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Related Person Transactions (Details) (USD $) | 1 Months Ended | 12 Months Ended | 1 Months Ended | 3 Months Ended | 1 Months Ended | 5 Months Ended | 10 Months Ended | 6 Months Ended | 1 Months Ended | 43 Months Ended | 1 Months Ended | 0 Months Ended | 1 Months Ended | 0 Months Ended | 2 Months Ended
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Feb. 28, 2015 | Apr. 30, 2014 | Jan. 31, 2013 | Jul. 31, 2012 | Dec. 31, 2014 sqft item property state | Dec. 31, 2013 | Dec. 31, 2012 | Aug. 31, 2012 item | Dec. 31, 2014 property | Jan. 31, 2015 property sqft | Dec. 31, 2013 property | Oct. 31, 2014 property | Sep. 30, 2014 property | Dec. 31, 2014 item | Sep. 30, 2013 | Apr. 30, 2012 | Jul. 31, 2014 item | Aug. 31, 2013 property | Jun. 30, 2013 property | May 31, 2011 property | Dec. 31, 2014 property item | Dec. 31, 2013 property | Oct. 31, 2014 | Jun. 30, 2014 property item | Jan. 31, 2014 | May 09, 2014 | May 08, 2014 | Sep. 30, 2014 | Jul. 31, 2013 item | Dec. 23, 2013 item | Feb. 24, 2015
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties agreed to be offered for sale |  |  |  |  | 5 snh_NumberOfRealEstatePropertiesHeldForSale |  |  |  | 5 snh_NumberOfRealEstatePropertiesHeldForSale |  |  |  |  | 5 snh_NumberOfRealEstatePropertiesHeldForSale |  |  |  |  |  |  | 5 snh_NumberOfRealEstatePropertiesHeldForSale |  |  |  |  |  |  |  |  |  |
Number of properties pending acquisition |  |  |  |  | 38 snh_NumberOfPropertiesPendingAcquisition |  |  |  | 38 snh_NumberOfPropertiesPendingAcquisition |  |  |  |  | 38 snh_NumberOfPropertiesPendingAcquisition |  |  |  |  |  |  | 38 snh_NumberOfPropertiesPendingAcquisition |  |  |  |  |  |  |  |  |  |
Number of employees |  |  |  |  | 0 snh_RelatedPartyEmployeesNumber |  |  |  | 0 snh_RelatedPartyEmployeesNumber |  |  |  |  | 0 snh_RelatedPartyEmployeesNumber |  |  |  |  |  |  | 0 snh_RelatedPartyEmployeesNumber |  |  |  |  |  |  |  |  |  |
Income recognized arising from equity investments |  |  |  |  | $ 87,000 us-gaap_IncomeLossFromEquityMethodInvestments | $ 334,000 us-gaap_IncomeLossFromEquityMethodInvestments | $ 316,000 us-gaap_IncomeLossFromEquityMethodInvestments |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of shares (in shares) | 31,050,000 us-gaap_StockIssuedDuringPeriodSharesNewIssues | 15,525,000 us-gaap_StockIssuedDuringPeriodSharesNewIssues | 11,500,000 us-gaap_StockIssuedDuringPeriodSharesNewIssues | 13,800,000 us-gaap_StockIssuedDuringPeriodSharesNewIssues |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of real estate properties leased (in square feet) |  |  |  |  | 750,000 snh_SquareFootageOfRealEstatePropertyLeased |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Interest and other income |  |  |  |  | 425,000 us-gaap_InterestAndOtherIncome | 711,000 us-gaap_InterestAndOtherIncome | 1,117,000 us-gaap_InterestAndOtherIncome |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of states in which properties are located |  |  |  |  | 38 us-gaap_NumberOfStatesInWhichEntityOperates |  |  |  | 38 us-gaap_NumberOfStatesInWhichEntityOperates |  |  |  |  | 38 us-gaap_NumberOfStatesInWhichEntityOperates |  |  |  |  |  |  | 38 us-gaap_NumberOfStatesInWhichEntityOperates |  |  |  |  |  |  |  |  |  |
Mortgages |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Early repayment of debt variable portion |  |  |  |  |  |  |  | 199,197,000 snh_EarlyRepaymentOfSeniorSecuredDebtVariablePortion / us-gaap_DebtInstrumentAxis = us-gaap_MortgagesMember | 23,234,000 snh_EarlyRepaymentOfSeniorSecuredDebtVariablePortion / us-gaap_DebtInstrumentAxis = us-gaap_MortgagesMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Properties released from mortgage as collateral |  |  |  |  |  |  |  | 11 snh_NumberOfRealEstatePropertiesReleasedFromMortgageCollateral / us-gaap_DebtInstrumentAxis = us-gaap_MortgagesMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of Real Estate Properties Collateralized |  |  |  |  | 45 snh_NumberOfRealEstatePropertiesCollateralized / us-gaap_DebtInstrumentAxis = us-gaap_MortgagesMember |  |  | 28 snh_NumberOfRealEstatePropertiesCollateralized / us-gaap_DebtInstrumentAxis = us-gaap_MortgagesMember | 45 snh_NumberOfRealEstatePropertiesCollateralized / us-gaap_DebtInstrumentAxis = us-gaap_MortgagesMember |  |  |  |  | 45 snh_NumberOfRealEstatePropertiesCollateralized / us-gaap_DebtInstrumentAxis = us-gaap_MortgagesMember |  |  |  |  |  |  | 45 snh_NumberOfRealEstatePropertiesCollateralized / us-gaap_DebtInstrumentAxis = us-gaap_MortgagesMember |  |  |  |  |  |  |  |  |  |
Senior living communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties agreed to be offered for sale |  |  |  |  | 4 snh_NumberOfRealEstatePropertiesHeldForSale / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember | 10 snh_NumberOfRealEstatePropertiesHeldForSale / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember |  |  | 4 snh_NumberOfRealEstatePropertiesHeldForSale / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember |  | 10 snh_NumberOfRealEstatePropertiesHeldForSale / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember |  |  | 4 snh_NumberOfRealEstatePropertiesHeldForSale / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember |  |  |  |  |  |  | 4 snh_NumberOfRealEstatePropertiesHeldForSale / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember | 10 snh_NumberOfRealEstatePropertiesHeldForSale / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember |  |  |  |  |  |  |  |  |
Number of living units |  |  |  |  | 312 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember | 744 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember |  |  | 312 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember |  | 744 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember |  |  | 312 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember |  |  |  |  |  |  | 312 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember | 744 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember |  |  |  |  |  |  |  |  |
MOBs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties agreed to be offered for sale |  |  |  |  | 4 snh_NumberOfRealEstatePropertiesHeldForSale / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember |  |  |  | 4 snh_NumberOfRealEstatePropertiesHeldForSale / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember |  |  |  |  |  |  |  |  | 4 snh_NumberOfRealEstatePropertiesHeldForSale / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember |  |  |  |  |  |  |  |  |
Acquisition | Senior living communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties acquired or agreed to be acquired |  |  |  |  | 2 snh_NumberOfPropertiesAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember | 6 snh_NumberOfPropertiesAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisition | MOBs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties acquired or agreed to be acquired |  |  |  |  | 2 snh_NumberOfPropertiesAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember | 6 snh_NumberOfPropertiesAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase price |  |  |  |  | 1,156,963,000 snh_RealEstateAggregatePurchasePrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember | 117,475,000 snh_RealEstateAggregatePurchasePrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of real estate properties (in square feet) |  |  |  |  | 1,776,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember | 385,171,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember |  |  | 1,776,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember |  | 385,171,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember |  |  | 1,776,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember |  |  |  |  |  |  | 1,776,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember | 385,171,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember |  |  |  |  |  |  |  |  |
