Real Estate [Abstract] Schedule of Real Estate Properties [Table] Schedule of Real Estate Properties [Table] Disposal Group Classification [Axis] Disposal Group Classification [Axis] Disposal Group Classification [Domain] Disposal Group Classification [Domain] Discontinued Operations, Held-for-sale Discontinued Operations, Held-for-sale [Member] Name of Property [Axis] Name of Property [Axis] Name of Property [Domain] Name of Property [Domain] One building One Building Disposition [Member] Represents one building sold during the period. Geographical [Axis] Geographical [Axis] Geographical [Domain] Geographical [Domain] Falls Church, VA Falls Church V A [Member] Represents the location, Falls Church, VA. Real Estate, Type of Property [Axis] Real Estate, Type of Property [Axis] Real Estate [Domain] Real Estate [Domain] Office Building Office Building [Member] Real Estate Properties [Line Items] Real Estate Properties [Line Items] Number of properties Number of Real Estate Properties Number of buildings Number of Buildings The number of buildings owned as of the balance sheet date. Rentable square feet of properties (in square feet) Area of Real Estate Property Net book value Real Estate Investment Property, Net Non-refundable deposit Disposition Of Property, Non-Refundable Deposit Disposition Of Property, Non-Refundable Deposit Aggregate sale price of properties sold, excluding closing costs Real Estate Aggregate Sales Price This element represents the aggregate sales price excluding closing costs, of real estate properties sold by the entity. Debt Disclosure [Abstract] Number of properties secured by mortgage notes Number of Real Estate Properties Collateralized Represents the number of real estate properties serving as a collateral for debt, as of the balance sheet date. Number of buildings secured by mortgage notes Number of Buildings Collateralized The number of buildings serving as collateral for debt as of the balance sheet date. Aggregate net book value of secured properties Aggregate Net Book Value of Real Estate Properties Collateralized Represents the aggregate net book value of real estate properties serving as a collateral for debt, as of the balance sheet date. Number of assumed secured mortgage loans Mortgage Loans on Real Estate Assumed in Acquisitions Number of Loans Represents the number of mortgage loans on real estate assumed in acquisitions during the period. Aggregate principal amount on secured properties Aggregate Principal Amount Of Real Estate Properties Collateralized The aggregate principal amount on real estate properties serving as collateral for debt as of the balance sheet date. Accounting Policies [Abstract] Recent Accounting Pronouncements New Accounting Pronouncements and Changes in Accounting Principles [Text Block] Disposal Groups, Including Discontinued Operations [Table] Disposal Groups, Including Discontinued Operations [Table] Disposal Group Name [Axis] Disposal Group Name [Axis] Disposal Group Name [Domain] Disposal Group Name [Domain] Discontinued operations Discontinued Operations [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] Rental income Disposal Group, Including Discontinued Operation, Rental Income Real estate taxes Disposal Group Including Discontinued Operation Real Estate Taxes Amount of real estate taxes attributable to disposal group, including, but not limited to, discontinued operation. Utility expenses Disposal Group Including Discontinued Operation Utility Expenses Amount of utility expenses attributable to disposal group, including, but not limited to, discontinued operation. Other operating expenses Disposal Group Including Discontinued Operation Other Operating Expenses Amount of other operating expenses attributable to disposal group, including, but not limited to, discontinued operation. General and administrative Disposal Group, Including Discontinued Operation, General and Administrative Expense Loss from discontinued operations Income (Loss) from Discontinued Operations, Net of Tax, Attributable to Parent Transferable Development Rights Transferable Development Rights [Member] Transferable Development Rights [Member] Manassas, VA Manassas, VA [Member] Manassas, VA [Member] Washington D.C. Washington D.C [Member] Washington D.C [Member] Number of properties Number of Properties Acquired Number of Properties Acquired Number of buildings acquired Number of Buildings Acquired Number of Buildings Acquired Percentage of property leased Percentage Of Property Leased Represents the percentage of property leased. Purchase price Payments to Acquire and Develop Real Estate Capitalized acquisition costs Asset Acquisition, Capitalized Transaction Costs Asset Acquisition, Capitalized Transaction Costs Land Business Combination, Recognized Identifiable Assets Acquired and Liabilities Assumed, Land