Summary of Significant Accounting Policies	12 Months Ended
Dec. 31, 2018
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies BASIS OF PRESENTATION. Our consolidated financial statements include the accounts of Senior Housing Properties Trust, or SNH, we, us or our, and our subsidiaries, all of which, except for the joint venture discussed below, are 100% owned directly or indirectly by us. All intercompany transactions and balances with or among our consolidated subsidiaries have been eliminated. Accounting principles generally accepted in the United States, or GAAP, require us to make estimates and assumptions that may affect the amounts reported in these financial statements and related notes. The actual results could differ from these estimates. We have made reclassifications to the prior years’ financial statements to conform to the current year’s presentation. These reclassifications had no effect on net income or equity. In March 2017, we entered a joint venture with a sovereign investor for one of our MOBs (two buildings) located in Boston, Massachusetts. We have determined that this joint venture is a variable interest entity, or VIE, as defined under the Consolidation Topic of the Financial Accounting Standards Board, or FASB, Accounting Standards Codification, or the Codification. We concluded that we must consolidate this VIE because we are the entity with the power to direct the activities that most significantly impact the VIE’s economic performance and we have the obligation to absorb losses of, and the right to receive benefits from, the VIE that could be significant to the VIE, and therefore are the primary beneficiary of the VIE. The assets of this VIE were $1,061,593 and $1,102,986 as of December 31, 2018 and 2017, respectively, and consist primarily of the net real estate owned by the joint venture. The liabilities of this VIE were $714,226 and $720,678 as of December 31, 2018 and 2017, respectively, and consist primarily of the secured debts on the property. The sovereign investor's interest in this consolidated entity is reflected as noncontrolling interest in our consolidated financial statements. See Note 10 for further information about this joint venture. REAL ESTATE PROPERTIES. We record properties at our cost and calculate depreciation on real estate investments on a straight line basis over estimated useful lives generally up 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. We record 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. For transactions that qualify as business combinations, we allocate the excess, if any, of the consideration over the fair value of the assets acquired to goodwill. We amortize capitalized above market lease values (included in acquired real estate leases in our consolidated balance sheets) as a reduction to rental income over the remaining non-cancelable terms of the respective leases. We amortize capitalized below market lease values (presented as acquired real estate lease obligations in our consolidated balance sheets) as an increase to rental income over the non-cancelable periods of the respective leases. For the years ended December 31, 2018, 2017 and 2016, such amortization resulted in an increase in rental income of $5,787, $5,349 and $4,941, respectively. We amortize the value of in place leases exclusive of the value of above market and below market in place leases to expense over the remaining non-cancelable periods of the respective leases. During the years ended December 31, 2018, 2017 and 2016, such amortization included in depreciation totaled $72,925, $72,035 and $92,818, respectively. If a lease is terminated prior to its stated expiration, the unamortized amount relating to that lease is written off. 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 consists of amounts escrowed for real estate taxes, insurance and capital expenditures at certain of our mortgaged properties, security deposits for residents of our managed senior living communities and cash held for the operations of our joint venture MOB. INVESTMENTS IN EQUITY SECURITIES. We classify the shares we own of The RMR Group Inc., or RMR Inc., and Five Star Senior Living Inc., or Five Star, as equity securities and carry them at fair value in other assets in our consolidated balance sheets. Unrealized gains and losses are recorded through earnings effective January 1, 2018 as a result of our adoption of FASB Accounting Standards Update, or ASU, No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities. Prior to the adoption of ASU No. 2016-01, unrealized gains and losses were recorded as a component of cumulative other comprehensive income in shareholder's equity. At December 31, 2018 and 2017, we owned 2,637,408 shares of class A common stock of RMR Inc. Our historical cost basis for these shares is $69,826. At December 31, 2018 and 2017, our investment in RMR Inc. had a fair value of $139,994 and $156,398, respectively, including unrealized gains of $70,168 and $86,572, respectively. In connection with our investment in RMR Inc., we recorded a liability for the amount by which the estimated fair value for accounting purposes exceeded the price we paid for our investment in RMR Inc. common stock in June 2015. This liability is being amortized on a straight line basis through December 31, 2035 as an allocated reduction to our business management and property management fee expense. We amortized $3,772 of this liability during each of the years ended December 31, 2018, 2017 and 2016. These amounts are included in the net business management and property management fee amounts for such periods. As of December 31, 2018, the remaining unamortized amount of this liability was $64,390. At December 31, 2018 and 2017, we owned 4,235,000 common shares of Five Star. Our adjusted