Summary of Significant Accounting Policies	12 Months Ended
Dec. 31, 2016
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 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 shareholders’ equity. 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. When we acquire a property, we estimate the purchase price allocations and the useful lives of our properties. In some circumstances, we engage third party 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 third party appraisers. For properties qualifying as acquired businesses under Accounting Standards Codification, or the Codification, Topic No. 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 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, 2016, 2015 and 2014, such amortization resulted in an increase in rental income of $4,941, $4,060 and $2,322, 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, 2016, 2015 and 2014, such amortization included in depreciation totaled $92,818, $80,040 and $38,970, 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 carry cash and cash equivalents, consisting of overnight repurchase agreements and short term investments with original maturities of three months or less at the date of purchase, at cost plus accrued interest, which approximates fair value. RESTRICTED CASH. Restricted cash consists of amounts escrowed for real estate taxes, insurance and capital expenditures at certain of our mortgaged properties and security deposits for residents of our managed senior living communities. INVESTMENTS IN AVAILABLE FOR SALE SECURITIES. We classify the shares we own of Five Star Quality Care, Inc., or Five Star, and The RMR Group Inc., or RMR Inc., as available for sale securities and carry them at fair value in other assets in our consolidated balance sheets, with unrealized gains and losses reported as a component of shareholders' equity. 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. At December 31, 2016 and 2015, we owned 4,235,000 common shares of Five Star. In performing our periodic evaluation of other than temporary impairment of our investment in Five Star for the fourth quarter of 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. 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). At December 31, 2016, our investment in Five Star had an adjusted cost basis and fair value of $11,435. At December 31, 2015, our investment in Five Star had a fair value of $13,467, including an unrealized loss of $747. At December 31, 2016 and 2015, 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, 2016 and 2015, our investment in RMR Inc. had a fair value of $104,178 and $38,005, respectively, including an unrealized gain of $34,352 and an unrealized loss of $31,821, respectively. We concluded, for accounting purposes, that the cash and share consideration of $60,700 we paid for our investment in 5,272,787 shares of class A common stock of RMR Inc. represented a discount to the fair value of these shares. We initially accounted for this investment under the cost method of accounting and recorded this investment at its estimated fair value of $136,278 as of June 5, 2015 using Level 3 inputs, as defined in the fair value hierarchy under GAAP. As a result, we recorded a liability for the amount by which the estimated fair value of these shares exceeded the price we paid for these shares. This liability is included in other liabilities in our consolidated balance sheets. 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 and $2,145 of this liability during the years ended December 31, 2016 and 2015, respectively. These amounts are included in the net business management and property management fee amounts for such periods. As of December 31, 2016, the remaining unamortized amount of this liability was $71,933. See Notes 5 and 7 for further information regarding our investments in Five Star and RMR Inc. EQUITY METHOD INVESTMENTS. At December 31, 2016, 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 $10,980 at both December 31, 2016 and 2015, and accumulated amortization of debt issuance costs totaled $9,039 and $7,174 at December 31, 2016 and 2015, 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 $49,331 and $39,497 at December 31, 2016 and 2015, respectively, and accumulated amortization of debt issuance costs totaled $17,560 and $15,608, 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, 2016 are estimated to be $5,829 in 2017, $4,084 in 2018, $3,225 in 2019, $1,810 in 2020, $1,695 in 2021 and $17,069 thereafter. DEFERRED LEASING COSTS. Deferred leasing costs include capitalized brokerage, legal 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 on our consolidated balance sheets. Deferred leasing costs totaled $24,825 and $21,708 at December 31, 2016 and 2015, respectively, and accumulated amortization of deferred leasing costs totaled $6,898 and $5,561 at December 31, 2016 and 2015, respectively. Included in deferred leasing costs at December 31, 2016, is $140 of estimated costs associated with leases under negotiation. At December 31, 2016, the remaining weighted average amortization period is approximately 8.5 years. Future amortization of deferred leasing costs to be recognized during the current terms of our existing leases as of December 31, 2016, are estimated to be $3,183 in 2017, $2,835 in 2018, $2,473 in 2019, $2,030 in 2020, $1,449 in 2021 and $5,817 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, 2016, 2015 and 2014, percentage rents earned aggregated $10,169, $10,062 and $10,155, respectively. As of December 31, 2016, we owned 68 senior living communities that are managed by Five Star for our account. Five communities were previously managed from the date we acquired these communities in May 2015 through December 14, 2016 by a third party operator that was affiliated with a triple net leased senior living tenant of ours that defaulted on its lease obligations to us in the first half of 2016. We refer to these 68 communities as the managed senior living communities. We derive our revenues at these managed senior living communities primarily from services our managers provide 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 Internal Revenue Code of 1986, as amended, 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, 2016, we have four operating segments, of which three are separate reporting segments. We aggregate our triple net leased senior living communities, our managed senior living communities and our MOBs into three reporting segments, based on their similar operating and economic characteristics. The first reporting segment includes triple net leased senior living communities that provide short term and long term residential care and other services for residents. The second reporting segment includes managed senior living communities that provide short term and long term residential care and other services for residents. The third reporting segment includes properties leased to medical providers, medical related businesses, clinics and biotech laboratory tenants, or MOBs. Our fourth segment includes all of our other operations, including certain properties that offer wellness, fitness and spa services to members, which we do not consider to be sufficiently material to constitute a separate reporting segment. See Note 10 for further information regarding our reportable operating segments. NEW ACCOUNTING PRONOUNCEMENTS. On January 1, 2016, we adopted the Financial Accounting Standards Board, or FASB, Accounting Standards Update, or ASU, No. 2015-02, Consolidation. Among