Buildings and Improvement Real Estate Purchase Price Allocation Building And Building Improvements Represents the amount of purchase price allocated to building and building improvements. Other assumed assets Real Estate Purchase Price Allocation Other Assumed Assets Represent the value of other assumed assets. Consideration transferred excluding acquisition costs Business Combination, Consideration Transferred Equity Method Investments and Joint Ventures [Abstract] Schedule of Equity Method Investments [Table] Schedule of Equity Method Investments [Table] Legal Entity [Axis] Legal Entity [Axis] Entity [Domain] Entity [Domain] SIR Select Income R E I T [Member] Represents information pertaining to Select Income REIT. Investment, Name [Axis] Investment, Name [Axis] Investment, Name [Domain] Investment, Name [Domain] Schedule of Equity Method Investments [Line Items] Schedule of Equity Method Investments [Line Items] Rental income Operating Leases, Income Statement, Lease Revenue Tenant reimbursements and other income Tenant Reimbursements And Other income In accordance with the provisions of their lease agreement, this element represents allowable charges due a landlord from its tenant. In retail store and office building leases, for example, tenant reimbursements may cover items such as taxes, utilities, and common area expenses. It also includes other real estate revenue. Total revenues Real Estate Revenue, Net Real estate taxes Real Estate Tax Expense Other operating expenses Other Cost and Expense, Operating Depreciation and amortization Depreciation, Depletion and Amortization, Nonproduction Acquisition related costs Business Combination, Acquisition Related Costs General and administrative General and Administrative Expense Reserve for straight line rent receivable, net Reserve For Straight Line Rent Receivable, Net Reserve For Straight Line Rent Receivable, Net Loss on asset impairment Asset Impairment Charges Total expenses Costs and Expenses Operating income Operating Income (Loss) Dividend income Other Interest and Dividend Income Interest expense Interest Expense Income from continuing operations before income taxes and equity in earnings of investees Income (Loss) from Continuing Operations before Equity Method Investments, Income Taxes, Noncontrolling Interest Income tax expense Income Tax Expense (Benefit) Equity in earnings of investees Income (Loss) from Equity Method Investments Net income Net Income (Loss), Including Portion Attributable to Noncontrolling Interest Net income allocated to noncontrolling interest Net Income (Loss) Attributable to Noncontrolling Interest Net income attributed to SIR Net Income (Loss) Attributable to Parent Weighted average common shares outstanding (basic) (in shares) Weighted Average Number of Shares Outstanding, Basic Weighted average common shares outstanding (diluted) (in shares) Weighted Average Number of Shares Outstanding, Diluted Net income attributed to SIR per common share (basic and diluted) (in dollars per share) Earnings Per Share, Basic and Diluted Indebtedness Debt Disclosure [Text Block] Revenue Recognition [Abstract] Increase in rental income to record revenue on straight line basis Straight Line Rent Straight line rent receivables Deferred Rent Receivables, Net Allowance for doubtful accounts Allowance For Doubtful Accounts Receivable, Deferred Rent Receivables Allowance For Doubtful Accounts Receivable, Deferred Rent Receivables Risks and Uncertainties [Abstract] Concentration Risk [Table] Concentration Risk [Table] Operating Activities [Axis] Operating Activities [Axis] Operating Activities [Domain] Operating Activities [Domain] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Axis] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Annualized rental income, excluding properties classified as discontinued operations Real Estate Revenue Net [Member] The revenue from real estate operations during the reporting period in the normal course of business, after deducting returns, allowances and discounts, when it serves as a benchmark in a concentration of risk calculation. Concentration Risk Type [Axis] Concentration Risk Type [Axis] Concentration Risk Type [Domain] Concentration Risk Type [Domain] Tenant concentration Customer Concentration Risk [Member] Customer [Axis] Customer [Axis] Customer [Domain] Customer [Domain] U.S. Government, state governments and Other Three Government U S Government State Governments And Other Government [Member] Represents the U.S. Government, state governments and Other Government, combined. U.S. Government U S Government [Member] Represents information pertaining to the government of United States of America. Virginia VIRGINIA California CALIFORNIA District of Columbia DISTRICT OF COLUMBIA Georgia GEORGIA New York NEW YORK Maryland MARYLAND Massachusetts