cost basis for these shares is $6,353. At December 31, 2018 and 2017, our investment in Five Star had a fair value of $2,033 and $6,353, respectively, including unrealized losses of $4,320 and $0, respectively. In performing our periodic evaluation of other than temporary impairment of our investment in Five Star for the year ended December 31, 2016, we determined, based on the length of time and the extent to which the market value of our Five Star investment was below our carrying value, that the decline in fair value was deemed to be other than temporary at December 31, 2016. Other than temporary impairment review of equity securities is no longer applicable subsequent to the adoption of ASU No. 2016-01. Accordingly, we recorded a $2,795 loss on impairment to reduce the carrying value of our Five Star investment to its estimated fair value during the fourth quarter of 2016. We estimated fair value using the closing price of Five Star common shares as of December 31, 2016 ($2.70 per share). We recorded an additional loss on impairment of $5,082 to reduce the carrying value of our Five Star investment to its estimated fair value during the second quarter of 2017. See Notes 5 and 7 for further information regarding our investments in RMR Inc. and Five Star. EQUITY METHOD INVESTMENTS. At December 31, 2018, we owned 14.3% of Affiliates Insurance Company, or AIC’s, outstanding equity. Although we own less than 20% of AIC, we use the equity method to account for this investment because we believe that we have significant influence over AIC because all of our Trustees are also directors of AIC. Under the equity method, we record our percentage share of net earnings from AIC in our consolidated statements of comprehensive income. See Note 7 for further information regarding our investment in AIC. We evaluate our equity method investments to determine if there are any events or circumstances (impairment indicators) that are likely to have a significant adverse effect on the fair value of the investment. Fair value estimates consider all available financial information related to the investee. Examples of such impairment indicators include, but are not limited to, a significant deterioration in earnings performance, a significant adverse change in the regulatory or economic environment of an investee; or a significant doubt about an investee's ability to continue as a going concern. If an impairment indicator is identified, an estimate of the fair value of the investment is compared to its carrying value. If the fair value of the investment is less than its carrying value, a determination is made as to whether the related impairment is other than temporary. 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. DEBT ISSUANCE COSTS. Debt issuance costs include issuance or assumption costs related to borrowings and we amortize those costs as interest expense over the terms of the respective loans. Debt issuance costs for our unsecured revolving credit facility totaled $17,170 at December 31, 2018 and 2017, and accumulated amortization of debt issuance costs totaled $12,364 and $10,784 at December 31, 2018 and 2017, respectively, and are included in other assets in our consolidated balance sheets. Debt issuance costs for our unsecured term loans, senior notes, and mortgage notes payable totaled $44,117 and $39,821 at December 31, 2018 and 2017, respectively, and accumulated amortization of debt issuance costs totaled $16,665 and $13,085, respectively, and are presented in our balance sheet as a direct deduction from the associated debt liability. Future amortization of debt issuance costs to be recognized with respect to our loans as of December 31, 2018 are estimated to be $4,801 in 2019, $3,909 in 2020, $3,795 in 2021, $1,952 in 2022, $1,635 in 2023 and $16,166 thereafter. DEFERRED LEASING COSTS. Deferred leasing costs include capitalized brokerage and other fees associated with the successful negotiation of leases, which are amortized to depreciation and amortization expense on a straight line basis over the terms of the respective leases. Deferred leasing costs are included in other assets in our consolidated balance sheets. Deferred leasing costs totaled $35,145 and $31,081 at December 31, 2018 and 2017, respectively, and accumulated amortization of deferred leasing costs totaled $11,422 and $8,769 at December 31, 2018 and 2017, respectively. At December 31, 2018, the remaining weighted average amortization period is approximately 7.5 years. Future amortization of deferred leasing costs to be recognized during the current terms of our existing leases as of December 31, 2018, are estimated to be $4,807 in 2019, $4,238 in 2020, $3,455 in 2021, $2,661 in 2022, $2,118 in 2023 and $6,444 thereafter. REVENUE RECOGNITION. We recognize rental income from operating leases on a straight line basis over the term of each lease agreement. We recognize percentage rents when realizable and earned, which is generally during the fourth quarter of the year. For the years ended December 31, 2018, 2017 and 2016, percentage rents earned aggregated $8,443, $10,168 and $10,169, respectively. As of December 31, 2018, we owned 76 senior living communities that are managed by Five Star for our account. We derive our revenues at these managed senior living communities primarily from services our manager provides to residents on our behalf and we record revenues when services are provided. We use the taxable REIT subsidiary, or TRS, structure authorized by the REIT Investment Diversification and Empowerment Act for nearly all of our managed senior living communities. PER COMMON SHARE AMOUNTS. We calculate basic earnings per common share by dividing net income by the weighted average number of our common shares of beneficial interest, $.01 par value, or our