Acquisition | MOBs | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties acquired or agreed to be acquired |  |  |  |  | 23 snh_NumberOfPropertiesAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  | 23 snh_NumberOfPropertiesAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase price |  |  |  |  |  |  |  |  |  | 539,000,000 snh_RealEstateAggregatePurchasePrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of real estate properties (in square feet) |  |  |  |  |  |  |  |  |  | 2,200,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Acquisition | MOBs | Texas |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties acquired or agreed to be acquired |  | 1 snh_NumberOfPropertiesAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember / us-gaap_StatementGeographicalAxis = stpr_TX |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Purchase price |  | 32,932,000 snh_RealEstateAggregatePurchasePrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember / us-gaap_StatementGeographicalAxis = stpr_TX |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of real estate properties (in square feet) |  | 125,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember / us-gaap_StatementGeographicalAxis = stpr_TX |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale price of properties under agreement to be sold |  |  |  |  |  |  |  |  |  |  | 92,550,000 snh_RealEstateAggregateSalesPrice / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember | 15,650,000 snh_RealEstateAggregateSalesPrice / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties sold or agreed to be sold |  |  |  |  |  |  |  |  |  |  | 3 snh_NumberOfPropertiesSold / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember | 6 snh_NumberOfPropertiesSold / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale | Senior living communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties sold or agreed to be sold |  |  |  |  | 6 snh_NumberOfPropertiesSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale | Rehabilitation hospitals |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties sold or agreed to be sold |  |  |  |  |  | 2 snh_NumberOfPropertiesSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_RehabilitationHospitalsMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  | 2 snh_NumberOfPropertiesSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_RehabilitationHospitalsMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale | MOBs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale price of properties under agreement to be sold |  |  |  |  |  |  |  |  |  |  |  |  | 11,675,000 snh_RealEstateAggregateSalesPrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties sold or agreed to be sold |  |  |  |  | 3 snh_NumberOfPropertiesSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  |  |  | 3 snh_NumberOfPropertiesSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Agreement to acquire | Senior living communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of living units |  |  |  |  | 3,466 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_AgreementToAcquireMember |  |  |  | 3,466 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_AgreementToAcquireMember |  |  |  |  | 3,466 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_AgreementToAcquireMember |  |  |  |  |  |  | 3,466 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_AgreementToAcquireMember |  |  |  |  |  |  |  |  |  |
Purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  | 790,000,000 snh_RealEstateAggregatePurchasePrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_AgreementToAcquireMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Five Star |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Beneficial ownership of common shares (as a percent) |  |  |  |  | 100.00%snh_InvestmentOwnershipPercentage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 100.00%snh_InvestmentOwnershipPercentage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 100.00%snh_InvestmentOwnershipPercentage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 100.00%snh_InvestmentOwnershipPercentage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Investment in common shares |  |  |  |  | 4,235,000 us-gaap_InvestmentOwnedBalanceShares / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 4,235,000 us-gaap_InvestmentOwnedBalanceShares / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 4,235,000 us-gaap_InvestmentOwnedBalanceShares / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 4,235,000 us-gaap_InvestmentOwnedBalanceShares / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Percentage of total shares outstanding |  |  |  |  | 8.60%snh_InvestmentOwnedPercentageOfTotalSharesOutstanding / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 8.60%snh_InvestmentOwnedPercentageOfTotalSharesOutstanding / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 8.60%snh_InvestmentOwnedPercentageOfTotalSharesOutstanding / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 8.60%snh_InvestmentOwnedPercentageOfTotalSharesOutstanding / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Minimum annual rent payable to entity |  |  |  |  | 190,663,000 snh_OperatingLeasesAnnualRent / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total rental income recognized |  |  |  |  | 196,269,000 us-gaap_OperatingLeasesIncomeStatementLeaseRevenue / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 203,724,000 us-gaap_OperatingLeasesIncomeStatementLeaseRevenue / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 200,912,000 us-gaap_OperatingLeasesIncomeStatementLeaseRevenue / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rents receivable |  |  |  |  | 17,310,000 snh_RentsReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 17,960,000 snh_RentsReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 17,680,000 snh_RentsReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  | 17,310,000 snh_RentsReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  | 17,960,000 snh_RentsReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  | 17,310,000 snh_RentsReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 17,310,000 snh_RentsReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 17,960,000 snh_RentsReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |
