Construction-in-progress, consolidated variable interest entities Constructioninprogresofconsolidatedvariableieestentity Construction-in-progress oc consolidated variable interest entity Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Title of 12(b) Security Title of 12(b) Security Subsequent Event Subsequent Event [Member] Net income available for common shareholders, diluted Net Income (Loss) Available to Common Stockholders, Diluted Carrying Value Reported Value Measurement [Member] Document Fiscal Year Focus Document Fiscal Year Focus Total capital Beginning balance Ending balance Partners' Capital, Including Portion Attributable to Noncontrolling Interest Common shares of beneficial interest, $.01 par, 200,000,000 shares authorized, 86,386,687 and 86,266,009 shares issued and outstanding, respectively Common Stock, Value, Issued Shares withheld for employee taxes Payment, Tax Withholding, Share-Based Payment Arrangement Interest expense Interest expense Interest expense Interest Expense, Operating and Nonoperating Common units issued under dividend reinvestment plan Common units issued under dividend reinvestment plan Common units issued under dividend reinvestment plan 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. Investment in partnerships Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Derivative Instrument [Axis] Derivative Instrument [Axis] Nature of Operations Subsidiary of Limited Liability Company or Limited Partnership [Line Items] Federal Realty GP LLC Federal Realty GP LLC [Member] Federal Realty GP LLC Measurement Frequency [Axis] Measurement Frequency [Axis] Acquired lease costs Leases, Acquired-in-Place [Member] Amendment Flag Amendment Flag Consolidated Entities [Axis] Consolidated Entities [Axis] Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Dividends paid to common and preferred unit holders Dividends paid to common and preferred unit holders Dividends paid to common and preferred unit holders Less accumulated depreciation and amortization (including $474,534 and $468,725 of consolidated variable interest entities, respectively) Real Estate Investment Property, Accumulated Depreciation Forward Sales Contracts Forward Sales Contracts [Member] Forward Sales Contracts Sales price of real estate Sales price of real estate The gross sales price of real estate sold. Weighted average interest rate, before amortization of debt fees LineofCreditFacilityWeightedAverageInterestRateBeforeAmortizationOfDebt Fees Line of credit facility weighted average interest rate, before amortization of debt fees. Consolidated Entities [Domain] Consolidated Entities [Domain] Three of our equity method investees Equity Method Investee [Member] Reconciliation of cash, cash equivalents, and restricted cash Schedule of Cash and Cash Equivalents [Table Text Block] Entity Address, State Entity Address, State or Province Repayment of mortgages, finance leases and notes payable Repayment of mortgages, finance leases, and notes payable Repayment of mortgages, finance leases, and notes payable Common shares of beneficial interest, par value Common Stock, Par or Stated Value Per Share Exchange [Domain] Exchange [Domain] Common units, 86,386,687 and 86,266,009 units issued and outstanding, respectively Common Units Capital Accounts Common Units Capital Accounts Value Total notional amounts of interest rate swap agreements Derivative, Notional Amount Weighted average number of common shares, Basic Weighted Average Number of Shares Outstanding, Basic Mortgages payable, net (including $191,475 and $194,176 of consolidated variable interest entities, respectively) Secured Debt Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Number of reportable segments Number of Reportable Segments 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). Acquired lease costs Acquired lease costs Acquired lease costs A residential building at our Santana Row property and our Courthouse Center retail property a residential building at our Santana Row property and our Courthouse Center retail property [Member] a residential building at our Santana Row property and our Courthouse Center retail property Real estate, at cost, total Real Estate Investment Property, at Cost Entity Address, City Entity Address, City or Town Supplemental disclosures related to the Consolidated Statements Of Cash Flows Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] Statement of Financial Position [Abstract] Statement of Financial Position [Abstract] 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. Basis of Presentation Basis of Accounting, Policy [Policy Text Block] Class of Stock [Axis] Class of Stock [Axis] NET INCOME AVAILABLE FOR COMMON