common shares, outstanding during the period. We calculate diluted earnings per common 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. INCOME TAXES. We have elected to be taxed as a REIT under the United States Internal Revenue Code of 1986, as amended, or the IRC, and as such are generally not subject to federal and most state income taxation on our operating income, provided we distribute our taxable income to our shareholders and meet certain organization and operating requirements. We do, however, lease nearly all of our managed senior living communities to our TRSs, that, unlike most of our subsidiaries, file separate tax returns and are subject to federal and state income taxes. Our consolidated income tax provision includes the income tax provision related to the operations of our TRSs and certain state income taxes incurred by us, despite our REIT status. The Income Taxes Topic of the Codification prescribes how we should recognize, measure and present in our financial statements uncertain tax positions that have been taken or are expected to be taken in a tax return. Tax benefits are recognized to the extent that it is “more likely than not” that a particular tax position will be sustained upon examination or audit. To the extent the “more likely than not” standard has been satisfied, the benefit associated with a tax position is measured as the largest amount that has a greater than 50% likelihood of being realized upon settlement. We classify interest and penalties related to uncertain tax positions, if any, in our financial statements as a component of general and administrative expense. SEGMENT REPORTING. As of December 31, 2018, we have four operating segments, of which three are separate reporting segments. We aggregate our MOBs, our triple net leased senior living communities and our managed senior living communities into three reporting segments, based on their similar operating and economic characteristics. The first reporting segment includes MOBs where the tenants pay us rent. The second reporting segment includes triple net leased senior living communities that provide short term and long term residential care and other services for residents and from which we receive rents from the operators. The third reporting segment includes managed senior living communities that provide short term and long term residential care and other services for residents where we pay fees to the operator to manage the communities for our account. Our fourth segment includes all of our other operations, including certain properties that offer wellness, fitness and spa services to members and with respect to which we receive rents from operators, which we do not consider to be sufficiently material to constitute a separate reporting segment. See Note 11 for further information regarding our reportable operating segments. NEW ACCOUNTING PRONOUNCEMENTS. On January 1, 2018, we adopted FASB ASU No. 2014-09 (and related clarifying guidance issued by the FASB), Revenue From Contracts With Customers, which outlines a comprehensive model for entities to use in accounting for revenue arising from contracts with customers. ASU No. 2014-09 states that “an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services.” While ASU No. 2014-09 specifically references contracts with customers, it may apply to certain other transactions such as the sale of real estate or equipment. A substantial portion of our total revenues includes residents fees and services which relate to contracts with residents for housing services at properties leased to our TRSs. In accordance with ASU No. 2018-11, Leases (Topic 842): Targeted Improvements issued in July 2018, we have concluded that the non-lease components of our contracts with residents for housing services at properties leased to our TRSs are the predominant component of the contract for our existing agreements as of January 1, 2019. Additionally, we currently expect that the non-lease components of our contracts with residents for housing services at properties leased to our TRSs entered into in 2019 will be identified as the predominant component of such contracts. Therefore, beginning January 1, 2019, we currently expect that we will recognize revenue for our contracts with residents for housing services at properties leased to our TRSs under ASU No. 2014-09 for our existing agreements as of January 1, 2019 and for agreements entered into thereafter. After the adoption of ASU No. 2016-02, Leases and ASU No. 2018-11, we currently expect the timing and pattern of revenue recognition will be substantially the same as that prior to the adoption of these standards. We have adopted ASU No. 2014-09 using the modified retrospective approach. The adoption of ASU No. 2014-09 did not have a material impact on the amount or timing of our revenue recognition in our consolidated financial statements. On January 1, 2018, we adopted FASB ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities, which changes how entities measure certain equity investments and present changes in the fair value of financial liabilities measured under the fair value option that are attributable to their own credit. The implementation of ASU No. 2016-01 resulted in the reclassification of historical changes in the fair value of our available for sale equity securities of $86,573 from cumulative other comprehensive income to cumulative net income. We also reclassified $841 from cumulative other comprehensive income to cumulative net income for our share of cumulative other comprehensive income of our equity method investee. Effective January 1, 2018, changes in the fair value of our equity securities are recorded through earnings in accordance with ASU No. 2016-01. On January 1, 2018, we adopted FASB ASU No. 2016-18, Restricted