Document and Entity Information Abstract Document And Entity Information Statement [Table] Statement [Line Items] Document Type Amendment Flag Document Period End Date Document Fiscal Year Focus Document Fiscal Period Focus Trading Symbol Entity Registrant Name Entity Central Index Key Current Fiscal Year End Date Entity Filer Category Entity Common Stock, Shares Outstanding Consolidated Balance Sheets ASSETS Assets Operating (including $97,265 and $68,643 of consolidated variable interest entities, respectively) Operating (including $139,785 and $78,846 of consolidated variable interest entities, respectively) Construction-in-progress Real Estate Held-for-sale Assets held for sale/disposal (discontinued operations) (including $0 and $18,311 of consolidated variable interest entities, respectively) Real Estate Investment Property, at Cost Real Estate Investment Property, At Cost, Total Less accumulated depreciation and amortization (including $3,803 and $3,053 of consolidated variable interest entities, respectively) Less accumulated depreciation and amortization (including $5,329 and $4,431 of consolidated variable interest entities, respectively) Less accumulated depreciation and amortization (including $5,329 and $4,431 of consolidated variable interest entities, respectively Net real estate Real estate, net Net real estate Cash and cash equivalents Cash and cash equivalents at end of period Cash and cash equivalents at beginning of year Cash and Cash Equivalents, at Carrying Value, Total Cash Accounts and notes receivable, net Accounts and Notes Receivable, Net, Total Mortgage notes receivable, net Mortgage Loans on Real Estate, Commercial and Consumer, Net, Total Investment in real estate partnerships Our investment in real estate partnership Investments in and Advance to Affiliates, Subsidiaries, Associates, and Joint Ventures, Total Investment in Partnership Prepaid expenses and other assets Prepaid Expense and Other Assets, Total Debt issuance costs, net of accumulated amortization of $8,545 and $8,291, respectively Debt issuance costs, net of accumulated amortization of $9,467 and $9,075, respectively Deferred Finance Costs, Net, Total Total assets TOTAL ASSETS TOTAL ASSETS Liabilities Mortgages payable (including $22,946 and $23,417 of consolidated variable interest entities, respectively) Mortgages payable Secured Debt, Total Mortgages payable (including $22,455 and $22,785 of consolidated variable interest entities, respectively) Capital lease obligations Capital Lease Obligations, Total Notes payable Notes Payable, Total Senior notes and debentures Senior notes and debentures, carrying value Senior Notes, Total Fixed senior notes Accounts payable and accrued expenses Accounts Payable and Accrued Liabilities, Total Dividends payable Security deposits payable Other liabilities & deferred credits which includes deferred revenue, prepaid rent and below market leases. Also includes liabilities not individually reported in the financial statements, or not separately disclosed in notes. Other liabilities and deferred credits Total liabilities Total liabilities Commitments and contingencies (Note 8) Stockholders' Equity, Including Portion Attributable to Noncontrolling Interest [Abstract] Shareholders' equity Preferred shares, authorized 15,000,000 shares, $.01 par: 5.417% Series 1 Cumulative Convertible Preferred Shares, (stated at liquidation preference $25 per share), 399,896 shares issued and outstanding Preferred Stock, Value, Issued, Ending Balance Preferred Stock, Value, Issued, Beginning Balance Preferred shares, authorized 15,000,000 shares, $.01 par: 5.417% Series 1 Cumulative Convertible Preferred Shares, (stated at liquidation preference $25 per share), 399,896 shares issued and outstanding Preferred Stock, Value, Issued, Total Common shares of beneficial interest, $.01 par, 100,000,000 shares authorized, 61,451,155 and 61,242,050 shares issued and outstanding, respectively Common Stock, Value, Issued, Ending Balance Common Stock, Value, Issued, Beginning Balance Common shares of beneficial interest, $.01 par, 100,000,000 shares authorized, 62,798,348 and 61,526,418 shares issued and outstanding, respectively Common Stock, Value, Issued, Total Additional Paid in Capital, Common Stock Additional Paid in Capital, Common Stock, Ending Balance Additional Paid in Capital, Common Stock, Beginning Balance Additional paid-in capital Accumulated Distributions in Excess of Net Income Accumulated dividends in excess of net income Total shareholders' equity of the Trust Stockholders' Equity Attributable to Parent, Ending Balance Stockholders' Equity Attributable to Parent, Beginning Balance Total shareholders' equity of the Trust Stockholders' Equity Attributable to Noncontrolling Interest Stockholders' Equity Attributable to Noncontrolling Interest, Ending Balance Stockholders' Equity