SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Abstract] Real Estate and Accumulated Depreciation, by Property [Table] SEC Schedule III, Real Estate and Accumulated Depreciation, by Property [Table] Name of Property Name of Property [Axis] Name of Property [Domain] Name of Property [Domain] 29th Place 29th Place [Member] 29th Place [Member] Andorra Andorra [Member] Andorra [Member] Assembly Row/Assembly Square Market Place Assembly Square Market Place Assembly Row [Member] Assembly Square Market Place Assembly Row [Member] Atlantic Plaza Atlantic Plaza [Member] Atlantic Plaza Azalea Azalea [Member] Azalea [Member] Bala Cynwyd Bala Cynwyd [Member] Bala Cynwyd [Member] Barcroft Plaza Barcroft Plaza [Member] Barcroft Plaza Barracks Road Barracks Road [Member] Barracks Road [Member] Bell Gardens Bell Gardens [Member] Bell Gardens [Member] Bethesda Row Bethesda Row [Member] Bethesda Row [Member] Brick Plaza Brick Plaza [Member] Brick Plaza [Member] Bristol Plaza Bristol [Member] Bristol [Member] Brook 35 Brook 35 [Member] Brook 35 [Member] Campus Plaza Campus Plaza [Member] Campus Plaza Chelsea Commons Chelsea [Member] Chelsea [Member] CocoWalk CocoWalk [Member] CocoWalk Colorado Blvd Colorado Blvd [Member] Colorado Blvd [Member] Congressional Plaza Congressional Plaza [Member] Congressional Plaza [Member] Courthouse Center Courthouse Center [Member] Courthouse Center [Member] Crossroads Crossroads [Member] Crossroads [Member] Crow Canyon Commons Crow Canyon [Member] Crow Canyon [Member] Darien Darien [Member] Darien [Member] Dedham Plaza Dedham Plaza [Member] Dedham Plaza [Member] Del Mar Village Del Mar Village [Member] Del Mar Village [Member] East Bay Bridge East Bay Bridge [Member] EastBayBridge [Member] Eastgate Crossing Eastgate [Member] Eastgate [Member] Elllisburg Elllisburg Circle [Member] Elllisburg Circle [Member] Escondido Promenade Escondido Promenade [Member] Former Mervyns Parcel, Escondido Promenade [Member] Falls Plaza Falls Plaza [Member] Falls Plaza [Member] Federal Plaza Federal Plaza [Member] Federal Plaza [Member] Finley Square Finley Square [Member] Finley Square [Member] Flourtown Flourtown [Member] Flourtown [Member] Fourth Street Fourth Street [Member] Fourth Street [Member] Free State Shopping Center Free State Shopping Center [Member] Free State Shopping Center Fresh Meadows Fresh Meadows [Member] Fresh Meadows [Member] Friendship Center Friendship Ctr [Member] Friendship Ctr [Member] Gaithersburg Square Gaithersburg Square [Member] Gaithersburg Square [Member] Garden Market Garden Market [Member] Garden Market [Member] Governor Plaza Governor Plaza [Member] Governor Plaza [Member] Graham Park Plaza Graham Park [Member] Graham Park Gratiot Plaza Gratiot Plaza [Member] Gratiot Plaza [Member] Greenlawn Plaza Greenlawn Plaza [Member] Greenlawn Plaza Greenwich Avenue Greenwich Avenue [Member] Greenwich Avenue [Member] Hastings Ranch Plaza Hastings Ranch Plaza [Member] Hastings Ranch Plaza Hauppauge Hauppauge [Member] Hauppauge [Member] Hermosa Avenue Hermosa Ave [Member] Hermosa Ave [Member] Hollywood Blvd. Hollywood Blvd [Member] Hollywood Blvd [Member] Huntington Huntington [Member] Huntington [Member] Huntington Square HuntingtonSquare [Member] Huntington Square [Member] Idylwood Plaza Idylwood Plaza [Member] Idylwood Plaza [Member] Kings Court Kings Court [Member] Kings Court [Member] Lancaster Lancaster [Member] Lancaster [Member] Langhorne Square Langhorne Square [Member] Langhorne Square [Member] Laurel Laurel [Member] Laurel [Member] Lawrence Park Lawrence Park [Member] Lawrence Park [Member] Leesburg Plaza Leesburg Plaza [Member] Leesburg Plaza [Member] Linden Square Linden Square [Member] Linden Square [Member] Melville Mall MelvilleMall [Member] MelvilleMall [Member] Mercer Mall Mercer Mall [Member] Mercer Mall [Member] Montrose Crossing Montrose Crossing [Member] Montrose Crossing [Member] Mount Vernon/South Valley/7770 Richmond Hwy, Mount Vernon [Member] Mount Vernon [Member] North Dartmouth North Dartmouth [Member] North Dartmouth [Member] Northeast Northeast [Member] Northeast [Member] Old Keene Mill Old Keene Mill [Member] Old Keene Mill [Member] Old Town Center Old Town Center [Member] Old Town Center [Member] Olivo at Mission Hills Olivo at Mission Hills [Member] Olivo at Mission Hills [Member] Pan Am Shopping Center Pan Am Shopping Center [Member] Pan Am Shopping Center [Member] Pentagon Row Pentagon Row [Member] Pentagon Row [Member] Perring Plaza Perring Plaza [Member] Perring Plaza [Member] Pike & Rose Pike & Rose [Member] Pike & Rose Pike 7 Pike 7 [Member] Pike 7 [Member] Plaza Del Mercado Plaza Del Mercado [Member] Plaza Del Mercado Plaza Del Sol Plaza Del Sol [Member] Plaza Del Sol [Member] Plaza El Segundo/The Point Plaza El Segundo/The Point [Member] Plaza El Segundo/The Point Plaza Pacoima Plaza Pacoima [Member] Plaza Pacoima [Member] Queen Anne Plaza Queen Anne Plaza [Member] Queen Anne Plaza [Member] Quince Orchard Plaza Quince Orchard Plaza [Member] Quince Orchard Plaza [Member] Riverpoint Center Riverpoint Center [Member] Riverpoint Center [Member] Rockville Town Square Rockville Town Square [Member] Rockville Town [Member] Rollingwood Apts. Rollingwood Apartments [Member] Rollingwood Apartments [Member] Sam's Park and Shop Sams Park and Shop [Member] Sams Park and Shop [Member] San Antonio Center San Antonio Center [Member] San Antonio Center Santana Row Santana Row [Member] Santana Row Saugus Saugus [Member] Saugus [Member] Sylmar Towne Center Sylmar Towne Center [Member] Sylmar Town Center The Avenue at White Marsh THE AVENUE at White Marsh [Member] THE AVENUE at White Marsh [Member] The Grove at Shrewsbury The Grove at Shrewsbury [Member] The Grove at Shrewsbury [Member] The Shoppes At Nottingham Square Shoppes At Nottingham Square [Member] Shoppes At Nottingham Square [Member] The Shops at Sunset Place Sunset Place [Member] Acquisition of the Shops at Sunset Place on 10/1/2015. Third Street Promenade Third Street Promenade [Member] Third Street Promenade [Member] Tower Tower [Member] Tower [Member] Tower Shops Tower Shops January 19 2011 [Member] Tower Shops 1/19/11 [Member] Town Center of New Britain Town Center of New Britain [Member] Town Center of New Britain [Member] Townson Residential Townson Residential [Member] Townson Residential [Member] Troy Troy [Member] Troy [Member] Tyson's Station Tyson Station [Member] Tyson Station [Member] Village at Shirlington Shirlington [Member] Shirlington [Member] Westgate Center Westgate Mall [Member] Westgate Mall [Member] White Marsh Plaza White Marsh Plaza [Member] White Marsh Plaza [Member] White Marsh Other White Marsh Other [Member] White Marsh Other [Member] Wildwood Wildwood [Member] Wildwood [Member] Willow Grove Willow Grove [Member] Willow Grove [Member] Willow Lawn Willow Lawn [Member] Willow Lawn [Member] Wynnewood Wynnewood [Member] Wynnewood [Member] Range [Axis] Range [Axis] Range [Domain] Range [Domain] Minimum Minimum [Member] Maximum Maximum [Member] Real Estate and Accumulated Depreciation [Line Items] SEC Schedule III, Real Estate and Accumulated Depreciation [Line Items] Encumbrances SEC Schedule III, Real Estate and Accumulated Depreciation, Amount of Encumbrances Initial cost to company, Land SEC Schedule III, Real Estate and Accumulated Depreciation, Initial Cost of Land Initial cost to company, Buildings and Improvements SEC Schedule III, Real Estate and Accumulated Depreciation, Initial Cost of Buildings and Improvements Cost Capitalized Subsequent to Acquisition SEC Schedule III, Real Estate and Accumulated Depreciation, Costs Capitalized Subsequent to Acquisition, Carrying Costs Gross amount at which carried at close of period, Land SEC Schedule III, Real Estate and Accumulated Depreciation, Carrying Amount of Land Gross amount at which carried at close of period, Buildings and Improvements SEC Schedule III, Real Estate and Accumulated Depreciation, Carrying Amount of Buildings and Improvements Gross amount at which carried at close of period, Total SEC Schedule III, Real Estate, Gross Accumulated Depreciation and Amortization SEC Schedule