SHAREHOLDERS Net Income (Loss) Available to Common Stockholders, Basic Shares issued under dividend reinvestment plan Stock Issued During Period, Value, Dividend Reinvestment Plan Fair Value, Inputs, Level 2 Fair Value, Inputs, Level 2 [Member] Other comprehensive income Other Comprehensive Income (Loss), Net of Tax Maximum borrowing capacity under revolving credit facility Line of Credit Facility, Maximum Borrowing Capacity Leasing costs Increase (Decrease) in Lease Acquisition Costs Preferred units, 398,878 units issued and outstanding Preferred Units, Preferred Partners' Capital Accounts Straight-line rent Straight Line Rent Name of Property [Axis] Name of Property [Axis] DownREIT operating partnership units issued with acquisition Value of downREIT Operating Partnership Units Issued With Acq. of Noncontrolling Interest Value of downREIT Operating Partnership Units Issued With Acq. of Noncontrolling Interest Subsequent Event Type [Axis] Subsequent Event Type [Axis] Capitalized share-based compensation Share-Based Payment Arrangement, Amount Capitalized Schedule of Long-term Debt Instruments [Table] Schedule of Long-Term Debt Instruments [Table] Gain on sale of real estate Gain (Loss) on Disposition of Property Plant Equipment Noncontrolling Interests Noncontrolling Interest [Member] Debt issuance cost amortization Amortization of Debt Issuance Costs Use of Estimates Use of Estimates, Policy [Policy Text Block] Related Party [Axis] Related and Nonrelated Parties [Axis] Shares issued under dividend reinvestment plan (in shares) Stock Issued During Period, Shares, Dividend Reinvestment Plan 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] Common units issued as a result of common stock issued by Parent Company, net of issuance costs Partners' Capital Account, Contributions Document Period End Date Document Period End Date Changes in assets and liabilities, net of effects of acquisitions and dispositions: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity, Increase (Decrease) in Operating Capital [Abstract] Minimum percentage of taxable income distributed to shareholders Minimum Percentage Of Taxable Income Distributed To Shareholders Minimum percentage of taxable income distributed to shareholders. Net cash provided by (used in) investing activities Cash Provided by (Used in) Investing Activity, Including Discontinued Operation Preferred shares, shares outstanding Preferred Stock, Shares Outstanding SHAREHOLDERS’ EQUITY Equity [Text Block] EARNINGS PER COMMON SHARE/UNIT, BASIC: Earnings Per Share, Basic [Abstract] Security Exchange Name Security Exchange Name Effective interest rate Debt Instrument, Interest Rate, Effective Percentage Contributions from noncontrolling interests Proceeds from Noncontrolling Interests Purchase price of real estate acquisition Purchase price of fee interest in real estate Purchase price of fee interest in real estate Share-based compensation expense, net of forfeitures Partners' Capital Account, Unit-Based Payment Arrangement, Amount Accumulated other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Entity Shell Company Entity Shell Company Per $1,000 principal amount Per $1,000 principal amount [Member] Per $1,000 principal amount Segment Information Segment Reporting, Policy [Policy Text Block] Finance lease right of use assets, net Finance Lease, Right-of-Use Asset, after Accumulated Amortization EARNINGS PER SHARE AND UNIT Earnings Per Share [Text Block] EARNINGS PER COMMON SHARE, BASIC AND DILUTED: Earnings Per Share [Abstract] Document Fiscal Period Focus Document Fiscal Period Focus 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. Total liabilities Liabilities Trading Symbol Trading Symbol Mortgage note receivable repaid with property acquisition Mortgage note receivable repaid with property acquisition Mortgage note receivable repaid with property acquisition Summary of outstanding interest rate swap agreements Schedule of Interest Rate Derivatives [Table Text Block] Net income available for common shareholders, basic Net income available for common shareholders, basic Net income available for common shareholders, basic Sale of Stock [Domain] Sale of Stock [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. Dividends paid per preferred share Preferred Stock, Dividends, Per Share, Cash Paid Fixed interest rate of derivative instrument Derivative, Fixed Interest Rate Mortgages and notes payable Long-Term Debt, Gross Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Earnings Per Share, Basic, by Common Class, Including Two Class Method [Line Items] Depreciation and amortization Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction OPERATING