Cash, which requires companies to show the changes in the total of cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. ASU No. 2016-18 also requires a reconciliation of the totals in the statement of cash flows to the related captions in the balance sheet. As a result, amounts included in restricted cash in our consolidated balance sheets are presented with cash and cash equivalents in our consolidated statements of cash flows to the related captions in the consolidated balance sheets. Restricted cash totaled $15,095 and $16,083 as of December 31, 2018 and 2017, respectively. The implementation of ASU No. 2016-18 resulted in an increase of $12,254 and a decrease of $2,326 to net cash provided by operating activities for the years ended December 31, 2017 and 2016, respectively. The adoption of ASU No. 2016-18 did not change our consolidated balance sheet presentation. In February 2016, the FASB issued ASU No. 2016-02, Leases. In July 2018, the FASB issued ASU No. 2018-10, Codification Improvements to Topic 842, Leases and ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. In December 2018, the FASB issued ASU No. 2018-20 Leases (Topic 842), Narrow-Scope Improvements for Lessors. Collectively, these standards set out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). ASU No. 2016-02 requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase of the leased asset by the lessee. This classification will determine whether the lease expense is recognized based on an effective interest method or on a straight line basis over the term of the lease. The new standard requires lessors to account for leases using an approach that is substantially equivalent to existing guidance for sales type leases, direct financing leases and operating leases. In addition, under ASU No. 2016-02, lessors will only capitalize incremental direct leasing costs. As a result, we will no longer be able to capitalize non-incremental legal costs and instead will be required to expense these costs as incurred. We adopted these standards as of January 1, 2019. Upon adoption, we applied the package of practical expedients that allows an entity to not reassess (i) whether any expired or existing contracts are or contain leases, (ii) lease classification for any expired or existing leases and (iii) initial direct costs for any expired or existing leases. Furthermore, we applied the optional transition method in ASU No. 2018-11, which allows entities to initially apply the new leases standard at the adoption date and recognize a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption, if any. Additionally, our leases met the criteria in ASU No. 2018-11 to not separate non-lease components from the related lease component, therefore the accounting for these leases remained largely unchanged from the previous standard. ASU No. 2018-11 also provides lessors with the option to elect a practical expedient allowing them to not separate lease and non-lease components in a contract for the purpose of revenue recognition and disclosure. This practical expedient is limited to circumstances in which: (i) the timing and pattern of transfer are the same for the non-lease component and the related lease component and (ii) the lease component, if accounted for separately, would be classified as an operating lease. This practical expedient causes an entity to assess whether a contract is predominantly lease or service based and recognize the entire contract under the relevant accounting guidance (i.e., predominantly lease-based would be accounted for under ASU No. 2016-02 and predominantly service-based would be accounted for under ASU No. 2014-09). Upon adoption of ASU No. 2016-02 and ASU No. 2018-11, we elected the lessor practical expedient within ASU No. 2018-11 and completed our assessment of predominance as it relates to our contracts with residents for housing services at properties leased to our TRSs and expect to recognize revenue from these properties under ASU No. 2014-09. For leases in which we are the lessee, primarily ground leases, we will recognize a right of use asset and a lease liability equal to the present value of the minimum lease payments with rental payments being applied to the lease liability and to interest expense and the right of use asset being amortized over the term of the lease. The adoption of this standard is expected to result in an increase to total assets and liabilities by $5,000 to $7,000. In addition, we are the lessee at certain of our managed senior living communities. These leases are short term in nature, are cancellable by either party with no fee or do not result in an annual expense in excess of our capitalization policy and, as a result, will not be recorded on our consolidated balance sheets. The adoption of ASU No. 2016-02 and the related ASU improvements did not have a material impact in our consolidated financial statements. In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires that entities use a new forward looking “expected loss” model that generally will result in the earlier recognition of allowance for credit losses. The measurement of expected credit losses is based upon historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. ASU No. 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. We are currently assessing the potential impact the adoption of ASU No. 2016-13 will have in our consolidated financial statements. On October 1, 2018, we adopted FASB ASU No. 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, which aligns the measurement and classification guidance for share based payments to nonemployees with the guidance for share based payments to employees, with certain exceptions. The adoption of this standard did not have a material impact in our consolidated financial statements.