other things, this update changed how an entity determines the primary beneficiary of a variable interest entity. The implementation of this update did not have an impact in our consolidated financial statements. On January 1, 2016, we adopted FASB ASU No. 2015-03, Simplifying the Presentation of Debt Issuance Costs, which requires debt issuance costs to be presented in the balance sheet as a direct deduction from the associated debt liability, and ASU No. 2015-15, Presentation and Subsequent Measurement of Debt Issuance Costs Associated with Line-of-Credit Arrangements – Amendments to SEC Paragraphs Pursuant to Staff Announcement at June 18, 2015 EITF Meeting, which addresses the presentation of debt issuance costs related to line of credit arrangements. The implementation of these updates resulted in the reclassification of certain of our capitalized debt issuance costs as an offset to the associated debt liability in our consolidated balance sheets. The classification of capitalized debt issuance costs related to our unsecured revolving credit facility remains unchanged in accordance with ASU No. 2015-15. As of December 31, 2015, debt issuance costs related to our unsecured term loans, senior unsecured notes and secured debt and capital leases of $3,695, $16,530 and $3,664, respectively, were reclassified from assets to an offset to the associated debt liability in our consolidated balance sheets. On January 1, 2016, we adopted FASB ASU No. 2015-16, Simplifying the Accounting for Measurement-Period Adjustments, which eliminates the requirement for an acquirer in a business combination to account for measurement period adjustments retrospectively. Instead, acquirers must recognize measurement period adjustments during the period in which they determine the amounts, including the effect on earnings of any amounts they would have recorded in previous periods if the accounting had been completed at the acquisition date. The implementation of this update did not have an impact in our consolidated financial statements. In December 2016, we adopted FASB ASU, No. 2014-15, Presentation of Financial Statements - Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. This update requires an entity to evaluate whether there are conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued (or within one year after the financial statements are available to be issued when applicable) and to provide related footnote disclosures in certain circumstances. The implementation of this update did not have an impact in our consolidated financial statements. In May 2014, the FASB issued ASU No. 2014-09, Revenue From Contracts With Customers, which outlines a comprehensive model for entities to use in accounting for revenue arising from contracts with customers. This ASU 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 2014-09 specifically references contracts with customers, it may apply to certain other transactions such as the sale of real estate or equipment. In 2015, the FASB provided for a one year deferral of the effective date for ASU 2014-09, which is now effective for us beginning January 1, 2018. A substantial portion of our revenue consists of rental income from leasing arrangements, including leases with residents at properties leased to our TRSs, which is specifically excluded from ASU 2014-09. We are continuing to evaluate ASU 2014-09 (and related clarifying guidance issued by the FASB); however, we do not expect its adoption to have a significant impact on the timing of our revenue recognition in our consolidated financial statements. We currently expect to adopt the standard using the modified retrospective approach. In January 2016, the FASB issued 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. This update is effective for interim and annual periods beginning after December 15, 2017, with early adoption permitted subject to certain conditions. Currently, changes in fair value of these investments are recorded through other comprehensive income. Under this ASU, these changes will be recorded through earnings. We are continuing to evaluate this guidance, but we expect the implementation of this guidance will affect how changes in the fair value of available for sale equity investments we hold are presented in our consolidated financial statements. In February 2016, the FASB issued ASU No. 2016-02, Leases, which sets 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. A lessee is also required to record a right of use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases today. 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. ASU No. 2016-02 is effective for reporting periods beginning after December 15, 2018, with early adoption permitted. We are currently assessing the potential impact the adoption of ASU No. 2016-02 will have in our consolidated financial statements. In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation, which identifies areas for simplification involving several aspects of accounting for share based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, an option to recognize gross stock compensation expense with actual forfeitures recognized as they occur, as well as certain classifications on the statement of cash flows. ASU No. 2016-09 is effective for reporting periods beginning after December 31, 2016. We do not expect the adoption of ASU No. 2016-09 to 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 that adoption of ASU No. 2016-13 will have in our consolidated financial statements. In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, which clarifies how companies present and classify certain cash receipts and cash payments in the statement of cash flows. ASU No. 2016-15 is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. We are currently assessing the potential impact that adoption of ASU No. 2016-15 will have in our consolidated financial statements. In November 2016, the FASB issued ASU No. 2016-18, Restricted Cash, which clarifies how companies should present restricted cash and restricted cash equivalents. Companies will show the changes in the total of cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. The new standard requires a reconciliation of the totals in the statement of cash flows to the related captions in the balance sheet. ASU No. 2016-18 is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. We are currently assessing the potential impact that adoption of ASU No. 2016-18 will have in our consolidated financial statements. In January 2017, the FASB issued ASU No. 2017-01, Clarifying the Definition of a Business, which provides additional guidance on evaluating whether transactions should be accounted for as an acquisition (or disposal) of assets or of a business. The update defines three requirements for a set of assets and activities (collectively referred to as a “set”) to be considered a business: inputs, processes and outputs. ASU No. 2017-01 is effective for annual periods beginning after December 15, 2017, including interim periods within those fiscal years. This update will be applied prospectively to any transactions occurring within the period of adoption. We are currently assessing the impact of the update; however, subsequent to adoption we believe certain property acquisitions which under previous guidance would have been accounted for as business combinations will be accounted for as acquisitions of assets. In an acquisition of assets, certain acquisition costs are capitalized as opposed to expensed under business combination guidance.

