Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2015
Summary of Significant Accounting Policies
Basis of Presentation	Basis of Presentation. These consolidated financial statements include the accounts of us and our subsidiaries, all of which are 100% owned directly or indirectly by us. All intercompany transactions and balances with or among our consolidated subsidiaries have been eliminated.
Equity Method Investments	Equity Method Investments. We account for our investments in Affiliates Insurance Company, or AIC, and SIR using the equity method of accounting. Significant influence is present through common representation on the boards of trustees or directors of us, AIC and SIR and our significant ownership interest in SIR. Our Managing Trustees are also the managing trustees of SIR. Our Managing Trustees are also directors, officers and controlling shareholders (through ABP Trust (formerly known as Reit Management & Research Trust)) of The RMR Group Inc., or RMR Inc. Substantially all of the business of RMR Inc. is conducted by its majority owned subsidiary, The RMR Group LLC, or RMR LLC, which is the manager of us, AIC and SIR. Each of our Trustees is a director of AIC and one of our Independent Trustees is also an independent trustee of SIR. See Notes 6 and 11 for a further discussion of our investments in AIC and SIR. We periodically evaluate our equity method investments for possible indicators of other than temporary impairment whenever events or changes in circumstances indicate the carrying amount of the investment might not be recoverable. These indicators may include the length of time and the extent to which the market value of our investment is below our carrying value, the financial condition of our investees, our intent and ability to be a long term holder of the investment and other considerations. If the decline in fair value is judged to be other than temporary, we record an impairment charge to adjust the basis of the investment to its estimated fair value. We recorded a $203,297 loss on impairment of our SIR investment in 2015. See Note 11 for more information on this impairment.
Available for Sale Investments	Available for Sale Securities. As of December 31, 2015, we owned 1,214,225 common shares of RMR Inc. This investment is accounted for as available for sale securities and recorded at fair value based on its quoted market price at the end of each reporting period. The unrealized gains (losses) on our investment in available for sale securities is recorded as a component of cumulative other comprehensive income (loss) in shareholders’ equity. See Notes 6 and 9 for further information regarding our investment in RMR Inc. We evaluate our investments in available for sale securities to determine if a decline in the fair value below our carrying value is other than temporary. We consider the severity and the duration of the decline, and our ability and intent to hold the investment until recovery when making this assessment. If a decline in fair value is determined to be other than temporary, an impairment loss equal to the difference between the investment’s carrying value and its fair value is recognized in earnings.
Real Estate Properties	Real Estate Properties. We record our properties at cost and provide depreciation on real estate investments on a straight line basis over estimated useful lives generally ranging from 7 to 40 years. In some circumstances, we engage independent real estate appraisal firms to provide market information and evaluations which are relevant to our purchase price allocations and determinations of useful lives; however, we are ultimately responsible for the purchase price allocations and determinations of useful lives. We allocate the purchase prices of our properties to land, building and improvements based on determinations of the fair values of these assets assuming the properties are vacant. We determine the fair value of each property using methods similar to those used by independent appraisers. For properties qualifying as acquired businesses under Accounting Standards Codification 805, Business Combinations, we allocate a portion of the purchase price of our properties to above market and below market leases based on the present value (using an interest rate which reflects the risks associated with acquired in place leases at the time each property was acquired by us) of the difference, if any, between (i) the contractual amounts to be paid pursuant to the acquired in place leases and (ii) our estimates of fair market lease rates for the corresponding leases, measured over a period equal to the terms of the respective leases. We allocate a portion of the purchase price to acquired in place leases and tenant relationships based upon market estimates to lease up the property based on the leases in place at the time of purchase. We allocate this aggregate value between acquired in place lease values and tenant relationships based on our evaluation of the specific characteristics of each tenant’s lease. However, we have not separated the value of tenant relationships from the value of acquired in place leases because such value and related amortization expense is immaterial to the accompanying consolidated financial statements. In making these allocations, we consider factors such as estimated carrying costs during the expected lease up periods, including real estate taxes, insurance and other operating income and expenses and costs, such as leasing commissions, legal and other related expenses, to execute similar leases in current market conditions at the time a property was acquired by us. If the value of tenant relationships becomes material in the future, we may separately allocate those amounts and amortize the allocated amounts over the estimated life of the relationships. We amortize capitalized above market lease values (included in acquired in place real estate leases in our consolidated balance sheets) and below market lease values (presented as assumed real estate lease obligations in our consolidated balance sheets) as a reduction or increase, respectively, to rental income over the terms of the associated leases. Such amortization resulted in net decreases to rental income of $1,155, $868, and $1,123 during the years ended December 31, 2015, 2014 and 2013, respectively. We amortize the value of acquired in place leases (included in acquired real estate leases in our consolidated balance sheets), exclusive of the value of above market and below market acquired in place leases, over the terms of the associated leases. Such amortization, which is included in depreciation and amortization expense, amounted to $27,467, $26,844, and $20,482 during the years ended December 31, 2015, 2014 and 2013, respectively. When a lease is terminated prior to its stated expiration, we write off the unamortized amounts relating to that lease. Capitalized above market lease values were $37,875 and $39,040 as of December 31, 2015 and 2014, respectively, net of accumulated amortization of $21,469 and $18,288, respectively. Capitalized below market lease values were $25,553 and $26,605 as of December 31, 2015 and 2014, respectively, net of accumulated amortization of $12,818 and $10,681, respectively. The value of acquired in place leases, exclusive of the value of above market and below market acquired in place leases, were $188,471 and $198,157 as of December 31, 2015 and 2014, respectively, net of accumulated amortization of $86,610 and $68,829, respectively. As of December 31, 2015, the weighted average amortization periods for capitalized above market leases, lease origination value and capitalized below market lease values were 5.1 years, 5.7 years, and 7.3 years, respectively. Future amortization of net intangible lease assets and liabilities, to be recognized over the current terms of the associated leases as of December 31, 2015 are estimated to be $25,997 in 2016, $23,731 in 2017, $19,458 in 2018, $14,406 in 2019, $6,939 in 2020 and $15,001 thereafter. We regularly evaluate whether events or changes in circumstances have occurred that could indicate an impairment in the value of long lived assets. If there is an indication that the carrying value of an asset is not recoverable, we estimate the projected undiscounted cash flows to determine if an impairment loss should be recognized. We determine the amount of any impairment loss by comparing the historical carrying value to estimated fair value. We estimate fair value through an evaluation of recent financial performance and projected discounted cash flows using standard industry valuation techniques. In addition to consideration of impairment upon the events or changes in circumstances described above, we regularly evaluate the remaining lives of our long lived assets. If we change our estimate of the remaining lives, we allocate the carrying value of the affected assets over their revised remaining lives.
