Units of Partnership Interest, Amount Units of Partnership Interest, Amount Square footage of real estate property Area of Real Estate Property Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Construction-in-progress, consolidated variable interest entities Constructioninprogresofconsolidatedvariableieestentity Construction-in-progress oc consolidated variable interest entity Laurel Laurel [Member] Laurel [Member] Receivable Type [Axis] Receivable Type [Axis] Outstanding at the end of year, Aggregate Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value 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 COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] Related Party [Axis] Related Party [Axis] Shares issued under dividend reinvestment plan (in shares) Stock Issued During Period, Shares, Dividend Reinvestment Plan Line of credit facility, annual facility fee Line of credit facility, annual facility fee Line of credit facility, annual facility fee Acquired Lease Assets Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract] Acquired Lease Liabilities Below Market Lease, Amortization Income, Maturity Schedule [Abstract] 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. Statistical Measurement [Domain] Statistical Measurement [Domain] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Distributions declared to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Finance Lease, amortization of right-of-use assets Finance Lease, Right-of-Use Asset, Amortization Investment in partnerships Payments to Acquire Interest in Subsidiaries and Affiliates Linden Square Linden Square [Member] Linden Square [Member] Preferred Shares Preferred Stock [Member] Security Exchange Name Security Exchange Name 2.55% notes 2.55% Senior Notes [Member] 2.55% Senior Notes [Member] The Commons at Darien Darien [Member] Darien [Member] Contractual Obligation [Axis] Contractual Obligation [Axis] Contractual Obligation [Axis] Operating lease, term Operating Lease, Term Operating Lease, Term Willow Lawn Willow Lawn [Member] Willow Lawn [Member] 3.25% Senior notes 3.25% Senior notes [Member] 3.25% Senior notes [Member] 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 Variable Rate [Domain] Variable Rate [Domain] Mortgage Loans on Real Estate, Description, Type of Property [Axis] Real Estate, Type of Property [Axis] Total future minimum finance lease payments Finance Lease, Liability, Payment, Due ASSETS Assets [Abstract] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Accounting Policies [Abstract] Accounting Policies [Abstract] Weighted average interest rate before amortization of debt fees LineofCreditFacilityWeightedAverageInterestRateBeforeAmortizationOfDebt Fees Line of credit facility weighted average interest rate, before amortization of debt fees. Operating cash flows for operating leases Operating Lease, Payments 2023 Long-Term Debt, Maturity, Year Three Fair Value, Balance Sheet Grouping, Financial Statement Captions Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Crow Canyon Commons Crow Canyon [Member] Crow Canyon [Member] Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Note Offering Percent Note Offering Percent Note offering percent of principal amount 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 Finite-Lived Intangible Liabilities By Major Class [Axis] Finite-Lived Intangible Liabilities By Major Class [Axis] Finite-Lived Intangible Liabilities By Major Class [Axis] Change in redemption value Temporary Equity, Other Changes Below Market Lease Below Market Lease [Member] Below Market Lease [Member] Total unrecognized compensation cost related to unvested share-based compensation arrangements Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Amount New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] The Shoppes At Nottingham Square Shoppes At Nottingham Square [Member] Shoppes At Nottingham Square [Member] Troy Troy [Member] Troy [Member] Beginning balance (in shares) Ending balance (in shares) Shares, Outstanding Preferred shares, authorized 15,000,000 shares, $.01 par: Preferred Stock, Value, Issued Total operating expenses Operating Expenses 401(k) Maximum annual contribution per employee Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount Common shares of beneficial interest, par value Common Stock, Par or Stated Value Per Share CocoWalk CocoWalk [Member] CocoWalk Comprehensive Income Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] 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 Financing cash flows for finance leases Finance Lease, Principal Payments Shares issued under dividend reinvestment plan Stock Issued During Period, Value, Dividend Reinvestment Plan Tower Shops Tower Shops January 19 2011 [Member] Tower Shops 1/19/11 [Member] Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Measurement Frequency [Domain] Measurement Frequency [Domain] Less amount representing interest Finance lease liability future minimum interest payments Finance lease liability future minimum interest payments Contractual term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Statement [Line Items] Statement [Line Items] DownREIT operating partnership units, outstanding Partners' Capital Account, Units Class of Stock [Domain] Class of Stock [Domain] 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] Statement [Table] Statement [Table] Return of capital, common shares Common shares, return of capital Common shares, return of capital Statistical Measurement [Axis] Statistical Measurement [Axis] Minimum percentage of taxable income distributed to shareholders Minimum Percentage Of Taxable Income Distributed To Shareholders Minimum percentage of taxable income distributed to shareholders. Other interest income Interest Income, Other Cash in excess of the FDIC insured limit Cash, Uninsured Amount At The Market Equity Program At The Market Equity Program [Member] At The Market Equity Program [Member] Entity Small Business Entity Small Business Principles of Consolidation Consolidation, Policy [Policy Text Block] Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Debt Disclosure [Text Block] Debt Disclosure [Text Block] First Mortgage First Mortgage [Member] Freedom Plaza Jordan Downs Plaza [Member] Jordan Downs Plaza [Member] Amendment Flag Amendment Flag Bell Gardens Bell Gardens [Member] Bell Gardens [Member] Depositary Shares Depository Shares [Member] Depository Shares [Member] Schedule of common shares awarded under various compensation plans Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Georgetowne Shopping Center Georgetowne Shopping Center [Member] Georgetowne Shopping Center Number of shares authorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Real Estate Properties [Domain] Real Estate Properties [Domain] 2022 Below Market Lease, Amortization Income, Year Two New York Stock Exchange, Inc. NEW YORK STOCK EXCHANGE, INC. [Member] 2023 Below Market Lease, Amortization Income, Year Three Third Street Promenade Third Street Promenade [Member] Third Street Promenade [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Commissions Commissions [Member] Commissions [Member] Summary of carrying amount and fair value of financial instruments Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block] Maximum exposure to loss in variable interest entity Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Fair Value Measurement [Domain] Fair Value Measurement [Domain] Derivative Instruments Derivatives, Policy [Policy Text Block] Subsequent Event Subsequent Events [Text Block] Early Repayment of Senior Debt Early Repayment of Senior Debt Common shares, qualified dividends, tax rate Common shares, qualified dividends, tax rate The tax rate on qualified dividends for common stock. Prepaid expenses and other assets prepaid expenses and other assets [Member] prepaid expenses and other assets 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] Property, Plant and Equipment, Type [Axis] Long-Lived Tangible Asset [Axis] Summary of restricted share activity Share-based Payment Arrangement, Restricted Stock and Restricted Stock Unit, Activity [Table Text Block] 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] Income Statement Location [Domain] Income Statement Location [Domain] FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities [Abstract] Amortization of above market leases, lessee Amortization Of Intangible Liability Amortization Of Intangible Liability (Decrease) increase 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. LEASE COST Lease, Cost [Table Text Block] Below Market Leases, Lessee BelowMarketLeasesLessee [Member] Below Market Leases, Lessee Exchange [Domain] Exchange [Domain] Plan Name [Axis] Plan Name [Axis] TOTAL ASSETS Assets Cumulative Effect on Retained Earnings Cumulativeimpacttoaccumulateddividendsinexcessofnetincome Cumulative impact to accumulated dividends in excess of net income 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] Colorado Blvd Colorado Blvd [Member] Colorado Blvd [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 Face Amount of Mortgages SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Face Amount of Mortgages 3.95% and 3.50% Senior Notes [Member] 3.95% and 3.50% Senior Notes [Member] 3.95% and 3.50% Senior Notes Total Operating Leases, Future Minimum Payments Receivable Finance Lease, Liability, Payment, Due [Abstract] Finance Lease, Liability, Payment, Due [Abstract] Graham Park Plaza Graham Park [Member] Graham Park 3.5% Senior Note [Member] 3.5% Senior Note [Member] 3.5% Senior Note Subsequent Event Type [Axis] Subsequent Event Type [Axis] Lessor, Lease, Description [Table] Lessor, Lease, Description [Table] OPERATING LEASES Lessor, Operating Leases [Text Block] Thereafter Operating Leases, Future Minimum Payments Receivable, Thereafter Debt yield to maturity percent Debt Securities, Held-to-Maturity, Weighted Average Yield, Maturity, after Year 10 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. Total liabilities Liabilities Del Mar Village Del Mar Village [Member] Del Mar Village [Member] Segment Reporting, Factors Used to Identify Entity's Reportable Segments Segment Reporting, Factors Used to Identify Entity's Reportable Segments Volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Number of condominium units sold Number of condominium units sold Number of condominium units sold Purchase Price Under Option Payments for Repurchase of Redeemable Noncontrolling Interest Rollforward table of the redeemable noncontrolling interest Redeemable Noncontrolling Interest [Table Text Block] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] Mount Vernon/South Valley/7770 Richmond Hwy, Mount Vernon [Member] Mount Vernon [Member] Level 1 Fair Value, Inputs, Level 1 [Member] Proceeds from partnership formation Payments for (Proceeds from) Real Estate Partnership Investment, Net Lancaster Lancaster [Member] Lancaster [Member] Real Estate [Abstract] Real Estate [Abstract] 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. Number of states in which entity has properties Number of States in which Entity Operates Preferred Units by Name [Axis] Preferred Units by Name [Axis] 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] Additional Paid-in Capital Additional Paid-in Capital [Member] 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 Finance Lease, interest on lease liabilities Finance Lease, Interest Expense Purchase of noncontrolling interest Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Common shares of beneficial interest, shares outstanding Common Stock, Shares, Outstanding Option By Type [Axis] Option By Type [Axis] Option By Type [Axis] Revolving credit facility Revolving Credit Facility [Member] Issuance of loans SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, New Mortgage Loan Lawrence Park Lawrence Park [Member] Lawrence Park [Member] 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 Common shares of beneficial interest, shares authorized Common Stock, Shares Authorized Stock options Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Total cash received from options exercised Proceeds from Stock Options Exercised Acquisitions and Dispositions Schedule of Real Estate Properties [Table Text Block] Wildwood Wildwood [Member] Wildwood [Member] Income Statement [Abstract] Income Statement [Abstract] Accumulated Other Comprehensive Income/(Loss) Accumulated Other Comprehensive Income (loss) AOCI Attributable to Parent [Member] Preferred stock, qualified dividends, tax rate Preferred Stock, Qualified Dividends, Tax Rate The tax rate for qualified dividends on preferred shares. Stock Issuance Costs by Type [Domain] Stock Issuance Costs by Type [Domain] [Domain] for Stock Issuance Costs by Type [Axis] 2021 Operating Leases, Future Minimum Payments Receivable, Current Increase in prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Name of Property Name of Property [Domain] Net increase in rental income Amortization of above and below Market Leases Net unamortized (discount) premium and debt issuance costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Use of Estimates Use of Estimates, Policy [Policy Text Block] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Domain] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Domain] Officer Officer [Member] Collectibility Adjustment Collectibility Adjustment Collecitbility adjustments recognized during the period. Sylmar Towne Center Sylmar Towne Center [Member] Sylmar Town Center Improvements SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Improvements Minor Improvements, Furniture and Equipment Minor Improvements, Furniture and Equipment [Member] Minor Improvements, Furniture and Equipment [Member] THE AVENUE at White Marsh THE AVENUE at White Marsh, Due 2021 [Member] THE AVENUE at White Marsh, Due 2021 [Member] Amortization of below market leases, lessor Amortization of Below Market Lease Scenario [Domain] Scenario [Domain] Counterparty Name [Domain] Counterparty Name [Domain] 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] Contractual Obligation [Domain] Contractual Obligation [Domain] Contractual Obligation [Domain] (Loss) income from real estate partnerships Loss from partnerships Income (Loss) from Equity Method Investments Issuance of senior notes, net of costs Proceeds from Issuance of Senior Long-term Debt Common Shares Of Beneficial Interest Common Shares Of Beneficial Interest [Member] Common Shares Of Beneficial Interest [Member] Notes Payable Notes Payable, Other Payables [Member] Pan Am Shopping Center Pan Am Shopping Center [Member] Pan Am Shopping Center [Member] Shares withheld for employee taxes Payment, Tax Withholding, Share-based Payment Arrangement 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] Number of leases Number Of Leases Number Of Leases ACQUIRED IN-PLACE LEASES Intangible Assets Disclosure [Text Block] Estimated maximum liability upon exercise of the put option Estimated Liability Upon Exercise Of Option Estimated Liability Upon Exercise Of Option Estimated useful lives Property, Plant and Equipment, Useful Life Payments of ordinary dividends, common stock Common Stock, Ordinary Dividends, Per Share, Cash Paid Common Stock, Ordinary Dividends, Per Share, Cash Paid Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] 2021 Operating Leases, Future Minimum Payments Due, Next Twelve Months Total debt Debt and Lease Obligation Restricted cash Restricted Cash and Cash Equivalents Brick Plaza Brick Plaza [Member] Brick Plaza [Member] Restricted Stock Restricted Stock [Member] Payments from reserves Standard and Extended Product Warranty Accrual, Decrease for Payments Share-based Payment Arrangement [Abstract] Share-based Payment Arrangement [Abstract] Reserves for warranties and general liability Standard and Extended Product Warranty Accrual ROU assets obtained in exchange for operating lease liabilities Right-of-Use Asset Obtained in Exchange for Finance Lease Liability Other operating Other Cost of Operating Revenue 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 Summary of weighted average assumptions used to value options granted Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] FAIR VALUE OF FINANCIAL INSTRUMENTS Fair Value Disclosures [Text Block] Prior Liens SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Prior Lien, Amount Remaining capacity to issue Remaining Capacity To Issue Remaining $ Capacity Of Shares To Issue Less amount representing interest Operating lease liability future