Attributable to Noncontrolling Interest, Beginning Balance Stockholders' Equity Attributable to Noncontrolling Interest, Total Noncontrolling interests Total shareholders' equity Ending balance Beginning balance Total shareholders' equity TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY TOTAL LIABILITIES AND SHAREHOLDERS' EQUITY Total liabilities and partners' capital Operating real estate balances from variable interest entities, or VIEs, for the periods presented. Operating Real Estate From Consolidated Variable Interest Entities Operating, consolidated variable interest entities Assets held for disposal balances from variable interest entities, or VIEs, for the periods presented. Assets Held For Disposal From Consolidated Variable Interest Entities Assets held for sale/disposal (discontinued operations), consolidated variable interest Accumulated Depreciation And Amortization, Consolidated Variable Interest Entities. Accumulated depreciation and amortization, consolidated variable interest entities Debt issuance costs, accumulated amortization Mortgages payable balances from variable interest entities, or VIEs, for the periods presented. Mortgage Payable From Consolidated Variable Interest Entities Mortgages payable, consolidated variable interest entities Preferred shares, authorized Preferred shares, par Preferred shares, par Preferred Stock, Dividend Rate, Percentage Preferred shares, percentage Cumulative convertible preferred shares, dividend rate Preferred shares, 5.417% Series 1 Cumulative Convertible liquidation preference Preferred shares, shares issued Preferred Stock, Shares Issued, Total Preferred shares, shares outstanding Preferred Stock, Shares Outstanding, Ending Balance Preferred Stock, Shares Outstanding, Beginning Balance Common shares of beneficial interest, par Common shares of beneficial interest, shares authorized Common shares of beneficial interest, shares issued Common stock shares issued Common Stock, Shares, Issued, Total Common shares of beneficial interest, shares outstanding Common Stock, Shares, Outstanding, Ending Balance Common Stock, Shares, Outstanding, Beginning Balance Consolidated Statements Of Operations REVENUE The total amount of rental revenue recognized for the period from real estate operations, including minimum rent, straight-line rent, percentage rent and tenant reimbursements. Rental income Total rental income Total rental income Other property income Interest income earned from mortgage notes receivable. Revenue Mortgage Interest Mortgage interest income Total revenue Total revenue Revenue EXPENSES Rental expenses Real estate taxes General and administrative General and Administrative Expense, Total Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction, Total Total operating expenses Total expenses Total operating expenses OPERATING INCOME OPERATING INCOME Other interest income Interest expense Interest expense Interest expense Interest expense Interest expense Interest Expense, Total Early extinguishment of debt Early extinguishment of debt Gains (Losses) on Extinguishment of Debt, Total Income from early extinguishment of debt Income from real estate partnerships Income from real estate partnerships Our share of net income from real estate partnership Income (Loss) from Equity Method Investments, Total Income Loss From Continuing Operations Including Portion Attributable To Noncontrolling Interest Income from continuing operations INCOME FROM CONTINUING OPERATIONS Income (Loss) from Discontinued Operations, Net of Tax, Including Portion Attributable to Noncontrolling Interest [Abstract] DISCONTINUED OPERATIONS Discontinued operations-income Discontinued operations - income Discontinued Operation, Income (Loss) from Discontinued Operation During Phase-out Period, Net of Tax, Total Income from discontinued operations Gain(loss) resulting from the deconsolidation of a variable interest entity Discontinued Operation Gain On Deconsolidation Of Variable Interest Entity Gain on deconsolidation of VIE Discontinued operations - gain on deconsolidation of VIE Gain on deconsolidation of VIE Discontinued Operation Gain Loss on Disposal of Discontinued Operation Net of Tax Discontinued operation - gain on sale of real estate Discontinued Operation, Gain (Loss) on Disposal of Discontinued Operation, Net of Tax, Total Discontinued operation (less then) - gain on sale Income Loss from Discontinued Operations Net of Tax Results from discontinued operations Results from discontinued operations Income (loss) from discontinued operations Income Loss Before Gain or Loss on Sale of Properties Extraordinary Items and Cumulative Effects of Accounting Changes INCOME BEFORE GAIN ON SALE OF REAL ESTATE Income Loss Before Gain Or Loss On Sale Of Properties Extraordinary Items And Cumulative Effects Of Accounting