MASSACHUSETTS Concentration Concentration Risk [Line Items] Number of state governments Number of State Governments Represents the number of state governments that are tenants of the entity. Number of other governments Number of other governments Represents the number of other governments that are tenants of the entity. Concentration risk percentage Concentration Risk, Percentage Number of states in which acquired properties located Number of States in which Real Estate Properties Held The number of states in which real estate owned by the entity is located as of the balance sheet date. Annualized Rental income percent Real Estate Revenue, Percent This element represents the percentage of rental income in each state. Income Statement [Abstract] Rental income Expenses: Costs and Expenses [Abstract] Utility expenses Utilities Costs Interest income Investment Income, Interest Interest expense (including net amortization of debt premiums and discounts and debt issuance costs of $807 and $471, respectively) Gain on early extinguishment of debt Gain (Loss) on Extinguishment of Debt Income from continuing operations Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Loss from discontinued operations Net income Net Income (Loss) Available to Common Stockholders, Basic Other comprehensive income Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent [Abstract] Unrealized gain on investment in available for sale securities Available-for-sale Securities, Gross Unrealized Gain (Loss) Equity in unrealized gain of investees Other Comprehensive Income, Other, Net of Tax Other comprehensive income Other Comprehensive Income (Loss), Net of Tax, Portion Attributable to Parent Comprehensive income Comprehensive Income (Loss), Net of Tax, Attributable to Parent Per common share amounts (basic and diluted): Earnings Per Share [Abstract] Income from continuing operations (in dollars per share) Income (Loss) from Continuing Operations, Per Basic and Diluted Share Loss from discontinued operations (in dollars per share) Discontinued Operation, Income (Loss) from Discontinued Operation, Net of Tax, Per Basic and Diluted Share Net income (in dollars per share) Fair Value Disclosures [Abstract] Fair Value of Assets and Liabilities Fair Value Disclosures [Text Block] Recent Accounting Pronouncements Description of New Accounting Pronouncements Not yet Adopted [Text Block] Equity [Abstract] Shareholders' Equity Stockholders' Equity Note Disclosure [Text Block] Equity Investment in Select Income REIT Equity Method Investments and Joint Ventures Disclosure [Text Block] Schedule of purchase prices of acquisitions allocated based on the estimated fair values of the acquired assets and assumed liabilities Schedule of Recognized Identified Assets Acquired and Liabilities Assumed [Table Text Block] Summarized balance sheet and income statement information for properties classified as discontinued operations Disposal Groups, Including Discontinued Operations [Table Text Block] Related Party Transactions [Abstract] Related Person Transactions Related Party Transactions Disclosure [Text Block] Organization, Consolidation and Presentation of Financial Statements [Abstract] Basis of Presentation Organization, Consolidation and Presentation of Financial Statements Disclosure [Text Block] Net amortization of debt premiums and discounts and deferred financing fees Amortization of Debt Issuance Costs 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] LIBOR London Interbank Offered Rate (LIBOR) [Member] Credit Facility [Axis] Credit Facility [Axis] Credit Facility [Domain] Credit Facility [Domain] Unsecured revolving credit facility Line of Credit [Member] Term loans Long-term Debt [Member] Senior unsecured notes Senior Notes [Member] Subsequent Event Type [Axis] Subsequent Event Type [Axis] Subsequent Event Type [Domain] Subsequent Event Type [Domain] Subsequent Event Subsequent Event [Member] Debt Instrument [Axis] Debt Instrument [Axis] Debt Instrument, Name [Domain] Debt Instrument, Name [Domain] Unsecured term loan, due in 2020 Unsecured Debt Due In2020 [Member] Represents the unsecured term loan due in 2020. Unsecured term loan, due in 2022 Unsecured Debt Due In2022 [Member] Represents the unsecured term loan due in 2022. Debt Instrument [Line Items] Debt Instrument [Line Items] Borrowings outstanding Long-term Line of Credit Maximum borrowing capacity on revolving credit facility Line of Credit Facility, Maximum Borrowing Capacity Face amount Debt Instrument, Face Amount Option to extend the maturity date subject to certain conditions and the payment of a fee Debt Instrument, Contingent Option to Extend Maturity Date The option to extend the maturity date subject to certain conditions and the payment of a fee under the credit facility. Interest rate premium (as a percent) Debt Instrument, Basis