III, Real Estate Accumulated Depreciation Life on which depreciation in latest income statements is computed SEC Schedule III, Real Estate and Accumulated Depreciation, Life Used for Depreciation Debt Disclosure [Abstract] Schedule of Long-term Debt Instruments [Table] Schedule of Long-term Debt Instruments [Table] Variable Rate [Axis] Variable Rate [Axis] Variable Rate [Domain] Variable Rate [Domain] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Revolving credit facility Revolving Credit Facility [Member] Term Loan TermLoan [Member] TermLoan [Member] Long-term Debt, Type [Axis] Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Long-term Debt, Type [Domain] Mortgages Payable Secured Debt [Member] Notes Payable Notes Payable, Other Payables [Member] Senior Notes and Debentures Senior Notes [Member] Debt Instrument [Line Items] Debt Instrument [Line Items] Line of credit facility, annual facility fee Line of credit facility, annual facility fee Line of credit facility, annual facility fee Revolving credit facility Long-term Line of Credit Principal balance Long-term Debt, Gross Interest rate Debt Instrument, Interest Rate, Stated Percentage 2018 Long-term Debt, Maturities, Repayments of Principal in Next Twelve Months 2019 Long-term Debt, Maturities, Repayments of Principal in Year Two 2020 Long-term Debt, Maturities, Repayments of Principal in Year Three 2021 Long-term Debt, Maturities, Repayments of Principal in Year Four 2022 Long-term Debt, Maturities, Repayments of Principal in Year Five Thereafter Long-term Debt, Maturities, Repayments of Principal after Year Five Other Notes Payable Other Notes Payable Long-term debt Long-term Debt Disclosure of Compensation Related Costs, Share-based Payments [Abstract] Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward] Outstanding at the beginning of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Number Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Grants in Period, Net of Forfeitures Exercised (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period Forfeited or expired (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Forfeitures and Expirations in Period Outstanding at the end of year (in shares) Exercisable at the end of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Number Outstanding at the beginning 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 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 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 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 Outstanding at the end of year, Weighted-Average Exercise Price (in dollars per share) 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 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 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 Outstanding at the end of year, Aggregate Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding, Intrinsic Value Exercisable at the end of year, Aggregate Intrinsic Value Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercisable, Intrinsic Value Real Estate [Abstract] REAL ESTATE Real Estate Acquisitions Dispositions Text Block Disclosure of real estate acquisitions and dispositions, and at year end, a summary of our real estate investments and related encumbrances. Accounting Policies [Abstract] SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES Significant Accounting Policies [Text Block] Quarterly Financial Information Disclosure [Abstract] Revenue Revenues Operating income Operating Income (Loss) Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest NET INCOME ATTRIBUTABLE TO THE TRUST Net Income (Loss) Attributable to Parent Net income available for common shareholders Net Income (Loss) Available to Common Stockholders, Basic Earnings Per Common Share, Basic Earnings Per Share, Basic Net income available for common shareholders Earnings Per Share, Diluted Savings and Retirement Plans [Abstract] Savings and Retirement Plans [Abstract] Schedule of Deferred Compensation Arrangement with Individual, Postretirement Benefits [Table] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Axis] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Domain] Other Postretirement Benefits, Individual Contracts, Type of Deferred Compensation [Domain] 401(K) and Deferred Compensation Plan Deferred Compensation Arrangement with Individual, by Type of Compensation, Pension and Other Postretirement Benefits [Member] Deferred Compensation Arrangement with Individual, Postretirement Benefits [Line Items] 401(k) Maximum annual contribution per employee Defined Contribution Plan, Maximum Annual Contributions Per Employee, Amount 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 401(k) Maximum of employer match as a percentage of employee eligible earnings Defined Contribution Plan, Employer Matching Contribution, Percent of Employees' Gross Pay 401(k) Employer contribution expense Deferred Compensation Arrangement with Individual, Contributions by Employer Deferred compensation liability to participants Deferred Compensation Arrangement with Individual, Recorded Liability Leases [Abstract] Property Subject to or Available for Operating Lease, by Major Property Class [Table] Real Estate Investments by Property Type [Axis] Real Estate Investments by Property Type [Axis] Real Estate Investments by Property Type [Axis] Real Estate Investments, Property Type [Domain] Real Estate Investments, Property Type [Domain] Real Estate Investments, Property Type [Domain] Retail and commercial Commercial Real Estate [Member] Residential Residential Real Estate [Member] Property Subject to or Available for Operating Lease [Line Items] Number of real estate properties Number of Real Estate Properties Number of states in which entity has properties Number of States in which Entity Operates Number of leases Number Of Leases Number Of Leases Percent of annualized base rent Percent of Annualized Base Rent Maximum Percent of Annualized Base Rent Maximum Operating lease, term Operating Lease, Term Operating Lease, Term Operating Leases, Future Minimum Payments Receivable [Abstract] 2018 Operating Leases, Future Minimum Payments Receivable, Current 2019 Operating Leases, Future Minimum Payments Receivable, in Two Years 2020 Operating Leases, Future Minimum Payments Receivable, in Three Years 2021 Operating Leases, Future Minimum Payments Receivable, in Four Years 2022 Operating Leases, Future Minimum Payments Receivable, in Five Years Thereafter Operating Leases, Future Minimum Payments Receivable, Thereafter Total Operating Leases, Future Minimum Payments Receivable Schedule of minimum future commercial property rentals from noncancelable operating leases Schedule of Future Minimum Rental Payments for Operating Leases [Table Text Block] Debt Instruments [Abstract] Summary of total debt outstanding Schedule of Debt [Table Text Block] Mortgage loans assumed in acquisition Mortgage loans assumed in acquisition [Table Text Block] Mortgage loans assumed in acquisition [Table 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] Schedule of future minimum lease payments and their present value for property under capital leases Schedule of Future Minimum Lease Payments for Capital Leases [Table Text Block] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Award Type [Axis] Award Type [Axis] Equity Award [Domain] Equity Award [Domain] Restricted Stock Restricted Stock [Member] Options Employee Stock Option [Member] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Granted (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Grants in Period Vesting Term Share-based Compensation Arrangement by Share-based Payment Award, Award Vesting Period Schedule of Business Acquisitions and Dispositions, by Acquisition [Table] Schedule of Business Acquisitions, by Acquisition [Table] Primestor Primestor [Member] Primestor [Member] Mortgages Mortgages [Member] Variable Interest Entities [Axis] Variable Interest Entities [Axis] Variable Interest Entity, Classification [Domain] Variable Interest Entity, Classification [Domain] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Axis] Property, Plant