minimum interest payments Operating lease liability future minimum interest payments Accounts, Notes, Loans and Financing Receivable [Line Items] Accounts, Notes, Loans and Financing Receivable [Line Items] Controlling interest percentage Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage 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 Interest Rate Swap Interest Rate Swap [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Perring Plaza Perring Plaza [Member] Perring Plaza [Member] Operating Leased Assets [Line Items] Operating Leased Assets [Line Items] Maximum amount of borrowings outstanding Line of Credit Facility, Maximum Amount Outstanding During Period Additional paid-in capital Additional Paid in Capital, Common Stock Entity Registrant Name Entity Registrant Name Subsequent Event Type [Domain] Subsequent Event Type [Domain] Business Acquisition and Disposition Business Acquisition [Line Items] Weighted-average discount rate - operating leases Operating Lease, Weighted Average Discount Rate, Percent Real estate, at cost, total Real Estate Investment Property, at Cost Redeemable Noncontrolling Interest, by Legal Entity [Table] Redeemable Noncontrolling Interest, by Legal Entity [Table] Deferred compensation liability to participants Deferred Compensation Arrangement with Individual, Recorded Liability Net unamortized discount and debt issuance costs Debt Issuance Costs, Net Capitalized lease costs amortization range Capitalized lease costs amortization range Capitalized lease costs amortization range Greenwich Avenue Greenwich Avenue [Member] Greenwich Avenue [Member] 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 Entity Incorporation, State or Country Code Entity Incorporation, State or Country Code Mortgage Loans on Real Estate, Name, Property Type [Domain] Real Estate [Domain] Pike 7 Pike 7 [Member] Pike 7 [Member] Langhorne Square Langhorne Square [Member] Langhorne Square [Member] Dividends declared to preferred shareholders Dividends, Preferred Stock, Cash Dividends on preferred shares Less: Preferred share dividends Preferred Stock Dividends, Income Statement Impact Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Adjustments for New Accounting Pronouncements [Axis] Accounting Standards Update [Axis] Reconcilition of cash, cash equivalents, and restricted cash Schedule of Cash and Cash Equivalents [Table Text Block] Wynnewood Wynnewood [Member] Wynnewood [Member] Various Various Notes Payable [Member] Various Notes Payable [Member] Mortgage Notes Receivable Financing Receivable, Held-for-investment [Policy Text Block] Real Estate Investments by Property Type [Axis] Real Estate Investments by Property Type [Axis] Real Estate Investments by Property Type [Axis] Subsidiary, Sale of Stock [Axis] Sale of Stock [Axis] Accounting Standards Update 2016-02 Accounting Standards Update 2016-02 [Member] Entity Address, Postal Zip Code Entity Address, Postal Zip Code 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] Repayment of mortgages, finance leases, and notes payable Repayment of Long-term Debt, Long-term Lease Obligation, and Capital Security Stock Issuance Costs by Type [Axis] Stock Issuance Costs by Type [Axis] Stock Issuance Costs by Type [Axis] 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 declared to common shareholders Common Stock, Dividends, Per Share, Declared Westgate Center Westgate Mall [Member] Westgate Mall [Member] Debt Instrument, Face Amount Debt Instrument, Face Amount Building and Building Improvements Building and Building Improvements [Member] Equity [Abstract] Preferred Units, Class [Domain] Preferred Units, Class [Domain] Contribution of noncontrolling interest Noncash contribution of noncontrolling interest Noncash contribution of noncontrolling interest NON-CASH INVESTING AND FINANCING TRANSACTIONS (1): Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] Aggregate cost basis for Federal tax purposes SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Federal Income Tax Basis Proceeds from Unsecured Notes Payable Proceeds from Unsecured Notes Payable Leasing costs Increase (Decrease) in Lease Acquisition Costs 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 Entities [Table] Entities [Table] 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] Derivative, Name [Domain] Derivative Contract [Domain] Weighted average number of common shares Weighted average common shares outstanding—diluted Weighted Average Number of Shares Outstanding, Diluted Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Debt Disclosure [Abstract] Debt Disclosure [Abstract] Increase (Decrease) in Derivative Assets Increase (Decrease) in Derivative Assets Net cash provided by (used in) financing activities Net Cash Provided by (Used in) Financing Activities Mortgage On Retail Buildings in Philadelphia, PA, Loan Two Mortgage On Retail Buildings in Philadelphia, PA, Loan Two [Member] Mortgage On Retail Buildings in Philadelphia, PA, Loan Two [Member] Material unrecognized tax benefits Unrecognized Tax Benefits Counterparty Name [Axis] Counterparty Name [Axis] Variable Interest Entity, Classification [Domain] Investments by Consolidated and Nonconsolidated Entities [Domain] Common shares of beneficial interest, $.01 par, 100,000,000 shares authorized, 76,727,394 and 75,540,804 shares issued and outstanding, respectively Common Stock, Value, Issued 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. Document Fiscal Year Focus Document Fiscal Year Focus 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] 2022 Finite-Lived Intangible Asset, Expected Amortization, Year Two 2024 Operating Leases, Future Minimum Payments Receivable, in Four Years Entity Current Reporting Status Entity Current Reporting Status Townson Residential Townson Residential [Member] Townson Residential [Member] COMPREHENSIVE INCOME Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Number of members with purchase options Number of Members With Purchase Options Number of Members With Purchase Options Final award earned percentage of original award Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Rights, Percentage Pike & Rose Pike & Rose [Member] Pike & Rose Schedule of Operating Leased Assets [Table] Schedule of Operating Leased Assets [Table] Common shares of beneficial interest, shares issued Common Stock, Shares, Issued Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Mercer Mall Mercer Mall [Member] Mercer Mall [Member] 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 Operating lease liabilities Operating Lease, Liability 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. Interest expense reclassified from other comprehensive income (less than for 2019) Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net Debt Instrument [Line Items] Debt Instrument [Line Items] Total shareholders’ equity of the Trust Stockholders' Equity Attributable to Parent BUSINESS AND ORGANIZATION Nature of Operations [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 Tower Tower [Member] Tower [Member] Entity Address, City or Town Entity Address, City or Town Additional credit losses recorded during the year Financing Receivable, Allowance for Credit Loss, Period Increase (Decrease) Notes payable Notes Payable 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 Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Restricted Stock Units (RSUs) Restricted Stock Units (RSUs) [Member] North Dartmouth North Dartmouth [Member] North Dartmouth [Member] Other Assets Other Assets [Member] Type of Adoption [Domain] Accounting Standards Update [Domain] Prepaid expenses and other assets Prepaid expenses and other assets [Line Items] Prepaid expenses and other assets 2024 Operating Leases, Future Minimum Payments, Due in Four Years 2.75% notes Senior 2 Point 75 Percent Notes [Member] Senior 2 Point 75 Percent Notes [Member] Liabilities Liabilities [Abstract] Mortgage notes receivable, net Mortgage Loans on Real Estate, Commercial and Consumer, Net Real Estate Disclosure Real Estate Disclosure [Text Block] 2023 Finite-Lived Intangible Asset, Expected Amortization, Year Three Northeast Northeast [Member] Northeast [Member] Preferred shares, ordinary dividend eligible for 15% rate Preferred Stock, Ordinary Dividends Eligible