Spread on Variable Rate Facility fee (as a percent) Line of Credit Facility, Commitment Fee Percentage Interest rate (as a percent) Debt Instrument, Interest Rate, Stated Percentage The weighted average annual interest rate (as a percent) Weighted Average Annual Interest Rate Represents the calculation of the average interest rate weighted by the amount of long-term debt outstanding by type or by instrument at that time. Equity investments, common shares owned (in shares) Equity investments, common shares owned Represents the total number of common shares of beneficial interest of equity method investee owned by an investor. Percentage of outstanding shares owned Equity Method Investment, Ownership Percentage Equity in unrealized gain (loss) of investees Other Comprehensive Income (Loss), Unrealized Holding Gain (Loss) on Securities Arising During Period, Net of Tax The amount of investment in exceed the underlying equity of the investee Equity Method Investment, Difference Between Carrying Amount and Underlying Equity Accretion in equity of earnings Equity Method Investment, Accretion of Equity in Earnings Equity Method Investment, Accretion of Equity in Earnings Investment at carrying value Equity Method Investments Equity Investments, market value Equity Method Investment, Quoted Market Value Cash distributions from SIR Proceeds from Equity Method Investment, Dividends or Distributions Real estate properties, net Acquired real estate leases, net Finite-Lived Intangible Assets, Net Cash and cash equivalents Cash and Cash Equivalents, at Carrying Value Rents receivable, net Accounts Receivable, Net Other assets, net Other Assets Total assets Assets Unsecured revolving credit facility Unsecured term loan, net Unsecured Debt Senior unsecured notes, net Senior Notes Mortgage notes payable, net Secured Debt Assumed real estate lease obligations, net Off-market Lease, Unfavorable Other liabilities Other Liabilities Shareholders' equity Stockholders' Equity Attributable to Parent Total liabilities and shareholders’ equity Liabilities and Equity Statement of Cash Flows [Abstract] CASH FLOWS FROM OPERATING ACTIVITIES: Net Cash Provided by (Used in) Operating Activities [Abstract] Net income Adjustments to reconcile net income to cash provided by operating activities: Adjustments to Reconcile Net Income (Loss) to Cash Provided by (Used in) Operating Activities [Abstract] Depreciation Depreciation Net amortization of debt premiums and discounts and debt issuance costs Amortization of Debt Issuance Costs and Discounts Gain on early extinguishment of debt Straight line rental income Straight Line Rent Continuing and Discontinuing Operations Difference between actual rental income due and rental income recognized on a straight-line basis for both continuing and discontinued operations. Amortization of acquired real estate leases Amortization of Intangible Assets Amortization of deferred leasing costs Amortization of Deferred Leasing Fees Other non-cash expenses (income), net Other Noncash Income (Expense) Equity in earnings of investees Distributions of earnings from Select Income REIT Change in assets and liabilities: Increase (Decrease) in Operating Capital [Abstract] Restricted cash Increase (Decrease) in Restricted Cash for Operating Activities Deferred leasing costs Increase (Decrease) in Deferred Leasing Fees Rents receivable Increase (Decrease) in Leasing Receivables Other assets Increase (Decrease) in Other Operating Assets Accounts payable and accrued expenses Increase (Decrease) in Accounts Payable and Accrued Liabilities Due to related persons Increase (Decrease) in Due to Related Parties Net cash provided by operating activities Net Cash Provided by (Used in) Operating Activities CASH FLOWS FROM INVESTING ACTIVITIES: Net Cash Provided by (Used in) Investing Activities [Abstract] Real estate acquisitions and deposits Real estate improvements Payments for Capital Improvements Distributions in excess of earnings from Select Income REIT Proceeds from Equity Method Investment, Dividends or Distributions, Return of Capital Net cash used in investing activities Net Cash Provided by (Used in) Investing Activities CASH FLOWS FROM FINANCING ACTIVITIES: Net Cash Provided by (Used in) Financing Activities [Abstract] Repayment of mortgage notes payable Repayments of Secured Debt Borrowings on unsecured revolving credit facility Proceeds from Long-term Lines of Credit Repayments on unsecured revolving credit facility Repayments of Long-term Lines of Credit Distributions to common shareholders Payments of Ordinary Dividends, Common Stock Net cash (used in) provided by financing activities Net Cash Provided by (Used in) Financing Activities Increase (decrease) in cash and cash equivalents Cash and Cash Equivalents, Period Increase (Decrease) Cash and cash equivalents at