounts and notes receivable Accounts and Financing Receivable, after Allowance for Credit Loss Valuation adjustments Valuation adjustments Mortgage loans on real estate valuation adjustments Total future minimum finance lease payments Finance Lease, Liability, Payment, Due Adjustments for New Accounting Pronouncements [Axis] Accounting Standards Update [Axis] Debt Instrument, Face Amount Debt Instrument, Face Amount Brick Plaza Brick Plaza [Member] Brick Plaza [Member] Operating (including $2,207,648 and $1,703,202 of consolidated variable interest entities, respectively) Rental Properties Grants of common shares and options Share-based Payment Arrangement [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Restricted stock units Restricted Stock Units (RSUs) [Member] Finance lease liabilities Finance lease liabilities Finance Lease, Liability Business Acquisition and Disposition Business Acquisition [Line Items] Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] Income Statement [Abstract] Income Statement [Abstract] Entity Registrant Name Entity Registrant Name Prepaid expenses and other assets Prepaid Expense and Other Assets 2024 Finance Lease, Liability, to be Paid, Year Three 2025 Finance Lease, Liability, to be Paid, Year Four Remaining capacity to issue Remaining Capacity To Issue Remaining $ Capacity Of Shares To Issue Hoboken (14 Buildings) Hoboken 14 Buildings [Member] Hoboken 14 Buildings [Member] [Member] Conversion price per share Convertible Preferred Stock, Conversion Price Per Share Convertible Preferred Stock, Conversion Price Per Share Perring Plaza Perring Plaza [Member] Perring Plaza [Member] Preferred shares, paid Preferred Stock, Dividends, Per Share, Cash Paid Entity Tax Identification Number Entity Tax Identification Number Document Fiscal Period Focus Document Fiscal Period Focus Total future minimum operating lease payments Lessee, Operating Lease, Liability, to be Paid Segment Reporting, Factors Used to Identify Entity's Reportable Segments Segment Reporting, Factors Used to Identify Entity's Reportable Segments Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Share Based Compensation Share-based Payment Arrangement [Policy Text Block] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] Capitalized lease costs amortization range Capitalized lease costs amortization range Capitalized lease costs amortization range Greenwich Avenue Greenwich Avenue [Member] Greenwich Avenue [Member] Property, Plant and Equipment, Type [Domain] Long-Lived Tangible Asset [Domain] Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Reconcilition of cash, cash equivalents, and restricted cash Schedule of Cash and Cash Equivalents [Table Text Block] Interest Rate Two Interest Rate Two [Member] Interest Rate Two [Member] 1.25% Senior Note [Member] 1.25% Senior Note [Member] 1.25% Senior Note Pike 7 Pike 7 [Member] Pike 7 [Member] Distribution from partnerships in excess of earnings Proceeds from Distributions Received from Real Estate Partnerships Langhorne Square Langhorne Square [Member] Langhorne Square [Member] Weighted average grant date fair value of options granted Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Weighted Average Grant Date Fair Value Equity Component [Domain] Equity Component [Domain] Accumulated Depreciation and Amortization Balance at beginning of year Balance at end of year SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation Adjustment to redeemable noncontrolling interests Stockholders' Equity, Other 2022 Lessee, Operating Lease, Liability, to be Paid, Year One Wynnewood Wynnewood [Member] Wynnewood [Member] Various Various Notes Payable [Member] Various Notes Payable [Member] Real Estate Investments by Property Type [Axis] Real Estate Investments by Property Type [Axis] Real Estate Investments by Property Type [Axis] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Schedule of Accounts, Notes, Loans and Financing Receivable [Table] Mortgage notes receivable, net Mortgage Loans on Real Estate, Commercial and Consumer, Net Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Settlement of partner loan via dilution Settlement of partner loan via dilution Settlement of partner loan receivable via dilution of partnership interest. THE AVENUE at White Marsh THE AVENUE at White Marsh [Member] THE AVENUE at White Marsh [Member] Garden Market Garden Market [Member] Garden Market [Member] Capital Improvement, Development, and Redevelopment Projects Capital Improvement, Development, And Redevelopment Projects [Member] Capital Improvement, Development, And Redevelopment Projects [Member] Stock Issuance Costs by Type [Axis] Stock Issuance Costs by Type [Axis] Stock Issuance Costs by Type [Axis] Liabilities Liabilities [Abstract] Collection and satisfaction of loans SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Collections of Principal Summary of carrying amount and fair value of financial instruments Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block] Counterparty Name [Domain] Counterparty Name [Domain] Westgate Center Westgate Mall [Member] Westgate Mall [Member] 2025 Lessee, Operating Lease, Liability, to be Paid, Year Four Level 2 Fair Value, Inputs, Level 2 [Member] Type of Adoption [Domain] Accounting Standards Update [Domain] Auditor Location Auditor Location Decrease in mortgage notes receivable, net valuation allowance Decrease in mortgage notes receivable, net valuation allowance Decrease in mortgage notes receivable, net valuation allowance Less accumulated depreciation and amortization (including $389,950 and $335,735 of consolidated variable interest entities, respectively) Real Estate Investment Property, Accumulated Depreciation Finance Lease, interest on lease liabilities Finance Lease, Interest Expense Second mortgage on a retail shopping center in Baltimore, MD Second mortgage on a retail shopping center in Baltimore, MD [Member] Second mortgage on a retail shopping center in Baltimore, MD Use of Estimates Use of Estimates, Policy [Policy Text Block] Schedule of earnings per share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Finance Lease, Liability, Payment, Due [Abstract] Finance Lease, Liability, Payment, Due [Abstract] Sales price of real estate Proceeds from Sale of Real Estate Title of 12(b) Security Title of 12(b) Security Common shares of beneficial interest, shares authorized Common Stock, Shares Authorized Repayments of Secured Debt Repayments of Secured Debt Title of Individual [Axis] Title of Individual [Axis] NET INCOME AVAILABLE FOR COMMON SHAREHOLDERS Net Income (Loss) Available to Common Stockholders, Basic Document Type Document Type Preferred shares, declared Preferred Stock, Dividends Per Share, Declared Share type [Axis] Share type [Axis] Share type 2023 Lessor, Operating Lease, Payment to be Received, Year Two Interest rate Debt Instrument, Interest Rate, Stated Percentage Gain on sale of real estate and change in control of interest, net of tax Gain on sale of real estate and change in control of interest, net of tax Gain on sale of real estate Gain (Loss) on Sale of Properties Net income, excluding amount attributable to redeemable noncontrolling interests