ACTIVITIES Cash Provided by (Used in) Operating Activity, Including Discontinued Operation [Abstract] Weighted average number of common shares, Diluted Weighted Average Number of Shares Outstanding, Diluted Dividends paid per common share Common Stock, Dividends, Per Share, Cash Paid Entity Emerging Growth Company Entity Emerging Growth Company Mortgages and notes payable, net Mortgages and notes payable Mortgages Payable And Notes Payable [Member] Mortgages Payable And Notes Payable [Member] Dividends payable Dividends Payable Entities [Table] Entities [Table] (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. Repayments of unsecured notes Repayments of Unsecured Debt Accumulated dividends in excess of net income Accumulated Distributions in Excess of Net Income Fair Value, Inputs, Level 1 Fair Value, Inputs, Level 1 [Member] Contributions from noncontrolling interests Contributions from noncontrolling interests Contributions from noncontrolling interests Net income available for common unit holders, Basic Income (Loss) from Continuing Operations, Per Outstanding General Partnership Unit, Net of Tax Exchange rate Debt Instrument, Convertible, Conversion Ratio Square footage of real estate property Area of Real Estate Property COMPREHENSIVE INCOME Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Preferred shares, par value Preferred Stock, Par or Stated Value Per Share Fair value of long-term debt Long-Term Debt, Fair Value Schedule of Subsidiary of Limited Liability Company or Limited Partnership [Table] Subsidiary of LLC or LP [Table] Redeemable noncontrolling interests Redeemable Noncontrolling Interest, Equity, Carrying Amount Weighted average unvested shares outstanding Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights Weighted average number of common units, Basic Weighted Average Limited Partnership and General Partnership Units Outstanding, Basic 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. Cash, Cash Equivalents, Restricted Cash and Restricted Cash Equivalents [Abstract] Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation [Abstract] Operating lease right of use assets, net Operating Lease, Right-of-Use Asset 1.25% senior unsecured notes 1.25% senior unsecured notes [Member] 1.25% senior unsecured notes Schedule of earnings per share and unit Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Fair Value Disclosures [Abstract] Fair Value Disclosures [Abstract] Debt Instrument Debt Instrument, Name [Domain] Revolving credit facility Long-Term Line of Credit Liabilities Liabilities [Abstract] Restricted cash Restricted Cash and Cash Equivalent Total shareholders’ equity Beginning balance Ending balance Equity, Including Portion Attributable to Noncontrolling Interest Federal Realty OP LP Partnership Interest [Member] Debt Conversion Description [Axis] Debt Conversion Description [Axis] Distributions declared to redeemable noncontrolling interests Redeemable noncontrolling interest, Decrease from Distributions to redeemable noncontrolling interest holders Redeemable noncontrolling interest, Decrease from Distributions to redeemable noncontrolling interest holders Significant Acquisition and Disposition Business Combination [Line Items] Senior notes and debentures, net Unsecured Debt Dividends [Abstract] Dividends [Abstract] OTHER INCOME/(EXPENSE) Other Income and Expenses [Abstract] Issuance of common shares, net of costs Proceeds from Issuance of Common Stock Common shares of beneficial interest, shares authorized Common Stock, Shares Authorized EARNINGS PER COMMON SHARE/UNIT, DILUTED: EARNINGS PER COMMON UNIT, BASIC: [Abstract] EARNINGS PER COMMON UNIT, BASIC: Net real estate Real Estate Investment Property, Net Statement [Table] Antidilutive Security, Excluded EPS Calculation [Table] Decrease in accounts receivable, net Increase (Decrease) in Accounts and Other Receivables Convertible Unit Type [Domain] Convertible Unit Type [Domain] Convertible Unit Type Summary of carrying amount and fair value of financial instruments Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block] 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. INVESTING ACTIVITIES Cash Provided by (Used in) Investing Activity, Including Discontinued Operation [Abstract] Fair Value, recurring Fair Value, Recurring [Member] Quarterly common dividend payable, if in excess will adjust the initial exchange rate Initial quarterly common dividend Initial quarterly common dividend Document Quarterly Report Document Quarterly Report Option Indexed to Issuer's Equity, Type [Axis] Option Indexed to Issuer's Equity, Type [Axis] Distributions on preferred units Distributions declared to preferred unit holders Distributions