Changes Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes Gain on sale of real estate property, net Gain (Loss) on Sale of Properties, Net of Applicable Income Taxes, Total Gain on sale of real estate Net income Net income/Comprehensive income NET INCOME Less: Net income attributable to noncontrolling interests Net income attributable to noncontrolling interests Net Income (Loss) Attributable to Noncontrolling Interest, Total NET INCOME ATTRIBUTABLE TO THE TRUST NET INCOME ATTRIBUTABLE TO THE TRUST Income from continuing operations attributable to the Trust Preferred Stock Dividends, Income Statement Impact Dividends on preferred shares NET INCOME AVAILABLE FOR COMMON SHAREHOLDERS NET INCOME AVAILABLE FOR COMMON SHAREHOLDERS EARNINGS PER COMMON SHARE, BASIC Income (Loss) from Continuing Operations, Per Basic Share Income (Loss) from Continuing Operations, Per Outstanding Share, Total Continuing operations Income (Loss) from Discontinued Operations, Net of Tax, Per Basic Share Income (Loss) from Discontinued Operations, Net of Tax, Per Outstanding Share, Total Discontinued operations Gain On Sale Of Real Estate Per Basic Share. Gain on Sale of Real Estate per Basic Share Gain on sale of real estate Earnings Per Share, Basic Earnings Per Share, Basic, Total EARNINGS PER COMMON SHARE, DILUTED Income (Loss) from Continuing Operations, Per Diluted Share Continuing operations Income (Loss) from Discontinued Operations, Net of Tax, Per Diluted Share Income (Loss) from Discontinued Operations, Net of Tax, Per Diluted Share, Total Discontinued operations Gain On Sale Of Real Estate Per Diluted Share. Gain on Sale of Real Estate per Diluted Share Gain on sale of real estate Earnings Per Share, Diluted Earnings Per Share, Diluted, Total Consolidated Statement Of Shareholders' Equity Statement, Equity Components [Axis] Equity Component [Domain] Preferred Shares [Member] Common Shares [Member] Additional Paid-in Capital [Member] Accumulated Dividends in Excess of Net Income [Member] Noncontrolling Interests [Member] Shares, Outstanding Ending balance (in shares) Beginning balance (in shares) Dividends declared to common shareholders Dividends declared to common shareholders Dividends declared to preferred shareholders Dividends declared to preferred shareholders Distributions declared to noncontrolling interests Distributions declared to noncontrolling interests Common shares issued (in shares) Shares issued under equity program Common shares issued Exercise of stock options (in shares) Stock options Exercise of stock options Shares issued under dividend reinvestment plan (in shares) Shares issued under dividend reinvestment plan 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 Shares Share-based compensation expense, net (in shares) 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). Share Based Compensation Expense Net Value Share-based compensation expense, net Decrease in noncontrolling interest as a result of redeeming, purchasing and/or converting to common stock the interests of Operating Partnership Units. Conversion And Redemption Of Operating Partnership Units Conversion and redemption of OP units Noncontrolling Interest, Decrease from Deconsolidation Deconsolidation of VIE Consolidated Statements Of Cash Flows OPERATING ACTIVITIES Adjustments to reconcile net income to net cash provided by operating activities The cash flow addback for the non-cash expense of depreciation and amortization including depreciation and amortization related to discontinued operations. Adjustment Depreciation And Amortization Depreciation and amortization, including discontinued operations Gain (Loss) on Sale of Properties Gain on sale of real estate Other, net Other Noncash Income (Expense), Total Changes in assets and liabilities, net of effects of acquisitions and dispositions: Changes in assets and liabilities, net of effects of acquisitions and dispositions Decrease in accounts receivable (Increase) decrease in accounts receivable Increase in prepaid expenses and other assets Decrease in prepaid expenses and other assets Decrease in prepaid expenses and other assets Increase (Decrease) in Prepaid, Deferred Expense and Other Assets, Total (Decrease) increase in accounts payable and accrued expenses Decrease in accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities, Total 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. Increase Decrease In Security Deposits And Other Liabilities (Decrease) increase in security deposits and other liabilities Decrease in security deposits and other liabilities Net cash provided by operating activities Net cash provided by operating activities INVESTING ACTIVITIES Acquisition of real estate Acquisition of real estate Payments to Acquire Real Estate, Total 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 Development Redevelopment Capital expenditures - development