Profit Loss Excluding Redeemable Noncontrolling Interests Net income (loss) excluding portion attributable to redeemable noncontrolling interests. Thereafter Lessor, Operating Lease, Payment to be Received, after Year Five Net income attributable to noncontrolling interests Less: Income from operations attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Revolving credit facility Revolving Credit Facility [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Mortgage Loans on Real Estate, Name, Property Type [Domain] Real Estate [Domain] Townson Residential Townson Residential [Member] Townson Residential [Member] Notional amount of interest rate swap agreements Derivative Liability, Notional Amount LEASE COST Lease, Cost [Table Text Block] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Number of members with purchase options Number of Members With Purchase Options Number of Members With Purchase Options Pike & Rose Pike & Rose [Member] Pike & Rose Mercer Mall Mercer Mall [Member] Mercer Mall [Member] Principal Amount of Loans Subject to delinquent Principal or Interest SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Principal Amount of Delinquent Loans Subsequent Event Subsequent Events [Text Block] Senior notes and debentures Senior Notes And Debentures [Member] Senior Notes And Debentures [Member] Shares issued under dividend reinvestment plan Dividends Reinvested in Noncash Financing Transaction Dividends reinvested in noncash financing transaction Net real estate assets of consolidated VIEs VariableInterestEntity, net Real Estate Assets VariableInterestEntity, net Real Estate Assets Mortgage interest income Revenue Mortgage Interest Interest income earned from mortgage notes receivable. Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities Vesting Term Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Income (loss) from partnerships (Income) loss from partnerships Income (Loss) from Equity Method Investments Tower Shopping Center Tower [Member] Tower [Member] Rental expenses Other Cost and Expense, Operating Summary of restricted share activity Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] 401(k) Employer match Deferred Compensation Arrangement with Individual, Employer Contribution Per Employee, Matching Percent Deferred Compensation Arrangement with Individual, Employer Contribution Per Employee, Matching Percent Finance Lease, Liability, Fiscal Year Maturity Finance Lease, Liability, Fiscal Year Maturity [Table Text Block] FAIR VALUE OF FINANCIAL INSTRUMENTS Fair Value Disclosures [Text Block] North Dartmouth North Dartmouth [Member] North Dartmouth [Member] Prepaid expenses and other assets Prepaid expenses and other assets [Line Items] Prepaid expenses and other assets 2.75% notes Senior 2 Point 75 Percent Notes [Member] Senior 2 Point 75 Percent Notes [Member] 2024 Finite-Lived Intangible Asset, Expected Amortization, Year Three Share-based Payment Arrangement, Expensed and Capitalized, Amount [Abstract] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Abstract] Reconciliation of Real Estate Accumulated Depreciation [Roll Forward] SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation [Roll Forward] Dividends payable Dividends Payable Preferred shares, capital gain Preferred shares, capital gain Preferred shares, capital gain REVENUE Revenues [Abstract] Other operating Other Cost of Operating Revenue Twinbrooke Shopping Centre Twinbrooke Shopping Centre [Member] Twinbrooke Shopping Centre Document Period End Date Document Period End Date Northeast Northeast [Member] Northeast [Member] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Net increase in rental expense Amortization Of Above And Below Market Leases, Lessee Amortization Of Above And Below Market Leases, Lessee Property Subject to or Available for Operating Lease, by Major Property Class [Table] Property, Plant, and Equipment, Lessor Asset under Operating Lease [Table] NON-CASH INVESTING AND FINANCING TRANSACTIONS: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Riverpoint Center Riverpoint Center [Member] Riverpoint Center [Member] Net real estate Real Estate Investment Property, Net Birch & Broad (formerly known as Falls Plaza) Falls Plaza [Member] Falls Plaza [Member] Leases Revenue Recognition, Leases [Policy Text Block] Total operating expenses Operating Expenses Dividends declared to preferred shareholders Dividends, Preferred Stock, Cash 7.48% debentures Debentures 7.48 Percent [Member] Debentures 7.48 Percent [Member] Amortization for acquired in-place leases during the next five years and thereafter Schedule of Finite-Lived Intangible Assets, Future Amortization Expense [Table Text Block] Earnings Per Share [Abstract] Earnings Per Share [Abstract] One of our equity method investees Equity Method Investee [Member] Above Market Leases, Lessor AboveMarketLeasesLessor [Member] Above Market Leases, Lessor Village at Shirlington Shirlington [Member] Shirlington [Member] Contributions from redeemable noncontrolling interests Contributions Contributions from redeemable noncontrolling interests Contributions from redeemable noncontrolling interests Bethesda Row Bethesda Row [Member] Bethesda Row [Member] Total revenue Revenues Common shares, capital gain Common shares, capital gain Common shares, capital gain Long Lived Assets and Impairment Property, Plant and Equipment, Impairment [Policy Text Block] Cost Capitalized Subsequent to Acquisition SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Cost Capitalized Subsequent to Acquisition, Cost Aggregate cost basis for Federal tax purposes SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Federal Income Tax Basis Outstanding at the beginning of year, Weighted-Average Exercise Price (in dollars per share) Outstanding at the end of year, Weighted-Average Exercise Price (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Weighted Average Exercise Price Melville Mall MelvilleMall [Member] MelvilleMall [Member] Kings Court Kings Court [Member] Kings Court [Member] Entity Current Reporting Status Entity Current Reporting Status Hoboken (24 Buildings) Hoboken (24 Buildings) [Member] Hoboken (24 Buildings) Prepaid expenses and other assets [Table] Prepaid expenses and other assets [Table] Prepaid expenses and other assets [Table] Counterparty Name [Axis] Counterparty Name [Axis] Adoption of new accounting standard Adoption of new accounting standard The cumulative effect of the adoption of a new accounting standard in the period. Willow Grove Willow Grove [Member] Willow Grove [Member] Flourtown Flourtown [Member] Flourtown [Member] Leases [Abstract] Leases [Abstract] Income Taxes Income Tax, Policy [Policy Text Block] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Axis] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Axis] Entity Address, Postal Zip Code Entity Address, Postal Zip Code Weighted average number of common shares Weighted average common shares outstanding—diluted Weighted Average Number of Shares Outstanding, Diluted Increase (Decrease) in Derivative Liabilities Increase (Decrease) in Derivative Liabilities Total future amortization expense from acquired below market leases Below