Summary of Significant Accounting Policies

BASIS OF PRESENTATION. Our consolidated financial statements include the accounts of Senior Housing Properties Trust, or SNH, we, us or our, and our subsidiaries, all of which, except for the joint venture discussed below, are 100% owned directly or indirectly by us. All intercompany transactions and balances with or among our consolidated subsidiaries have been eliminated. Accounting principles generally accepted in the United States, or GAAP, require us to make estimates and assumptions that may affect the amounts reported in these financial statements and related notes. The actual results could differ from these estimates. We have made reclassifications to the prior years’ financial statements to conform to the current year’s presentation. These reclassifications had no effect on net income or equity.

In March 2017, we entered a joint venture with a sovereign investor for one of our MOBs (two buildings) located in Boston, Massachusetts. We have determined that this joint venture is a variable interest entity, or VIE, as defined under the Consolidation Topic of the Financial Accounting Standards Board, or FASB, Accounting Standards Codification, or the Codification. We concluded that we must consolidate this VIE because we are the entity with the power to direct the activities that most significantly impact the VIE’s economic performance and we have the obligation to absorb losses of, and the right to receive benefits from, the VIE that could be significant to the VIE, and therefore are the primary beneficiary of the VIE. The assets of this VIE were $1,061,593 and $1,102,986 as of December 31, 2018 and 2017, respectively, and consist primarily of the net real estate owned by the joint venture. The liabilities of this VIE were $714,226 and $720,678 as of December 31, 2018 and 2017, respectively, and consist primarily of the secured debts on the property. The sovereign investor's interest in this consolidated entity is reflected as noncontrolling interest in our consolidated financial statements. See Note 10 for further information about this joint venture.

REAL ESTATE PROPERTIES. We record properties at our cost and calculate depreciation on real estate investments on a straight line basis over estimated useful lives generally up 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. We record 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. For transactions that qualify as business combinations, we allocate the excess, if any, of the consideration over the fair value of the assets acquired to goodwill.

We amortize capitalized above market lease values (included in acquired real estate leases in our consolidated balance sheets) as a reduction to rental income over the remaining non-cancelable terms of the respective leases. We amortize capitalized below market lease values (presented as acquired real estate lease obligations in our consolidated balance sheets) as an increase to rental income over the non-cancelable periods of the respective leases. For the years ended December 31, 2018, 2017 and 2016, such amortization resulted in an increase in rental income of $5,787, $5,349 and $4,941, respectively. We amortize the value of in place leases exclusive of the value of above market and below market in place leases to expense over the remaining non-cancelable periods of the respective leases. During the years ended December 31, 2018, 2017 and 2016, such amortization included in depreciation totaled $72,925, $72,035 and $92,818, respectively. If a lease is terminated prior to its stated expiration, the unamortized amount relating to that lease is written off.

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 consists of amounts escrowed for real estate taxes, insurance and capital expenditures at certain of our mortgaged properties, security deposits for residents of our managed senior living communities and cash held for the operations of our joint venture MOB.

INVESTMENTS IN EQUITY SECURITIES. We classify the shares we own of The RMR Group Inc., or RMR Inc., and Five Star Senior Living Inc., or Five Star, as equity securities and carry them at fair value in other assets in our consolidated balance sheets. Unrealized gains and losses are recorded through earnings effective January 1, 2018 as a result of our adoption of FASB Accounting Standards Update, or ASU, No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities. Prior to the adoption of ASU No. 2016-01, unrealized gains and losses were recorded as a component of cumulative other comprehensive income in shareholder's equity.

At December 31, 2018 and 2017, we owned 2,637,408 shares of class A common stock of RMR Inc. Our historical cost basis for these shares is $69,826. At December 31, 2018 and 2017, our investment in RMR Inc. had a fair value of $139,994 and $156,398, respectively, including unrealized gains of $70,168 and $86,572, respectively. In connection with our investment in RMR Inc., we recorded a liability for the amount by which the estimated fair value for accounting purposes exceeded the price we paid for our investment in RMR Inc. common stock in June 2015. This liability is being amortized on a straight line basis through December 31, 2035 as an allocated reduction to our business management and property management fee expense. We amortized $3,772 of this liability during each of the years ended December 31, 2018, 2017 and 2016. These amounts are included in the net business management and property management fee amounts for such periods. As of December 31, 2018, the remaining unamortized amount of this liability was $64,390.