Real estate improvements purchased |  |  |  |  | 25,804,000 snh_RealEstateImprovementsByLesseePurchased / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 27,208,000 snh_RealEstateImprovementsByLesseePurchased / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 30,520,000 snh_RealEstateImprovementsByLesseePurchased / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase or decrease in annual lease rent payable |  |  |  |  | 2,066,000 snh_IncreaseDecreaseOperatingLeasesAnnualRent / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 2,177,000 snh_IncreaseDecreaseOperatingLeasesAnnualRent / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 2,456,000 snh_IncreaseDecreaseOperatingLeasesAnnualRent / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  | (9,500,000)snh_IncreaseDecreaseOperatingLeasesAnnualRent / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of combination or pooling agreements |  |  |  |  | 4 snh_NumberOfPoolingAgreements / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 4 snh_NumberOfPoolingAgreements / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 4 snh_NumberOfPoolingAgreements / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 4 snh_NumberOfPoolingAgreements / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Property management agreement expense |  |  |  |  | 9,765,000 snh_RelatedPartyTransactionExpensesFromPropertyManagementAgreementTransactionsWithRelatedParty / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 9,229,000 snh_RelatedPartyTransactionExpensesFromPropertyManagementAgreementTransactionsWithRelatedParty / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 5,582,000 snh_RelatedPartyTransactionExpensesFromPropertyManagementAgreementTransactionsWithRelatedParty / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum percentage of ownership of lessee's voting stock above which the entity has the option to cancel all its rights, minimum |  |  |  |  | 9.80%snh_MinimumInvestmentOwnershipPercentageEligibleForOptionToCancelRightsOfLessee / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 9.80%snh_MinimumInvestmentOwnershipPercentageEligibleForOptionToCancelRightsOfLessee / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 9.80%snh_MinimumInvestmentOwnershipPercentageEligibleForOptionToCancelRightsOfLessee / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 9.80%snh_MinimumInvestmentOwnershipPercentageEligibleForOptionToCancelRightsOfLessee / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Annual return as a percentage of invested surplus specified as a base for determining incentive fee |  |  |  |  | 35.00%snh_RelatedPartyTransactionPropertyManagementAgreementAnnualReturnAsPercentageOfInvestedCapital / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 35.00%snh_RelatedPartyTransactionPropertyManagementAgreementAnnualReturnAsPercentageOfInvestedCapital / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 35.00%snh_RelatedPartyTransactionPropertyManagementAgreementAnnualReturnAsPercentageOfInvestedCapital / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 35.00%snh_RelatedPartyTransactionPropertyManagementAgreementAnnualReturnAsPercentageOfInvestedCapital / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Incentive fee as percentage of the annual net operating income after the entity realizes an annual return equal to 8% of invested capital |  |  |  |  | 8.00%snh_RelatedPartyTransactionPropertyManagementAgreementIncentiveFeeAsPercentageOfAnnualNetOperatingIncomeAfterRealizationOfSpecifiedPercentageOfAnnualReturn / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 8.00%snh_RelatedPartyTransactionPropertyManagementAgreementIncentiveFeeAsPercentageOfAnnualNetOperatingIncomeAfterRealizationOfSpecifiedPercentageOfAnnualReturn / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 8.00%snh_RelatedPartyTransactionPropertyManagementAgreementIncentiveFeeAsPercentageOfAnnualNetOperatingIncomeAfterRealizationOfSpecifiedPercentageOfAnnualReturn / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 8.00%snh_RelatedPartyTransactionPropertyManagementAgreementIncentiveFeeAsPercentageOfAnnualNetOperatingIncomeAfterRealizationOfSpecifiedPercentageOfAnnualReturn / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Renewal period |  |  |  |  | 15 years |  |  | 5 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Maximum percentage of any class of equity shares that can be acquired without approval |  |  |  |  | 9.80%snh_ShareOwnershipRestrictionsMaximumPercentageOfEquitySharesThatCanBeAcquiredWithoutApproval / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 9.80%snh_ShareOwnershipRestrictionsMaximumPercentageOfEquitySharesThatCanBeAcquiredWithoutApproval / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 9.80%snh_ShareOwnershipRestrictionsMaximumPercentageOfEquitySharesThatCanBeAcquiredWithoutApproval / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 9.80%snh_ShareOwnershipRestrictionsMaximumPercentageOfEquitySharesThatCanBeAcquiredWithoutApproval / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Number of consecutive period during which the entity must not receive the minimum return for the property management agreement to be subject to the pooling agreement |  |  |  |  | 3 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of consecutive renewal terms of agreement |  |  |  |  | 2 snh_RelatedPartyTransactionPropertyManagementAgreementNumberOfConsecutiveRenewalTerms / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  | 9 snh_RelatedPartyTransactionPropertyManagementAgreementNumberOfConsecutiveRenewalTerms / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Management fees as a percentage of gross revenues |  |  |  |  | 3.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 3.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 3.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 3.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Amount agreed to be lent under Bridge Loan Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 80,000,000 us-gaap_MortgageLoansOnRealEstateFaceAmountOfMortgages / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |
Interest and other income |  |  |  |  |  |  | 314,000 us-gaap_InterestAndOtherIncome / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Proceeds from repayment of bridge loan |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 38,000,000 us-gaap_MortgageLoansOnRealEstateCollectionsOfPrincipal / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Incentive fee payable |  |  |  |  | 0 snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 0 snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 0 snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 0 snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Five Star | AL Pooling Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of combination or pooling agreements |  |  |  |  | 3 snh_NumberOfPoolingAgreements / snh_RealEstateAgreementsByTypeAxis = snh_ALPoolingAgreementsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 3 snh_NumberOfPoolingAgreements / snh_RealEstateAgreementsByTypeAxis = snh_ALPoolingAgreementsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 3 snh_NumberOfPoolingAgreements / snh_RealEstateAgreementsByTypeAxis = snh_ALPoolingAgreementsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 3 snh_NumberOfPoolingAgreements / snh_RealEstateAgreementsByTypeAxis = snh_ALPoolingAgreementsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Number of communities that include assisted living units |  |  |  |  | 20 snh_NumberOfCommunitiesThatIncludeAssistedLivingUnits / snh_RealEstateAgreementsByTypeAxis = snh_ALPoolingAgreementsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Five Star | IL Pooling Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of communities that include assisted living units |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 snh_NumberOfCommunitiesThatIncludeAssistedLivingUnits / snh_RealEstateAgreementsByTypeAxis = snh_ILPoolingAgreementMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of communities that include independent living units |  |  |  |  | 2 snh_NumberOfCommunitiesThatIncludeIndependentLivingUnits / snh_RealEstateAgreementsByTypeAxis = snh_ILPoolingAgreementMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Five Star | Second AL Pooling Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of communities that include assisted living units |  |  |  |  | 19 snh_NumberOfCommunitiesThatIncludeAssistedLivingUnits / snh_RealEstateAgreementsByTypeAxis = snh_SecondALPoolingAgreementsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  | 19 snh_NumberOfCommunitiesThatIncludeAssistedLivingUnits / snh_RealEstateAgreementsByTypeAxis = snh_SecondALPoolingAgreementsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |
Five Star | Third AL Pooling Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of communities that include assisted living units |  |  |  |  | 3 snh_NumberOfCommunitiesThatIncludeAssistedLivingUnits / snh_RealEstateAgreementsByTypeAxis = snh_ThirdLPoolingAgreementsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Five Star | Senior living communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of real estate properties leased |  |  |  |  | 181 us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 181 us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 181 us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 181 us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Increase or decrease in annual lease rent payable |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (255,000)snh_IncreaseDecreaseOperatingLeasesAnnualRent / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties sold or agreed to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 snh_NumberOfPropertiesSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties agreed to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 11 snh_NumberOfPropertiesPreviouslyAgreedToBeSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |
Number of properties acquired, referred to as managed properties |  |  |  |  | 46 snh_NumberOfPropertiesAcquiredManagedProperties / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties acquired or agreed to be acquired |  |  |  |  | 46 snh_NumberOfPropertiesAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  | 2 snh_NumberOfPropertiesAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  | 6 snh_NumberOfPropertiesAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember | 36 snh_NumberOfPropertiesAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Purchase price |  |  |  |  |  |  |  |  |  |  |  |  |  | 47,430,000 snh_RealEstateAggregatePurchasePrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Management fees as a percentage of gross revenues |  |  |  |  | 5.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  | 5.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  | 5.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  | 5.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |  |
Five Star | Rehabilitation hospitals |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties sold or agreed to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 snh_NumberOfPropertiesSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_RehabilitationHospitalsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember |  |  |  |  |  |  |  |  |
Five Star | Acquisition | Senior living communities | New York |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of living units |  |  |  |  | 310 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember / us-gaap_StatementGeographicalAxis = stpr_NY |  |  |  | 310 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember / us-gaap_StatementGeographicalAxis = stpr_NY |  |  |  |  | 310 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember / us-gaap_StatementGeographicalAxis = stpr_NY |  |  |  |  |  |  | 310 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember / us-gaap_StatementGeographicalAxis = stpr_NY |  |  |  |  |  |  |  |  |  |
Five Star | Sale | Senior living communities |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase or decrease in annual lease rent payable |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 285,000 snh_IncreaseDecreaseOperatingLeasesAnnualRent / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember | (452,000)snh_IncreaseDecreaseOperatingLeasesAnnualRent / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember | 210,000 snh_IncreaseDecreaseOperatingLeasesAnnualRent / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  |
Sale price of properties under agreement to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,550,000 snh_RealEstateAggregateSalesPrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  | 4,500,000 snh_RealEstateAggregateSalesPrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  |  |
Number of properties sold or agreed to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 snh_NumberOfPropertiesSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  |  |
Number of living units |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 112 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  | 156 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember |  |  |  |  |  |  |
Five Star | Sale | Senior living communities | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase or decrease in annual lease rent payable | (23,000)snh_IncreaseDecreaseOperatingLeasesAnnualRent / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale price of properties under agreement to be sold | 250,000 snh_RealEstateAggregateSalesPrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of living units | 120 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Five Star | Sale | Senior living communities | Texas |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale price of properties under agreement to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,400,000 snh_RealEstateAggregateSalesPrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_StatementGeographicalAxis = stpr_TX |  |  |  |  |  |
Number of properties agreed to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 snh_NumberOfPropertiesPreviouslyAgreedToBeSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_StatementGeographicalAxis = stpr_TX |  |  |  |  |  |
Number of living units |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 36 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_StatementGeographicalAxis = stpr_TX |  |  |  |  |  |
Five Star | Sale | Senior living communities | Virginia |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale price of properties under agreement to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,850,000 snh_RealEstateAggregateSalesPrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_StatementGeographicalAxis = stpr_VA |  |  |  |  |  |  |  |
Number of living units |  |  |  |  |  |  |  |  |  |  |  | 70 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_StatementGeographicalAxis = stpr_VA |  |  |  |  |  |  |  |  |  |  | 70 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_StatementGeographicalAxis = stpr_VA |  |  |  |  |  |  |  |