Market Lease, Net Related Party [Domain] Related Party [Domain] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Summary of option activity Share-based Payment Arrangement, Option, Activity [Table Text Block] Basis Spread on LIBOR Interest Debt Instrument, Basis Spread on Variable Rate Real Estate [Abstract] Real Estate [Abstract] Other comprehensive income (loss) attributable to redeemable noncontrolling interests Other comprehensive income (loss) - change in value of interest rate swaps Other Comprehensive Income (Loss) Attributable to Redeemable Noncontrolling Interests Other Comprehensive Income (Loss) Attributable to Redeemable Noncontrolling Interests Officer Officer [Member] Hoboken2Buildings Hoboken2Buildings [Member] Hoboken2Buildings Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Maximum exposure to loss in variable interest entity Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Class of Stock [Line Items] Class of Stock [Line Items] Name of Property [Axis] Name of Property Name of Property [Axis] Old Town Center Old Town Center [Member] Old Town Center [Member] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Entity Address, Address Line One Entity Address, Address Line One Capital expenditures - other Capital expenditures other Capital expenditures other Property Subject to or Available for Operating Lease [Line Items] Property, Plant, and Equipment, Lessor Asset under Operating Lease [Line Items] Member One In Plaza El Segundo Member One In Plaza El Segundo [Member] Member One In Plaza El Segundo [Member] OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities [Abstract] Principles of Consolidation Consolidation, Policy [Policy Text Block] Entity Shell Company Entity Shell Company Second Mortgage on a retail shopping center in Rockville, MD One Second Mortgage on a retail shopping center in Rockville, MD One [Member] Second Mortgage on a retail shopping center in Rockville, MD One Expected term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term 2025 Below Market Lease, Amortization Income, Year Four Shares withheld for employee taxes Payment, Tax Withholding, Share-based Payment Arrangement Total rental expenses Direct Costs of Leased and Rented Property or Equipment Loss Contingencies [Table] Loss Contingencies [Table] 401(k) Maximum of employer match as a percentage of employee eligible earnings Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay Current Fiscal Year End Date Current Fiscal Year End Date Net unamortized (discount) premium and debt issuance costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Purchase price of real estate acquisition Purchase price of real estate acquisition Purchase price of real estate acquisition Number of consolidated variable interest entities Number of Consolidated Variable Interest Entities Number of consolidated entities that meet the criteria of a variable interest entity in which the Company holds a variable interest under ASU 2015-02. The Grove at Shrewsbury The Grove at Shrewsbury [Member] The Grove at Shrewsbury [Member] Statement [Table] Statement [Table] Bala Cynwyd Bala Cynwyd [Member] Bala Cynwyd [Member] Total unrecognized compensation cost related to unvested share-based compensation arrangements Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount Aggregate offering price of common shares Aggregate Offering Price Of Common Share Maximum aggregate offering price of common shares. Real Estate Disclosure Real Estate Disclosure [Text Block] Statistical Measurement [Axis] Statistical Measurement [Axis] Subsequent Event Subsequent Event [Member] Performance Incentive Plan 2010 Performance Incentive Plan 2010 [Member] Performance Incentive Plan 2010 [Member] Finite-Lived Intangible Assets, Net Finite-Lived Intangible Assets, Net Rollingwood Apts. Rollingwood Apartments [Member] Rollingwood Apartments [Member] Greenlawn Plaza Greenlawn Plaza [Member] Greenlawn Plaza Noncontrolling interests Stockholders' Equity Attributable to Noncontrolling Interest Number of real estate properties Number of Real Estate Properties Thereafter Below Market Lease, Amortization Income, after Year Five Insurance Real Estate Insurance Scenario [Domain] Scenario [Domain] Adjustments to reconcile net income to net cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Operating lease cost Operating Lease, Cost Hilton Village Hilton Village [Member] Hilton Village Impairment of property Impairment of property Impairment of property Summary of dividends declared and paid per share Schedule of Dividends Declared and Paid Per Share [Table Text Block] Schedule of Dividends Declared and Paid Per Share [Table Text Block] Stock options Stock options [Member] Stock options Hoboken (1 Building) Hoboken 210 14th Street [Member] Hoboken 210 14th Street [Member] Senior notes and debentures, net Senior Notes Real Estate and Accumulated Depreciation, Carrying Amount of Land and Buildings and Improvements [Abstract] SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Gross [Abstract] Dividends [Abstract] Dividends [Abstract] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] NET INCOME ATTRIBUTABLE TO THE TRUST Net Income (Loss) Attributable to Parent Issuance of loans SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, New Mortgage Loan Purchase price under option Purchase Price Under Option Purchase Price Under Option Operating lease right of use assets Operating Lease, Right-of-Use Asset Interest Rate One Interest Rate One [Member] Interest Rate One [Member] Finite-Lived Intangible Assets, Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Statistical Measurement [Domain] Statistical Measurement [Domain] Schedule of principal payments on mortgages payable, notes payable, senior notes and debentures Schedule of Maturities of Long-term Debt [Table Text Block] Segment Information Segment Reporting, Policy [Policy Text Block] Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Additional paid-in capital Additional Paid in Capital, Common Stock Costs associated with property sold under threat of condemnation, net Costs associated with property sold under threat of condemnation, net Costs associated with lease buyout for a property sold Costs associated with lease buyout for a property sold 3.2% Senior Note 3.2% Senior Note [Member] 3.2% Senior Note [Member] Pentagon Row Pentagon Row [Member] Pentagon Row [Member] Expected dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Components Of Rental Expense [Abstract] Components Of Rental Expense [Abstract] Components Of Rental Expense [Abstract] Entity File Number Entity File Number Nonrecourse Nonrecourse [Member] Fresh Meadows Fresh Meadows [Member] Fresh Meadows [Member] Condominiums Condominiums [Member] Condominiums [Member] Forfeited or expired (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period Decrease in operating lease right of use assets Decrease in operating lease right of use assets Decrease in operating lease right of use assets Depreciation Expense Real Estate Depreciation Expense Real Estate Depreciation Expense on Real Estate only Variable lease cost Variable Lease, Cost Indexed ownership interest percentage Ownership Interest