and redevelopment Capital expenditures-development and redevelopment Capital expenditures-other Capital expenditures - other Proceeds From Sale of Real Estate Heldforinvestment Proceeds from sale of real estate Proceeds from sale of real estate Proceeds from Sale of Real Estate Held-for-investment, Total Proceeds from sale of real estate Payments to Acquire Interest in Subsidiaries and Affiliates Investment in real estate partnerships Payments to Acquire Interest in Subsidiaries and Affiliates, Total Distribution from real estate partnership in excess of earnings Leasing costs Leasing costs 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. Issuance And Repayments Of Mortgage And Other Notes Receivable Net Repayment (issuance) of mortgage and other notes receivable, net Issuance of mortgage and other notes receivable, net Repayment (issuance) of mortgage and other notes receivable, net Net cash used in investing activities Net cash used in investing activities FINANCING ACTIVITIES The net cash inflow (outflow) from a contractual arrangement with the lender, including letter of credit, standby letter of credit and revolving credit arrangements, under which borrowings can be made up to a specific amount at any point in time with either short term or long term maturity net of costs incurred. Proceeds From Repayments Of Credit Facility Net borrowings under revolving credit facility, net of costs Issuance of senior notes, net of costs Purchase and retirement of senior notes Purchase and retirement of senior notes Repayments of Senior Debt, Total Repayment of senior notes Proceeds From Issuance of Long Term Debt and Capital Securities Net Issuance of mortgages, capital leases and notes payable, net of costs Proceeds from Issuance of Long-term Debt and Capital Securities, Net, Total Repayment of mortgages, capital leases and notes payable Repayment of mortgages, capital leases and notes payable Repayments of Long-term Debt, Long-term Capital Lease Obligations, and Capital Securities, Total Issuance of common shares Net cash proceeds of common stock The cash outflow from distribution of an entity's earnings to common and preferred stockholders. Dividends Paid To Common And Preferred Shareholders Dividends paid to common and preferred shareholders Distributions to noncontrolling interests Distributions to noncontrolling interests Net cash (used in) provided by financing activities Net cash used in financing activities (Decrease) increase in cash and cash equivalents Increase (decrease) in cash and cash equivalents Nature Of Operations [Abstract] Business And Organization Nature of Operations [Text Block] Business And Organization Summary Of Significant Accounting Policies Significant Accounting Policies [Text Block] Summary Of Significant Accounting Policies Real Estate Disclosure of real estate acquisitions, dispositions and discontinued operations and at year end, a summary of our real estate investments and related encumbrances. Real Estate Acquisitions Dispositions Discontinued Operations Text Block REAL ESTATE Real Estate Mortgage Notes Receivable Disclosure [Abstract] Mortgage Notes Receivable Loans Notes Trade And Other Receivables Disclosure Text Block Mortgage Notes Receivable MORTGAGE NOTES RECEIVABLE Real Estate Partnerships Equity Method Investments Disclosure Text Block Real Estate Partnerships REAL ESTATE PARTNERSHIPS Debt Debt Disclosure Text Block Debt Fair Value Of Financial Instruments Fair Value Disclosures Text Block Fair Value Of Financial Instruments Commitments And Contingencies Commitments And Contingencies Disclosure Text Block Commitments And Contingencies Shareholders' Equity Stockholders' Equity Note Disclosure [Text Block] Shareholders' Equity SHAREHOLDERS' EQUITY Components Of Rental Income And Expense [Abstract] Components Of Rental Income The principal components of rental income and/or rental expense recognized for the period. Operating Leases Revenue And Expense Text Block COMPONENTS OF RENTAL INCOME AND EXPENSE Components Of Rental Income Discontinued Operations Disposal Groups Including Discontinued Operations Disclosure Text Block Discontinued Operations DISCONTINUED OPERATIONS Share Based Compensation Plans Disclosure Of Compensation RelatedCosts Share Based Payments Text Block Share-Based Compensation Plans SHARE-BASED COMPENSATION PLANS Earnings Per Share Earnings Per Share Earnings Per Share Text Block Earnings Per Share EARNINGS PER SHARE Subsequent Event Subsequent Events [Text Block] Subsequent Event Consolidation, Policy [Policy Text Block] Principles of Consolidation Use of Estimates, Policy [Policy Text Block] Use of Estimates Business Combinations Policy [Policy Text Block] Acquisition Of Real Estate Cash Flow, Supplemental Disclosures [Text Block] Schedule Of Supplemental Disclosures Related To Consolidated Statements Of Cash Flows Schedule