At December 31, 2018 and 2017, we owned 4,235,000 common shares of Five Star. Our adjusted cost basis for these shares is $6,353. At December 31, 2018 and 2017, our investment in Five Star had a fair value of $2,033 and $6,353, respectively, including unrealized losses of $4,320 and $0, respectively. In performing our periodic evaluation of other than temporary impairment of our investment in Five Star for the year ended December 31, 2016, we determined, based on the length of time and the extent to which the market value of our Five Star investment was below our carrying value, that the decline in fair value was deemed to be other than temporary at December 31, 2016. Other than temporary impairment review of equity securities is no longer applicable subsequent to the adoption of ASU No. 2016-01. Accordingly, we recorded a $2,795 loss on impairment to reduce the carrying value of our Five Star investment to its estimated fair value during the fourth quarter of 2016. We estimated fair value using the closing price of Five Star common shares as of December 31, 2016 ($2.70 per share). We recorded an additional loss on impairment of $5,082 to reduce the carrying value of our Five Star investment to its estimated fair value during the second quarter of 2017.

See Notes 5 and 7 for further information regarding our investments in RMR Inc. and Five Star.

EQUITY METHOD INVESTMENTS. At December 31, 2018, we owned 14.3% of Affiliates Insurance Company, or AIC’s, outstanding equity. Although we own less than 20% of AIC, we use the equity method to account for this investment because we believe that we have significant influence over AIC because all of our Trustees are also directors of AIC. Under the equity method, we record our percentage share of net earnings from AIC in our consolidated statements of comprehensive income. See Note 7 for further information regarding our investment in AIC.

We evaluate our equity method investments to determine if there are any events or circumstances (impairment indicators) that are likely to have a significant adverse effect on the fair value of the investment. Fair value estimates consider all available financial information related to the investee. Examples of such impairment indicators include, but are not limited to, a significant deterioration in earnings performance, a significant adverse change in the regulatory or economic environment of an investee; or a significant doubt about an investee's ability to continue as a going concern. If an impairment indicator is identified, an estimate of the fair value of the investment is compared to its carrying value. If the fair value of the investment is less than its carrying value, a determination is made as to whether the related impairment is other than temporary. 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.

DEBT ISSUANCE COSTS. Debt issuance costs include issuance or assumption costs related to borrowings and we amortize those costs as interest expense over the terms of the respective loans. Debt issuance costs for our unsecured revolving credit facility totaled $17,170 at December 31, 2018 and 2017, and accumulated amortization of debt issuance costs totaled $12,364 and $10,784 at December 31, 2018 and 2017, respectively, and are included in other assets in our consolidated balance sheets. Debt issuance costs for our unsecured term loans, senior notes, and mortgage notes payable totaled $44,117 and $39,821 at December 31, 2018 and 2017, respectively, and accumulated amortization of debt issuance costs totaled $16,665 and $13,085, respectively, and are presented in our balance sheet as a direct deduction from the associated debt liability. Future amortization of debt issuance costs to be recognized with respect to our loans as of December 31, 2018 are estimated to be $4,801 in 2019, $3,909 in 2020, $3,795 in 2021, $1,952 in 2022, $1,635 in 2023 and $16,166 thereafter.

DEFERRED LEASING COSTS. Deferred leasing costs include capitalized brokerage and other fees associated with the successful negotiation of leases, which are amortized to depreciation and amortization expense on a straight line basis over the terms of the respective leases. Deferred leasing costs are included in other assets in our consolidated balance sheets. Deferred leasing costs totaled $35,145 and $31,081 at December 31, 2018 and 2017, respectively, and accumulated amortization of deferred leasing costs totaled $11,422 and $8,769 at December 31, 2018 and 2017, respectively. At December 31, 2018, the remaining weighted average amortization period is approximately 7.5 years. Future amortization of deferred leasing costs to be recognized during the current terms of our existing leases as of December 31, 2018, are estimated to be $4,807 in 2019, $4,238 in 2020, $3,455 in 2021, $2,661 in 2022, $2,118 in 2023 and $6,444 thereafter.

REVENUE RECOGNITION. We recognize rental income from operating leases on a straight line basis over the term of each lease agreement. We recognize percentage rents when realizable and earned, which is generally during the fourth quarter of the year. For the years ended December 31, 2018, 2017 and 2016, percentage rents earned aggregated $8,443, $10,168 and $10,169, respectively.

As of December 31, 2018, we owned 76 senior living communities that are managed by Five Star for our account. We derive our revenues at these managed senior living communities primarily from services our manager provides to residents on our behalf and we record revenues when services are provided. We use the taxable REIT subsidiary, or TRS, structure authorized by the REIT Investment Diversification and Empowerment Act for nearly all of our managed senior living communities.

PER COMMON SHARE AMOUNTS. We calculate basic earnings per common share by dividing net income by the weighted average number of our common shares of beneficial interest, $.01 par value, or our common shares, outstanding during the period. We calculate diluted earnings per common 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.