and Equipment, Type [Domain] Property, Plant and Equipment, Type [Domain] Land Land [Member] Condominiums Condominiums [Member] Condominiums [Member] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] FRIT/Primestor JV FRIT/Primestor JV [Member] FRIT/Primestor JV Income Statement Location [Axis] Income Statement Location [Axis] Income Statement Location [Domain] Income Statement Location [Domain] General and Administrative Expense General and Administrative Expense [Member] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other Assets Other Assets [Member] Other Liabilities Other Liabilities [Member] 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] Intangible lease assets acquired Leases, Acquired-in-Place [Member] Intangible lease liabilities acquired Lease liabilities [Member] Lease Liabilities [Member] Above Market Leases Above Market Leases [Member] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] Clarion Clarion [Member] Clarion [Member] A building adjacent to our Barcroft Plaza property A building adjacent to our Barcroft Plaza property [Member] A building adjacent to our Barcroft Plaza property Coconut Grove Coconut Grove [Member] Coconut Grove Hastings Ranch Plaza Assembly Row Fourth Street 1700-1730 4th Street [Member] 1700-1730 4th Street [Member] Bell Gardens Bell Gardens Centers [Member] Bell Gardens Centers [Member] La Alameda La Alameda [Member] La Alameda [Member] 150 Post Street 150 Post Street [Member] 150 Post Street [Member] North Lake Commons North Lake Commons [Member] North Lake Commons [Member] Business Acquisition and Disposition Business Acquisition [Line Items] Square footage of real estate property Area of Real Estate Property Purchase Price Business Combination, Consideration Transferred Net assets acquired allocated to intangible lease assets or liabilities Finite-lived Intangible Assets Acquired Net assets acquired allocated to below market leases Below Market Lease, Acquired Number of members with purchase options Number of Members With Purchase Options Number of Members With Purchase Options Ownership percentage in partnership Equity Method Investment, Ownership Percentage Purchase price of real estate acquisition Purchase price of real estate acquisition Purchase price of real estate acquisition Gross value of acquisition Real estate acquisition, gross value Real estate acquisition, gross value Controlling interest percentage Variable Interest Entity, Qualitative or Quantitative Information, Ownership Percentage Noncontrolling interest allocated in acquisition Noncontrolling Interest in Variable Interest Entity Cash paid in acquisition Payments to Acquire Businesses, Gross Mortgage loans assumed with acquisition Noncash or Part Noncash Acquisition, Debt Assumed Gain on acquisition of controlling interest Business Combination, Step Acquisition, Equity Interest in Acquiree, Remeasurement Gain Ownership interest Ownership interest Ownership interest in property Contributions from noncontrolling interests Noncontrolling Interest, Increase from Business Combination Proceeds from sale Sales of Real Estate Gain (Loss) on Sale of Properties Gain (Loss) on Sale of Properties Gain on sale of real estate, net of income taxes Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes Income taxes related to gain on sale Gain (Loss) on Sale of Properties, Applicable Income Taxes Accounts Receivable, Gross Accounts Receivable, Gross Assets held for sale Real Estate Held-for-sale Acquisition costs Business Combination, Acquisition Related Costs Gain on sale of real estate, net of noncontrolling interests Gain (loss) on sale of real estate, net of noncontrolling interests Our share of gain (loss) on sale of real estate, net of noncontrolling interests Purchase price of equity method investment Purchase price of equity method investment Purchase price of equity method investment Mortgage Loan on Unconsolidated Real Estate Property Mortgage Loan on Unconsolidated Real Estate Property Mortgage Loan on Unconsolidated Real Estate Property Our share of unconsolidated mortgage debt Our share of unconsolidated mortgage debt Our share of unconsolidated mortgage debt Asset Acquisitions, Pro Forma depreciation and amortization Asset Acquisitions, Pro Forma depreciation and amortization Asset Acquisitions, Pro Forma depreciation and amortization Asset Acquisitions Pro Forma Revenue Asset Acquisitions Pro Forma Revenue Pro forma revenue as if asset acquisitions happened at the beginning of the period. Asset Acquisitions, Pro Forma Net Inome (Loss) Asset Acquisitions, Pro Forma Net Inome (Loss) Pro Forma net inome (loss) as if the acquisitions had occured at the beginning of the period. Nature Of Operations [Abstract] Nature Of Operations [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. Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Business Acquisition [Axis] gain on sale of real estate gain on sale of real estate [Member] gain on sale of real estate [Member] 150 Post Street And North Lake Commons 150 Post Street And North Lake Commons [Member] 150 Post Street And North Lake Commons [Member] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Income Statement, Balance Sheet and Additional Disclosures by Disposal Groups, Including Discontinued Operations [Line Items] Reversal of warranty reserve Standard and Extended Product Warranty Accrual, Period Increase (Decrease) Gain on sale of real estate Early extinguishment of debt Gain (Loss) on Extinguishment of Debt Earnings Per Share [Abstract] Earnings Per Share Narrative [Table] Earnings Per Share Narrative [Table] Earnings Per Share Narrative [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] 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 excluded from dilutive earnings per share calculation Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Cumulative convertible preferred share, dividend rate Preferred Stock, Dividend Rate, Percentage BUSINESS AND ORGANIZATION Nature of Operations [Text Block] Commitments and Contingencies Disclosure [Abstract] COMMITMENTS AND CONTINGENCIES Commitments and Contingencies Disclosure [Text Block] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Table] New Accounting Pronouncements or Change in Accounting Principle [Line Items] New Accounting Pronouncements or Change in Accounting Principle [Line Items] Cumulative Effect on Retained Earnings, Net of Tax Cumulative Effect on Retained Earnings, Net of Tax Payments Related to Tax Withholding for Share-based Compensation Payments Related to Tax Withholding for Share-based Compensation Cash in excess of the FDIC insured limit Cash, Uninsured Amount Statement of Cash Flows [Abstract] OPERATING ACTIVITIES Net Cash Provided by (Used in) Operating Activities [Abstract] 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] 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. Gain on sale of real estate and change in control of interests, net Gain (loss) on change in control of interests and sale of real estate Gain (loss) on change in control of interests and sale of real estate Early extinguishment of debt Loss (income) from real estate partnerships Income (Loss) from Equity Method Investments Other, net Other Noncash Income (Expense) Changes in assets and liabilities, net of effects of acquisitions and dispositions: Increase (Decrease) in Operating Capital [Abstract] Decrease (increase) in accounts receivable, net Increase (Decrease) in Accounts and Other Receivables Increase in prepaid expenses and other assets Increase (Decrease) in Prepaid Expense and Other Assets Increase (decrease) in accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities Increase (decrease) in security deposits and other liabilities Increase Decrease In Security Deposits And Other Liabilities The net change in Security Deposits And Other Liabilities which includes security deposits, deferred revenue and prepaid rent. Also includes liabilities not individually reported in the financial statements, or not separately disclosed in notes. 