Of Balance Sheets and Operating Results Of Unconsolidated Joint Ventures [Table Text Block] Schedule Of Balance Sheets and Operating Results Of Unconsolidated Joint Ventures [Table Text Block] Summarized Operating Results And Financial Position Of Partnership Schedule of Carrying Amount and Fair Value of Financial Instruments [Table Text Block] Schedule of Carrying Amount and Fair Value of Financial Instruments [Table Text Block] Summary Of Carrying Amount And Fair Value Of Financial Instruments Schedule of Dividends Declared and Paid Per Share [Table Text Block] Schedule of Dividends Declared and Paid Per Share [Table Text Block] Summary Of Dividends Declared And Paid Per Share Schedule of Component of Rental Income [Table Text Block] Schedule of Component of Rental Income [Table Text Block] Schedule Of Principal Components Of Rental Income Schedule of Minimum Rents Components [Table Text Block] Schedule Of Minimum Rents Components [Table TextBlock] Schedule of Minimum Rents Components Schedule Of Discontinued Operations Financial Information Table Text Block Schedule Of Discontinued Operations Financial Information Table Text Block Summary Of The Financial Information For The Discontinued Operations Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table Text Block] Summary Of Share Based Compensation Expense Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Schedule Of Earnings Per Share Number of Real Estate Properties Number of real estate projects owned Total number of properties in the portfolio Minimum percentage of taxable income distributed to shareholders. Minimum Percentage Of Taxable Income Distributed To Shareholders Percentage of taxable income distributed to shareholders Interest Costs Incurred Total interest costs incurred Interest Costs Incurred, Total Interest Costs, Capitalized During Period Interest capitalized Interest Paid, Net Interest Paid, Net, Total Cash paid for interest, net of amounts capitalized Income Taxes Paid, Net Cash paid for income taxes Income Taxes Paid, Net, Total Loans Assumed Mortgage loan assumed with acquisition Non-cash investing amount related to the deconsoliation of a variable interest entity. NonCash Deconsolidation Of Variable Interest Entity Deconsolidation of VIE Schedule of Business Acquisitions, by Acquisition [Table] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Tower Shops [Member] Tower Shops [Member] Feasterville Shopping Center [Member] Feasterville Shopping Center [Member] Month, date and year in which the reverse Section 1031 like-kind exchange agreement ended. Business Acquisition Section 1031 Agreement End Date Business Acquisition, Effective Date of Acquisition Date of acquisition of leasehold interest Date of acquisition of Newbury Street partnership property The purchase price of the acquired entity. Business Acquisition Purchase Price Purchase price of leasehold property Acquisition of real estate Debt Instrument, Face Amount Mortgage loan face amount Mortgage loan face amount Debt Instrument, Fair Value Disclosure Mortgage loan fair value Square Footage of Real Estate Property Leasable area (square feet) Gross leasable area (square feet) Acres of Real Estate Property Acres of Real Estate Property Acres of real estate property Business Acquisition, Purchase Price Allocation, Amortizable Intangible Assets Purchase price allocation, other assets The amount of acquisition cost of a business combination allocated to below market lease liabilities that will be amortized. Business Acquisition Purchase Price Allocation Amortizable Intangible Below Market Lease Liabilities Purchase price allocation, liabilities Business Combination, Acquisition Related Costs Acquisition and formation expenses Acquisition costs Maximum period on sale of properties to defer gains. Maximum Period On Sale Of Properties To Defer Gains Maximum period of sale to defer gain on sale of other property, days Sales of Real Estate Proceeds from sale of buildings he carrying amount of the oustanding balance due under the mortgage loan prior to refinancing. Mortgage loan carrying balance Mortgage Loans on Real Estate, Face Amount of Mortgages Mortgage loan face amount Principal balance of first mortgage loan Mortgage Loans on Real Estate, Interest Rate Interest rate of first mortgage loan Mortgage loan interest rate Mortgage Loans on Real Estate, Final Maturity Date Maturity date of first mortgage loan The amount of cash received at refinancing of a mortgage note receivable related to a previously consolidated VIE. Mortgage Loan On Real Estate Refinancing Payment Cash used to pay down the existing principal balance The amount of maximum exposure to loss related to the mortgage loan. Mortgage Loan On Real Estate Maximum Exposure Maximum exposure to loss related to investment Schedule of Equity Method Investments [Table] The number of properties