Five Star | Sale | Senior living communities | Arizona |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Increase or decrease in annual lease rent payable |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | (590,000)snh_IncreaseDecreaseOperatingLeasesAnnualRent / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_StatementGeographicalAxis = stpr_AZ |  |  |  |  |  |  |  |
Sale price of properties under agreement to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,900,000 snh_RealEstateAggregateSalesPrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_StatementGeographicalAxis = stpr_AZ |  |  |  |  |  |  |  |
Number of properties sold or agreed to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 snh_NumberOfPropertiesSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_StatementGeographicalAxis = stpr_AZ |  |  |  |  |  |  |  |
Number of living units |  |  |  |  |  |  |  |  |  |  |  | 177 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_StatementGeographicalAxis = stpr_AZ |  |  |  |  |  |  |  |  |  |  | 177 us-gaap_NumberOfUnitsInRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_SeniorLivingCommunityMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_SaleOfAssetsMember / us-gaap_StatementGeographicalAxis = stpr_AZ |  |  |  |  |  |  |  |
Five Star | Purchase Agreement | Rehabilitation hospitals |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale price of properties under agreement to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90,000,000 snh_RealEstateAggregateSalesPrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_RehabilitationHospitalsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_PurchaseAgreementMember |  |  |  |  |  |  |  |  |
Number of properties sold or agreed to be sold |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 snh_NumberOfPropertiesSold / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_RehabilitationHospitalsMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_FiveStarQualityCareIncMember / us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis = snh_PurchaseAgreementMember |  |  |  |  |  |  |  |  |
D&R Yonkers LLC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Management fees as a percentage of gross revenues |  |  |  |  | 3.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  | 3.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  |  | 3.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  |  |  |  | 3.00%snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  |  |  |  |  |  |  |
Incentive fee payable |  |  |  |  | 0 snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  | 0 snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  |  | 0 snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  |  |  |  | 0 snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  |  |  |  |  |  |  |
Sublease income receivable |  |  |  |  | 3,008,000 snh_OperatingLeasesIncomeStatementAnnualSubleaseRentalRevenueReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  | 3,008,000 snh_OperatingLeasesIncomeStatementAnnualSubleaseRentalRevenueReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  |  | 3,008,000 snh_OperatingLeasesIncomeStatementAnnualSubleaseRentalRevenueReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  |  |  |  | 3,008,000 snh_OperatingLeasesIncomeStatementAnnualSubleaseRentalRevenueReceivable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  |  |  |  |  |  |  |
Sublease rental |  |  |  |  | 2,949,000 us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember | 2,863,000 us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember | 945,000 us-gaap_OperatingLeasesIncomeStatementSubleaseRevenue / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_DAndRYonkersLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
RMR |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property management agreement expense |  |  |  |  | 8,259,000 snh_RelatedPartyTransactionExpensesFromPropertyManagementAgreementTransactionsWithRelatedParty / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 6,568,000 snh_RelatedPartyTransactionExpensesFromPropertyManagementAgreementTransactionsWithRelatedParty / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 5,791,000 snh_RelatedPartyTransactionExpensesFromPropertyManagementAgreementTransactionsWithRelatedParty / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of agreements to avail management and administrative services |  |  |  |  | 2 snh_NumberOfServiceAgreements / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  | 2 snh_NumberOfServiceAgreements / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  | 2 snh_NumberOfServiceAgreements / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  | 2 snh_NumberOfServiceAgreements / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |
Period before which the written notice is required to be given for cancellation of business management agreement and the property management agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 120 days | 60 days |  |  |  |
Number of business days before which the notice is required to be given for termination of property management agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5 days |  |  |  |
Notice period subject to approval by majority vote of independent trustees |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 60 days |  |  |  |
Termination fee ratio |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2.75 snh_RelatedPartyTransactionTerminalFeeRatio / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |
Period on which termination fees computation is based |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 24 months |  |  |  |
Period Within Which Property Management Agreement To Be Renewed Or Terminated |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 months |  |  |  |
Additional termination fee ratio |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12 snh_RelatedPartyTransactionAdditionalTerminationFeeMultiple / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |
Period for providing transition services under business management agreement and property management agreement |  |  |  |  | 120 days |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Business management agreement expense |  |  |  |  | 30,794,000 snh_RelatedPartyTransactionExpensesFromBusinessManagementAgreementTransactionsWithRelatedParty / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 27,013,000 snh_RelatedPartyTransactionExpensesFromBusinessManagementAgreementTransactionsWithRelatedParty / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 25,372,000 snh_RelatedPartyTransactionExpensesFromBusinessManagementAgreementTransactionsWithRelatedParty / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of entities to which RMR provides management services |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 3 snh_NumberOfEntitiesToWhichRelatedPartyProvidesServices / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |
Premium paid for combined and separate directors' and officers' liability insurance policy |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 51,000 snh_CombinedAndSeparateDirectorsAndOfficersLiabilityInsurancePolicyPremiumPaid / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  | 343,000 snh_CombinedAndSeparateDirectorsAndOfficersLiabilityInsurancePolicyPremiumPaid / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |
Issuance of shares (in shares) |  |  |  |  | 123,462 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 21,968 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 20,462 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Liability insurance policy term |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 years |  |  |
Aggregate coverage of combined directors' and officers' liability insurance policy purchased by the related party |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10,000,000 snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPurchasedByRelatedPartyAggregateCoverage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |
Additional liability insurance policy term |  |  |  |  | 1 year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate additional coverage of combined directors' and officers' liability insurance policy purchased by the related party |  |  |  |  | 20,000,000 snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPurchasedByRelatedPartyAdditionalAggregateCoverage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  | 20,000,000 snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPurchasedByRelatedPartyAdditionalAggregateCoverage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  | 20,000,000 snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPurchasedByRelatedPartyAdditionalAggregateCoverage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  | 20,000,000 snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPurchasedByRelatedPartyAdditionalAggregateCoverage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |
Non-indemnifiable coverage of combined directors' and officers' liability insurance policy purchased by the related party |  |  |  |  | 5,000,000 snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPurchasedByRelatedPartyNonIndemnifiableCoverage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Premium payable for combined directors' and officers' liability insurance policy |  |  |  |  | 685,000 snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPremiumPayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  | 685,000 snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPremiumPayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  | 685,000 snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPremiumPayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  | 685,000 snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPremiumPayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |
Incentive fee earned |  |  |  |  | 0 snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeeEarned / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 0 snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeeEarned / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Base management fee payable as a percentage of aggregate book value of real estate assets or transferred assets |  |  |  |  |  | 0.50%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAggregateBookValueOfRealEstateAssetsOrTransferredAssets / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 0.50%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAggregateBookValueOfRealEstateAssetsOrTransferredAssets / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  | 0.50%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAggregateBookValueOfRealEstateAssetsOrTransferredAssets / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  | 0.50%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAggregateBookValueOfRealEstateAssetsOrTransferredAssets / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |
Base management fee payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments up to specified amount |  |  |  |  |  | 0.70%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageHistoricalCostOfRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsUpToSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 0.70%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageHistoricalCostOfRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsUpToSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  | 0.70%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageHistoricalCostOfRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsUpToSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  | 0.70%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageHistoricalCostOfRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsUpToSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |
Base management fee payable as a percentage of historical cost of other real estate investments, excluding transferred assets for investments after specified amount |  |  |  |  |  | 0.50%snh_RelatedPartyTransactionBaseBusinessManagementFeePayableAsPercentageOfHistoricalCostOfOtherRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsAfterTheSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 0.50%snh_RelatedPartyTransactionBaseBusinessManagementFeePayableAsPercentageOfHistoricalCostOfOtherRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsAfterTheSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  | 0.50%snh_RelatedPartyTransactionBaseBusinessManagementFeePayableAsPercentageOfHistoricalCostOfOtherRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsAfterTheSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  | 0.50%snh_RelatedPartyTransactionBaseBusinessManagementFeePayableAsPercentageOfHistoricalCostOfOtherRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsAfterTheSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |
Percentage of incentive fee payable |  |  |  |  |  | 15.00%snh_RelatedPartyTransactionPercentageOfIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 15.00%snh_RelatedPartyTransactionPercentageOfIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  | 15.00%snh_RelatedPartyTransactionPercentageOfIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  | 15.00%snh_RelatedPartyTransactionPercentageOfIncentiveFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |
Cap on the value of incentive fee |  |  |  |  |  | $ 0.02 snh_RelatedPartyTransactionIncentiveFeePerShareMaximum / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | $ 0.02 snh_RelatedPartyTransactionIncentiveFeePerShareMaximum / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  | $ 0.02 snh_RelatedPartyTransactionIncentiveFeePerShareMaximum / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  | 0.02 snh_RelatedPartyTransactionIncentiveFeePerShareMaximum / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |
Pro rata share of internal audit costs |  |  |  |  | 262,000 snh_RelatedPartyTransactionProRataShareOfInternalAuditCosts / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 201,000 snh_RelatedPartyTransactionProRataShareOfInternalAuditCosts / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 193,000 snh_RelatedPartyTransactionProRataShareOfInternalAuditCosts / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period by which business management agreement and property management agreement get automatically renewed |  |  |  |  | 1 year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Rental revenue from related party |  |  |  |  |  |  | 186,000 us-gaap_RevenueFromRelatedParties / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate coverage of separate directors' and officers' liability insurance policy purchased |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 5,000,000 snh_SeparateDirectorsAndOfficersLiabilityInsurancePolicyPurchasedByRelatedPartyAggregateCoverage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |
RMR | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Threshold amount of real estate investments for payment of base management fee |  |  |  |  |  | 250,000,000 snh_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfRealEstateInvestments / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 250,000,000 snh_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfRealEstateInvestments / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  | 250,000,000 snh_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfRealEstateInvestments / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  | 250,000,000 snh_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfRealEstateInvestments / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |
RMR | Restricted shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Awards granted (in shares) |  |  |  |  | 81,700 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = snh_RestrictedSharesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 82,600 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = snh_RestrictedSharesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 78,492 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = snh_RestrictedSharesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Aggregate value of awards granted during the period |  |  |  |  | 1,750,000 snh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue / us-gaap_PlanNameAxis = snh_RestrictedSharesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 1,888,000 snh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue / us-gaap_PlanNameAxis = snh_RestrictedSharesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember | 1,775,000 snh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue / us-gaap_PlanNameAxis = snh_RestrictedSharesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Portion of the awards granted that vested on grant date (as a percent) |  |  |  |  | 20.00%snh_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRightsPercentVestedOnGrantDate / us-gaap_PlanNameAxis = snh_RestrictedSharesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Portion of the awards granted which will vest on each of the next four anniversaries of the grant date |  |  |  |  | 20.00%snh_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRightsToBeVestedOnEachOfNextFourAnniversaries / us-gaap_PlanNameAxis = snh_RestrictedSharesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Award vesting period |  |  |  |  | 4 years |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
RMR | Amended Agreement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Base business management fee payable in common shares (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 10.00%snh_RelatedPartyTransactionPercentageOfBaseBusinessManagementFeePayableInCommonShares / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Base management fee payable as a percentage of aggregate book value of real estate assets or transferred assets |  |  |  |  | 0.50%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAggregateBookValueOfRealEstateAssetsOrTransferredAssets / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |  |  |  | 0.50%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAggregateBookValueOfRealEstateAssetsOrTransferredAssets / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |  |  |  |  | 0.50%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAggregateBookValueOfRealEstateAssetsOrTransferredAssets / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |  |  |  |  |  |  | 0.50%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAggregateBookValueOfRealEstateAssetsOrTransferredAssets / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |  |  |  |  |  |  |  |  |  |
Base management fee payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments up to specified amount |  |  |  |  | 0.70%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageHistoricalCostOfRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsUpToSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |  |  |  | 0.70%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageHistoricalCostOfRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsUpToSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |  |  |  |  | 0.70%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageHistoricalCostOfRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsUpToSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |  |  |  |  |  |  | 0.70%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageHistoricalCostOfRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsUpToSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |  |  |  |  |  |  |  |  |  |
Base management fee payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments exceeding specified amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.50%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageHistoricalCostOfRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsExceedingSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Threshold amount of other real estate investments for payment of base management fee |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 250,000,000.000 snh_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfOtherRealEstateInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Base management fee payable as a percentage of average closing price per share of common shares on NYSE |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.70%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageClosingStockPriceOnStockExchange / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Base management fee payable as a percentage of average market capitalization exceeding specified amount |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 0.50%snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageMarketCapitalizationExceedingSpecifiedAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Threshold amount of average market capitalization for payment of base management fee |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 250,000,000.000 snh_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfAverageMarketCapitalization / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Base business management fee payable in cash (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 90.00%snh_RelatedPartyTransactionPercentageOfBaseBusinessManagementFeePayableInCash / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Incentive management fee payable (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 12.00%snh_RelatedPartyTransactionPercentageForLimitationAndAdjustmentsOfIncentiveManagementFeePayable / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Portion of shares issued in payment of an incentive management fee (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 33.33%snh_RelatedPartyTransactionPercentageOfSharesIssuedInPaymentOfIncentiveManagementFees / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Portion of remaining shares to be vested in equal annual installments (as a percent) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 66.67%snh_RelatedPartyTransactionPercentageOfRemainingSharesToBeVestedInEqualAnnualInstallments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Number of equal annual installments for vesting of common shares |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 snh_RelatedPartyTransactionNumberOfEqualAnnualInstallmentsForVestingOfCommonShares / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Number of times registration right can be exercisable |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2 snh_RelatedPartyTransactionNumberOfTimesRegistrationRightCanBeExercisableByEligibleTransferee / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
