Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Statement, Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Preferred Shares Preferred Stock [Member] Common shares Common Stock [Member] Additional Paid-in Capital Additional Paid-in Capital [Member] Accumulated Dividends in Excess of Net Income Accumulated Distributions in Excess of Net Income [Member] Accumulated Other Comprehensive Loss Accumulated Other Comprehensive Income (Loss) [Member] Noncontrolling Interests Noncontrolling Interest [Member] Statement [Line Items] Statement [Line Items] Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Beginning balance (in shares) Shares, Outstanding Beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest Net income, excluding $2,475 attributable to redeemable noncontrolling interests Profit Loss Excluding Redeemable Noncontrolling Interests Net income (loss) excluding portion attributable to redeemable noncontrolling interests. Other comprehensive loss - change in value of interest rate swaps Other Comprehensive Income (Loss), Net of Tax Dividends declared to common shareholders Dividends, Common Stock, Cash Dividends declared to preferred shareholders Dividends, Preferred Stock, Cash Distributions declared to noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Common shares issued (in shares) Stock Issued During Period, Shares, New Issues Common shares issued Stock Issued During Period, Value, New Issues Exercise of stock options (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Exercise of stock options Stock Issued During Period, Value, Stock Options Exercised Shares issued under dividend reinvestment plan (in shares) Stock Issued During Period, Shares, Dividend Reinvestment Plan Shares issued under dividend reinvestment plan Stock Issued During Period, Value, Dividend Reinvestment Plan Share-based compensation expense, net of shares withheld for employee taxes (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 and of shares withheld for employee taxes. Share-based compensation expense, net of shares withheld for employee taxes 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). 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 Redemption of OP units Conversion And Redemption Of Operating Partnership Units Decrease in noncontrolling interest as a result of redeeming, purchasing and/or converting to common stock the interests of Operating Partnership Units. Contributions from noncontrolling interests Noncontrolling Interest, Increase from Business Combination Adjustment to redeemable noncontrolling interests Stockholders' Equity, Other Ending balance (in shares) Ending balance Document And Entity Information [Abstract] Document and Entity Information Abstract Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Current Fiscal Year End Date Current Fiscal Year End Date Entity Filer Category Entity Filer Category Document Type Document Type Document Period End Date Document Period End Date Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Amendment Flag Amendment Flag Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Fair Value Disclosures [Abstract] FAIR VALUE OF FINANCIAL INSTRUMENTS Fair Value Disclosures [Text Block] Stockholders' Equity Note [Abstract] Stockholders' Equity [Table] Stockholders' Equity [Table] Stockholders' Equity [Table] Class of Stock [Axis] Class of Stock [Axis] Class of Stock [Domain] Class of Stock [Domain] 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] Sale of Stock [Axis] Sale of Stock [Axis] Information by type of stock transaction made by the entity. Sale of Stock [Domain] Sale of Stock [Domain] [Domain] for Information by type of stock transaction made by the entity. At The Market Equity Program At The Market Equity Program [Member] At The Market Equity Program [Member] Stock Issuance Costs by Type [Axis] Stock Issuance Costs by Type [Axis] Stock Issuance Costs by Type [Axis] Stock Issuance Costs by Type [Domain] Stock Issuance Costs by Type [Domain] [Domain] for Stock Issuance Costs by Type [Axis] Commissions Commissions [Member] Commissions [Member] Additional offering expenses Other Offering Costs [Member] Other Offering Costs [Member] Aggregate offering price of common share Aggregate Offering Price Of Common Share Maximum aggregate offering price of common shares. Shares issued under equity program Weighted average price per common share Weighted Average Price Per Common Share Weighted average price per common share Net cash proceeds of common stock Proceeds from Issuance of Common Stock Payments of stock issuance costs Payments of Stock Issuance Costs Remaining capacity of common shares to issue Remaining Capacity To Issue Remaining $ Capacity Of Shares To Issue Accounting Policies [Abstract] Principles of Consolidation Consolidation, Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] Reporting Discontinued Operations and Disclosures of Disposals of Components of an Entity Discontinued Operations, Policy [Policy Text Block] Recently Issued Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] Discontinued Operations and Disposal Groups [Abstract] DISCONTINUED OPERATIONS Disposal Groups, Including Discontinued Operations, Disclosure [Text Block] Earnings Per