of Other Partner in Put Option The percentage of partnership interest we are required to purchase in a put option. Payroll Property Payroll Expense Property Payroll Expense related to property management which includes salaries and benefits. Put Option Put Option [Member] Ground rent Ground Rent Expense Ground Rent Expense Total vesting-date fair value of shares vested during the year Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Fair Value Granted, Weighted-Average Grant-Date Fair Value (in dollars per share) Weighted-average grant-date fair value of stock awarded Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period, Weighted Average Grant Date Fair Value Debt Instruments [Abstract] Debt Instruments [Abstract] Title of Individual [Domain] Title of Individual [Domain] Schedule of Operating Leased Assets [Table] Schedule of Operating Leased Assets [Table] Rent abatement agreements RentAbatementinPeriod Abatements of rent agreed upon during period. Barracks Road Barracks Road [Member] Barracks Road [Member] Friendship Center Friendship Ctr [Member] Friendship Ctr [Member] Share-based compensation expense, net of forfeitures Share Based Compensation Expense Net Value This element represents the amount of recognized equity-based compensation related to other long-term incentive and bonus plans during the period, that is, the amount recognized as expense in the income statement (or as asset if compensation is capitalized). Elllisburg Elllisburg Circle [Member] Elllisburg Circle [Member] Acquired lease costs Acquired lease costs Acquired lease costs Number of properties exceeding segment reporting threshold Number of Properties Exceeding Segment Reporting Threshold Number of Properties Exceeding Segment Reporting Threshold ASSETS Assets [Abstract] Encumbrances SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Amount of Encumbrances 2024 Long-Term Debt, Maturity, Year Three Deduction during period—dispositions and retirements of property Real Estate Dispositions and Retirements Carrying amount of real estate sold, cap ex disposals, and transfers to joint venture during the period. Prepaid Expenses and Other Assets Prepaid Expenses and Other Assets [Policy Text Block] Description of entity's accounting policy related to prepaid expenses and other assets. Other Liabilities Other Liabilities [Member] Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Mortgage Notes Receivable Financing Receivable, Held-for-investment [Policy Text Block] Real Estate Property, Plant and Equipment, Policy [Policy Text Block] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Domain] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Domain] Capital expenditures - development and redevelopment Capital Expenditures Development Redevelopment Payments to develop or redevelop real estate assets is the process of adding improvements on or to a parcel of land. Such improvements may include drainage, utilities, subdividing, access, buildings, and any combination of these elements. In addition, the cash outflow from construction costs to date on capital projects that have not been completed and assets being constructed that are not ready to be placed into service. Outstanding at the beginning of year (in shares) Outstanding at the end of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Debt Instrument [Axis] Debt Instrument [Axis] Increase in prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Retail and commercial Commercial Real Estate [Member] COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] Chesterbrook Chesterbrook [Member] Chesterbrook Related Party [Axis] Related Party [Axis] Mortgages Payable Mortgage Payable Secured Debt [Member] ROU assets obtained in exchange for operating lease liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Final award earned percentage of original award Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Capitalized share-based compensation Share-based Payment Arrangement, Amount Capitalized Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Fourth Street Fourth Street [Member] Fourth Street [Member] Number of interest rate swap agreements Number of Interest Rate Derivatives Held La Alameda & Assembly Row Hotel La Alameda & Assembly Row Hotel [Member] La Alameda & Assembly Row Hotel 2024 Lessee, Operating Lease, Liability, to be Paid, Year Three 5.0% Series C Cumulative Redeemable Preferred Shares, (stated at liquidation preference $25,000 per share), 6,000 shares issued and outstanding 5.0% Series C Cumulative Redeemable Preferred Shares 5.0% Series C Cumulative Redeemable Preferred [Member] Five point Zero Percentage Series C Redeemable Convertible Preferred Stock [Member] Below market leases Below Market Lease, Acquired Federal Plaza Federal Plaza [Member] Federal Plaza [Member] Thereafter Finite-Lived Intangible Asset, Expected Amortization, after Year Five Performance Based Unvested Shares Performance Based Unvested Shares [Member] Performance Based Unvested Shares Other Offering Costs Other Offering Costs [Member] Other Offering Costs [Member] Real estate accumulated depreciation impairment of property Real estate accumulated depreciation impairment of property Real estate accumulated depreciation impairment of property 2026 Long-Term Debt, Maturity, Year Five Real estate, at cost, total Real Estate Investment Property, at Cost Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Three properties 2020 Three properties 2020 [Member] Three properties 2020 Shares withheld for employee taxes Share-based Payment Arrangement, Decrease for Tax Withholding Obligation Number of shares authorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Operating cash flows for operating leases Operating Lease, Payments Santana Row Santana Row [Member] Santana Row Schedule of Deferred Compensation Arrangement with Individual, Postretirement Benefits [Table] Schedule of Deferred Compensation Arrangement with Individual, Postretirement Benefits [Table] SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward] SEC Schedule, 12-29, Real Estate Companies, Investment in Movement in Mortgage Loans on Real Estate [Roll Forward] Leasing costs Increase (Decrease) in Lease Acquisition Costs Preferred shares, percentage Preferred Stock, Dividend Rate, Percentage 2026 Lessor, Operating Lease, Payment to be Received, Year Five Assembly Row Hotel Assembly Row Hotel [Member] Assembly Row Hotel Depreciation and amortization Adjustment Depreciation And Amortization The cash flow addback for the non-cash expense of depreciation and amortization including depreciation and amortization related to discontinued operations. Earnings Per Share Narrative [Table] Earnings Per Share Narrative [Table] Earnings Per Share Narrative [Table] Principal balance Mortgage payable Long-term Debt, Gross January 1, 2019 adoption of new accounting standard - See Note 2 Reduction of Real Estate Reduction of real estate cost Finance lease right of use assets Finance Lease, Right-of-Use Asset, after Accumulated Amortization Accumulated depreciation and amortization, consolidated variable interest entities Accumulated depreciation and amortization, consolidated variable interest entities