beginning of period Cash and cash equivalents at end of period Supplemental cash flow information: Supplemental Cash Flow Information [Abstract] Interest paid Interest Paid Income taxes paid Income Taxes Paid Fair Value, by Balance Sheet Grouping [Table] Fair Value, by Balance Sheet Grouping [Table] Measurement Basis [Axis] Measurement Basis [Axis] Fair Value Measurement [Domain] Fair Value Measurement [Domain] Portion at Fair Value Measurement [Member] Portion at Fair Value Measurement [Member] Carrying Amount Reported Value Measurement [Member] Fair Value Estimate of Fair Value Measurement [Member] 3.75% Senior unsecured note due In 2019 Senior Secured Note3.75 Percent Due In2019 [Member] Represents the senior unsecured note bearing an interest rate of 3.75 percent due in 2019. 5.875% Senior unsecured notes due In 2046 Senior Unsecured Notes5.875 Percent Due In2046 [Member] Represents the senior unsecured notes due in 2046 5.88% interest rate, due in 2021 Mortgage Note5.88 Percent Due In2021 [Member] Represents the mortgage note bearing an interest rate of 5.88 percent due in 2021. 7.00% interest rate, due in 2019 Mortgage Note7 Percent Due In2019 [Member] Represents the mortgage note bearing an interest rate of 7 percent due in 2019. 8.15% Mortgage notes due in 2021 Mortgage Note8.15 Percent Due In2021 [Member] Represents the mortgage note bearing an interest rate of 8.15 percent due in 2021. Fair Value of Financial Instruments Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items] Senior Notes Document and Entity Information Entity Registrant Name Entity Registrant Name Entity Central Index Key Entity Central Index Key Document Type Document Type Document Period End Date Document Period End Date Amendment Flag Amendment Flag Current Fiscal Year End Date Current Fiscal Year End Date Entity Current Reporting Status Entity Current Reporting Status Entity Filer Category Entity Filer Category Entity Common Stock, Shares Outstanding Entity Common Stock, Shares Outstanding Document Fiscal Year Focus Document Fiscal Year Focus Document Fiscal Period Focus Document Fiscal Period Focus Schedule of assets measured on a recurring and non-recurring basis at fair value, categorized by the level of inputs used in the valuation assets Fair Value Measurements, Recurring and Nonrecurring [Table Text Block] Schedule of fair value and carrying value of financial instruments Fair Value, by Balance Sheet Grouping [Table Text Block] Concentration Concentration Risk Disclosure [Text Block] Statement [Line Items] Statement [Line Items] Schedule Of Summarized Balance Sheet Information Of Equity Method Investee Schedule Of Summarized Balance Sheet Information Of Equity Method Investee Table Text Block Tabular disclosure of summarized balance sheet information of an equity method investee. Schedule Of Summarized Income Statement Information Of Equity Method Investee Schedule Of Summarized Income Statement Information Of Equity Method Investee Table Text Block Tabular disclosure of summarized income statement information of an equity method investee. Deferred gain on sale of real estate Deferred Gain on Sale of Property Statement of Financial Position [Abstract] ASSETS Assets [Abstract] Real estate properties: Real Estate Investment Property, Net [Abstract] Land Land Buildings and improvements Investment Building and Building Improvements Total real estate properties, gross Real Estate Investment Property, at Cost Accumulated depreciation Real Estate Investment Property, Accumulated Depreciation Total real estate properties, net Equity investment in Select Income REIT Assets of discontinued operations Disposal Group, Including Discontinued Operation, Assets Restricted cash Restricted Cash and Cash Equivalents Deferred leasing costs, net Deferred Costs, Leasing, Net LIABILITIES AND SHAREHOLDERS’ EQUITY Liabilities and Equity [Abstract] Unsecured revolving credit facility Unsecured term loans, net Mortgage notes payable, net Liabilities of discontinued operations Disposal Group, Including Discontinued Operation, Liabilities Accounts payable and other liabilities Due to related persons Due to Related Parties Total liabilities Liabilities Commitments and contingencies Commitments and Contingencies Shareholders’ equity: Stockholders' Equity Attributable to Parent [Abstract] Common shares of beneficial interest, $.01 par value: 100,000,000 shares authorized, 71,177,906 shares issued and outstanding Common Stock, Value, Issued Additional paid in capital Additional Paid in Capital, Common Stock Cumulative net income Retained Earnings (Accumulated Deficit) Cumulative other comprehensive income Accumulated Other Comprehensive Income (Loss), Net of Tax Cumulative common distributions Cumulative Common Stock Distributions The amount as of the balance sheet date representing cumulative