Share [Abstract] Income from continuing operations Income (Loss) from Continuing Operations, Including Portion Attributable to Noncontrolling Interest Less: Preferred share dividends Preferred Stock Dividends, Income Statement Impact Less: Income from continuing operations attributable to noncontrolling interests Income (Loss) from Continuing Operations Attributable to Noncontrolling Interest Less: Earnings allocated to unvested shares Earnings Allocated To Unvested Shares Earnings allocated to unvested shares Income from continuing operations available for common shareholders Income Loss From Continuing Operations Available For Common Shareholders This element represents the income or loss from continuing operations attributable to the parent after earnings allocated to unvested shares and adjustments for dividends on preferred stock. Results from discontinued operations attributable to the Trust Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Gain on sale of real estate Gain (Loss) on sale of properties & real estate partnership properties, net of applicable income taxes This element represents the amount of gain (loss) on sale of properties and real estate partnership properties during the reporting period net of the applicable income taxes realized. 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. Weighted average common shares outstanding—basic Weighted Average Number of Shares Outstanding, Basic Stock options Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Weighted average common shares outstanding—diluted Weighted Average Number of Shares Outstanding, Diluted Continuing operations Income (Loss) from Continuing Operations, Per Basic Share Discontinued operations Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Basic Share Gain on sale of real estate Gain on Sale of Real Estate per Basic Share Gain On Sale Of Real Estate Per Basic Share. Earnings per common share, basic, total Earnings Per Share, Basic Continuing operations Income (Loss) from Continuing Operations, Per Diluted Share Discontinued operations Income (Loss) from Discontinued Operations and Disposal of Discontinued Operations, Net of Tax, Per Diluted Share Gain on sale of real estate Gain on Sale of Real Estate per Diluted Share Gain On Sale Of Real Estate Per Diluted Share. Earnings per common share, diluted, total Earnings Per Share, Diluted Income from continuing operations attributable to the Trust Income (Loss) from Continuing Operations Attributable to Parent Statement of Financial Position [Abstract] Operating, 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. 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. Debt issuance costs, accumulated amortization Accumulated Amortization, Deferred Finance Costs Mortgages payable, consolidated variable interest entities Mortgage Payable From Consolidated Variable Interest Entities Mortgages payable balances from variable interest entities, or VIEs, for the periods presented. Preferred shares, authorized Preferred Stock, Shares Authorized Preferred shares, par value Preferred Stock, Par or Stated Value Per Share Preferred Shares, percentage Preferred Stock, Dividend Rate, Percentage Preferred Shares, 5.417% Series 1 Cumulative Convertible liquidation preference Preferred Stock, Liquidation Preference Per Share Preferred shares, shares issued Preferred Stock, Shares Issued Preferred shares, shares outstanding Preferred Stock, Shares Outstanding Common shares of beneficial interest, par value Common Stock, Par or Stated Value Per Share Common shares of beneficial interest, shares authorized Common Stock, Shares Authorized Common shares of beneficial interest, shares issued Common Stock, Shares, Issued Common shares of beneficial interest, shares outstanding Common Stock, Shares, Outstanding Commitments and Contingencies Disclosure [Abstract] downREIT operating partnership units, outstanding Partners' Capital Account, Units downREIT operating partnership units outstanding, fair value Operating Partnership Units Fair Value Fair value of operating partnership units at the balance sheet date. Debt Instruments [Abstract] Contractual terms of secured mortgage loans assumed in acquisition SecuredDebtAssumedinAcquisition [Table Text Block] [Table Text Block] for Secured Debt Assumed in Acquisition [Table] Dividends [Table] Dividends [Table] Dividends [Table] Dividends [Line Items] Dividends [Line Items] [Line Items] for Dividends [Table] Dividends declared per common share Common Stock, Dividends, Per Share, Declared Dividends paid per common share Common Stock, Dividends, Per Share, Cash Paid Dividends declared per preferred share Preferred Stock, Dividends Per Share, Declared Dividends paid per preferred share Preferred Stock, Dividends, Per Share, Cash Paid Statement of Cash Flows [Abstract] OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Adjustment 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] Depreciation and amortization, including discontinued operations 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. Gain on sale of real estate Gain (Loss) on Sale of Properties Gain on sale of real estate in real estate partnership Gain (Loss) On Sale Of Properties in Real Estate Partnership Gain (loss) on sale of properties in real estate partnership Income from real estate partnership Income (Loss) from Equity Investment before gain on sale from real estate partnership Income (Loss) from Equity Investment before gain on sale from real estate partnership Other, net Other Noncash Income (Expense) Changes in assets and liabilities, net of effects of acquisitions and dispositions: Increase (Decrease) in Operating Capital [Abstract] Increase in accounts receivable Increase (Decrease) in Accounts and Other Receivables Increase in prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Increase in accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities 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. Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities INVESTING ACTIVITIES Net Cash Provided by (Used in) Investing Activities [Abstract] Acquisition of real estate Payments to Acquire Real Estate 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. Capital expenditures - other Payments for Capital Improvements Proceeds from sale of real estate Proceeds from Sale of Real Estate Held-for-investment Proceeds from sale of real estate in real estate partnership Payments for (Proceeds from) Real Estate Partnership Investment, Net Investment in real estate partnership Payments to Acquire Interest in Subsidiaries and Affiliates Distribution from real estate partnership in excess of earnings Proceeds from Distributions Received from Real Estate Partnerships Leasing costs Increase (Decrease) in Lease Acquisition Costs Repayment of mortgage and other notes receivable, net Issuance And 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. Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities FINANCING ACTIVITIES Net Cash Provided by (Used in) Financing Activities [Abstract] Net borrowings under revolving credit facility, net of costs Proceeds From Repayments Of Credit Facility The net cash inflow (outflow) from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with either short term or long term maturity net of costs incurred. Issuance of senior notes, net of costs Proceeds from Issuance of Senior Long-term Debt Redemption and retirement of senior notes Repayments of Senior Debt Repayment of mortgages, capital leases and notes payable Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities Issuance of common shares 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. 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. Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities (Decrease) increase in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of year Cash and Cash Equivalents, at Carrying Value Cash and cash equivalents at end of period Nature Of Operations [Abstract] Nature Of Operations [Abstract] Number of real estate properties owned or had a majority interest in Number of Real Estate Properties Minimum percentage of taxable income distributed to shareholders Minimum Percentage Of Taxable Income Distributed To Shareholders Minimum percentage of taxable income distributed to shareholders. Earnings Per Share Narrative [Table] Earnings Per Share Narrative [Table] Earnings Per Share Narrative [Table] Earnings Per Share Narrative [Line Items] Earnings Per Share Narrative [Line Items] Earnings Per Share Narrative [Line Items] Weighted average unvested shares outstanding Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights Anti-dilutive stock options Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Grants of common shares Restricted Stock [Member] Grants of options Employee Stock Option [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation, Allocation and Classification in Financial Statements [Abstract] Share-based compensation incurred Allocated Share-based Compensation Expense Capitalized share-based compensation Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount Share-based compensation expense Share-based Compensation Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Carrying Value Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Derivative, by Nature [Axis] Derivative, Name [Domain] Fair value of interest rate swaps Interest Rate Swap [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Term loan TermLoan [Member] TermLoan [Member] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair value, measurements, recurring Fair Value, Measurements, Recurring [Member] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Mortgages and notes payable, carrying value Mortgages and Notes Payable Mortgages and Notes Payable Senior notes and debentures, carrying value Senior Notes Mortgages and notes payable, fair value Mortgages and Notes Payable, Fair Value Disclosure Mortgages and Notes Payable, Fair Value Disclosure Senior notes and debentures, fair value Senior Notes and Debentures, Fair Value Disclosure Senior Notes and Debentures, Fair Value Disclosure Number of interest rate swap agreements Number of Interest Rate Derivatives Held Notional amount of interest rate swap agreements Derivative Liability, Notional Amount Notes payable Notes Payable Derivative, fixed interest rate Derivative, Fixed Interest Rate Interest rate cash flow hedge to be reclassified within next 12 