Accumulated depreciation and amortization related to real estate, Consolidated Variable Interest Entities. Pike&Rose Hotel JV Pike&Rose Hotel JV [Member] Pike&Rose Hotel JV Fairfax Junction Fairfax Junction [Member] Fairfax Junction TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY Liabilities and Equity Impairment charge Impairment charge Other Asset Impairment Charges Residential Residential Real Estate [Member] Total Lessor, Operating Lease, Payments to be Received 2026 Lessee, Operating Lease, Liability, to be Paid, Year Five Exercised, Weighted-Average Exercise Price (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Exercises in Period, Weighted Average Exercise Price Forward Contract Indexed to Issuer's Equity, Shares Forward Contract Indexed to Issuer's Equity, Shares EARNINGS PER SHARE Earnings Per Share [Text Block] EXPENSES Operating Expenses [Abstract] Minimum Minimum [Member] 2020 Property Acquisitions Schedule of Real Estate Properties [Table Text Block] 2023 Lessee, Operating Lease, Liability, to be Paid, Year Two Revolving credit facility Long-term Line of Credit Governor Plaza Governor Plaza [Member] Governor Plaza [Member] 3.625% Senior notes 3.625% Senior notes [Member] 3.625% Senior notes [Member] Hastings Ranch Plaza Hastings Ranch Plaza [Member] Hastings Ranch Plaza Forfeited or Expired, Weighted-Average Exercise Price (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period, Weighted Average Exercise Price Net unamortized discount and debt issuance costs Debt Issuance Costs, Net San Antonio Center San Antonio Center [Member] San Antonio Center [Member] Issuance of notes payable, net of costs Proceeds from Notes Payable COMPREHENSIVE INCOME Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Preferred shares, authorized Preferred Stock, Shares Authorized Leases, Acquired-in-Place Leases, Acquired-in-Place [Member] Contributions from noncontrolling interests, excluding amounts attributable to redeemable noncontrolling interests Contributions from noncontrolling interests Contributions from noncontrolling interests 2023 Below Market Lease, Amortization Income, Year Two 2025 Long-Term Debt, Maturity, Year Four Common shares issued, net Stock Issued During Period, Value, New Issues Debt Disclosure [Text Block] Debt Disclosure [Text Block] SHARE-BASED COMPENSATION PLANS Share-based Payment Arrangement [Text Block] Senior Notes and Debentures Senior Notes [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Escondido Promenade Escondido Promenade [Member] Former Mervyns Parcel, Escondido Promenade [Member] Period for recognition (in years) Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition Years Share-based Compensation, Nonvested Awards, Total Compensation Cost Not yet Recognized, Period for Recognition Years Percent of annualized base rent Percent of Annualized Base Rent Maximum Percent of Annualized Base Rent Maximum Commissions related to sales of common shares Payments of Stock Issuance Costs Common shares issued, net (in shares) Shares issued Stock Issued During Period, Shares, New Issues Number of segments Number of Reportable Segments Investment in partnerships Payments to Acquire Interest in Subsidiaries and Affiliates Brook 35 Brook 35 [Member] Brook 35 [Member] 2025 Lessor, Operating Lease, Payment to be Received, Year Four Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities Letters of credit outstanding, amount Letters of Credit Outstanding, Amount Deferred Rent Receivables, Collected Deferred Rent Receivables, Collected Deferred Rent Receivables, Collected SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Other Disclosure [Abstract] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Other Disclosure [Abstract] Commitments and contingencies (Note 7) Commitments and Contingencies Subsequent Event [Table] Subsequent Event [Table] Rollforward table of the redeemable noncontrolling interest Redeemable Noncontrolling Interest [Table Text Block] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Emerging Growth Company Entity Emerging Growth Company January 1, 2019 adoption of new accounting standard - See Note 2 Reduction of Accumulated Depreciation and Amortization of Real Estate Reduction of Accumulated Depreciation and Amortization of Real Estate Distributions delcared to redeemable noncontrolling interests Distributions & redemptions Redeemable noncontrolling interest, Decrease from Distributions to redeemable noncontrolling interest holders Redeemable noncontrolling interest, Decrease from Distributions to redeemable noncontrolling interest holders Restricted Stock Restricted Stock [Member] Real Estate, Type of Property [Axis] Mortgage Loans on Real Estate, Description, Type of Property [Axis] Real Estate, Type of Property [Axis] Auditor Name Auditor Name Cover [Abstract] Cover [Abstract] Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Less amount representing interest Lessee, Operating Lease, Liability, Undiscounted Excess Amount Term Loan Term loan [Member] Term loan [Member] Town Center of New Britain Town Center of New Britain [Member] Town Center of New Britain [Member] Federal Realty OP LP Federal Realty OP LP [Member] Federal Realty OP LP Gaithersburg Square Gaithersburg Square [Member] Gaithersburg Square [Member] Less amount representing interest Finance Lease, Liability, Undiscounted Excess Amount Share-based compensation expense, net of forfeitures (in shares) Share Based Compensation Expense Net Shares Number of shares issued during the period as a result of our long term incentive, bonus or other share based compensation plans, net of restricted share award forfeitures. Acquisitions SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Other Acquisition Operating Leases, Future Minimum Payments Lessor, Operating Lease, Payments, Fiscal Year Maturity [Abstract] Ownership % ControllingInterestPercent ControllingInterestPercent Carrying Value Reported Value Measurement [Member] Interest Rate Mortgage Loans on Real Estate, Participation Plus Interest Rate, Interest Rate Mortgage Loans on Real Estate, Participation Plus Interest Rate, Interest Rate Life on  which depreciation in latest income statements is computed SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Life Used for Depreciation 2026 Finance Lease, Liability, to be Paid, Year Five Common shares Common Stock [Member] OPERATING INCOME Operating Income (Loss) 2023 Finite-Lived Intangible Asset, Expected Amortization, Year Two Real Estate and Accumulated Depreciation [Line Items] SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items] Hauppauge Hauppauge [Member] Hauppauge [Member] Share-based compensation expense Share-based Payment Arrangement, Noncash Expense Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Straight line rent receivable Straight line rent receivable Straight line rent receivable Above Market Leases, Lessee Above Market Leases, Lessee [Member] Above Market Leases, Lessee [Member] Preferred Shares, liquidation preference per share Preferred shares, liquidation preference per share Preferred Stock, Liquidation Preference Per Share Summary of restricted stock units activity Share-based Payment