declared to preferred unit holders Interest rate swap Interest Rate Swap [Member] DEBT Debt Disclosure [Text Block] Repayment of mortgage loans Repayments of Long-Term Debt Unsecured term loan Term loan [Member] Term loan [Member] Preferred shares, liquidation preference per share Preferred Stock, Liquidation Preference Per Share Federal Realty OP LP Federal Realty OP LP [Member] Federal Realty OP LP Real Estate Disclosure Real Estate Disclosure [Text Block] Schedule of Significant Acquisitions and Dispositions Business Combination [Table] Total interest costs incurred Interest Costs Incurred Equity Component [Domain] Equity Component [Domain] 3.25% notes Senior 3 Point 25 Percent Notes [Member] Senior 3 Point 25 Percent Notes Mortgages payable Secured Debt [Member] Real estate taxes Real Estate Tax Expense 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 Debt Instrument, Interest Rate, Stated Percentage Dividends declared to common shareholders Dividends, Common Stock, Cash downREIT OP units downREIT OP units [Member] downREIT OP units Total shareholders’ equity of the Trust Equity, Attributable to Parent Entity Listings, Exchange [Axis] Entity Listings, Exchange [Axis] ASSETS Assets [Abstract] Accounting Policies [Abstract] Accounting Policies [Abstract] Operating lease liabilities Operating Lease, Liability Finance lease liabilities Finance Lease, Liability Noncontrolling interests in consolidated partnerships Partners' Capital Attributable to Noncontrolling Interest Preferred Units 5.417% Series 1 Cumulative Convertible Preferred Units Preferred Units [Member] Preferred Units COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] Rental income Operating Lease, Lease Income Construction-in-progress (including $30,376 and $28,418 of consolidated variable interest entities, respectively) Construction in Progress, Gross Anti-dilutive issuable shares Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount DownREIT operating partnership units Common shares attributable to dilutive effect of downREIT operating partnership units Common shares attributable to dilutive effect of downREIT operating partnership units Entity Central Index Key Entity Central Index Key Additional paid-in capital Additional Paid in Capital, Common Stock Name of Property [Domain] Name of Property [Domain] Net cash provided by operating activities Cash Provided by (Used in) Operating Activity, Including Discontinued Operation Distributions declared to noncontrolling interests in consolidated partnerships, excluding amounts attributable to redeemable noncontrolling interests Distributions declared to noncontrolling interests in consolidated partnerships, excluding amounts attributable to redeemable noncontrolling interests Distributions declared to noncontrolling interests in consolidated partnerships, excluding amounts attributable to redeemable noncontrolling interests Income Statement [Abstract] Income Statement [Abstract] Document Transition Report Document Transition Report Ownership [Axis] Ownership [Axis] Maximum borrowing capacity after option to increase credit facility Maximum borrowing capacity after option to increase credit facility Maximum borrowing capacity after option to increase credit facility Fair Value Hierarchy and NAV [Axis] Fair Value Hierarchy and NAV [Axis] Conversion and redemption of downREIT OP units Partners' Capital Account, Exchanges and Conversions Dividends declared to preferred shareholders Dividends, Preferred Stock, Cash EXPENSES Operating Expenses [Abstract] Preferred shares, percentage Preferred Stock, Dividend Rate, Percentage Basis spread on SOFR Interest Debt Instrument, Basis Spread on Variable Rate Interest capitalized Interest Costs Capitalized Adjustment Property operating income Property operating income Property operating income Net income available for common unit holders, Diluted Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Diluted, Net of Tax Net Income (Loss), Per Outstanding Limited Partnership and General Partnership Unit, Diluted, Net of Tax City Area Code City Area Code Conversion of downREIT OP units Stock Issued During Period, Value, Conversion of Units Accumulated Other Comprehensive Income (Loss) Accumulated other comprehensive income AOCI Attributable to Parent [Member] Subsequent Event Subsequent Events [Text Block] Net income available for common unit holders, basic Net income available for common unit holders, basic Net income available for common unit holders, basic Statement [Line Items] Statement [Line Items] TOTAL ASSETS Assets Common units, outstanding Common Unit, Outstanding Entity [Domain] Entity [Domain] Call Option Call Option [Member] Preferred