securing loans. Number Of Real Estate Properties Secured Number of properties secured by loans Equity Method Investment, Ownership Percentage Ownership interest in partnership Limited Liability Company (LLC) or Limited Partnership (LP), Members or Limited Partners, Ownership Interest Remaining ownership interest in partnership Ownership interest in partnership The planned amount to spend on acquisition, operating and redeveloping properties. Planned Amount To Acquire Operate And Redevelop Properties Planned amount to acquire operate and redevelop properties Payments to Acquire Equity Method Investments Contribute towards acquisition of property Carrying value as of the balance sheet date of collateralized debt obligations for which we are the lender. Secured Debt F R T Secured loan Debt Instrument, Maturity Date, Description Mortgage loan maturity date Debt Instrument, Interest Rate Terms Loan interest rate Line of credit facility, interest rate The date that the buy-sell provision can be exercised under certain circumstances. Buy-Sell Date Buy-sell date Operating Costs and Expenses Other operating expenses Operating Costs and Expenses, Total Total expenses including operating expenses, interest expense, depreciation and amortization, and other expenses. Total Expenses Total expenses Total expenses Other Assets Other assets Other Assets, Total Other Liabilities Other liabilities Other Liabilities, Total Partners' capital Partners' Capital, Ending Balance Partners' Capital, Beginning Balance Partners' Capital, Total Share Of Unconsolidated Debt Share Of Unconsolidated Debt Our share of unconsolidated debt Schedule of Long-term Debt Instruments [Table] Date [Axis] Date [Axis] Date [Domain] Date [Domain] June Thirtieth Two Thousand And Eleven [Member] June 30, 2011 [Member] Mortgage Loans on Real Estate, Description, Type of Property [Axis] Mortgage Loans on Real Estate, Name, Property Type [Domain] Federal Plaza [Member] Federal Plaza [Member] Tyson Station [Member] Tyson Station [Member] Debt Instrument, Interest Rate, Stated Percentage Senior notes fixed interest rate Mortgage loan interest rate Debt Instrument, Maturity Date Mortgage loan maturity date Maturity date Percentage of Prepayment Premium on Mortgage Loan Percentage of Prepayment Premium on Mortgage Loan Percentage of prepayment premium on mortgage loan Repayments of Secured Debt Repayment of mortgage loan Repayment of mortgage loan Prepayment Premium on Mortgage Loan. Prepayment Premium On Mortgage Loan Prepayment premium on mortgage loan The amount of unamortized debt premium that was written off due to the early repayment of debt. Debt Instrument Unamortized Premium WriteOff Unamortized debt premium Line of Credit Facility, Maximum Borrowing Capacity Unsecured revolving credit facility New revolving credit facility Line of Credit Facility, Maximum Amount Outstanding During Period Revolving credit facility, maximum outstanding Line of Credit Facility, Average Outstanding Amount Line of credit facility, weighted average amount outstanding Line of credit facility weighted average interest rate, before amortization of debt fees Line of credit facility weighted average interest rate before amortization of debt fees Line of Credit Facility, Amount Outstanding Line of credit facility, amount outstanding Mortgages and Notes Payable Mortgages and Notes Payable Mortgages and notes payable, carrying value Mortgages and Notes Payable, Fair Value Disclosure Mortgages and Notes Payable, Fair Value Disclosure Mortgages and notes payable, fair value Senior Notes and Debentures, Fair Value Disclosure Senior Notes and Debentures, Fair Value Disclosure Senior notes and debentures, fair value Litigation settlement, gross inculding interest and legal suit costs Final judgment related to a previously disclosed lawsuit Partners' Capital Account, Units Partners' Capital Account, Units, Ending Balance Partners' Capital Account, Units, Beginning Balance Operating partnership units, outstanding Fair value of operating partnership units at the balance sheet date. Operating Partnership Units Fair Value Operating partnership units outstanding, fair value Stockholders' Equity [Table] Stockholders' Equity [Table] Maximum aggregate offering price of common shares. Aggregate Offering Price Of Common Share Aggregate offering price of common share Weighted average price per common share Weighted Average Price Per Common Share Weighted average price per common share Payments of Stock Issuance Costs Commissions related to sales of common shares Class of Stock [Axis] Class of Stock [Domain] Five point Four One Seven Percentage Series One Cumulative Convertible Preferred Stock [Member] 5.417% Series 1 Cumulative Convertible Preferred [Member] Dividend declared, common share Common Shares Aggregate Offering Price Common Stock, Dividends, Per Share, Cash Paid