distributions to common shareholders. Total shareholders’ equity Revenue Recognition Revenue Recognition Disclosure [Text Block] Represents the disclosure of revenue recognition. Schedule of changes in each component of cumulative other comprehensive income (loss) Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Earnings Per Share, Basic and Diluted [Abstract] Weighted average common shares for basic earnings per share (in shares) Effect of dilutive securities: unvested share awards (in shares) Weighted Average Number Diluted Shares Outstanding Adjustment Weighted average common shares for diluted earnings per share (in shares) Property Management Fee [Abstract] Schedule of Related Party Transactions, by Related Party [Table] Schedule of Related Party Transactions, by Related Party [Table] Related Party Transaction [Axis] Related Party Transaction [Axis] Related Party Transaction [Domain] Related Party Transaction [Domain] Net Property Management and Construction Supervision Fees Net Property Management and Construction Supervision Fees [Member] Net Property Management and Construction Supervision Fees [Member] Related Party [Axis] Related Party [Axis] Related Party [Domain] Related Party [Domain] RMR LLC Reit Management And Research L L C [Member] Represents details pertaining to Reit Management and Research LLC, or RMR. Related Party Transaction [Line Items] Related Party Transaction [Line Items] Number of employees Number Of Employees Represents the number of employees in the company. Number of agreements Number Of Agreements With RMR LLC Represents the number of agreements with RMR LLC to provide management services to the company. Related party expense Related Party Transaction, Expenses from Transactions with Related Party Related party transaction amount Related Party Transaction, Amounts of Transaction Reimbursement expense Related Party Reimbursement Expense Total expense amount to reimburse a related party. Internal audit costs Internal Audit Costs Internal Audit Costs Segment Reporting [Abstract] Segment Information Segment Reporting Disclosure [Text Block] Weighted Average Common Share Amounts Schedule of Earnings Per Share, Basic and Diluted [Table Text Block] Business and Property Management Agreements with RMR LLC Business and Property Management Agreements [Text Block] Business and Property Management Agreements [Text Block] Schedule of Segment Information Schedule of Segment Reporting Information, by Segment [Table Text Block] AIC Affiliates Insurance Company [Member] Represents details pertaining to Affiliates Insurance Company, also referred to as AIC in which the entity has an investment in shares accounted for under the equity method of accounting and for which certain information is required or determined to be disclosed. Business Acquisition [Axis] Business Acquisition [Axis] Business Acquisition, Acquiree [Domain] Business Acquisition, Acquiree [Domain] RMR Inc Reit Management And Research Inc [Member] Represents the information pertaining to Reit Management & Research Inc. (RMR) Equity Interest Type [Axis] Equity Interest Type [Axis] Equity Interest Issued or Issuable, Type [Domain] Equity Interest Issued or Issuable, Type [Domain] Class A common shares Common Class A [Member] Shares holding (in shares) Subsidiary or Equity Method Investee, Cumulative Number of Shares Issued for All Transactions Carrying value of equity method investments Equity Method Investment, Aggregate Cost Schedule of Segment Reporting Information, by Segment [Table] Schedule of Segment Reporting Information, by Segment [Table] Consolidation Items [Axis] Consolidation Items [Axis] Consolidation Items [Domain] Consolidation Items [Domain] Operating Segments Operating Segments [Member] Corporate, Non-Segment Corporate, Non-Segment [Member] Segments [Axis] Segments [Axis] Segment [Domain] Segments [Domain] Investment in Real Estate Investment In Real Estate Segment [Member] Represents information pertaining to investment in real estate, a business segment. Investment in SIR Investment In Select Income R E I T Segment [Member] Represents information pertaining to investment in Select Income REIT, a business segment. Segment Reporting Information [Line Items] Segment Reporting Information [Line Items] Number of segments Number of Operating Segments Total assets Fair Value Measurements, Recurring and Nonrecurring [Table] Fair Value Measurements, Recurring and Nonrecurring [Table] Balance Sheet Location [Axis] Balance Sheet Location [Axis] Balance Sheet Location [Domain] Balance Sheet Location [Domain] Other Comprehensive Income (Loss) Other Comprehensive Income (Loss) [Member] Measurement Frequency [Axis] Measurement Frequency [Axis] Fair Value, Measurement Frequency [Domain] Fair Value, Measurement Frequency [Domain] Recurring Fair Value, Measurements, Recurring [Member] Nonrecurring Fair Value, Measurements, Nonrecurring [Member] Fair Value, Hierarchy [Axis] Fair Value, Hierarchy [Axis] Fair Value Hierarchy [Domain] Fair Value Hierarchy [Domain] Level 1 inputs Fair Value, Inputs, Level 1 [Member] Level 3 inputs Fair Value, Inputs, Level 3 [Member] Fair Value of Assets and Liabilities Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] Investment in RMR Inc. Investments in Affiliates, Subsidiaries, Associates, and Joint Ventures, Fair Value Disclosure Property held for sale and classified as discontinued operations Disposal Group Including Discontinued Operation Real Estate Investment Property Net Amount classified as real estate properties attributable to disposal group held for sale or disposed of. Common shares owned in RMR Inc. (in shares) Available-For-Sale Securities, Common Shares Owned Common shares owned accounted for as available for sale securities. Historical cost Historical Cost Represents the historical cost during the period Real estate properties, net Other assets Disposal Group, Including Discontinued Operation, Other Assets Assets of discontinued operations Other liabilities Disposal Group, Including Discontinued Operation, Other Liabilities Liabilities of discontinued operations Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Schedule of Share-based Compensation Arrangements by Share-based Payment Award [Table] Share Awards Share-based Compensation Arrangement by Share-based Payment Award [Line Items] Distributions Dividends, Common Stock [Abstract] Cash distribution to common shareholders (in dollars per share) Common Stock, Dividends, Per Share, Cash Paid Distribution paid to common shareholders Dividends, Common Stock, Cash Distribution payable to common shareholders (in dollars per share) Dividends Payable, Amount Per Share Accumulated Other Comprehensive Income (Loss) [Table] Accumulated Other Comprehensive Income (Loss) [Table] Equity Components [Axis] Equity Components [Axis] Equity Component [Domain] Equity Component [Domain] Unrealized Gain on Investment in Available for Sale Securities Accumulated Net Investment Gain (Loss) Attributable to Parent [Member] Equity in Unrealized Gain of an Investee Accumulated Net Unrealized Gain Loss Investee [Member] Accumulated other comprehensive income (loss) pertaining to an investee. Accumulated Other Comprehensive Income (Loss) [Line Items] Accumulated Other Comprehensive Income (Loss) [Line Items] AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] AOCI Including Portion Attributable to Noncontrolling Interest, Net of Tax [Roll Forward] Balance at the beginning of the period Other comprehensive income before reclassifications Other Comprehensive Income (Loss), before Reclassifications, Net of Tax Amounts reclassified from cumulative other comprehensive income to net income Reclassification from Accumulated Other Comprehensive Income, Current Period, Net of Tax Net current period other comprehensive income Other Comprehensive Income (Loss), Net of Tax Balance at the end of the period Continuing operations Continuing Operations [Member] Carrying value of real estate properties Number of leases entered Number of Operating Lease Executed Represents number of leases executed during the reporting period. Rentable square feet (in feet) Operating Leases Committed Expenditures on Leases Executed in Period Area of Leased Property Represents the area of leased property related to operating leases executed during the period. Weighted average lease term Operating Leases Weighted Average Lease Term Represents the weighted average lease term of operating leases. Expenditures committed on leases Operating Leases Committed Expenditures on Leases Executed in Period Represents committed expenditures for operating leases executed during the period. Committed but unspent tenant related obligations estimated Operating Leases Committed Expenditures on Leases Executed in Period Committed but Unspent Tenant Related Obligations Represents committed but unspent tenant related obligations based on executed operating leases as of the balance sheet date. Square foot expansion cost Operating Leases Expected Current Expansion Cost Represents the expected cost of expansion during the current period. Interest costs capitalized Interest Costs Capitalized Common shares of beneficial interest, par value (in dollars per share) Common Stock, Par or Stated Value Per Share Common shares of beneficial interest, shares authorized (in shares) Common Stock, Shares Authorized Common shares of beneficial interest, shares issued (in shares) Common Stock, Shares, Issued Common shares of beneficial interest, shares outstanding (in shares) Common Stock, Shares, Outstanding Real Estate Properties Real Estate Disclosure [Text Block] Weighted Average Common Shares Earnings Per Share [Text Block]