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 and real estate partnership interests Proceeds from Sale of Real Estate Held-for-investment Investment in real estate partnerships 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 (Issuance) repayment of mortgage and other notes receivable, net Issuance (Repayments) Of Mortgage And Other Notes Receivable Net The cash outflow from the issuance and purchase of receivables arising from the mortgage note on real estate and other notes receivable, net of repayments. 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 (repayment) under revolving credit facility, net of costs Proceeds from (Repayments of) Lines of Credit 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, net of costs Proceeds from Issuance of Common Stock Issuance of preferred shares, net of costs Proceeds from Issuance of Preferred Stock and Preference Stock 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. Shares withheld for employee taxes Contributions from 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. Distributions to and redemptions of noncontrolling interests Payments for Repurchase of Redeemable Noncontrolling Interest Net cash provided by (used in) 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 year 2018 Capital Leases, Future Minimum Payments Due, Next Twelve Months 2019 Capital Leases, Future Minimum Payments Due in Two Years 2020 Capital Leases, Future Minimum Payments Due in Three Years 2021 Capital Leases, Future Minimum Payments Due in Four Years 2022 Capital Leases, Future Minimum Payments Due in Five Years Thereafter Capital Leases, Future Minimum Payments Due Thereafter Future minimum lease payments Capital Leases, Future Minimum Payments Due Less amount representing interest Capital Leases, Future Minimum Payments, Interest Included in Payments Present value Capital Leases, Future Minimum Payments, Present Value of Net Minimum Payments Fair Value Disclosures [Abstract] Summary of carrying amount and fair value of financial instruments Schedule of Carrying Values and Estimated Fair Values of Debt Instruments [Table Text Block] Summary of financial assets/(liabilities) measured at fair value on a recurring basis Fair Value, Liabilities Measured on Recurring Basis [Table Text Block] Components Of Rental Income and Expense [Abstract] Components Of Rental Income And Expense [Abstract] Straight-line rents Straight Line Rent Net amortization of above and below market leases Amortization of above and below Market Leases OPERATING LEASES Lessor, Operating Leases [Text Block] Statement of Stockholders' Equity [Abstract] Statement [Table] Statement [Table] Common shares Common Stock [Member] Preferred Shares Preferred Stock [Member] Equity Components Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] 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)/Income AOCI Attributable to Parent [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 January 1, 2017 adoption of new accounting standard - See Note 2 Cumulative Effect of New Accounting Principle in Period of Adoption Beginning balance Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest 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. Other comprehensive income (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 Shares issued (in shares) Stock Issued During Period, Shares, New Issues Shares issued Stock Issued During Period, Value, New Issues Exercise of stock options (in shares) 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 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. 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). Shares withheld for employee taxes (in shares) Shares Paid for Tax Withholding for Share Based Compensation Shares withheld for employee taxes Adjustments Related to Tax Withholding for Share-based Compensation 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 Conversion and 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. Purchase of noncontrolling interests Noncontrolling Interest, Decrease from Redemptions or Purchase of Interests Adjustment to redeemable noncontrolling interests Stockholders' Equity, Other Ending balance (in shares) Ending balance Goodwill and Intangible Assets Disclosure [Abstract] Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Schedule of Acquired Finite-Lived Intangible Asset by Major Class [Table] Finite-Lived Intangible Liabilities By Major Class [Axis] Finite-Lived Intangible Liabilities By Major Class [Axis] Finite-Lived Intangible Liabilities By Major Class [Axis] 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] Below Market Leases, Lessor BelowMarketLeasesLessor [Member] Below Market Leases, Lessor Above Market Leases, Lessee Above Market Leases, Lessee [Member] Above Market Leases, Lessee [Member] Leases, Acquired-in-Place Above Market Leases, Lessor AboveMarketLeasesLessor [Member] Above Market Leases, Lessor Below Market Leases, Lessee BelowMarketLeasesLessee [Member] Below Market Leases, Lessee Below Market Lease Below Market Lease [Member] Below Market Lease [Member] Acquired Finite-Lived Intangible Assets [Line Items] Finite-Lived Intangible Assets, Gross Finite-Lived Intangible Assets, Gross Finite-Lived Intangible Assets, Accumulated Amortization Finite-Lived Intangible Assets, Accumulated Amortization Finite-Lived Intangible Liabilities, Gross Finite-Lived Intangible Liabilities, Gross Finite-Lived Intangible Liabilities, Gross Finite-Lived Intangible Liabilities, Accumulated Amortization Finite-Lived Intangible Liabilities, Accumulated Amortization Finite-Lived Intangible Liabilities, Accumulated Amortization Finite-Lived Intangible LIabilities, Net Finite-Lived Intangible LIabilities, Net Finite-Lived Intangible LIabilities, Net Amortization of above market leases, lessor Amortization of Intangible Assets Amortization of below market leases, lessor Amortization of Below Market Lease Net increase in rental income Amortization of Below Market Lease, Lessee Amortization of Below Market Lease, Lessee Amortization of Below Market Lease, Lessee Amortization of above market leases, lessee Amortization Of Intangible Liability Amortization Of Intangible Liability Net increase in rental expense Amortization Of Above And Below Market Leases, Lessee Amortization Of Above And Below Market Leases, Lessee Acquired Finite-lived Intangible Assets, Weighted Average Useful Life Acquired Finite-lived Intangible Assets, Weighted Average Useful Life 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 Acquired Lease Assets Finite-Lived Intangible Assets, Net, Amortization Expense, Fiscal Year Maturity [Abstract] 2018 Finite-Lived Intangible Assets, Amortization Expense, Next Twelve Months 2019 Finite-Lived Intangible Assets, Amortization Expense, Year Two 2020 Finite-Lived Intangible Assets, Amortization Expense, Year Three 2021 Finite-Lived Intangible Assets, Amortization Expense, Year Four 2022 Finite-Lived Intangible Assets, Amortization Expense, Year Five Thereafter Finite-Lived Intangible Assets, Amortization Expense, after Year Five Total future amortization expense from acquired above market leases Finite-Lived Intangible Assets, Net Acquired Lease Liabilities Below Market Lease, Amortization Income, Maturity Schedule [Abstract] 2018 Below Market Lease, Amortization Income, Next Twelve Months 2019 Below Market Lease, Amortization Income, Year Two 2020 Below Market Lease, Amortization Income, Year Three 2021 Below Market Lease, Amortization Income, Year Four 2022 Below Market Lease, Amortization Income, Year Five Thereafter Below Market Lease, Amortization Income, after Year Five Total future amortization expense from acquired below market leases Below Market Lease, Net Volatility Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Volatility Rate Expected dividend yield Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Dividend Rate Expected term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Expected Term Risk free interest rate Share-based Compensation Arrangement by Share-based Payment Award, Fair Value Assumptions, Risk Free Interest Rate Plaza El Segundo Plaza El Segundo [Member] Plaza El Segundo [Member] 3.25% and 4.50% Senior notes