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 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 shareholders’ equity.

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. When we acquire a property, we estimate the purchase price allocations and the useful lives of our properties. In some circumstances, we engage third party 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 third party appraisers. For properties qualifying as acquired businesses under Accounting Standards Codification, or the Codification, Topic No. 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 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, 2016, 2015 and 2014, such amortization resulted in an increase in rental income of $4,941, $4,060 and $2,322, 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, 2016, 2015 and 2014, such amortization included in depreciation totaled $92,818, $80,040 and $38,970, 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 carry cash and cash equivalents, consisting of overnight repurchase agreements and short term investments with original maturities of three months or less at the date of purchase, at cost plus accrued interest, which approximates fair value.

RESTRICTED CASH. Restricted cash consists of amounts escrowed for real estate taxes, insurance and capital expenditures at certain of our mortgaged properties and security deposits for residents of our managed senior living communities.

INVESTMENTS IN AVAILABLE FOR SALE SECURITIES. We classify the shares we own of Five Star Quality Care, Inc., or Five Star, and The RMR Group Inc., or RMR Inc., as available for sale securities and carry them at fair value in other assets in our consolidated balance sheets, with unrealized gains and losses reported as a component of shareholders' equity. 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.

At December 31, 2016 and 2015, we owned 4,235,000 common shares of Five Star. In performing our periodic evaluation of other than temporary impairment of our investment in Five Star for the fourth quarter of 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. 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). At December 31, 2016, our investment in Five Star had an adjusted cost basis and fair value of $11,435. At December 31, 2015, our investment in Five Star had a fair value of $13,467, including an unrealized loss of $747.

At December 31, 2016 and 2015, 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, 2016 and 2015, our investment in RMR Inc. had a fair value of $104,178 and $38,005, respectively, including an unrealized gain of $34,352 and an unrealized loss of $31,821, respectively. We concluded, for accounting purposes, that the cash and share consideration of $60,700 we paid for our investment in 5,272,787 shares of class A common stock of RMR Inc. represented a discount to the fair value of these shares. We initially accounted for this investment under the cost method of accounting and recorded this investment at its estimated fair value of $136,278 as of June 5, 2015 using Level 3 inputs, as defined in the fair value hierarchy under GAAP. As a result, we recorded a liability for the amount by which the estimated fair value of these shares exceeded the price we paid for these shares. This liability is included in other liabilities in our consolidated balance sheets. 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 and $2,145 of this liability during the years ended December 31, 2016 and 2015, respectively. These amounts are included in the net business management and property management fee amounts for such periods. As of December 31, 2016, the remaining unamortized amount of this liability was $71,933.