For 15 Percent Tax Rate, Per Share, Cash Paid Preferred Stock, Ordinary Dividends Eligible For 15 Percent Tax Rate, Per Share, Cash Paid 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 Reconciliation of Real Estate Accumulated Depreciation [Roll Forward] SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation [Roll Forward] 2024 Below Market Lease, Amortization Income, Year Four Net increase in rental expense Amortization Of Above And Below Market Leases, Lessee Amortization Of Above And Below Market Leases, Lessee Other comprehensive 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 Leases [Abstract] Leases [Abstract] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Abstract] Share-based Payment Arrangement, Expensed and Capitalized, Amount [Abstract] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Number of interest rate swap agreements Number of Interest Rate Derivatives Held Riverpoint Center Riverpoint Center [Member] Riverpoint Center [Member] Comprehensive income attributable to noncontrolling interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest Earnings Per Share [Abstract] Earnings Per Share [Abstract] Falls Plaza Falls Plaza [Member] Falls Plaza [Member] Above Market Leases Above Market Leases [Member] 7.48% debentures Debentures 7.48 Percent [Member] Debentures 7.48 Percent [Member] Schedule of Deferred Compensation Arrangement with Individual, Postretirement Benefits [Table] Schedule of Deferred Compensation Arrangement with Individual, Postretirement Benefits [Table] 2025 Finite-Lived Intangible Asset, Expected Amortization, Year Five Document Fiscal Period Focus Document Fiscal Period Focus Above Market Leases, Lessor AboveMarketLeasesLessor [Member] Above Market Leases, Lessor Village at Shirlington Shirlington [Member] Shirlington [Member] Bethesda Row Bethesda Row [Member] Bethesda Row [Member] Mortgages [Member] Mortgages [Member] Schedule of Stockholders Equity Schedule of Stockholders Equity [Table Text Block] Entity Filer Category Entity Filer Category Summary of share-based compensation expense Share-based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Melville Mall MelvilleMall [Member] MelvilleMall [Member] Common shares Common Stock [Member] Loans and Leases Receivable Disclosure [Table] Loans and Leases Receivable Disclosure [Table] Kings Court Kings Court [Member] Kings Court [Member] Weighted-average discount rate - finance leases Finance Lease, Weighted Average Discount Rate, Percent Mortgages Payable Mortgage Payable Secured Debt [Member] 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] Senior notes and debentures, net Senior notes Senior Notes Interest rate Stated Interest Rate Debt Instrument, Interest Rate, Stated Percentage Initial cost to company, Land SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Initial Cost of Land Grants of common shares and options Share-based Payment Arrangement [Member] 2022 Operating Leases, Future Minimum Payments Receivable, in Two Years Name of Property [Axis] Name of Property Name of Property [Axis] EARNINGS PER COMMON SHARE, DILUTED Earnings Per Share, Diluted [Abstract] Proceeds from new market tax credit transaction, net of deferred costs Proceeds from new market tax credit transaction, net of deferred costs Proceeds from new market tax credit transaction, net of deferred costs Exercise of stock options (in shares) Exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Increase in cash, cash equivalents, and restricted cash Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents, Period Increase (Decrease), Including Exchange Rate Effect 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] Options Share-based Payment Arrangement, Option [Member] Subsequent Events [Abstract] Subsequent Events [Abstract] Sale of Stock, Name of Transaction [Domain] Sale of Stock [Domain] 2025 Long-Term Debt, Maturity, Year Five Ownership [Domain] Ownership [Domain] Utilities Utilities Operating Expense Cash paid for interest, net of amounts capitalized Interest Paid, Excluding Capitalized Interest, Operating Activities 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] Total shareholders’ equity Beginning balance Ending balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Leases Revenue Recognition, Leases [Policy Text Block] 2021 Finite-Lived Intangible Asset, Expected Amortization, Year One Total revenue Revenues 2023 Operating Leases, Future Minimum Payments, Due in Three Years Class of Stock [Axis] Class of Stock [Axis] Hoboken2Buildings [Member] Hoboken2Buildings [Member] Hoboken2Buildings Cash paid for income taxes Income Taxes Paid, Net Old Town Center Old Town Center [Member] Old Town Center [Member] New Accounting Pronouncements or Change in Accounting Principle [Table] Accounting Standards Update and Change in Accounting Principle [Table] Capital expenditures other Capital expenditures other Capital expenditures other Net income available for common shareholders Earnings Per Share, Diluted 2022 Operating Leases, Future Minimum Payments, Due in Two Years 2021 Below Market Lease, Amortization Income, Year One Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] Encumbrances SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation, Amount of Encumbrances Member One In Plaza El Segundo Member One In Plaza El Segundo [Member] Member One In Plaza El Segundo [Member] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] 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 3.50% Senior Note [Member] 3.50% Senior Note [Member] 3.50% Senior Note Summary of total debt outstanding Schedule of Debt [Table Text Block] Unconsolidated variable interest entities Unconsolidated Properties [Member] Entity Address, Address Line One Entity Address, Address Line One Entity Emerging Growth Company Entity Emerging Growth Company 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] Finite-Lived Intangible Assets, Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Maximum Maximum [Member] Distribution from partnerships in excess of earnings Proceeds from Distributions Received from Real Estate Partnerships Preferred shares, authorized Preferred Stock, Shares Authorized Noncontrolling Interests Noncontrolling Interest [Member] 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] Bala Cynwyd Bala Cynwyd [Member] Bala Cynwyd [Member] Dividends declared to common shareholders ($4.14 per share) Dividends, Common Stock, Cash 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 Aggregate offering price of common shares Aggregate Offering Price Of Common Share Maximum aggregate offering price of common shares. Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Performance Incentive Plan 2010 Performance Incentive Plan 2010 [Member] Performance Incentive Plan 2010 [Member] Trading Symbol Trading Symbol Rollingwood Apts. Rollingwood Apartments [Member] Rollingwood Apartments [Member] Greenlawn Plaza Greenlawn Plaza [Member] Greenlawn Plaza Gain on sale of real estate, net of tax Gain on sale of real estate, net of tax Gain (Loss) on Sale of Properties Debt Instrument, Increase, Accrued Interest Debt Instrument, Increase, Accrued Interest Entity Shell Company Entity Shell Company Fair Value, Measurements, Recurring Fair Value, Recurring [Member] Impairment of property Impairment of property Impairment of property 2022 Finance Lease, Liability, to be Paid, Year Two Segment Information Segment Reporting, Policy [Policy Text Block] Net real estate Real Estate Investment Property, Net 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] Hoboken (1 Building) Hoboken 210 14th Street [Member] Hoboken 210 14th Street [Member] Entity Public Float Entity Public Float Acquisition of real estate Payments to Acquire Real Estate Net assets acquired allocated to below market leases Below Market Lease, Acquired Document Type Document Type ICFR Auditor Attestation Flag ICFR Auditor Attestation Flag Insurance Real Estate Insurance Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Gross Total interest costs incurred Interest Costs Incurred Increase in accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities Purchase price under option Purchase Price Under Option Purchase Price Under Option Interest Rate One Interest Rate One [Member] Interest