months, net Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net Fair value of interest rate swaps Derivative Liability Other comprehensive income (loss) - change in value of interest rate swaps Interest expense reclassified from other comprehensive loss Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net Summary of financial information for discontinued operations Schedule of Disposal Groups, Including Discontinued Operations, Income Statement, Balance Sheet and Additional Disclosures [Table Text Block] Equity Method Investments and Joint Ventures [Abstract] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Name of Property [Axis] Name of Property [Axis] Name of Property [Domain] Name of Property [Domain] Pleasant Shops Pleasant Shops [Member] Pleasant Shops Real Estate Property Ownership [Axis] Real Estate Property Ownership [Axis] Real Estate Properties [Domain] Real Estate Properties [Domain] Federal Realty Investment Trust / ING Clarion Partners Partnership Federal / Lion Venture LP [Member] Federal / Lion Venture LP [Member] Legal Entity [Axis] Entity [Domain] Federal Realty Investment Trust Federal Realty Investment Trust [Member] Federal Realty Investment Trust [Member] ING Clarion Partners Clarion [Member] Clarion [Member] Investment, Name [Axis] Investment, Name [Domain] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Ownership interest in Partnership Equity Method Investment, Ownership Percentage Repayments of secured mortgage loan Repayments of Secured Debt Total capital contributions from partners to repay mortgage loan Proceeds from Partnership Contribution Capital contribution to repay mortgage loan Payments to Acquire Interest in Joint Venture Sales price of real estate Sales of Real Estate Gain on sale of real estate Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes REAL ESTATE PARTNERSHIP Equity Method Investments and Joint Ventures Disclosure [Text Block] Supplemental disclosures related to the Consolidated Statements Of Cash Flows Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] SHARE-BASED COMPENSATION PLANS Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Components Of Rental Income and Expense [Abstract] Components Of Rental Income And Expense [Abstract] Schedule of Minimum Rents [Table] Schedule of Minimum Rents [Table] Schedule of Minimum Rents [Table] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets by Major Class [Axis] Finite-Lived Intangible Assets, Major Class Name [Domain] Finite-Lived Intangible Assets, Major Class Name [Domain] Amortization of above market leases Above Market Leases [Member] Amortization of below market leases BelowMarketLease [Member] BelowMarketLease [Member] Minimum Rent [Line Items] Minimum Rent [Line Items] Minimum Rent [Line Items] Straight-line rents Straight Line Rent Amortization of above and below market leases Amortization of above and below Market Leases Income Statement [Abstract] REVENUE Revenues [Abstract] Rental income Rental income The total amount of rental revenue recognized for the period from real estate operations, including minimum rent, straight-line rent, percentage rent and tenant reimbursements. Other property income Other Real Estate Revenue Mortgage interest income Revenue Mortgage Interest Interest income earned from mortgage notes receivable. Total revenue Revenues EXPENSES Operating Expenses [Abstract] Rental expenses Direct Costs of Leased and Rented Property or Equipment Real estate taxes Real Estate Tax Expense General and administrative General and Administrative Expense Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Total operating expenses Operating Expenses OPERATING INCOME Operating Income (Loss) Other interest income Interest Income, Other Interest expense Interest Expense Early extinguishment of debt Gains (Losses) on Extinguishment of Debt INCOME FROM CONTINUING OPERATIONS DISCONTINUED OPERATIONS Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] Discontinued operations - income Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax Discontinued operations - gain on sale of real estate Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax Results from discontinued operations Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest INCOME BEFORE GAIN ON SALE OF REAL ESTATE Income (Loss) before Gain or Loss on Sale of Properties, and Extraordinary Items NET INCOME Net income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest NET INCOME ATTRIBUTABLE TO THE TRUST Net Income (Loss) Attributable to Parent Dividends on preferred shares NET INCOME AVAILABLE FOR COMMON SHAREHOLDERS Net Income (Loss) Available to Common Stockholders, Basic EARNINGS PER COMMON SHARE, BASIC Earnings Per Share, Basic [Abstract] Weighted average number of common shares, basic EARNINGS PER COMMON SHARE, DILUTED Earnings Per Share, Diluted [Abstract] Weighted average number of common shares, diluted COMPREHENSIVE INCOME Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest COMPREHENSIVE INCOME ATTRIBUTABLE TO THE TRUST Comprehensive Income (Loss), Net of Tax, Attributable to Parent Total interest costs incurred Interest Costs Incurred Interest capitalized Interest Costs Capitalized Interest expense Cash paid for interest, net of amounts