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

EQUITY METHOD INVESTMENTS. At December 31, 2016, 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 $10,980 at both December 31, 2016 and 2015, and accumulated amortization of debt issuance costs totaled $9,039 and $7,174 at December 31, 2016 and 2015, 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 $49,331 and $39,497 at December 31, 2016 and 2015, respectively, and accumulated amortization of debt issuance costs totaled $17,560 and $15,608, 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, 2016 are estimated to be $5,829 in 2017, $4,084 in 2018, $3,225 in 2019, $1,810 in 2020, $1,695 in 2021 and $17,069 thereafter.

DEFERRED LEASING COSTS. Deferred leasing costs include capitalized brokerage, legal 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 on our consolidated balance sheets. Deferred leasing costs totaled $24,825 and $21,708 at December 31, 2016 and 2015, respectively, and accumulated amortization of deferred leasing costs totaled $6,898 and $5,561 at December 31, 2016 and 2015, respectively. Included in deferred leasing costs at December 31, 2016, is $140 of estimated costs associated with leases under negotiation. At December 31, 2016, the remaining weighted average amortization period is approximately 8.5 years. Future amortization of deferred leasing costs to be recognized during the current terms of our existing leases as of December 31, 2016, are estimated to be $3,183 in 2017, $2,835 in 2018, $2,473 in 2019, $2,030 in 2020, $1,449 in 2021 and $5,817 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, 2016, 2015 and 2014, percentage rents earned aggregated $10,169, $10,062 and $10,155, respectively.

As of December 31, 2016, we owned 68 senior living communities that are managed by Five Star for our account. Five communities were previously managed from the date we acquired these communities in May 2015 through December 14, 2016 by a third party operator that was affiliated with a triple net leased senior living tenant of ours that defaulted on its lease obligations to us in the first half of 2016. We refer to these 68 communities as the managed senior living communities. We derive our revenues at these managed senior living communities primarily from services our managers provide 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 Internal Revenue Code of 1986, as amended, 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, 2016, we have four operating segments, of which three are separate reporting segments. We aggregate our triple net leased senior living communities, our managed senior living communities and our MOBs into three reporting segments, based on their similar operating and economic characteristics. The first reporting segment includes triple net leased senior living communities that provide short term and long term residential care and other services for residents. The second reporting segment includes managed senior living communities that provide short term and long term residential care and other services for residents. The third reporting segment includes properties leased to medical providers, medical related businesses, clinics and biotech laboratory tenants, or MOBs. Our fourth segment includes all of our other operations, including certain properties that offer wellness, fitness and spa services to members, which we do not consider to be sufficiently material to constitute a separate reporting segment.

See Note 10 for further information regarding our reportable operating segments.

NEW ACCOUNTING PRONOUNCEMENTS. On January 1, 2016, we adopted the Financial Accounting Standards Board, or FASB, Accounting Standards Update, or ASU, No. 2015-02, Consolidation. Among other things, this update changed how an entity determines the primary beneficiary of a variable interest entity. The implementation of this update did not have an impact in our consolidated financial statements.

On January 1, 2016, we adopted FASB ASU No. 2015-03, Simplifying the Presentation of Debt Issuance Costs, which requires debt issuance costs to be presented in the balance sheet as a direct deduction from the associated debt liability, and ASU No. 2015-15, Presentation and Subsequent Measurement of Debt Issuance Costs Associated with Line-of-Credit Arrangements – Amendments to SEC Paragraphs Pursuant to Staff Announcement at June 18, 2015 EITF Meeting, which addresses the presentation of debt issuance costs related to line of credit arrangements. The implementation of these updates resulted in the reclassification of certain of our capitalized debt issuance costs as an offset to the associated debt liability in our consolidated balance sheets. The classification of capitalized debt issuance costs related to our unsecured revolving credit facility remains unchanged in accordance with ASU No. 2015-15. As of December 31, 2015, debt issuance costs related to our unsecured term loans, senior unsecured notes and secured debt and capital leases of $3,695, $16,530 and $3,664, respectively, were reclassified from assets to an offset to the associated debt liability in our consolidated balance sheets.

On January 1, 2016, we adopted FASB ASU No. 2015-16, Simplifying the Accounting for Measurement-Period Adjustments, which eliminates the requirement for an acquirer in a business combination to account for measurement period adjustments retrospectively. Instead, acquirers must recognize measurement period adjustments during the period in which they determine the amounts, including the effect on earnings of any amounts they would have recorded in previous periods if the accounting had been completed at the acquisition date. The implementation of this update did not have an impact in our consolidated financial statements.