Rate One [Member] SAVINGS AND RETIREMENT PLANS Retirement Benefits [Text Block] 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 Level 3 Fair Value, Inputs, Level 3 [Member] Contractual obligations Contractual Obligation Fair value of interest rate swaps Derivative financial asset Derivative Asset 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] Interest capitalized Interest Costs Capitalized Adjustment Pentagon Row Pentagon Row [Member] Pentagon Row [Member] Components Of Rental Expense [Abstract] Components Of Rental Expense [Abstract] Components Of Rental Expense [Abstract] (Increase) decrease in accounts receivable, net Increase (Decrease) in Accounts and Other Receivables OPERATING INCOME Operating Income (Loss) Fresh Meadows Fresh Meadows [Member] Fresh Meadows [Member] Condominiums Condominiums [Member] Condominiums [Member] Mortgage loans assumed with acquisition Mortgage loans assumed with acquisition Noncash or Part Noncash Acquisition, Debt Assumed Variable Interest Entities [Axis] Investments by Consolidated and Nonconsolidated Entities [Axis] Depreciation Expense Real Estate Depreciation Expense Real Estate Depreciation Expense on Real Estate only Variable Rate [Axis] Variable Rate [Axis] Schedule of Business Acquisitions and Dispositions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Commitments and contingencies (Note 7) Commitments and Contingencies Shares withheld for employee taxes Share-based Payment Arrangement, Decrease for Tax Withholding Obligation Vesting Term Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Entity Address, State or Province Entity Address, State or Province Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period 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. Mortgages payable, net (including $413,681 and $469,184 of consolidated variable interest entities, respectively) Mortgages payable Secured Debt Ground rent Ground Rent Expense Ground Rent Expense Operating lease right of use assets Operating Lease, Right-of-Use Asset Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] Early extinguishment of debt Early extinguishment of debt Gain (Loss) on Extinguishment of Debt Rent abatement agreements RentAbatementinPeriod Abatements of rent agreed upon during period. Barracks Road Barracks Road [Member] Barracks Road [Member] 2021 Finance Lease, Liability, to be Paid, Year One Shareholders’ equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] 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] Number of properties exceeding segment reporting threshold Number of Properties Exceeding Segment Reporting Threshold Number of Properties Exceeding Segment Reporting Threshold Notional amount of interest rate swap agreements Derivative Liability, Notional Amount Other liabilities and deferred credits Deferred Credits and Other Liabilities 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. Income Taxes Income Tax, Policy [Policy Text Block] Total Lease Cost Lease, Cost Exercisable at the end of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Mortgage On Retail Buildings in Philadelphia, PA, Loan One Mortgage On Retail Buildings in Philadelphia, PA, Loan One [Member] Mortgage On Retail Buildings in Philadelphia, PA, Loan One [Member] Payment for Debt Extinguishment or Debt Prepayment Cost Payment for Debt Extinguishment or Debt Prepayment Cost 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. Acquired Finite-Lived Intangible Assets [Line Items] Acquired Finite-Lived Intangible Assets [Line Items] Forfeited or expired (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period Construction-in-progress (including $44,896 and $102,583 of consolidated variable interest entities, respectively) Construction in Progress, Gross Thereafter Long-Term Debt, Maturity, after Year Five 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 Business Acquisition [Axis] Business Acquisition [Axis] 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] Charge related to the buyout of a lease Gain (Loss) on Termination of Lease Scenario, Forecast Forecast [Member] Entity Voluntary Filers Entity Voluntary Filers Fourth Street Fourth Street [Member] Fourth Street [Member] Thereafter Finite-Lived Intangible Asset, Expected Amortization, after Year Five Preferred shares, shares issued Preferred Stock, Shares Issued 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] Federal Plaza Federal Plaza [Member] Federal Plaza [Member] 2023 Operating Leases, Future Minimum Payments Receivable, in Three Years 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 Earnings per common share, basic and diluted Earnings Per Share, Basic and Diluted 3.00% Senior Note [Member] 3.00% Senior Note [Member] 3.00% Senior Note Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Three properties 2020 [Member] Three properties 2020 [Member] Three properties 2020 Common shares, ordinary dividend eligible for 15% rate Common Stock, Ordinary Dividends Eligible For 15 Percent Tax Rate, Per Share, Cash Paid Common Stock, Ordinary Dividends Eligible For 15 Percent Tax Rate, Per Share, Cash Paid 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 Exercisable at the end of year, Weighted-Average Remaining Contractual Term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Weighted Average Remaining Contractual Term Residual profit maximum Residual Profit Maximum Residual Profit Maximum received as additional interest on mortgage note receivable Issuance of common shares, net of costs Net cash proceeds of common stock Proceeds from Issuance of Common Stock Santana Row Santana Row [Member] Santana Row Schedule of earnings per share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Total future minimum operating lease payments Operating Leases, Future Minimum Payments Due 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] Revolving credit facility Long-term Line of Credit Repayments of Debt Repayments of Debt Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities January 1, 2019 adoption of new accounting standard - See Note 2 Reduction of Real Estate Reduction of real estate cost Entity Central Index Key Entity Central Index Key Related Party [Domain] Related Party [Domain] 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 Additions during period—depreciation and amortization expense SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Accumulated Depreciation, Depreciation Expense Derivative Instrument Derivative Instrument [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Schedule of Finite-Lived Intangible Assets [Table Text Block] Schedule of Finite-Lived Intangible Assets [Table Text Block] Fairfax Junction Fairfax Junction [Member] Fairfax Junction Senior Notes and Debentures Senior Notes [Member] Repairs and maintenance Cost of Property Repairs and Maintenance Escrow Deposit Escrow Deposit Number of Units in Real Estate Property Number of Units in Real Estate Property Recourse Status [Axis] Recourse Status [Axis] Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] 2024 Long-Term Debt, Maturity, Year Four 2025 Operating Leases, Future Minimum Payments Receivable, in Five Years Income Statement Location [Axis] Income Statement Location [Axis] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Stockholders' Equity Note [Abstract] Stockholders' Equity Note [Abstract] Thereafter Below Market Lease, Amortization Income, after Year Five Amortization of above market leases, lessor Amortization of Intangible Assets Governor Plaza Governor Plaza [Member] Governor Plaza [Member] 3.625% Senior notes 3.625% Senior notes [Member] 3.625% Senior notes [Member] Total future amortization expense from acquired below market leases Below Market Lease, Net Hastings Ranch Plaza Hastings Ranch Plaza [Member] Hastings Ranch Plaza Shares issued Stock Issued During Period, Value, New Issues San Antonio Center San Antonio Center [Member] San Antonio Center [Member] Operating cash flows for finance leases Finance Lease, Interest Payment on Liability Scenario [Axis] Scenario [Axis] Contributions from noncontrolling interests Contributions from noncontrolling interests Contributions from noncontrolling interests Title of 12(b) Security Title of 12(b) Security Finite-Lived Intangible Assets, Net Finite-Lived