offering 3.25 and 4.50 senior notes [Member] 3.25 and 4.50 senior notes 3.25% Senior notes 3.25% Senior notes [Member] 3.25% Senior notes [Member] 4.50% notes 4.50% Senior notes [Member] 4.50% Senior notes 5.90% notes Senior 5.90 Percent Notes [Member] Senior 5.90 Percent Notes [Member] Mortgages Payable Senior Notes Principal balance Repayment of mortgage loan Repayments of Long-term Debt Note Offering Percent Note Offering Percent Note offering percent of principal amount Debt yield to maturity percent Debt Yield To Maturity Percent Debt yield to maturity percent Fair value of mortgage loan Debt Instrument, Fair Value Disclosure Mortgage loans refinanced Refinance of mortgage loan Refinance of mortgage loan Repayments of Senior Debt Make-whole premium Payment for Debt Extinguishment or Debt Prepayment Cost Accrued but unpaid interest Debt Instrument, Increase, Accrued Interest Maximum outstanding under revolving credit facility Line of Credit Facility, Maximum Borrowing Capacity Maximum amount of borrowings outstanding Line of Credit Facility, Maximum Amount Outstanding During Period Weighted average amount of 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. Minimum annual payments Lessee, Operating Lease, Disclosure [Table Text Block] Operating Leases, Future Minimum Payments Due, Fiscal Year Maturity [Abstract] 2018 Operating Leases, Future Minimum Payments Due, Next Twelve Months 2019 Operating Leases, Future Minimum Payments, Due in Two Years 2020 Operating Leases, Future Minimum Payments, Due in Three Years 2021 Operating Leases, Future Minimum Payments, Due in Four Years 2022 Operating Leases, Future Minimum Payments, Due in Five Years Thereafter Operating Leases, Future Minimum Payments, Due Thereafter Total Operating Leases, Future Minimum Payments Due SELECTED QUARTERLY FINANCIAL DATA (UNAUDITED) Quarterly Financial Information [Text Block] EARNINGS PER SHARE Earnings Per Share [Text Block] DEBT Debt Disclosure [Text Block] Property, Plant and Equipment [Table] Property, Plant and Equipment [Table] Building and Building Improvements Building and Building Improvements [Member] Minor Improvements, Furniture and Equipment Minor Improvements, Furniture and Equipment [Member] Minor Improvements, Furniture and Equipment [Member] Property, Plant and Equipment [Line Items] Property, Plant and Equipment [Line Items] Estimated useful lives Property, Plant and Equipment, Useful Life Real estate depreciation expense Depreciation Expense Real Estate Depreciation Expense on Real Estate only Statement of Financial Position [Abstract] 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] 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. Construction-in-progress, consolidated variable interest entities Constructioninprogresofconsolidatedvariableieestentity Construction-in-progress oc consolidated variable interest entity 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. 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 Shares, liquidation preference per share 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 Schedule III - Summary of Real Estate and Accumulated Depreciation SEC Schedule III, Real Estate and Accumulated Depreciation Disclosure [Text Block] SAVINGS AND RETIREMENT PLANS Pension and Other Postretirement Benefits Disclosure [Text Block] Stockholders' Equity Note [Abstract] Schedule of Stock by Class [Table] Schedule of Stock by Class [Table] Preferred Units by Name [Axis] Preferred Units by Name [Axis] Preferred Units, Class [Domain] Preferred Units, Class [Domain] Depository Shares Depository Shares [Member] Depository Shares Subsidiary, Sale of Stock [Axis] Sale of Stock [Axis] Sale of Stock, Name of Transaction [Domain] Sale of Stock [Domain] 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] Other Offering Costs Other Offering Costs [Member] Other Offering Costs [Member] Class of Stock [Line Items] Class of Stock [Line Items] Preferred shares, liquidation preference per share Preferred shares, par value Conversion price per share Convertible Preferred Stock, Conversion Price Per Share Convertible Preferred Stock, Conversion Price Per Share Shares issued Net cash proceeds of common stock Aggregate offering price of common shares Aggregate Offering Price Of Common Share Maximum aggregate offering price of common shares. Weighted average price per common share Weighted Average Price Per Common Share Weighted average price per common share Commissions related to sales of common shares Payments of Stock Issuance Costs Remaining capacity to issue Remaining Capacity To Issue Remaining $ Capacity Of Shares To Issue Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Fair Values Derivatives, Balance Sheet Location, by Derivative Contract Type [Table] Derivative Instrument Derivative Instrument [Axis] Derivative, Name [Domain] Derivative Contract [Domain] Interest Rate Swap Interest Rate Swap [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Fair Value, Measurements, Recurring Fair Value, Measurements, Recurring [Member] Derivatives, Fair Value [Line Items] Derivatives, Fair Value [Line Items] Interest rate swaps associated with cash flow hedges to be reclassified within the next twelve months Interest Rate Cash Flow Hedge Gain (Loss) to be Reclassified During Next 12 Months, Net Number of interest rate swap agreements Number of Interest Rate Derivatives Held Residual profit maximum Residual Profit Maximum Residual Profit Maximum received as additional interest on mortgage note receivable Aggregate tax basis for Federal tax purposes Mortgage Loans on Real Estate, Federal Income Tax Basis Interest Rate Mortgage Loans on Real Estate, Participation Plus Interest Rate, Interest Rate Mortgage Loans on Real Estate, Participation Plus Interest Rate, Interest Rate Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Products and Services [Axis] Products and Services [Domain] Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Operating Leases, Income Statement, Lease Revenue [Abstract] Operating Leases, Income Statement, Lease Revenue [Abstract] 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. Rental Income Operating Leases, Income Statement, Lease Revenue Schedule of earnings per share Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Mortgage Loans on Real Estate [Abstract] Schedule IV - Mortgage Loans on Real Estate Mortgage Loans on Real Estate, by Loan Disclosure [Text Block] Repairs and maintenance Cost of Property Repairs and Maintenance Utilities Utilities Costs Management fees and costs Service Management Costs Payroll Property Payroll Expense Property Payroll Expense related to property management which includes salaries and benefits. Marketing Marketing Expense Insurance Real Estate Insurance Ground rent Ground Rent Expense Ground Rent Expense Bad debt expense Provision for Doubtful Accounts Other operating Other Cost of Operating Revenue Total rental expenses Direct Costs of Leased and Rented Property or Equipment Dividends [Abstract] 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] 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] Rollforward of Redeemable Noncontrolling Interests Increase (Decrease) in Temporary Equity [Roll Forward] Beginning balance Redeemable Noncontrolling Interest, Equity, Carrying Amount Contributions Redeemable Noncontrolling Interests Contributions Redeemable Noncontrolling Interests Contributions Net income Net Income (Loss) Attributable to Redeemable Noncontrolling Interest Distributions & Redemptions Redeemable Noncontrolling Interests Distributions Redeemable Noncontrolling Interests Distributions Change in redemption value Temporary Equity, Other Changes Ending balance Redeemable Noncontrolling Interest, by Legal Entity [Table] Redeemable Noncontrolling Interest, by Legal Entity [Table] Real Estate Property Ownership [Axis] Real Estate Property Ownership [Axis] Real Estate Properties [Domain] Real Estate Properties [Domain] Galaxy/Hollywood Galaxy/Hollywood [Member] Galaxy/Hollywood [Member] Name of Property Redeemable Noncontrolling Interest [Line Items] Redeemable Noncontrolling Interest [Line