Cash and Cash Equivalents	Cash and Cash Equivalents. We consider highly liquid investments with original maturities of three months or less at the date of purchase to be cash equivalents.
Restricted Cash	Restricted Cash. Restricted cash consists of amounts escrowed for future real estate taxes, insurance, leasing costs, capital expenditures and debt service, as required by certain of our mortgage debts.
Deferred leasing costs	Deferred Leasing Costs. Deferred leasing costs include brokerage, legal and other fees associated with our entering leases and we amortize those costs, which are included in depreciation and amortization expense, on a straight line basis over the terms of the respective leases. Deferred leasing costs totaled $20,300 and $15,401 at December 31, 2015 and 2014, respectively, and accumulated amortization of deferred leasing costs totaled $6,001 and $3,951 at December 31, 2015 and 2014, respectively. Future amortization of deferred leasing costs to be recognized during the current terms of our existing leases as of December 31, 2015, are estimated to be $2,866 in 2016, $2,376 in 2017, $2,128 in 2018, $2,018 in 2019, $1,871 in 2020 and $3,040 thereafter.
Deferred financing fees	Deferred Financing Fees. Deferred financing fees include issuance or assumption costs related to borrowings and we amortize those costs as interest expense over the terms of the respective loans. Deferred financing fees totaled $13,692 and $14,055 at December 31, 2015 and 2014, respectively, and accumulated amortization of deferred financing fees totaled $3,817 and $1,273 at December 31, 2015 and 2014, respectively. Future amortization of deferred financing fees to be recognized with respect to our loans as of December 31, 2015 are estimated to be $2,637 in 2016, $2,552 in 2017, $2,552 in 2018, $1,296 in 2019, $450 in 2020 and $388 thereafter.
Revenue Recognition	Revenue Recognition. We recognize rental income from operating leases that contain fixed contractual rent changes on a straight line basis over the term of the lease agreements. We increased rental income by $3,978, $4,501 and $2,739 to record revenue on a straight line basis during the years ended December 31, 2015, 2014 and 2013, respectively. Rents receivable include $18,995 and $15,017 of straight line rent receivables at December 31, 2015 and 2014, respectively. Certain of our leases with government tenants provide the tenant the right to terminate its lease if its respective legislature or other funding authority does not appropriate the funding necessary for the government tenant to meet its lease obligations. We have determined the fixed non-cancelable lease term of these leases to be the fully executed term of the lease because we believe the occurrence of termination to be a remote contingency based on both our historical experience and our assessment of the likelihood of lease cancellation on a separate lease basis.
Income Taxes	Income Taxes. We have elected to be taxed as a REIT under the Internal Revenue Code of 1986, as amended, or the IRC, and, accordingly, we generally will not be subject to federal income taxes provided we distribute our taxable income and meet certain other requirements to qualify as a REIT. We are, however, subject to certain state and local taxes.
Cumulative Other Comprehensive Income (Loss)	Cumulative Other Comprehensive Income (Loss). Cumulative other comprehensive income (loss) consists of unrealized gains and losses related to our investments in SIR, RMR Inc. and AIC. See Notes 6 and 11 for further information regarding these investments.
Reclassifications	Reclassifications. Certain reclassifications have been made to the prior years’ financial statements to conform to the current year’s presentation.
Use of Estimates	Use of Estimates. Preparation of these financial statements in conformity with U.S. generally accepted accounting principles, or GAAP, requires us to make estimates and assumptions that may affect the amounts reported in these consolidated financial statements and related notes. The actual results could differ from these estimates.
Per Common Share Amounts	Per Common Share Amounts. We calculate basic earnings per common share by dividing net income (loss) by the weighted average number of our common shares of beneficial ownership, $.01 par value, or common shares, or our common shares, outstanding during the period. We calculate diluted earnings per share using the more dilutive of the two class method or the treasury stock method. Unvested share awards and other potentially dilutive common shares and the related impact on earnings, are considered when calculating diluted earnings per share.
Segment Reporting	Segment Reporting. We operate in two business segments: ownership of properties that are primarily leased to government tenants and our equity method investment in SIR.