Intangible Assets, Net 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 Put Option Put Option [Member] Dividends [Abstract] Dividends [Abstract] Finance Lease, Liability, Fiscal Year Maturity Finance Lease, Liability, Fiscal Year Maturity [Table Text Block] Interest expense Interest expense Interest Expense Adjustment to redeemable noncontrolling interests Stockholders' Equity, Other Andorra Andorra [Member] Andorra [Member] Ownership Interest of Other Partner in Put Option Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Noncontrolling Interest, Ownership Percentage by Noncontrolling Owners Preferred Shares, liquidation preference per share Preferred shares, liquidation preference per share Preferred Stock, Liquidation Preference Per Share Escondido Promenade Escondido Promenade [Member] Former Mervyns Parcel, Escondido Promenade [Member] Marketing Marketing Expense 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 Brook 35 Brook 35 [Member] Brook 35 [Member] Fair value of property Property, Plant, and Equipment, Fair Value Disclosure Weighted-average period for recognition Share-based Payment Arrangement, Nonvested Award, Cost Not yet Recognized, Period for Recognition 2025 Finance Lease, Liability, to be Paid, Year Five Issuance of notes payable, net of costs Proceeds from Notes Payable 2022 Long-Term Debt, Maturity, Year Two NET INCOME AVAILABLE FOR COMMON SHAREHOLDERS Net Income (Loss) Available to Common Stockholders, Basic Other Notes Payable Other Notes Payable 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 Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Common shares, paid Common Stock, Dividends, Per Share, Cash Paid Debt Instrument [Axis] Debt Instrument [Axis] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Loan Category [Domain] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Loan Category [Domain] Leesburg Plaza Leesburg Plaza [Member] Leesburg Plaza [Member] Accumulated Dividends in Excess of Net Income Accumulated Distributions in Excess of Net Income [Member] Class of Stock [Line Items] Class of Stock [Line Items] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Axis] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Axis] 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] Entity Information [Line Items] Entity Information [Line Items] Variable lease cost Variable Lease, Cost 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 2025 Below Market Lease, Amortization Income, Year Five Schedule IV - Mortgage Loans on Real Estate SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Text Block] 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] Accumulated dividends in excess of net income Accumulated Distributions in Excess of Net Income Impairment charge Impairment charge Other Asset Impairment Charges Subsequent Event Subsequent Event [Member] Gaithersburg Square Gaithersburg Square [Member] Gaithersburg Square [Member] Letters of credit outstanding, amount Letters of Credit Outstanding, 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. Interest Rate Mortgage Loans on Real Estate, Participation Plus Interest Rate, Interest Rate Mortgage Loans on Real Estate, Participation Plus Interest Rate, Interest Rate Fair Value Estimate of Fair Value Measurement [Member] Redemption and retirement of senior notes Repayments of Senior Debt 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 2024 Finite-Lived Intangible Asset, Expected Amortization, Year Four Hauppauge Hauppauge [Member] Hauppauge [Member] Number of properties subject to operating leases Number of Properties Subject to Ground Leases Ownership interest subsequent to redemption Ownership interest subsequent to redemption Ownership interest subsequent to redemption of noncontrolling interest. Rental Income Operating Leases, Income Statement, Lease Revenue Straight line rent receivable Straight line rent receivable Straight line rent receivable Total rental expenses Direct Costs of Leased and Rented Property or Equipment COMPREHENSIVE INCOME ATTRIBUTABLE TO THE TRUST Comprehensive Income (Loss), Net of Tax, Attributable to Parent 2023 Finance Lease, Liability, to be Paid, Year Three Above Market Leases, Lessee Above Market Leases, Lessee [Member] Above Market Leases, Lessee [Member] Expected dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Preferred shares, par value Preferred shares, par value Preferred Stock, Par or Stated Value Per Share 2021 Long-Term Debt, Maturity, Year One Nonrecourse [Member] Nonrecourse [Member] City Area Code City Area Code Plaza El Segundo/The Point Plaza El Segundo/The Point [Member] Plaza El Segundo/The Point Document Period End Date Document Period End Date Security deposits payable Security Deposit Liability Redeemable Noncontrolling Interest [Line Items] Redeemable Noncontrolling Interest [Line Items] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Loan Category [Axis] SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Loan Category [Axis] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Real estate taxes Real Estate Tax Expense 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] Payment of ordinary dividends, preferred stock Preferred Stock, Ordinary Dividends, Per Share, Cash Paid Preferred Stock, Ordinary Dividends, Per Share, Cash Paid Capitalized share-based compensation Share-based Payment Arrangement, Amount Capitalized Share-based compensation expense Share-based Payment Arrangement, Noncash Expense Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Contributions Redeemable Noncontrolling Interests Contributions Redeemable Noncontrolling Interests Contributions Congressional Plaza Congressional Plaza [Member] Congressional Plaza [Member] Cover [Abstract] Cover [Abstract] 401(k) Maximum of employer match as a percentage of employee eligible earnings Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay 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 Equity Method Investee Equity Method Investee [Member] Long-term Debt Long-term Debt Saugus Saugus [Member] Saugus [Member] Weighted average unvested shares outstanding Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights Old Keene Mill Old Keene Mill [Member] Old Keene Mill [Member] Other Comprehensive Income (loss), net of portion attributable to noncontrolling interest 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] Equity Components Equity Components [Axis] Finley Square Finley Square [Member] Finley Square [Member] Chelsea Chelsea Commons Chelsea [Member] Chelsea [Member] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Net repayments under revolving credit facility, including costs Proceeds from (Repayments of) Lines of Credit Minimum Minimum [Member] Real Estate Property Ownership [Axis] Real Estate Property Ownership [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] 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. Schedule of supplemental disclosures related to the Consolidated Statements Of Cash Flows Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Hoboken Hoboken Provident [Member] Hoboken Provident [Member] Net income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Summary of financial assets/(liabilities) measured at fair value on a recurring basis Fair Value, Liabilities Measured on Recurring Basis [Table Text Block] Entity Interactive Data Current Entity Interactive Data Current 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 REVENUE Revenues [Abstract] 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] OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities [Abstract] SHAREHOLDERS’ EQUITY Stockholders' Equity Note Disclosure [Text Block] Summary of option activity Share-based Payment Arrangement, Option, Activity [Table Text Block] Gain or loss on sale of properties, net of tax Gain or loss on sale of properties, net of tax Gain or loss on sale of properties, net of tax The Shops at Sunset Place Sunset Place [Member] Acquisition of the Shops at Sunset Place on 10/1/2015. Share Based Compensation Share-based Payment Arrangement [Policy Text Block] Quince Orchard Plaza Quince Orchard Plaza [Member] Quince Orchard Plaza [Member] Operating partnership units outstanding, fair value Operating Partnership Units Fair Value Fair value of operating