Items] Payments to Acquire Outstanding Interest Payments to Acquire Outstanding Interest Payments to acquire outstanding interest in partnership Number of downREIT units issued in connection with purchase option Number of downREIT units issued in connection with purchase option Number of downREIT units issued in connection with purchase option Noncontrolling interest percent acquired Percentage of noncontrolling interest acquired Percentage of noncontrolling interest acquired Redemption of redeemable noncontrolling interests Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Accumulated other comprehensive income (loss) Term loan Prepaid expenses and other assets prepaid expenses and other assets [Member] prepaid expenses and other assets Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities [Member] Fair Value, Balance Sheet Grouping, Financial Statement Captions Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Notional amount of interest rate swap agreements Derivative Liability, Notional Amount Term loan Interest rate of variable portion of term loan Derivative, Fixed Interest Rate Fair value of interest rate swaps (less than for 2017) 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 Schedule of principal components of rental income Schedule of Component of Rental Income [Table Text Block] Schedule of Component of Rental Income [Table Text Block] Schedule of minimum rents Schedule Of Minimum Rents Components [Table TextBlock] Schedule of Minimum Rents Components [Table Text Block] 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] The Grove at Shrewsbury (West) Grove at Shrewsbury (WEST) [Member] Grove at Shrewsbury (WEST) [Member] Rollingwood Apartments THE AVENUE at White Marsh THE AVENUE at White Marsh, Due 2021 [Member] THE AVENUE at White Marsh, Due 2021 [Member] The Grove at Shrewsbury (East) Grove at Shrewsbury (East) [Member] Grove at Shrewsbury (East) [Member] Chelsea Revolving credit facility Various Various Notes Payable [Member] Various Notes Payable [Member] 2.55% notes 2.55% Senior Notes [Member] 2.55% Senior Notes [Member] 3.00% notes Senior300PercentNotes [Member] Senior300PercentNotes [Member] 2.75% notes Senior 2 Point 75 Percent Notes [Member] Senior 2 Point 75 Percent Notes [Member] 3.95% notes Senior395percentnotes [Member] Senior395percentnotes [Member] 7.48% debentures Debentures 7.48 Percent [Member] Debentures 7.48 Percent [Member] 6.82% medium term notes Medium Term Notes 6.82 Percent [Member] Medium Term Notes 6.82 Percent [Member] 3.625% Senior notes 3.625% Senior notes [Member] 3.625% Senior notes [Member] Debt Instrument, Basis Spread on Variable Rate Debt Instrument, Basis Spread on Variable Rate Net unamortized (discount)/premium and debt issuance costs Debt Instrument, Unamortized Discount (Premium) and Debt Issuance Costs, Net Mortgages payable Secured Debt Notes payable Notes Payable Net unamortized debt issuance costs Debt Issuance Costs, Net Senior notes and debentures Senior Notes Capital lease obligations Capital Lease Obligations Total debt and capital lease obligations Debt and Capital Lease Obligations Real Estate and Accumulated Depreciation, Carrying Amount of Land and Buildings and Improvements [Abstract] SEC Schedule III, Real Estate, Gross [Abstract] Balance at beginning of year Acquisitions SEC Schedule III, Real Estate, Other Acquisitions Improvements SEC Schedule III, Real Estate, Improvements 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. Balance at end of year Aggregate cost basis for Federal tax purposes SEC Schedule III, Real Estate, Federal Income Tax Basis Reconciliation of Real Estate Accumulated Depreciation [Roll Forward] SEC Schedule III, Reconciliation of Real Estate Accumulated Depreciation [Roll Forward] Balance at beginning of year Additions during period—depreciation and amortization expense SEC Schedule III, Real Estate Accumulated Depreciation, Depreciation Expense Deductions during period—dispositions and retirements of property Real Estate Accumulated Depreciation Dispositions and Retirements Real Estate Accumulated Depreciation Dispositions and Retirements Balance at end of year Summary of real estate investments and related encumbrances Property, Plant and Equipment [Table Text Block] Signficant property acquisition - Primestor Schedule of Real Estate Properties [Table Text Block] Pro Forma Information, Primestor acquisition Business Acquisition, Pro Forma Information [Table Text Block] Amounts attributable to redeemable noncontrolling interest Loss Contingencies [Table] Loss Contingencies [Table] Litigation Status [Axis] Litigation Status [Axis] Litigation Status [Domain] Litigation Status [Domain] Pending Litigation Pending Litigation [Member] Counterparty Name [Axis] Counterparty Name [Axis] Counterparty Name [Domain] Counterparty Name [Domain] Member One In Plaza El Segundo Member One In Plaza El Segundo [Member] Member One In Plaza El Segundo [Member] Member Two In Plaza El Segundo Member Two In Plaza El Segundo [Member] Member Two In Plaza El Segundo [Member] Contractual Obligation [Axis] Contractual Obligation [Axis] Contractual Obligation [Domain] Contractual Obligation [Domain] Capital improvement, development, and redevelopment projects Capital Improvement, Development, And Redevelopment Projects [Member] Capital Improvement, Development, And Redevelopment Projects [Member] Scenario [Axis] Scenario [Axis] Scenario, Unspecified [Domain] Scenario, Unspecified [Domain] Scenario, Forecast Scenario, Forecast [Member] Grove at Shrewsbury and Brook 35 Grove At Shrewsbury And Brook 35 [Member] GroveatShrewsbury & Brook 35 [Member] Option By Type [Axis] Option By Type [Axis] Option By Type [Domain] Option By Type [Domain] Put Option Put Option [Member] Loss Contingencies [Line Items] Settlement amount Litigation Settlement, Amount Awarded to Other Party Additional liability Loss Contingency, Estimate of Possible Loss Number of defendants Loss Contingency, Number of Defendants Reserves for warranties and general liability Standard and Extended Product Warranty Accrual Payments from reserves Standard and Extended Product Warranty Accrual, Decrease for Payments Letters of credit outstanding, amount Letters of Credit Outstanding, Amount Contractual obligations Contractual Obligation Purchase price under option Purchase Price Under Option Purchase Price Under Option 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 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. Estimated maximum liability upon exercise of the put option Estimated Liability Upon Exercise Of Option Estimated Liability Upon Exercise Of Option DownREIT operating partnership units, outstanding Partners' Capital Account, Units Operating partnership units outstanding, fair value Operating Partnership Units Fair Value Fair value of operating partnership units at the balance sheet date. Material unrecognized tax benefits Unrecognized Tax Benefits Number of properties exceeding segment reporting threshold Number of Properties Exceeding Segment Reporting Threshold Number of Properties Exceeding Segment Reporting Threshold Segment reporting threshold Segment Reporting, Factors Used to Identify Entity's Reportable Segments Number of segments Number of Reportable Segments Rollforward table of the redeemable noncontrolling interest Redeemable Noncontrolling Interest [Table Text Block] Schedule of supplemental disclosures related to the Consolidated Statements Of Cash Flows Schedule of Cash Flow, Supplemental Disclosures [Table Text Block] 5.0% Series C Cumulative Redeemable Preferred shares Series C Preferred Stock [Member] 5.417% Series 1 Cumulative Convertible Preferred shares Series 1 Preferred Stock [Member] Series 1 Preferred Stock [Member] ASSETS Assets [Abstract] Operating (including $1,639,486 and $1,211,605 of consolidated variable interest entities, respectively) Rental Properties Construction-in-progress (including $43,393 and $15,313 of consolidated variable interest entities, respectively) Construction in Progress, Gross Real estate, at cost, total Real Estate Investment Property, at Cost Less accumulated