Arrangement, Restricted Stock Unit, Activity [Table Text Block] Real Estate Property Ownership [Axis] Real Estate Property Ownership [Axis] Plaza El Segundo/The Point Plaza El Segundo/The Point [Member] Plaza El Segundo/The Point Payments from reserves Standard and Extended Product Warranty Accrual, Decrease for Payments Schedule IV - Mortgage Loans on Real Estate SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Text Block] Dividends on preferred shares Less: Preferred share dividends Preferred Stock Dividends, Income Statement Impact Total liabilities Liabilities Straight Line Rent Adjustments Straight Line Rent Adjustments 2022 Finite-Lived Intangible Asset, Expected Amortization, Year One Granted, Weighted-Average Exercise Price (in dollars per share) Share-based Compensation Arrangements by Share-based Payment Award, Options, Grants in Period, Weighted Average Exercise Price Outstanding at the end of year, Aggregate Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Gross amount at which carried at close of period, Total Balance at beginning of year Balance at end of year SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Gross OPERATING LEASES Lessor, Operating Leases [Text Block] Payment of ordinary dividends, preferred stock Preferred Stock, Ordinary Dividends, Per Share, Cash Paid Preferred Stock, Ordinary Dividends, Per Share, Cash Paid Common shares of beneficial interest, shares issued Common Stock, Shares, Issued Security deposits payable Security Deposit Liability Preferred shares, shares issued Preferred Stock, Shares Issued Schedule III - Summary of Real Estate and Accumulated Depreciation SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation Disclosure [Text Block] Face Amount of Mortgages SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Face Amount of Mortgages Improvements SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Improvements Congressional Plaza Congressional Plaza [Member] Congressional Plaza [Member] Recourse Status [Axis] Recourse Status [Axis] Entity Address, City or Town Entity Address, City or Town Gross amount at which carried at close of period, Buildings and Improvements SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Building and Improvements, Amount Early extinguishment of debt Early extinguishment of debt Gain (Loss) on Extinguishment of Debt Acquired Finite-Lived Intangible Liabilities, Weighted Average Useful Life Acquired Finite-Lived Intangible Liabilities, Weighted Average Useful Life Acquired Finite-Lived Intangible Liabilities, Weighted Average Useful Life 2021 Property Acquisitions Asset Acquisition [Table Text Block] Variable Interest Entities Consolidation, Variable Interest Entity, Policy [Policy Text Block] Costs to amend revolving credit facility Proceeds from (Repayments of) Lines of Credit Deferred compensation liability to participants Deferred Compensation Arrangement with Individual, Recorded Liability Balance Sheet Location [Axis] Balance Sheet Location [Axis] Share type [Domain] Share type [Domain] Share type [Domain] Two properties 2021 Two properties 2021 [Member] Two properties 2021 Measurement Frequency [Domain] Measurement Frequency [Domain] Senior notes and debentures, net Unsecured Debt Old Keene Mill Old Keene Mill [Member] Old Keene Mill [Member] Accounting Standards Update 2016-02 Accounting Standards Update 2016-02 [Member] Interest expense Interest expense Interest Expense 2022 Finance Lease, Liability, to be Paid, Year One Other comprehensive income (loss) - change in value of interest rate swaps, excluding amounts attributable to redeemable noncontrolling interests Other Comprehensive Income (loss), net of portion attributable to noncontrolling interest Other Comprehensive Income (loss), net of portion attributable to noncontrolling interest Assembly Square Marketplace Assembly Square Marketplace [Member] Assembly Square Marketplace [Member] Finley Square Finley Square [Member] Finley Square [Member] Chelsea Chelsea Commons Chelsea [Member] Chelsea [Member] Acquired Lease Liabilities Below Market Lease, Amortization Income, Maturity Schedule [Abstract] Contractual term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Revenue Recognition and Accounts Receivable Revenue Recognition and Accounts Receivable [Policy Text Block] Disclosure of accounting policy for revenue recognition for operating leases and trade and other accounts receivable. Includes how an entity determines the level of its allowance for doubtful accounts. Entity Filer Category Entity Filer Category Risk free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Hoboken Hoboken Provident [Member] Hoboken Provident [Member] Fair Value Estimate of Fair Value Measurement [Member] Interest capitalized Interest Costs Capitalized Adjustment SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items] Other Notes Payable Other Notes Payable Finite-Lived Intangible Liabilities By Major Class [Domain] Finite-Lived Intangible Liabilities By Major Class [Domain] [Domain] for Finite-Lived Intangible Liabilities By Major Class [Axis] Recent Accounting Pronouncements Accounting Standards Update and Change in Accounting Principle [Text Block] The Shops at Sunset Place Sunset Place [Member] Acquisition of the Shops at Sunset Place on 10/1/2015. Quince Orchard Quince Orchard Plaza [Member] Quince Orchard Plaza [Member] 2023 Finance Lease, Liability, to be Paid, Year Two Operating partnership units outstanding, fair value Operating Partnership Units Fair Value Fair value of operating partnership units at the balance sheet date. Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Total shareholders’ equity Beginning balance Ending balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Ownership interest of partner in our joint venture Ownership interest of partner in our joint venture Ownership interest of partner in our joint venture Amendment Flag Amendment Flag Equity Components Equity Components [Axis] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Barcroft Plaza Barcroft Plaza [Member] Barcroft Plaza Less: Earnings allocated to unvested shares Earnings Allocated To Unvested Shares Earnings allocated to unvested shares Olivo at Mission Hills Olivo at Mission Hills [Member] Olivo at Mission Hills [Member] Finite-Lived Intangible Liabilities, Total Finite-Lived Intangible Liabilities, Gross Finite-Lived Intangible Liabilities, Gross Sale of Stock, Name of Transaction [Domain] Sale of Stock [Domain] Granted (in shares) Number of options granted in period Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures Equity Method Investment, Nonconsolidated Investee [Domain] Equity Method Investment, Nonconsolidated Investee [Domain] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Thereafter Lessee, Operating Lease, Liability, to be Paid, after Year Five Assembly Row/Assembly Square Market Place Assembly Square Market Place Assembly Row [Member] Assembly Square Market Place Assembly Row [Member] Number of properties subject to operating leases Number of Properties Subject to Ground Leases Deductions during period—dispositions and retirements of property Real Estate Accumulated Depreciation Dispositions and Retirements