partnership units at the balance sheet date. Ownership interest of partner in our joint venture Ownership interest of partner in our joint venture Ownership interest of partner in our joint venture Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [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 Management fees and costs Management Fee Expense Rental expenses Other Cost and Expense, Operating Entity Listings, Exchange [Axis] Entity Listings, Exchange [Axis] Number of segments Number of Reportable Segments Assembly Row/Assembly Square Market Place Assembly Square Market Place Assembly Row [Member] Assembly Square Market Place Assembly Row [Member] 401(k) Employer contribution expense Deferred Compensation Arrangement with Individual, Contributions by Employer Deductions during period—dispositions and retirements of property Real Estate Accumulated Depreciation Dispositions and Retirements Real Estate Accumulated Depreciation Dispositions and Retirements Rent deferral agreements Deferred Rent Receivables, Net Performance Incentive Plan 2020 Performance Incentive Plan 2020 [Member] Performance Incentive Plan 2020 Recourse Status [Domain] Recourse Status [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 Plaza El Segundo Plaza El Segundo [Member] Plaza El Segundo [Member] Real Estate and Accumulated Depreciation [Line Items] SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate and Accumulated Depreciation [Line Items] Finite-Lived Intangible Liabilities, Accumulated Amortization Finite-Lived Intangible Liabilities, Accumulated Amortization Finite-Lived Intangible Liabilities, Accumulated Amortization 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 Operating Leases, Future Minimum Payments Receivable [Abstract] Operating Leases, Future Minimum Payments Receivable [Abstract] 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. Accounts and notes receivable Accounts and Financing Receivable, after Allowance for Credit Loss 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] Document Transition Report Document Transition Report Title of Individual [Axis] Title of Individual [Axis] Proceeds from sale Proceeds from Sale of Real Estate Level 2 Fair Value, Inputs, Level 2 [Member] Minimum annual payments Lessee, Operating Lease, Disclosure [Table Text Block] Acquisitions of loans, net of valuation adjustements Acquisitions of loans, net of valuation adjustements Acquisitions of loans, net of valuation adjustements Accounting Standards Update 2016-13 Accounting Standards Update 2016-13 [Member] Fixed interest rate of derivative instrument Fixed interest rate of derivative instrument Derivative, Fixed Interest Rate Subsequent Event [Line Items] Subsequent Event [Line Items] 4.50% notes 4.50% Senior notes [Member] 4.50% Senior notes Other Liabilities Other Liabilities [Member] Recent Accounting Pronouncements Accounting Standards Update and Change in Accounting Principle [Text Block] Proceeds from sale of real estate Proceeds from Sale of Real Estate Held-for-investment Below Market Leases, Lessor BelowMarketLeasesLessor [Member] Below Market Leases, Lessor Net income available for common shareholders Earnings Per Share, Basic Expected term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Entity File Number Entity File Number Weighted-average remaining lease term - operating leases Operating Lease, Weighted Average Remaining Lease Term White Marsh Plaza White Marsh Plaza [Member] White Marsh Plaza [Member] Net assets acquired allocated to intangible lease assets or liabilities Finite-lived Intangible Assets Acquired Proceeds from Noncontrolling Interests Proceeds from Noncontrolling Interests Dedham Plaza Dedham Plaza [Member] Dedham Plaza [Member] Grants of common shares and options Share-based Payment Arrangement, Expense Three properties [Member] Three properties [Member] Three properties Distributions & redemptions Redeemable Noncontrolling Interests Distributions Redeemable Noncontrolling Interests Distributions Balance Sheet Location [Axis] Balance Sheet Location [Axis] Straight Line Rent Adjustments Straight Line Rent Adjustments Goodwill and Intangible Assets Disclosure [Abstract] Goodwill and Intangible Assets Disclosure [Abstract] Document Annual Report Document Annual Report Exercisable at the end of year, Aggregate Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Property Subject to or Available for Operating Lease, by Major Property Class [Table] Property Subject to or Available for Operating Lease, by Major Property Class [Table] Retail and commercial Commercial Real Estate [Member] 2024 Finance Lease, Liability, to be Paid, Year Four 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] Receivable [Domain] Receivable [Domain] Weighted average interest rate on mortgage note receivables WeightedAverageInterestRateonFinancingReceivable The weighted average interest rate on outstanding financing recievables Subsequent Event [Table] Subsequent Event [Table] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Redeemable Noncontrolling Interests Redeemable Noncontrolling Interests [Policy Text Block] Redeemable Noncontrolling Interests [Policy Text Block] Noncontrolling interests Stockholders' Equity Attributable to Noncontrolling Interest 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 INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities [Abstract] Estimated Litigation Liability Estimated Litigation Liability Debt Issuance Costs Debt, Policy [Policy Text Block] 3.00% notes Senior300PercentNotes [Member] Senior300PercentNotes [Member] Acquisitions SEC Schedule, 12-28, Real Estate Companies, Investment in Real Estate, Other Acquisition Commissions related to sales of common shares Payments of Stock Issuance Costs Idylwood Plaza Idylwood Plaza [Member] Idylwood Plaza [Member] Purchase price of partner's interest Purchase price of partner's interest Purchase price of partner's interest Payments to Acquire Limited Partnership Interests Payments to Acquire Limited Partnership Interests Rockville Town Square Rockville Town Square [Member] Rockville Town [Member] TOTAL LIABILITIES AND SHAREHOLDERS’ EQUITY Liabilities and Equity DownREIT operating partnership units redeemed for common shares Redemptionofoperatingpartnershipunitsforcommonshares Redemption of operating partnership units for common shares Loss Contingencies [Line Items] Loss Contingencies [Line Items] Azalea Azalea [Member] Azalea [Member] Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Number of mortgage receivables SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate, Number of Loans Operating lease cost Operating Lease, Cost Mortgage receivable, net of valuation allowances Financing Receivable, after Allowance for Credit Loss General and administrative General and Administrative Expense Anti-dilutive stock options excluded from dilutive earnings per share calculation Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Weighted average price per common share Weighted Average Price Per Common Share Weighted average price per common share Weighted-average remaining lease term - finance leases Finance Lease, Weighted Average Remaining Lease Term Other, net Other Noncash Income (Expense) Equity Component [Domain] Equity Component [Domain] Entity Tax Identification Number Entity Tax Identification Number 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 SHARE-BASED COMPENSATION PLANS Share-based Payment Arrangement [Text Block] NET INCOME ATTRIBUTABLE TO THE TRUST Net Income (Loss) Attributable to Parent Changes in assets and liabilities, net of effects of acquisitions and dispositions: Increase (Decrease) in Operating Capital [Abstract] Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Rental Expenses Rental Expenses [Member] Rental Expenses Current Fiscal Year End Date Current Fiscal Year End Date EXPENSES Operating Expenses [Abstract] 6.82% medium term notes Medium Term Notes 6.82 Percent [Member] Medium Term Notes 6.82 Percent [Member] Finance lease liabilities Finance lease liabilities Finance Lease, Liability 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] 401(K) and Deferred Compensation Plan Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits [Member] 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] COMPONENTS