shares, shares issued Preferred Stock, Shares Issued Exchangeable senior notes Convertible Debt [Member] Common units, issued Common Unit, Issued Preferred units, outstanding Preferred Units, Outstanding Summary of share-based compensation expense included in net income Share-Based Payment Arrangement, Expensed and Capitalized, Amount [Table Text Block] Convertible Unit Type [Axis] Convertible Unit Type [Axis] Convertible Unit Type Total partner capital Partners' Capital Share Type [Domain] Share Type [Domain] Share Type [Domain] SHARE-BASED COMPENSATION PLANS Share-Based Payment Arrangement [Text Block] BUSINESS AND ORGANIZATION Nature of Operations [Text Block] Common shares issued, net (in shares) Stock Issued During Period, Shares, New Issues Other comprehensive income (loss) - change in fair value of interest rate swaps, excluding portion attributable to redeemable noncontrolling interests Other comprehensive (loss) income - change in fair value of interest rate swaps, excluding portion attributable to redeemable noncontrolling interests Other Comprehensive Income (loss), net of portion attributable to noncontrolling interest Other Comprehensive Income (loss), net of portion attributable to noncontrolling interest Beginning balance (in shares) Ending balance (in shares) Shares, Outstanding New York Stock Exchange NEW YORK STOCK EXCHANGE, INC. [Member] Maximum amount outstanding under revolving credit facility Line of Credit Facility, Maximum Amount Outstanding During Period Grants of common shares, restricted stock units, and options Share-Based Payment Arrangement, Expense Initial cap price Capped call cap share price Capped call cap share price Measurement Basis [Axis] Measurement Basis [Axis] Proceeds from sale of real estate Proceeds from Real Estate and Real Estate Joint Ventures Subsequent Event Type [Domain] Subsequent Event Type [Domain] Total operating expenses Operating Expenses Revolving credit facility Revolving Credit Facility [Member] 5.417% Series 1 Cumulative Convertible Preferred Units 5.417% Series 1 Cumulative convertible preferred units Incremental common units attributable to dilutive effect of conversion of debt securities Increase (Decrease) in Stockholders' Equity [Roll Forward] Increase (Decrease) in Stockholders' Equity [Roll Forward] Common shares of beneficial interest, shares outstanding Common Stock, Shares, Outstanding Net income available for common shareholders, Diluted Earnings Per Share, Diluted Entity Current Reporting Status Entity Current Reporting Status Net cash used in financing activities Cash Provided by (Used in) Financing Activity, Including Discontinued Operation Shares withheld for employee taxes Share-Based Payment Arrangement, Decrease for Tax Withholding Obligation Decrease in prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Acquisition of real estate Payments to Acquire Real Estate Summary of financial assets that are measured at fair value on a recurring basis Fair Value, Liabilities Measured on Recurring Basis [Table Text Block] Stockholders' Equity Note [Abstract] Stockholders' Equity Note [Abstract] downREIT operating partnership units outstanding, fair value Operating Partnership Units Fair Value Fair value of operating partnership units at the balance sheet date. Limited liability company ownership interest Limited Liability Company (LLC) or Limited Partnership (LP), Managing Member or General Partner, Ownership Interest Ownership [Domain] Ownership [Domain] Adjustments to reconcile net income to net cash provided by operating activities: Adjustment to Reconcile Net Income to Cash Provided by (Used in) Operating Activity [Abstract] Above market leases Intangible Asset, Finite-Lived, Acquired 5.417% Series 1 Cumulative Convertible Preferred Shares Incremental Common Shares Attributable to Dilutive Effect of Conversion of Preferred Stock Share-based Payment Arrangement [Abstract] Share-Based Payment Arrangement [Abstract] FINANCING ACTIVITIES Cash Provided by (Used in) Financing Activity, Including Discontinued Operation [Abstract] Earnings Allocated To Unvested Shares Earnings Allocated To Unvested Shares Earnings allocated to unvested shares Depositary Shares Depositary Shares [Member] Depositary Shares Other liabilities and deferred credits Deferred Credits and Other Liabilities Derivative Asset Derivative Asset Intangible Asset, Finite-Lived, Class [Axis] Intangible Asset, Finite-Lived, Class [Axis] Fair Value Estimate of Fair Value Measurement [Member] Common shares issued, net Stock Issued During Period, Value, New Issues Preferred Shares Preferred Stock [Member] Accumulated Dividends in Excess of Net Income Accumulated Distributions in Excess of Net