depreciation and amortization (including $247,410 and $209,239 of consolidated variable interest entities, respectively) Real Estate Investment Property, Accumulated Depreciation Net real estate Real Estate Investment Property, Net Cash and cash equivalents Accounts and notes receivable Accounts and Notes Receivable, Net Mortgage notes receivable, net Mortgage Loans on Real Estate, Commercial and Consumer, Net Investment in real estate partnerships Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures Prepaid expenses and other assets Prepaid Expense and Other Assets TOTAL ASSETS Assets Liabilities Liabilities [Abstract] Mortgages payable (including $460,372 and $439,120 of consolidated variable interest entities, respectively) 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 Shareholders’ equity Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] 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, 73,090,877 and 71,995,897 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 income (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 Liabilities and Equity Summary of quarterly financial data Quarterly Financial Information [Table Text Block] Income Statement [Abstract] REVENUE Revenues [Abstract] Other property income Other Real Estate Revenue Mortgage interest income Revenue Mortgage Interest Interest income earned from mortgage notes receivable. Total revenue EXPENSES Operating Expenses [Abstract] Rental expenses 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 Other interest income Interest Income, Other Interest expense Interest Expense (Loss) income from real estate partnerships INCOME FROM CONTINUING OPERATIONS Income (Loss) from Continuing Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest Gain on sale of real estate and change in control of interests, net Net income Net income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest NET INCOME ATTRIBUTABLE TO THE TRUST Dividends on preferred shares Preferred Stock Dividends, Income Statement Impact NET INCOME AVAILABLE FOR COMMON SHAREHOLDERS EARNINGS PER COMMON SHARE, BASIC Earnings Per Share, Basic [Abstract] Net income available for common shareholders Weighted average common shares outstanding, basic Weighted Average Number of Shares Outstanding, Basic EARNINGS PER COMMON SHARE, DILUTED Earnings Per Share, Diluted [Abstract] Weighted average number of common shares, diluted Weighted Average Number of Shares Outstanding, Diluted Comprehensive Income Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] COMPREHENSIVE INCOME Comprehensive Income (Loss), Net of Tax, Including Portion Attributable to Noncontrolling Interest Comprehensive income attributable to noncontrolling interests Comprehensive Income (Loss), Net of Tax, Attributable to Noncontrolling Interest COMPREHENSIVE INCOME ATTRIBUTABLE TO THE TRUST Comprehensive Income (Loss), Net of Tax, Attributable to Parent Grants of common shares and options Stock Compensation Plan [Member] Plan Name [Axis] Plan Name [Axis] Plan Name [Domain] Plan Name [Domain] Performance Incentive Plan 2010 Performance Incentive Plan 2010 [Member] Performance Incentive Plan 2010 [Member] Long Term Incentive Plan 2001 Long Term Incentive Plan 2001 [Member] Long Term Incentive Plan 2001 [Member] Number of share-based compensation plans Number Of Share Based Compensation Plans Number Of Share Based Compensation Plans with outstanding grants Number of shares authorized Share-based Compensation Arrangement by Share-based Payment Award, Number of Shares Authorized Contractual term (in years) Share-based Compensation Arrangement by Share-based Payment Award, Expiration Period Number of options granted in period 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 Total cash received from options exercised Proceeds from Stock Options Exercised Total intrinsic value of options exercised Share-based Compensation Arrangement by Share-based Payment Award, Options, Exercises in Period, Intrinsic Value 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 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 Total unrecognized compensation cost related to unvested share-based compensation arrangements Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized 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 Weighted-average period for recognition Employee Service Share-based Compensation, Nonvested Awards, Compensation Cost Not yet Recognized, Period for Recognition Principles of Consolidation Consolidation, Policy [Policy Text Block] Use of Estimates Use of Estimates, Policy [Policy Text Block] 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. Real Estate Property, Plant and Equipment, Policy [Policy Text Block] Cash and Cash Equivalents Cash and Cash Equivalents, Policy [Policy Text Block] 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. Debt Issuance Costs Debt, Policy [Policy Text Block] Derivative Instruments Derivatives, Policy [Policy Text Block] Mortgage Notes Receivable Finance, Loan and Lease Receivables, Held-for-investment, Policy [Policy Text Block] Share Based Compensation Share-based Compensation, Option and Incentive Plans Policy [Policy Text Block] Variable Interest Entities Consolidation, Variable Interest Entity, Policy [Policy Text Block] Redeemable Noncontrolling Interests Redeemable Noncontrolling Interests [Policy Text Block] Redeemable Noncontrolling Interests [Policy Text Block] Income Taxes Income Tax, Policy [Policy Text Block] Segment Information Segment Reporting, Policy [Policy Text Block] Recent Accounting Pronouncements New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Recent Accounting Pronouncements New Accounting Pronouncements, Policy [Policy Text Block] COMPONENTS OF RENTAL INCOME AND EXPENSE Operating Leases Revenue And Expense Text Block The principal components of rental income and/or rental expense recognized for the period. Schedule of Variable Interest Entities [Table] Schedule of Variable Interest Entities [Table] Unconsolidated variable interest entities Unconsolidated Properties [Member] Variable Interest Entity [Line Items] Variable Interest Entity [Line Items] 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. Net real estate assets of consolidated VIEs Variable Interest Entity, Consolidated, Carrying Amount, Assets and Liabilities, Net Mortgage Payable From Consolidated Variable Interest Entities Maximum exposure to loss in variable interest entity Variable Interest Entity, Reporting Entity Involvement, Maximum Loss Exposure, Amount Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number of Shares [Roll Forward] Unvested at the beginning of year (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Nonvested, Number Vested (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Vested in Period Forfeited (in shares) Share-based Compensation Arrangement by Share-based Payment Award, Equity Instruments Other than Options, Forfeited in Period Unvested at the end of year (in shares) Unvested at the beginning 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 Granted, Weighted-Average Grant-Date Fair Value (in dollars per share) 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 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 Unvested at the end of year, Weighted-Average Grant-Date Fair Value (in dollars per share) 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 Property Subject to or Available for Operating Lease, by Major Property Class [Table] Assembly Row and Pike & Rose Assembly Row and Pike & Rose [Member] Assembly Row and Pike & Rose [Member] Property Subject to or Available for Operating Lease [Line Items] Number of Units in Real Estate Property Number of Units in Real Estate Property Allowance for doubtful accounts Allowance for Doubtful Accounts Receivable Collection of accounts receivable, period Straight Line Rents Collection Of Accounts Receivable Period Straight Line Rents, Collection Of Accounts Receivable, Period Accounts receivable related to straight-line rents Deferred Rent Receivables, Net Common shares, declared Common Stock, Dividends, Per Share, Declared Common