INCOME TAXES. We have elected to be taxed as a REIT under the United States Internal Revenue Code of 1986, as amended, or the IRC, and as such are generally not subject to federal and most state income taxation on our operating income, provided we distribute our taxable income to our shareholders and meet certain organization and operating requirements. We do, however, lease nearly all of our managed senior living communities to our TRSs, that, unlike most of our subsidiaries, file separate tax returns and are subject to federal and state income taxes. Our consolidated income tax provision includes the income tax provision related to the operations of our TRSs and certain state income taxes incurred by us, despite our REIT status.

The Income Taxes Topic of the Codification prescribes how we should recognize, measure and present in our financial statements uncertain tax positions that have been taken or are expected to be taken in a tax return. Tax benefits are recognized to the extent that it is “more likely than not” that a particular tax position will be sustained upon examination or audit. To the extent the “more likely than not” standard has been satisfied, the benefit associated with a tax position is measured as the largest amount that has a greater than 50% likelihood of being realized upon settlement. We classify interest and penalties related to uncertain tax positions, if any, in our financial statements as a component of general and administrative expense.

SEGMENT REPORTING. As of December 31, 2018, we have four operating segments, of which three are separate reporting segments. We aggregate our MOBs, our triple net leased senior living communities and our managed senior living communities into three reporting segments, based on their similar operating and economic characteristics. The first reporting segment includes MOBs where the tenants pay us rent. The second reporting segment includes triple net leased senior living communities that provide short term and long term residential care and other services for residents and from which we receive rents from the operators. The third reporting segment includes managed senior living communities that provide short term and long term residential care and other services for residents where we pay fees to the operator to manage the communities for our account. Our fourth segment includes all of our other operations, including certain properties that offer wellness, fitness and spa services to members and with respect to which we receive rents from operators, which we do not consider to be sufficiently material to constitute a separate reporting segment.

See Note 11 for further information regarding our reportable operating segments.

NEW ACCOUNTING PRONOUNCEMENTS. On January 1, 2018, we adopted FASB ASU No. 2014-09 (and related clarifying guidance issued by the FASB), Revenue From Contracts With Customers, which outlines a comprehensive model for entities to use in accounting for revenue arising from contracts with customers. ASU No. 2014-09 states that “an entity recognizes revenue to depict the transfer of promised goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services.” While ASU No. 2014-09 specifically references contracts with customers, it may apply to certain other transactions such as the sale of real estate or equipment. A substantial portion of our total revenues includes residents fees and services which relate to contracts with residents for housing services at properties leased to our TRSs. In accordance with ASU No. 2018-11, Leases (Topic 842): Targeted Improvements issued in July 2018, we have concluded that the non-lease components of our contracts with residents for housing services at properties leased to our TRSs are the predominant component of the contract for our existing agreements as of January 1, 2019. Additionally, we currently expect that the non-lease components of our contracts with residents for housing services at properties leased to our TRSs entered into in 2019 will be identified as the predominant component of such contracts. Therefore, beginning January 1, 2019, we currently expect that we will recognize revenue for our contracts with residents for housing services at properties leased to our TRSs under ASU No. 2014-09 for our existing agreements as of January 1, 2019 and for agreements entered into thereafter. After the adoption of ASU No. 2016-02, Leases and ASU No. 2018-11, we currently expect the timing and pattern of revenue recognition will be substantially the same as that prior to the adoption of these standards. We have adopted ASU No. 2014-09 using the modified retrospective approach. The adoption of ASU No. 2014-09 did not have a material impact on the amount or timing of our revenue recognition in our consolidated financial statements.

On January 1, 2018, we adopted FASB ASU No. 2016-01, Recognition and Measurement of Financial Assets and Financial Liabilities, which changes how entities measure certain equity investments and present changes in the fair value of financial liabilities measured under the fair value option that are attributable to their own credit. The implementation of ASU No. 2016-01 resulted in the reclassification of historical changes in the fair value of our available for sale equity securities of $86,573 from cumulative other comprehensive income to cumulative net income. We also reclassified $841 from cumulative other comprehensive income to cumulative net income for our share of cumulative other comprehensive income of our equity method investee. Effective January 1, 2018, changes in the fair value of our equity securities are recorded through earnings in accordance with ASU No. 2016-01.