Income [Member] Mortgage notes receivable repaid with property acquisition, number Mortgage notes receivable repaid with property acquisition, number Mortgage notes receivable repaid with property acquisition, number Sale of Stock [Axis] Sale of Stock [Axis] Commitments and Contingencies Disclosure [Abstract] Commitments and Contingencies Disclosure [Abstract] OPERATING INCOME Operating Income (Loss) Summary of dividends declared and paid per share Dividends Declared [Table Text Block] Current Fiscal Year End Date Current Fiscal Year End Date Proceeds from issuance of debt Proceeds from Issuance of Debt Dividends declared to common shareholders (in dollars per share) Divdends declared per common share Common Stock, Dividends, Per Share, Declared Other comprehensive income (loss) attributable to redeemable noncontrolling interests Other comprehensive income (loss) attributable to Redeemable Noncontrolling interest Other comprehensive income (loss) attributable to redeemable noncontrolling interest Entity File Number Entity File Number Distributions declared to noncontrolling interests, excluding amounts attributable to redeemable noncontrolling interests Noncontrolling Interest, Decrease from Distributions to Noncontrolling Interest Holders Add: Dividends on 5.417% Series 1 Cumulative Convertible Preferred Shares Dividends on 5.417% Series 1 Cumulative Convertible Preferred Shares Dividends on 5.417% Series 1 Cumulative Convertible Preferred Shares Dividends declared per preferred share Preferred Stock, Dividends Per Share, Declared Distributions declared to common unit holders Distributions declared to common unit holders Distributions declared to common unit holders Common shares of beneficial interest, shares issued Common Stock, Shares, Issued Preferred units, issued Preferred Units, Issued Entity Information [Line Items] Entity Information [Line Items] Issuance of common units, net of costs Issuance of common units, net of costs Issuance of common units, net of costs Weighted average common units outstanding, diluted weighted average number partnership units outstanding, diluted weighted average number partnership units outstanding, diluted Increase (Decrease) in Partners' Capital [Roll Forward] Increase (Decrease) in Partners' Capital [Roll Forward] Statement, Equity Components [Axis] Equity Components [Axis] Equity Components [Axis] Rental expenses Other Cost and Expense, Operating Share-based Payment Arrangement, Expensed and Capitalized, Amount [Abstract] Share-Based Payment Arrangement, Recognized Amount [Abstract] Cash paid for income taxes Income Tax Paid, after Refund Received Issuance of downREIT partnership units at acquisition Units of Partnership Interest, Amount Entity Interactive Data Current Entity Interactive Data Current Net income attributable to noncontrolling interests Less: Income from operations attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest Conversion downREIT OP units (in Shares) Stock Issued During Period, Shares, Conversion of Units Entity Small Business Entity Small Business COMPREHENSIVE INCOME ATTRIBUTABLE TO THE TRUST / PARTNERSHIP Comprehensive Income (Loss), Net of Tax, Attributable to Parent Share Type [Axis] Share Type [Axis] Share Type Shares withheld for employee taxes (in shares) Share-Based Payment Arrangement, Shares Withheld for Tax Withholding Obligation downREIT operating partnership units, outstanding Partners' Capital Account, Units Subsequent Events [Abstract] Fair Value, Recurring and Nonrecurring [Table] Fair Value, Recurring and Nonrecurring [Table] Document Type Document Type Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Significant Accounting Policies [Text Block] Earnings Per Share, Basic, by Common Class, Including Two-Class Method [Table] Earnings Per Share, Basic, by Common Class, Including Two-Class Method [Table] Subsequent Event [Line Items] Subsequent Event [Line Items] Statement of Stockholders' Equity [Abstract] Statement of Stockholders' Equity [Abstract] Registrant's Telephone Number Local Phone Number Entity Address, Zip Code Entity Address, Postal Zip Code Name of Registrant Entity Registrant Name DownREIT operating partnership units redeemed for common shares RedemptionofdownREIToperatingpartnershipunitsforcommonshares Redemption of downREIT operating partnership units for common shares Commitments and contingencies (Note 6) Commitments and Contingencies Option Indexed to Issuer's Equity, Type [Domain] Option Indexed to Issuer's Equity, Type [Domain] Total revenue Revenues Senior notes and debentures, net Senior Notes And Debentures [Member] Senior Notes And Debentures [Member] Income from partnerships Income from partnerships