Real Estate Accumulated Depreciation Dispositions and Retirements Proceeds from sale of real estate Proceeds from Sale of Real Estate Held-for-investment Preferred shares, par value Preferred shares, par value Preferred Stock, Par or Stated Value Per Share Entity Public Float Entity Public Float Performance Incentive Plan 2020 Performance Incentive Plan 2020 [Member] Performance Incentive Plan 2020 Plaza El Segundo Plaza El Segundo [Member] Plaza El Segundo [Member] Finite-Lived Intangible Liabilities, Accumulated Amortization Finite-Lived Intangible Liabilities, Accumulated Amortization Finite-Lived Intangible Liabilities, Accumulated Amortization Net income available for common shareholders, basic and diluted Net income available for common shareholders, basic and diluted Net income after adjustments for dividends on preferred stock and earnings allocated to unvested shares. Statement [Line Items] Statement [Line Items] Fair Value, Balance Sheet Grouping, Financial Statement Captions Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Schedule of principal components of rental expenses Schedule Of Principal Components Of Rental Expenses [Table Text Block] Schedule Of Principal Components Of Rental Expenses [Table Text Block] Debt Disclosure [Abstract] Debt Disclosure [Abstract] Schedule of common shares awarded under various compensation plans Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Property, Plant and Equipment, Type [Axis] Long-Lived Tangible Asset [Axis] Acquisitions of loans, net of valuation adjustements Acquisitions of loans, net of valuation adjustements Acquisitions of loans, net of valuation adjustements Weighted average unvested shares outstanding Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights 4.50% notes 4.50% Senior notes [Member] 4.50% Senior notes Camelback Colonnade and Hilton Village Camelback Colonnade and Hilton Village [Member] Camelback Colonnade and Hilton Village SAVINGS AND RETIREMENT PLANS Retirement Benefits [Text Block] Below Market Leases, Lessor BelowMarketLeasesLessor [Member] Below Market Leases, Lessor 401(k) Employer contribution expense Deferred Compensation Arrangement with Individual, Contributions by Employer Schedule of Significant Acquisitions [Table] Schedule of Business Acquisitions, by Acquisition [Table] Document Annual Report Document Annual Report Summary of share-based compensation expense Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Scenario, Forecast Forecast [Member] White Marsh Plaza White Marsh Plaza [Member] White Marsh Plaza [Member] Issuance of common shares, net of costs Net cash proceeds of common stock Proceeds from Issuance of Common Stock TOTAL ASSETS Assets Plan Name [Domain] Plan Name [Domain] Cash paid for interest, net of amounts capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities Dedham Plaza Dedham Plaza [Member] Dedham Plaza [Member] Noncontrolling Interests Noncontrolling Interest [Member] Audit Information [Abstract] Audit Information [Abstract] Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Derivative, Name [Domain] Derivative Contract [Domain] Accumulated dividends in excess of net income Accumulated Distributions in Excess of Net Income Forward Equity Sales Policy Forward Equity Sales Policy [Policy Text Block] Forward Equity Sales Policy SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Significant Accounting Policies [Text Block] Fair value of property Property, Plant, and Equipment, Fair Value Disclosure Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Subsequent Event [Line Items] Subsequent Event [Line Items] DownREIT Partnership Units, issued in acquisition Units of Partnership Interest, Amount Weighted average interest rate on mortgage note receivables WeightedAverageInterestRateonFinancingReceivable The weighted average interest rate on outstanding financing recievables EARNINGS PER COMMON SHARE, BASIC Earnings Per Share, Basic [Abstract] Redeemable Noncontrolling Interests Redeemable Noncontrolling Interests [Policy Text Block] Redeemable Noncontrolling Interests [Policy Text Block] Net income available for common shareholders Earnings Per Share, Diluted Weighted average number of common shares Weighted average common shares outstanding—basic Weighted Average Number of Shares Outstanding, Basic Open forward contracts for share issuances Weighted Average Number Diluted Shares Outstanding Adjustment Net income attributable to redeemable noncontrolling interests Net income Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Cash paid for income taxes Income Taxes Paid, Net Investment in partnerships Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Finite-lived Intangible Assets Amortization Expense [Table Text Block] Finite-lived Intangible Assets Amortization Expense [Table Text Block] COMPREHENSIVE INCOME ATTRIBUTABLE TO THE TRUST Comprehensive Income (Loss), Net of Tax, Attributable to Parent Debt Issuance Costs Debt, Policy [Policy Text Block] Idylwood Plaza Idylwood Plaza [Member] Idylwood Plaza [Member] Rockville Town Square Rockville Town Square [Member] Rockville Town [Member] DownREIT operating partnership units redeemed for common shares Redemptionofoperatingpartnershipunitsforcommonshares Redemption of operating partnership units for common shares Azalea Azalea [Member] Azalea [Member] Repairs and maintenance Cost of Property Repairs and Maintenance Notes payable, net Notes Payable Notes Payable Weighted average price per common share Weighted Average Price Per Common Share Weighted average price per common share 2024 Below Market Lease, Amortization Income, Year Three Accumulated Other Comprehensive Loss Accumulated Other Comprehensive loss AOCI Attributable to Parent [Member] Common shares of beneficial interest, shares outstanding Common Stock, Shares, Outstanding Rollforward of Redeemable Noncontrolling Interests Increase (Decrease) in Temporary Equity [Roll Forward] Reserves for warranties and general liability Standard and Extended Product Warranty Accrual Entity Central Index Key Entity Central Index Key Amortization of below market leases, lessor Amortization of Below Market Lease Camelback Colonnade Camelback Colonnade [Member] Camelback Colonnade Total Lease Cost Lease, Cost Acquisition of real estate Payments to Acquire Real Estate Shareholders’ equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Lessor, Lease, Description [Line Items] Lessor, Lease, Description [Line Items] 6.82% medium term notes Medium Term Notes 6.82 Percent [Member] Medium Term Notes 6.82 Percent [Member] Loss Contingencies [Line Items] Loss Contingencies [Line Items] 2022 Below Market Lease, Amortization Income, Year One Debt Instrument [Line Items] Debt Instrument [Line Items] Trading Symbol Trading Symbol DIVIDENDS Dividends Disclosure [Text Block] This text block may be used to disclose all or some of the information related to dividends declared, dividends paid, and the tax status of dividends as of the financial reporting date. Gratiot Plaza Gratiot Plaza [Member] Gratiot Plaza [Member] 401(K) and Deferred Compensation Plan Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits [Member] Plaza Del Sol Plaza Del Sol [Member] Plaza