On January 1, 2018, we adopted FASB ASU No. 2016-18, Restricted Cash, which requires companies to show the changes in the total of cash and cash equivalents and restricted cash and restricted cash equivalents in the statement of cash flows. ASU No. 2016-18 also requires a reconciliation of the totals in the statement of cash flows to the related captions in the balance sheet. As a result, amounts included in restricted cash in our consolidated balance sheets are presented with cash and cash equivalents in our consolidated statements of cash flows to the related captions in the consolidated balance sheets. Restricted cash totaled $15,095 and $16,083 as of December 31, 2018 and 2017, respectively. The implementation of ASU No. 2016-18 resulted in an increase of $12,254 and a decrease of $2,326 to net cash provided by operating activities for the years ended December 31, 2017 and 2016, respectively. The adoption of ASU No. 2016-18 did not change our consolidated balance sheet presentation.

In February 2016, the FASB issued ASU No. 2016-02, Leases. In July 2018, the FASB issued ASU No. 2018-10, Codification Improvements to Topic 842, Leases and ASU No. 2018-11, Leases (Topic 842): Targeted Improvements. In December 2018, the FASB issued ASU No. 2018-20 Leases (Topic 842), Narrow-Scope Improvements for Lessors. Collectively, these standards set out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). ASU No. 2016-02 requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase of the leased asset by the lessee. This classification will determine whether the lease expense is recognized based on an effective interest method or on a straight line basis over the term of the lease. The new standard requires lessors to account for leases using an approach that is substantially equivalent to existing guidance for sales type leases, direct financing leases and operating leases. In addition, under ASU No. 2016-02, lessors will only capitalize incremental direct leasing costs. As a result, we will no longer be able to capitalize non-incremental legal costs and instead will be required to expense these costs as incurred. We adopted these standards as of January 1, 2019. Upon adoption, we applied the package of practical expedients that allows an entity to not reassess (i) whether any expired or existing contracts are or contain leases, (ii) lease classification for any expired or existing leases and (iii) initial direct costs for any expired or existing leases. Furthermore, we applied the optional transition method in ASU No. 2018-11, which allows entities to initially apply the new leases standard at the adoption date and recognize a cumulative effect adjustment to the opening balance of retained earnings in the period of adoption, if any. Additionally, our leases met the criteria in ASU No. 2018-11 to not separate non-lease components from the related lease component, therefore the accounting for these leases remained largely unchanged from the previous standard. ASU No. 2018-11 also provides lessors with the option to elect a practical expedient allowing them to not separate lease and non-lease components in a contract for the purpose of revenue recognition and disclosure. This practical expedient is limited to circumstances in which: (i) the timing and pattern of transfer are the same for the non-lease component and the related lease component and (ii) the lease component, if accounted for separately, would be classified as an operating lease. This practical expedient causes an entity to assess whether a contract is predominantly lease or service based and recognize the entire contract under the relevant accounting guidance (i.e., predominantly lease-based would be accounted for under ASU No. 2016-02 and predominantly service-based would be accounted for under ASU No. 2014-09). Upon adoption of ASU No. 2016-02 and ASU No. 2018-11, we elected the lessor practical expedient within ASU No. 2018-11 and completed our assessment of predominance as it relates to our contracts with residents for housing services at properties leased to our TRSs and expect to recognize revenue from these properties under ASU No. 2014-09.

For leases in which we are the lessee, primarily ground leases, we will recognize a right of use asset and a lease liability equal to the present value of the minimum lease payments with rental payments being applied to the lease liability and to interest expense and the right of use asset being amortized over the term of the lease. The adoption of this standard is expected to result in an increase to total assets and liabilities by $5,000 to $7,000. In addition, we are the lessee at certain of our managed senior living communities. These leases are short term in nature, are cancellable by either party with no fee or do not result in an annual expense in excess of our capitalization policy and, as a result, will not be recorded on our consolidated balance sheets.

The adoption of ASU No. 2016-02 and the related ASU improvements did not have a material impact in our consolidated financial statements.

In June 2016, the FASB issued ASU No. 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which requires that entities use a new forward looking “expected loss” model that generally will result in the earlier recognition of allowance for credit losses. The measurement of expected credit losses is based upon historical experience, current conditions, and reasonable and supportable forecasts that affect the collectability of the reported amount. ASU No. 2016-13 is effective for fiscal years beginning after December 15, 2019, including interim periods within those fiscal years. We are currently assessing the potential impact the adoption of ASU No. 2016-13 will have in our consolidated financial statements.

On October 1, 2018, we adopted FASB ASU No. 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Nonemployee Share-Based Payment Accounting, which aligns the measurement and classification guidance for share based payments to nonemployees with the guidance for share based payments to employees, with certain exceptions. The adoption of this standard did not have a material impact in our consolidated financial statements.