Income from partnerships Income (Loss) from Equity Method Investments Shares issued under dividend reinvestment plan Dividends Reinvested in Noncash Financing Transaction Dividends reinvested in noncash financing transaction Increase in accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities Mortgage interest income Revenue Mortgage Interest Interest income earned from mortgage notes receivable. Preferred units, percentage Preferred unit distribution rate percentage Preferred unit distribution rate percentage Commitments [Table] Other Commitments [Table] Intangible Asset, Finite-Lived, Class [Domain] Intangible Asset, Finite-Lived, Class [Domain] FAIR VALUE OF FINANCIAL INSTRUMENTS Fair Value Disclosures [Text Block] Fair Value, Inputs, Level 3 Fair Value, Inputs, Level 3 [Member] Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities Noncontrolling Interests in Consolidated Partnerships Noncontrolling Interests in Consolidated Partnerships [Member] Nonredeemable Noncontrolling Interests in Consolidated Partnerships IRS Employer Identification No. Entity Tax Identification Number Co-Registrant Legal Entity [Axis] Interest expense Interest Expense, Debt Prepaid expenses and other assets Prepaid Expense and Other Assets Notes payable, net Notes Payable Commitments [Line Items] Other Commitments [Line Items] Cash, cash equivalents, and restricted cash at beginning of year Cash, cash equivalents, and restricted cash at end of period Total cash, cash equivalents, and restricted cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Continuing Operation Dividends on preferred shares Preferred Stock Dividends, Income Statement Impact State of Organization Entity Incorporation, State or Country Code Congressional North Shopping Center Congressional North Shopping Center [Member] Congressional North Shopping Center COMPREHENSIVE INCOME Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Measurement Frequency [Domain] Measurement Frequency [Domain] Debt Instrument [Axis] Debt Instrument [Axis] Subsequent Event [Table] Subsequent Event [Table] Share-based compensation expense Share-Based Payment Arrangement, Noncash Expense Long-term Debt, Type Long-Term Debt, Type [Domain] Net income available for common shareholders, Basic Earnings Per Share, Basic Partner capital Partners' Capital [Abstract] Common Shares of Beneficial Interest Common Shares Common Stock [Member] Fair Value Measurement [Domain] Fair Value Measurement [Domain] One of our ground leases at Bethesda Row Bethesda Row [Member] Bethesda Row Issuance and extension of notes payable, net of costs Issuance of notes and mortgages payable, net of costs Issuance of notes and mortgages payable, net of costs Cover [Abstract] Cover [Abstract] Gain on sale of real estate Gain on sale of real estate Gain on sale of real estate Gain on sale of real estate Derivative Contract [Domain] Derivative Contract [Domain] Other property income Other property income Other property income Security deposits payable Security Deposit Liability TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY / CAPITAL Liabilities and Equity Other interest income Interest Income, Other Fair Value, Balance Sheet Grouping, Financial Statement Captions Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Noncontrolling interests Equity, Attributable to Noncontrolling Interest Exchangeable senior notes, net Exchangeable senior notes [Member] Exchangeable senior notes Related Party [Domain] Related and Nonrelated Parties [Domain] Below market leases Below Market Lease, Acquired Common units withheld for employee taxes Partners capital account employee tax withholdings Partners capital account employee tax withholdings Total Partner Capital Parent [Member] Repayment of senior notes Repayments of Senior Debt Weighted average borrowings outstanding Line of Credit Facility, Average Outstanding Amount Shareholders’ equity Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Hoboken Hoboken [Member] Hoboken [Member] General and administrative General and administrative expense General and Administrative Expense Unsecured term loan borrowed Other Notes Payable Preferred shares, authorized Preferred Stock, Shares Authorized Preferred shares, authorized 15,000,000 shares, $.01 par: Preferred Stock, Value, Issued Number of real estate properties Number of Real Estate Properties Net income attributable to redeemable noncontrolling interests Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Net income available for common unit holders, diluted Net income available for common unit holders, diluted Net income available for common unit holders, diluted Dividends Dividends Payable [Line Items] Dividends Payable [Table] Dividends Payable [Table] Class of Stock Class of Stock [Domain] Part of Kingstowne Towne Center Part of Kingstowne Towne Center [Member] Part of Kingstowne Towne Center Cash paid for interest, net of amounts capitalized Interest Paid, Excluding Capitalized Interest, Operating Activity Statement of Cash Flows [Abstract] Statement of Cash Flows [Abstract] Conversion and Redemption of downREIT OP units Conversion and Redemption of downREIT OP units Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Fair Value Hierarchy and NAV [Domain] Fair Value Hierarchy and NAV [Domain] Other, net Other Noncash Income (Expense) Debt Instrument [Line Items] Debt Instrument [Line Items] Capital expenditures - other Capital Expenditures - Other Payments to improve operating real estate that is not included in development or redevelopment. Such improvements may include drainage, utilities, subdividing, access, buildings, and any combination of these elements. Add: Income attributable to downREIT operating partnership units Income attributable to downREIT operating partnership units Income attributable to downREIT operating partnership units Additional Paid-in Capital Additional Paid-in Capital [Member] NET INCOME AVAILABLE FOR COMMON UNIT HOLDERS Net Income (Loss) Allocated to General Partners Entity Filer Category Entity Filer Category Cash and cash equivalents Cash and Cash Equivalent Reconciliation of property operating income to consolidated net income Segment Reporting, Reconciliation of Profit (Loss) by Segment to Consolidated [Table Text Block] Common Units Common Units [Member] Common Units Distribution from partnerships in excess of earnings Proceeds from Distributions Received from Real Estate Partnerships Nature Of Operations [Abstract] Nature Of Operations [Abstract] Nature Of Operations [Abstract] NET INCOME Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Real Estate [Abstract] Real Estate [Abstract] Debt Conversion, Name [Domain] Debt Conversion, Name [Domain] 5.417% Series 1 Cumulative Convertible Preferred Shares, (stated at liquidation preference $25 per share), 392,878 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] Senior Notes Senior Notes [Member] Entity Address, Address Entity Address, Address Line One Operating (including $1,898,790 and $1,832,190 of consolidated variable interest entities, respectively) Rental Properties Net income, excluding amounts attributable to redeemable noncontrolling interests Net Income, excluding amounts attributable to redeemable noncontrolling Interests Net Income (Loss), Including Portion Attributable to Nonredeemable Noncontrolling Interest Principles of Consolidation Consolidation, Policy [Policy Text Block] Increase (decrease) in cash, cash equivalents and restricted cash Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Amount reclassified from other comprehensive income to interest expense Interest Rate Cash Flow Hedge Gain (Loss) Reclassified to Earnings, Net Accounts and notes receivable, net Accounts and Financing Receivable, after Allowance for Credit Loss Earnings allocated to unvested units Earnings allocated to unvested units Earnings allocated to unvested units Anti-dilutive issuable units Antidilutive Securities Excluded from Computation of Net Income, Per Outstanding Unit, units Antidilutive Securities Excluded from Computation of Net Income, Per Outstanding Unit, units Recently Adopted Accounting Pronouncements Accounting Standards Update and Change in Accounting Principle [Text Block] NET INCOME ATTRIBUTABLE TO THE TRUST / PARTNERSHIP Net income attributable to the trust Net Income (Loss) Attributable to Parent Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Unamortized debt issuance costs Unamortized Debt Issuance Expense Statement [Table] Statement [Table] Above market leases Above Market Leases [Member] 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. Exchange rate principal amount Debt Conversion, Converted Instrument, Amount Weighted average unvested units outstanding Incremental common units attributable to participating nonvested shares Incremental common units attributable to participating nonvested shares Debt Instruments [Abstract] Debt Instruments [Abstract] Mortgage notes receivable, net Mortgage Loans on Real Estate, Commercial and Consumer, Net Net borrowings under revolving credit facility Proceeds from (Repayments of) Lines of Credit Add: Dividends on 5.417% Series 1 Cumulative Convertible Preferred Units Dividends on 5.417% Series 1 Cumulative Convertible Preferred Units Dividends on 5.417% Series 1 Cumulative Convertible Preferred Units REVENUE Revenues [Abstract] Stock Options Stock Options [Member] Stock Options