Dividend paid, common share Preferred Stock, Dividends Per Share, Declared Dividend declared, preferred share Preferred Stock, Dividends, Per Share, Cash Paid Dividend paid, preferred share Components of Rental Income [Table] Components of Rental Income [Table] Defined Benefit Plan by Plan Asset Categories [Axis] Plan Asset Categories [Domain] Retail And Commercial [Member] Residential [Member] Minimum rents Minimum rents Tenant Reimbursements Cost reimbursement Operating Leases, Income Statement, Percentage Revenue Percentage rent This element represents other rental revenue earned during the period. Other Rental Income Other This element represents the adjustment made to recognize base rents on a straight line basis from when the tenant controls the space through the term of the related lease, net of valuation adjustments. Straight Line Rent Straight-line Rents Amortization of Acquired Intangible Assets Amortization of above market leases This element represents the amortization of acquired below market lease liabilities over the related lease term. The amortization is reflected as additional rental income from below market leases. Amortization Of Acquired Below Market Leases Amortization of below market leases Disposal Group, Including Discontinued Operation, Revenue Revenue from discontinued operations Schedule of Employee Service Share-based Compensation, Allocation of Recognized Period Costs [Table] Antidilutive Securities Excluded from Computation of Earnings Per Share, by Antidilutive Securities [Axis] Antidilutive Securities, Name [Domain] Grants Of Options [Member] Grants of Common Shares [Member] Grants Of Common Shares [Member] Allocated Share-based Compensation Expense Share-based compensation incurred Share-based Compensation Expense, Total Employee Service Share-based Compensation, Allocation of Recognized Period Costs, Capitalized Amount Capitalized share-based compensation Share-based Compensation Share-based compensation expense Share-based compensation expense Incremental Common Shares Attributable to Participating Nonvested Shares with Non-forfeitable Dividend Rights Weighted average unvested shares outstanding Antidilutive Securities Excluded from Computation of Earnings Per Share, Amount Stock options excluded from computation of earnings per share Less: Income from continuing operations attributable to noncontrolling interests Less: Income from continuing operations attributable to noncontrolling interests Earnings allocated to unvested shares Earnings Allocated To Unvested Shares Less: Earnings allocated to unvested shares Less: Earnings allocated to unvested shares 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. Income Loss From Continuing Operations Available For Common Shareholders Income from continuing operations available for common shareholders Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Results from discontinued operations attributable to the Trust Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent, Total Net income after adjustments for dividends on preferred stock and earnings allocated to unvested shares. Net income available for common shareholders, basic and diluted Net income available for common shareholders, basic and diluted Net income available for common shareholders, basic and diluted Weighted average number of common shares-basic Weighted average common shares outstanding-basic Weighted Average Number of Shares Outstanding, Basic, Total Incremental Common Shares Attributable to Share-based Payment Arrangements Stock options Incremental Common Shares Attributable to Share-based Payment Arrangements, Total Weighted average number of common shares-diluted Weighted average common shares outstanding-diluted Weighted average common shares outstanding-diluted Income from continuing operations Income from continuing operations attributable to the Trust Income (Loss) from Continuing Operations Attributable to Parent, Total Line of Credit Facility [Axis] Line of Credit Facility, Lender [Domain] Existing Revolving Credit Facility [Member] Existing Revolving Credit Facility [Member] New Revolving Credit Facility [Member] New Revolving Credit Facility [Member] Line of Credit Facility, Expiration Date Maturity date of new credit facility Revolving credit facility, maturity date Long-term Debt, Type [Axis] Long-term Debt, Type [Domain] Loan Secured By Two Buildings [Member] Loan Secured By Two Buildings [Member] Schedule of Equity Method Investment, Equity Method Investee, Name [Axis] Equity Method Investee, Name [Domain] Federal / Lion Venture LP [Member] Federal / Lion Venture LP [Member] Taurus Newbury Street JV II Limited Partnership [Member] Newbury Street Partnership [Member] Subsidiary, Sale of Stock [Axis] Sale of Stock, Name of Transaction [Domain] At The Market Equity Program [Member] At The Market Equity Program [Member]