capitalized Interest Paid, Net Cash paid for income taxes Income Taxes Paid, Net Mortgage loans assumed with acquisition Liabilities assumed unpaid principal balance The unpaid principal balance of loans assumed in noncash investing or financing activities. DownREIT operating partnership units issued with acquisition ValueofdownREITOperatingPartnershipUnitsIssuedinConnectionwithBusinessAcqu Value of downREIT Operating Partnership Units Issued in Connection with Business Acquisition Mortgage loan refinanced Refinance of mortgage loan Refinance of mortgage loan Repayment of note payable with public funding/related construction-in-progress offset Repayment of Note Payable with Public Funding Settlement of note payable with public funding Shares issued under dividend reinvestment plan Dividends Reinvested in Noncash Financing Transaction Dividends reinvested in noncash financing transaction COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] COMPONENTS OF RENTAL INCOME Operating Leases Revenue And Expense Text Block The principal components of rental income and/or rental expense recognized for the period. Real Estate [Abstract] REAL ESTATE Real Estate Acquisitions Dispositions Discontinued Operations Text Block Disclosure of real estate acquisitions, dispositions and discontinued operations and at year end, a summary of our real estate investments and related encumbrances. BUSINESS AND ORGANIZATION Nature of Operations [Text Block] Schedule of earnings per share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] SHAREHOLDERS’ EQUITY Stockholders' Equity Note Disclosure [Text Block] Entity Real Estate Partnership Operating Results [Line Items] Real Estate Partnerships Operating Results [Line Items] Real Estate Partnerships Operating Results [Line Items] Gain on sale of real estate Revenue Other operating expenses Other Expenses Total expenses Total Expenses Total expenses including operating expenses, interest expense, depreciation and amortization, and other expenses. Net income before gain on sale of real estate Our share of net income before gain on sale of real estate in real estate partnership Real estate, net Real Estate Investment Property, Net Cash Other assets Other Assets Total assets Assets Mortgages payable Secured Debt Other liabilities Other Liabilities Partners’ capital Partners' Capital Total liabilities and partners’ capital Liabilities and Equity Our share of unconsolidated debt Share Of Unconsolidated Debt Share Of Unconsolidated Debt Our investment in real estate partnership Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Net income attributable to redeemable noncontrolling interests Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Summarized operating results and financial position of the Partnership Schedule Of Balance Sheets and Operating Results Of Unconsolidated Joint Ventures [Table Text Block] Schedule Of Balance Sheets and Operating Results Of Unconsolidated Joint Ventures [Table Text Block] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] The Grove at Shrewsbury & Brook 35 GroveatShrewsbury & Brook 35 [Member] GroveatShrewsbury & Brook 35 [Member] Melville Mall MelvilleMall [Member] MelvilleMall [Member] Brook 35 Brook 35 [Member] Brook 35 [Member] The Grove at Shrewsbury (East) TheGroveatShrewsbury(East) [Member] The Grove at Shrewsbury (East) [Member] The Grove at Shrewsbury (West) The Grove at Shrewsbury (West) [Member] The Grove at Shrewsbury (West) [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Principal Long-term Debt, Gross Fair value Debt Instrument, Fair Value Disclosure Stated Interest Rate Debt Instrument, Interest Rate, Stated Percentage Face amount Debt Instrument, Face Amount Change in Basis Points spread Change in Basis Points spread The change in the number of basis points added to LIBOR to compute the total interest rate Debt Instrument, Basis Spread over LIBOR Debt Instrument, Basis Spread on Variable Rate Maximum borrowing capacity under revolving credit facility Line of Credit Facility, Maximum Borrowing Capacity Maximum amount outstanding under revolving credit facility Line of Credit Facility, Maximum Amount Outstanding During Period Weighted average borrowings outstanding Line of Credit Facility, Average Outstanding Amount Weighted average interest rate, before amortization of debt fees LineofCreditFacilityWeightedAverageInterestRateBeforeAmortizationOfDebt Fees Line of credit facility weighted average interest rate, before amortization of debt fees. Outstanding balance of revolving credit facility Line of Credit Facility, Amount Outstanding SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Significant Accounting Policies [Text Block] Revenue from discontinued operations Disposal Group, Including Discontinued Operation, Revenue Income from discontinued operations DEBT Debt Disclosure [Text Block] ASSETS Assets [Abstract] Operating (including $281,960 and $265,138 of consolidated variable interest entities, respectively) Rental Properties Construction-in-progress Construction in Progress, Gross Real Estate Investment Property, at Cost, total Real Estate Investment Property, at Cost Less accumulated depreciation and amortization (including $24,714 and $19,086 of consolidated variable interest entities, respectively) Real Estate Investment Property, Accumulated Depreciation Net real estate Cash and cash equivalents Accounts and notes receivable, net Accounts and Notes Receivable, Net Mortgage notes receivable, net Mortgage Loans on Real Estate, Commercial and Consumer, Net Investment in real estate partnership Prepaid expenses and other assets Prepaid Expense and Other Assets Debt issuance costs, net of accumulated amortization of $11,653 and $9,535, respectively Deferred Finance Costs, Net TOTAL ASSETS Liabilities Liabilities [Abstract] Mortgages payable (including $188,189 and $202,782 of consolidated variable interest entities) Capital lease obligations Capital Lease Obligations Senior notes and debentures Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities Dividends payable Dividends Payable Security deposits payable Security Deposit Liability Other liabilities and deferred credits Deferred Credits and Other Liabilities Total liabilities Liabilities Commitments and contingencies (Note 7) Commitments and Contingencies Redeemable noncontrolling interests Redeemable Noncontrolling Interest, Equity, Carrying Amount Shareholders’ equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Preferred shares, authorized 15,000,000 shares, $.01 par: 5.417% Series 1 Cumulative Convertible Preferred Shares, (stated at liquidation preference $25 per share), 399,896 shares issued and outstanding Preferred Stock, Value, Issued Common shares of beneficial interest, $.01 par, 100,000,000 shares authorized, 68,128,519 and 66,701,422 shares issued and outstanding, respectively Common Stock, Value, Issued Additional paid-in capital Additional Paid in Capital, Common Stock Accumulated dividends in excess of net income Accumulated Distributions in Excess of Net Income Accumulated other comprehensive loss Accumulated Other Comprehensive Income (Loss), Net of Tax Total shareholders’ equity of the Trust Stockholders' Equity Attributable to Parent Noncontrolling interests Stockholders' Equity Attributable to Noncontrolling Interest Total shareholders’ equity TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY Summary of carrying amount and fair value of financial instruments Schedule of Carrying Amount and Fair Value of Financial Instruments [Table Text Block] Schedule of Carrying Amount and Fair Value of Financial Instruments [Table Text Block] Summary of financial liabilities measured at fair value on a recurring basis Fair Value, Liabilities Measured on Recurring Basis [Table Text Block] EARNINGS PER SHARE Earnings Per Share [Text Block] Principal components of rental income Schedule of Component of Rental Income [Table Text Block] Schedule of Component of Rental Income [Table Text Block] Minimum rents Schedule Of Minimum Rents Components [Table TextBlock] Schedule of Minimum Rents Components [Table Text Block] Summary of dividends declared and paid per share Dividends Declared [Table Text Block] Schedule of Significant Acquisitions and Disposals [Table] Schedule of Significant Acquisitions and Disposals [Table] Asset Class [Axis] Asset Class [Axis] Asset Class [Domain] Asset Class [Domain] Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] The Grove at Shrewsbury GroveatShrewsbury [Member] GroveatShrewsbury [Member] Significant Acquisitions and Disposals [Line Items] Significant Acquisitions and Disposals [Line Items] Square footage of real estate property Area of Real Estate Property Gross value of business acquisition BusinessAcquisitionGrossValue Gross value of business acquisition. Effective economic interest of acquisition Effective Economic Interest Acquisition Effective Economic Interest in Acquisition Mortgage debt assumed in acquisition Noncash or Part Noncash Acquisition, Debt Assumed Number of downREIT operating partnership units assumed in acquisition Number of downREIT Operating Partnership Units Issued in Connection with Business Acquisition Number of downREIT Operating Partnership Units Issued in Connection with Business Acquisition Cash paid in acquisition Payments to Acquire Businesses, Gross Net assets acquired allocated to other assets for above market leases Finite-lived Intangible Assets Acquired Net assets acquired allocated to other liabilities for below market leases Below Market Lease, Acquired Acquisition costs incurred Business Combination, Acquisition Related Costs Price to acquire non-controlling interest Price to Acquire Non-Controlling Interest Price to Acquire Non-Controlling Interest Summary of share-based compensation expense included in net income Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Components of Rental Income [Table] Components of Rental Income [Table] Components of Rental Income [Table] Products and Services [Axis] Products and Services [Domain] Retail and commercial Commercial Real Estate [Member] Residential Residential Real Estate [Member] Minimum rents Operating Leases, Income Statement, Minimum Lease Revenue Cost reimbursement Tenant Reimbursements Percentage rent Operating Leases, Income Statement, Percentage Revenue Other Other Rental Income This element represents other rental revenue earned during the period. Total rental income