Del Sol [Member] Tyson's Station Tyson Station [Member] Tyson Station [Member] Courthouse Center Courthouse Center [Member] Courthouse Center [Member] Real Estate Investments, Property Type [Domain] Real Estate Investments, Property Type [Domain] Real Estate Investments, Property Type [Domain] Additions during period—depreciation and amortization expense SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation, Depreciation Expense Hollywood Blvd. Hollywood Blvd [Member] Hollywood Blvd [Member] Total debt Debt and Lease Obligation Grants of common shares and options Share-based Payment Arrangement, Expense Amortization of Below Market Lease, Lessee Amortization of Below Market Lease, Lessee Amortization of Below Market Lease, Lessee Gain on acquisition of controlling interest Gain on Acquisition of Controlling Interest Gain on acquisition of controlling interest in a joint venture. Entities [Table] Entities [Table] Campus Plaza Campus Plaza [Member] Campus Plaza Weighted average amount of borrowings outstanding Line of Credit Facility, Average Outstanding Amount Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Conversion and redemption of OP units (in shares) Conversion and Redemption of Operating Partnership Units in Shares Number of shares issued during the period as a result of the conversion and redemption of operating partnership units into shares Cash, cash equivalents, and restricted cash at beginning of year Cash, cash equivalents, and restricted cash at end of year Total cash, cash equivalents, and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents Second Mortgage on a retail shopping center in Rockville, MD Two Second Mortgage on a retail shopping center in Rockville, MD Two [Member] Second Mortgage on a retail shopping center in Rockville, MD Two Hoboken Hoboken [Member] Hoboken [Member] Common shares of beneficial interest, par value Common Stock, Par or Stated Value Per Share Finite-Lived Intangible Assets, Total Finite-Lived Intangible Assets, Gross Initial cost to company, Land SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Initial Cost of Land DownREIT operating partnership units, outstanding Partners' Capital Account, Units Schedule of Finite-Lived Intangible Assets [Table Text Block] Schedule of Finite-Lived Intangible Assets [Table Text Block] Exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Other comprehensive income (loss) - change in value of interest rate swaps Other comprehensive loss - change in value of interest rate swaps Other Comprehensive Income (Loss), Net of Tax Fair Value, Measurements, Recurring Fair Value, Recurring [Member] 29th Place 29th Place [Member] 29th Place [Member] Estimated Litigation Liability Estimated Litigation Liability Crossroads Crossroads [Member] Crossroads [Member] SHAREHOLDERS’ EQUITY Stockholders' Equity Note Disclosure [Text Block] Measurement Basis [Axis] Measurement Basis [Axis] 2026 Finite-Lived Intangible Asset, Expected Amortization, Year Five Grove at Shrewsbury and Brook 35 Grove At Shrewsbury And Brook 35 [Member] GroveatShrewsbury & Brook 35 [Member] Auditor Firm ID Auditor Firm ID Queen Anne Plaza Queen Anne Plaza [Member] Queen Anne Plaza [Member] Bristol Plaza Bristol [Member] Bristol [Member] 3.95% notes Senior395percentnotes [Member] Senior395percentnotes [Member] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Building and Building Improvements Building and Building Improvements [Member] Changes in assets and liabilities, net of effects of acquisitions and dispositions: Increase (Decrease) in Operating Capital [Abstract] Vested, Weighted-Average Grant-Date Fair Value (in dollars per share) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period, Weighted Average Grant Date Fair Value Class of Stock [Domain] Class of Stock [Domain] Interest Rate [Axis] Interest Rate [Axis] Interest Rate [Axis] Operating cash flows for finance leases Finance Lease, Interest Payment on Liability Maximum borrowing capacity under revolving credit facility Line of Credit Facility, Maximum Borrowing Capacity SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate Schedule [Table] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate Schedule [Table] Repayment (issuance) of mortgage and other notes receivable, net Issuance (Repayments) Of Mortgage And Other Notes Receivable Net The cash outflow from the issuance and purchase of receivables arising from the mortgage note on real estate and other notes receivable, net of repayments. Above Market Liability Above Market Liability Above Market Liability Summary of income tax status of dividends per share paid Schedule Of Income Tax Status Of Dividends Paid [Table Text Block] Schedule Of Income Tax Status Of Dividends Paid [Table Text Block] Number of mortgage receivables SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Number of Loans Nature Of Operations [Abstract] Nature Of Operations [Abstract] Nature Of Operations [Abstract] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Operating Leased Assets [Line Items] Operating Leased Assets [Line Items] Huntington Square HuntingtonSquare [Member] Huntington Square [Member] 5.417% Series 1 Cumulative Convertible Preferred Shares, (stated at liquidation preference $25 per share), 399,896 shares issued and outstanding 5.417% Series 1 Cumulative Convertible Preferred Shares 5.417% Series 1 Cumulative Convertible Preferred [Member] Five point Four One Seven Percentage Series One Cumulative Convertible Preferred Stock [Member] Rent deferral agreements Deferred Rent Receivables, Net Mortgages Mortgages [Member] Stockholders' Equity Note [Abstract] Stockholders' Equity Note [Abstract] Preferred Shares Preferred Stock [Member] Shares issued under dividend reinvestment plan Stock Issued During Period, Value, Dividend Reinvestment Plan Construction-in-progress (including $18,752 and $44,896 of consolidated variable interest entities, respectively) Construction in Progress, Gross 2024 Lessor, Operating Lease, Payment to be Received, Year Three Name of Property Name of Property [Domain] Dividends paid to common and preferred shareholders Dividends Paid To Common And Preferred Shareholders The cash outflow from distribution of an entity's earnings to common and preferred stockholders. Aggregate tax basis for Federal tax purposes SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Federal Income Tax Basis Gross amount at which carried at close of period, Land SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Land, Amount BUSINESS AND ORGANIZATION Nature of Operations [Text Block] White Marsh Other White Marsh Other [Member] White Marsh Other [Member] Percentage of tenants with revenue recognized on a cash basis Tenants with revenue recognized on a cash basis method Tenants with revenue recognized on a cash basis method Grossmont Center Grossmont Center [Member] Grossmont Center Huntington Huntington [Member] Huntington [Member] Gross Value of Real Estate GrossValueofRealEstate Gross value of real estate acquisition. Interest Rate [Domain] Interest Rate [Domain] Interest Rate [Domain] Grove at Shrewsbury (East) Grove at Shrewsbury (East) [Member] Grove at Shrewsbury (East) [Member]