OF RENTAL EXPENSE Operating Leases Revenue And Expense Text Block The principal components of rental income and/or rental expense recognized for the period. Earnings Per Share Narrative [Line Items] Earnings Per Share Narrative [Line Items] Earnings Per Share Narrative [Line Items] Plaza Del Sol Plaza Del Sol [Member] Plaza Del Sol [Member] Number of real estate properties Number of Real Estate Properties Tyson's Station Tyson Station [Member] Tyson Station [Member] Thereafter Finance Lease, Liability, to be Paid, after Year Five Courthouse Center Courthouse Center [Member] Courthouse Center [Member] 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 3.95% Senior Note [Member] 3.95% Senior Note [Member] 3.95% Senior Note Real Estate Investments, Property Type [Domain] Real Estate Investments, Property Type [Domain] Real Estate Investments, Property Type [Domain] Supplemental Cash Flow Information [Abstract] Supplemental Cash Flow Information [Abstract] Long Lived Assets and Impairment Property, Plant and Equipment, Impairment [Policy Text Block] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Assets held for sale Real Estate Held-for-sale Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Amounts attributable to redeemable noncontrolling interest Net income Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Property, Plant and Equipment, Type [Domain] Long-Lived Tangible Asset [Domain] Hollywood Blvd. Hollywood Blvd [Member] Hollywood Blvd [Member] Amortization of Below Market Lease, Lessee Amortization of Below Market Lease, Lessee Amortization of Below Market Lease, Lessee Preferred shares, percentage Cumulative convertible preferred share, dividend rate Preferred Stock, Dividend Rate, Percentage Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] Shares issued (in shares) Shares issued Stock Issued During Period, Shares, New Issues Campus Plaza Campus Plaza [Member] Campus Plaza Finite-Lived Intangible Assets, Total Finite-Lived Intangible Assets, Gross Lessor, Lease, Description [Line Items] Lessor, Lease, Description [Line Items] Bad debt Accounts Receivable, Credit Loss Expense (Reversal) Preferred shares, paid Preferred Stock, Dividends, Per Share, Cash Paid 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 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 Debt Instruments [Abstract] Debt Instruments [Abstract] Hoboken Hoboken [Member] Hoboken [Member] Finance lease right of use assets Finance Lease, Right-of-Use Asset, after Accumulated Amortization Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Operating (including $1,703,202 and $1,676,866 of consolidated variable interest entities, respectively) Rental Properties Weighted average common shares outstanding, basic Weighted average common shares outstanding—basic Weighted Average Number of Shares Outstanding, Basic Debt Instrument, Basis Spread on Variable Rate Debt Instrument, Basis Spread on Variable Rate Risk free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Investment in partnerships Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Ownership [Axis] Ownership [Axis] Rollforward of Redeemable Noncontrolling Interests Increase (Decrease) in Temporary Equity [Roll Forward] Variable Interest Entities Consolidation, Variable Interest Entity, Policy [Policy Text Block] Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items] Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items] Schedule of minimum future commercial property rentals from noncancelable operating leases Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Loss Contingencies [Table] Loss Contingencies [Table] 29th Place 29th Place [Member] 29th Place [Member] Carrying Value Reported Value Measurement [Member] Crossroads Crossroads [Member] Crossroads [Member] Plan Name [Domain] Plan Name [Domain] Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Ownership percentage in partnership Equity Method Investment, Ownership Percentage Dividends payable Dividends Payable ROU assets obtained in exchange for operating lease liabilities Right-of-Use Asset Obtained in Exchange for Operating Lease Liability Preferred shares, declared Preferred Stock, Dividends Per Share, Declared Grove at Shrewsbury and Brook 35 Grove At Shrewsbury And Brook 35 [Member] GroveatShrewsbury & Brook 35 [Member] Fair value of long-term debt Long-term Debt, Fair Value Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] Queen Anne Plaza Queen Anne Plaza [Member] Queen Anne Plaza [Member] Bristol Plaza Bristol [Member] Bristol [Member] Residential Residential Real Estate [Member] 2025 Operating Leases, Future Minimum Payments, Due in Five Years 3.95% notes Senior395percentnotes [Member] Senior395percentnotes [Member] 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 Real Estate Property, Plant and Equipment, Policy [Policy Text Block] Schedule of principal payments on mortgages payable, notes payable, senior notes and debentures Schedule of Maturities of Long-term Debt [Table Text Block] Title of Individual [Domain] Title of Individual [Domain] Local Phone Number Local Phone Number Finite-lived Intangible Assets Amortization Expense [Table Text Block] Finite-lived Intangible Assets Amortization Expense [Table Text Block] Weighted average amount of borrowings outstanding Line of Credit Facility, Average Outstanding Amount Total intrinsic value of options exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value Interest Rate [Axis] Interest Rate [Axis] Interest Rate [Axis] Principal balance Mortgage payable Long-term Debt, Gross Exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Increase in 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. 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] Maximum borrowing capacity under revolving credit facility Line of Credit Facility, Maximum Borrowing Capacity Award Type [Axis] Award Type [Axis] Nature Of Operations [Abstract] Nature Of Operations [Abstract] Nature Of Operations [Abstract] Prepaid expenses and other assets Prepaid Expense and Other Assets Repayments of Secured Debt Repayments of Secured Debt 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 Property Subject to or Available for Operating Lease [Line Items] Property Subject to or Available for Operating Lease [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] Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities Preferred shares, shares outstanding Preferred Stock, Shares Outstanding Measurement Basis [Axis] Measurement Basis [Axis] SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Significant Accounting Policies [Text Block] Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities 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 Award Type [Domain] Award Type [Domain] Assembly Row and Pike & Rose Assembly Row and Pike & Rose [Member] Assembly Row and Pike & Rose [Member] Other comprehensive loss - change in value of interest rate swaps, attributable to redeemable noncontrolling interests Other comprehensive loss - change in value of interest rate swaps Other Comprehensive Loss Attributable to Redeemable Noncontrolling Interests Other Comprehensive Loss Attributable to Redeemable Noncontrolling Interests 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 Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] 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. Less accumulated depreciation and amortization (including $335,735 and $296,165 of consolidated variable interest entities, respectively) Real Estate Investment Property, Accumulated Depreciation EARNINGS PER SHARE Earnings Per Share [Text Block] Redeemable noncontrolling interests Beginning balance Ending balance Redeemable Noncontrolling Interest, Equity, Carrying Amount 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 Shares withheld for employee taxes (in shares) Share-based Payment Arrangement, Shares Withheld for Tax Withholding Obligation Huntington Huntington [Member] Huntington [Member] Interest Rate [Domain] Interest Rate [Domain] Interest Rate [Domain] Grove at Shrewsbury (East) Grove at Shrewsbury (East) [Member] Grove at Shrewsbury (East) [Member] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] EARNINGS PER COMMON SHARE, BASIC Earnings Per Share, Basic [Abstract]