In December 2016, we adopted FASB ASU, No. 2014-15, Presentation of Financial Statements - Going Concern: Disclosure of Uncertainties about an Entity’s Ability to Continue as a Going Concern. This update requires an entity to evaluate whether there are conditions or events that raise substantial doubt about the entity’s ability to continue as a going concern within one year after the date that the financial statements are issued (or within one year after the financial statements are available to be issued when applicable) and to provide related footnote disclosures in certain circumstances. The implementation of this update did not have an impact in our consolidated financial statements.

In May 2014, the FASB issued ASU No. 2014-09, Revenue From Contracts With Customers, which outlines a comprehensive model for entities to use in accounting for revenue arising from contracts with customers. This ASU 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 2014-09 specifically references contracts with customers, it may apply to certain other transactions such as the sale of real estate or equipment. In 2015, the FASB provided for a one year deferral of the effective date for ASU 2014-09, which is now effective for us beginning January 1, 2018. A substantial portion of our revenue consists of rental income from leasing arrangements, including leases with residents at properties leased to our TRSs, which is specifically excluded from ASU 2014-09. We are continuing to evaluate ASU 2014-09 (and related clarifying guidance issued by the FASB); however, we do not expect its adoption to have a significant impact on the timing of our revenue recognition in our consolidated financial statements. We currently expect to adopt the standard using the modified retrospective approach.

In January 2016, the FASB issued 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. This update is effective for interim and annual periods beginning after December 15, 2017, with early adoption permitted subject to certain conditions. Currently, changes in fair value of these investments are recorded through other comprehensive income. Under this ASU, these changes will be recorded through earnings. We are continuing to evaluate this guidance, but we expect the implementation of this guidance will affect how changes in the fair value of available for sale equity investments we hold are presented in our consolidated financial statements.

In February 2016, the FASB issued ASU No. 2016-02, Leases, which sets 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. A lessee is also required to record a right of use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less will be accounted for similar to existing guidance for operating leases today. 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. ASU No. 2016-02 is effective for reporting periods beginning after December 15, 2018, with early adoption permitted. We are currently assessing the potential impact the adoption of ASU No. 2016-02 will have in our consolidated financial statements.

In March 2016, the FASB issued ASU No. 2016-09, Compensation - Stock Compensation, which identifies areas for simplification involving several aspects of accounting for share based payment transactions, including the income tax consequences, classification of awards as either equity or liabilities, an option to recognize gross stock compensation expense with actual forfeitures recognized as they occur, as well as certain classifications on the statement of cash flows. ASU No. 2016-09 is effective for reporting periods beginning after December 31, 2016. We do not expect the adoption of ASU No. 2016-09 to 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 that adoption of ASU No. 2016-13 will have in our consolidated financial statements.

In August 2016, the FASB issued ASU No. 2016-15, Statement of Cash Flows (Topic 230): Classification of Certain Cash Receipts and Cash Payments, which clarifies how companies present and classify certain cash receipts and cash payments in the statement of cash flows. ASU No. 2016-15 is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. We are currently assessing the potential impact that adoption of ASU No. 2016-15 will have in our consolidated financial statements.

In November 2016, the FASB issued ASU No. 2016-18, Restricted Cash, which clarifies how companies should present restricted cash and restricted cash equivalents. Companies will show the changes in the total of cash, cash equivalents, restricted cash and restricted cash equivalents in the statement of cash flows. The new standard requires a reconciliation of the totals in the statement of cash flows to the related captions in the balance sheet. ASU No. 2016-18 is effective for fiscal years beginning after December 15, 2017, including interim periods within those fiscal years. We are currently assessing the potential impact that adoption of ASU No. 2016-18 will have in our consolidated financial statements.

In January 2017, the FASB issued ASU No. 2017-01, Clarifying the Definition of a Business, which provides additional guidance on evaluating whether transactions should be accounted for as an acquisition (or disposal) of assets or of a business. The update defines three requirements for a set of assets and activities (collectively referred to as a “set”) to be considered a business: inputs, processes and outputs. ASU No. 2017-01 is effective for annual periods beginning after December 15, 2017, including interim periods within those fiscal years. This update will be applied prospectively to any transactions occurring within the period of adoption. We are currently assessing the impact of the update; however, subsequent to adoption we believe certain property acquisitions which under previous guidance would have been accounted for as business combinations will be accounted for as acquisitions of assets. In an acquisition of assets, certain acquisition costs are capitalized as opposed to expensed under business combination guidance.