shares, paid Common Stock, Dividends, Per Share, Cash Paid Preferred shares, declared Preferred Stock, Dividends Per Share, Declared Preferred shares, paid Preferred Stock, Dividends, Per Share, Cash Paid Common shares, ordinary dividend Common Stock, Ordinary Dividends, Per Share, Cash Paid Common Stock, Ordinary Dividends, Per Share, Cash Paid Common shares, capital gain Common Stock, Capital Gain Dividends, Per Share, Cash Paid Common Stock, Capital Gain Dividends, Per Share, Cash Paid 5.417% Series 1 Cumulative Convertible Preferred shares, ordinary dividend Preferred Stock, Ordinary Dividends, Per Share, Cash Paid Preferred Stock, Ordinary Dividends, Per Share, Cash Paid 5.417% Series 1 Cumulative Convertible Preferred shares, capital gain Preferred Stock, Capital Gain Dividends, Per Share, Cash Paid Preferred Stock, Capital Gain Dividends, Per Share, Cash Paid Common Stock, Ordinary Dividends, Tax Rate Common Stock, Ordinary Dividends, Tax Rate Common Stock, Ordinary Dividends, Tax Rate Preferred Stock, Ordinary Dividends, Tax Rate Preferred Stock, Ordinary Dividends, Tax Rate Preferred Stock, Ordinary Dividends, Tax Rate Mortgages payable and notes payable Mortgages Payable And Notes Payable [Member] Mortgages Payable And Notes Payable [Member] Senior notes and debentures Senior Notes And Debentures [Member] Senior Notes And Debentures [Member] Measurement Basis [Axis] Fair Value Measurement [Domain] Portion at Fair Value Measurement Portion at Fair Value Measurement [Member] Carrying Value Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] Fair value of long-term debt Long-term Debt, Fair Value Mortgage Loans on Real Estate Schedule [Table] Mortgage Loans on Real Estate Schedule [Table] Interest Rate [Axis] Interest Rate [Axis] Interest Rate [Axis] Interest Rate [Domain] Interest Rate [Domain] Interest Rate [Domain] Interest Rate One Interest Rate One [Member] Interest Rate One [Member] Interest Rate Two Interest Rate Two [Member] Interest Rate Two [Member] Mortgage Loans on Real Estate, Description, Type of Property [Axis] Real Estate, Type of Property [Axis] Mortgage Loans on Real Estate, Name, Property Type [Domain] Real Estate [Domain] 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] 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] Mortgage Loans on Real Estate, Description, Loan Category [Axis] Mortgage Loans on Real Estate, Description, Loan Category [Axis] Mortgage Loans on Real Estate, Loan Category [Domain] Mortgage Loans on Real Estate, Loan Category [Domain] Mortgage Loans on Real Estate [Line Items] Mortgage Loans on Real Estate [Line Items] Prior Liens Mortgage Loans on Real Estate, Prior Liens Face Amount of Mortgages Mortgage Loans on Real Estate, Face Amount of Mortgages Carrying Amount of Mortgages Mortgage Loans on Real Estate, Carrying Amount of Mortgages Principal Amount of Loans Subject to delinquent Principal or Interest Mortgage Loans on Real Estate, Principal Amount of Delinquent Loans Mortgage Loans on Real Estate, Other Required Disclosures [Abstract] Mortgage Loans on Real Estate, Other Required Disclosures [Abstract] Movement in Mortgage Loans on Real Estate [Roll Forward] Movement in Mortgage Loans on Real Estate [Roll Forward] Balance at beginning of year Mortgage Loans on Real Estate Issuance of loans Mortgage Loans on Real Estate, New Mortgage Loans Collection and satisfaction of loans Mortgage Loans on Real Estate, Collections of Principal Amortization of discount Mortgage Loans on Real Estate, Amortization of Premium Balance at end of year 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 Trading Symbol Trading Symbol Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Entity Well-known Seasoned Issuer Entity Well-known Seasoned Issuer Entity Voluntary Filers Entity Voluntary Filers Entity Current Reporting Status Entity Current Reporting Status Entity Public Float Entity Public Float ACQUIRED IN-PLACE LEASES Intangible Assets Disclosure [Text Block] Schedule of Finite-Lived Intangible Assets [Table Text Block] Schedule of Finite-Lived Intangible Assets [Table Text Block] Finite-lived Intangible Assets Amortization Expense [Table Text Block] Finite-lived Intangible Assets Amortization Expense [Table Text Block] 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] SHARE-BASED COMPENSATION PLANS Disclosure of Compensation Related Costs, Share-based Payments [Text Block] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Level 1 Fair Value, Inputs, Level 1 [Member] Level 2 Fair Value, Inputs, Level 2 [Member] Level 3 Fair Value, Inputs, Level 3 [Member] Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Fair value of interest rate swaps SHAREHOLDERS’ EQUITY Stockholders' Equity Note Disclosure [Text Block] Income from continuing operations Less: Preferred share dividends Less: Income from continuing operations attributable to noncontrolling interests Net income attributable to noncontrolling interests, net of amounts from gain on real estate Net income attributable to noncontrolling interests, net of amounts from gain on real estate 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. Gain on sale of real estate and change in control of interests, net Gain (loss) on change in control of interests and sale of real estate, net Gain (loss) on change in control of interests and sale of real estate, net of noncontrolling interests 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 Stock options Incremental Common Shares Attributable to Dilutive Effect of Share-based Payment Arrangements Weighted average common shares outstanding—diluted Earnings Per Common Share, Diluted Income from continuing operations attributable to the Trust Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent FAIR VALUE OF FINANCIAL INSTRUMENTS Fair Value Disclosures [Text Block] 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. Schedule of Operating Leased Assets [Table] Schedule of Operating Leased Assets [Table] Operating Leased Assets [Line Items] Operating Leased Assets [Line Items] Supplemental Cash Flow Information [Abstract] Total interest costs incurred Interest Costs Incurred Interest capitalized Interest Costs Capitalized Adjustment Interest expense Cash paid for interest, net of amounts capitalized Interest Paid, Net Cash paid for income taxes Income Taxes Paid, Net NON-CASH INVESTING AND FINANCING TRANSACTIONS: Cash Flow, Noncash Investing and Financing Activities Disclosure [Abstract] DownREIT operating partnership units issued with acquisition ValueofdownREITOperatingPartnershipUnitsIssuedinConnectionwithBusinessAcquisition Value of downREIT Operating Partnership Units Issued in Connection with Business Acquisition DownREIT operating partnership units redeemed for common shares Redemptionofoperatingpartnershipunitsforcommonshares Redemption of operating partnership units for common shares Shares issued under dividend reinvestment plan Dividends Reinvested in Noncash Financing Transaction Dividends reinvested in noncash financing transaction Summary of share-based compensation expense Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Summary of weighted average assumptions used to value options granted Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block] Summary of option activity Share-based Compensation, Stock Options, Activity [Table Text Block] Summary of restricted share activity Schedule of Share-based Compensation, Restricted Stock and Restricted Stock Units Activity [Table Text Block] Schedule of common shares awarded under various compensation plans Disclosure of Share-based Compensation Arrangements by Share-based Payment Award [Table Text Block] Schedule of Real Estate Properties [Table] Schedule of Real Estate Properties [Table] Retail and mixed-use properties Retail And Mixed-Use Properties [Member] Retail And Mixed-Use Properties [Member] Retail properties under capital leases Retail Properties Under Capital Leases [Member] Retail Properties Under Capital Leases [Member] Residential Real Estate Properties [Line Items] Real Estate Properties [Line Items] Cost Accumulated Depreciation and Amortization