RMR | Amended Agreement | Maximum |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Threshold amount of real estate investments for payment of base management fee |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 250,000,000 snh_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfRealEstateInvestments / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
Base management fee payable, average market capitalization |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 250,000,000 snh_RelatedPartyTransactionBaseManagementFeePayableAverageMarketCapitalization / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_TransactionTypeAxis = snh_AmendedAndRestateBusinessManagementAgreementMember |
RMR | Subsequent event |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Issuance of shares (in shares) |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 25,263 us-gaap_StockIssuedDuringPeriodSharesNewIssues / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember / us-gaap_SubsequentEventTypeAxis = us-gaap_SubsequentEventMember
RMR | Regional Offices |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of real estate properties leased (in square feet) |  |  |  |  |  |  | 4,100 snh_SquareFootageOfRealEstatePropertyLeased / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_OfficeMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties agreed to be acquired, or agreed to be acquired, referred as leased properties |  |  |  |  |  |  | 1 snh_NumberOfPropertiesAcquiredLeasedProperties / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_OfficeMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
RMR | MOBs |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Construction supervision fees payable under property management agreement as a percentage of construction costs |  |  |  |  | 5.00%snh_RelatedPartyTransactionPropertyManagementAgreementConstructionSupervisionFeesAsPercentageOfConstructionCosts / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  | 5.00%snh_RelatedPartyTransactionPropertyManagementAgreementConstructionSupervisionFeesAsPercentageOfConstructionCosts / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  | 5.00%snh_RelatedPartyTransactionPropertyManagementAgreementConstructionSupervisionFeesAsPercentageOfConstructionCosts / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  | 5.00%snh_RelatedPartyTransactionPropertyManagementAgreementConstructionSupervisionFeesAsPercentageOfConstructionCosts / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_MedicalOfficeBuildingMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_ReitManagementAndResearchLLCMember |  |  |  |  |  |  |  |  |  |
AIC |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Ownership percentage held by the entity and other shareholders |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 14.30%us-gaap_EquityMethodInvestmentOwnershipPercentage / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |
Term of property insurance policy |  |  |  |  | 1 year | 1 year | 1 year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Total premiums including taxes and fees |  |  |  |  | 3,118,000 snh_EquityMethodInvestmentPropertyInsuranceAnnualPremiumAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember | 4,748,000 snh_EquityMethodInvestmentPropertyInsuranceAnnualPremiumAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember | 4,438,000 snh_EquityMethodInvestmentPropertyInsuranceAnnualPremiumAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
The entity owns less than this percentage of an equity method investment |  |  |  |  | 20.00%snh_EquityMethodInvestmentOwnershipPercentageHeld / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  | 20.00%snh_EquityMethodInvestmentOwnershipPercentageHeld / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  | 20.00%snh_EquityMethodInvestmentOwnershipPercentageHeld / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |  |  | 20.00%snh_EquityMethodInvestmentOwnershipPercentageHeld / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |  |  |  |  |  |
Amount invested in equity investee |  |  |  |  | 6,034,000 us-gaap_EquityMethodInvestmentAggregateCost / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  | 6,034,000 us-gaap_EquityMethodInvestmentAggregateCost / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  | 6,034,000 us-gaap_EquityMethodInvestmentAggregateCost / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |  |  | 6,034,000 us-gaap_EquityMethodInvestmentAggregateCost / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |  |  |  |  |  |
Equity method investments, carrying value |  |  |  |  | 6,827,000 us-gaap_EquityMethodInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember | 5,913,000 us-gaap_EquityMethodInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember | 5,629,000 us-gaap_EquityMethodInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  | 6,827,000 us-gaap_EquityMethodInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  | 5,913,000 us-gaap_EquityMethodInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  | 6,827,000 us-gaap_EquityMethodInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |  |  | 6,827,000 us-gaap_EquityMethodInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember | 5,913,000 us-gaap_EquityMethodInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |  |  |  |  |
Income recognized arising from equity investments |  |  |  |  | 87,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember | 334,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember | 316,000 us-gaap_IncomeLossFromEquityMethodInvestments / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Coverage of property insurance |  |  |  |  | 500,000,000 snh_EquityMethodInvestmentPropertyInsuranceCoverageAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember | 500,000,000 snh_EquityMethodInvestmentPropertyInsuranceCoverageAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember | 500,000,000 snh_EquityMethodInvestmentPropertyInsuranceCoverageAmount / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of shares purchased |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 2,857 snh_RelatedPartyTransactionSharesPurchased / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |
Payments for share purchased |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 825,000 snh_PaymentsForSharesPurchasedToRelatedParty / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_AffiliatesInsuranceCompanyMember |  |  |  |  |
SIR |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Period for which the Company has agreed not to make Unsolicited Proposals to Acquire |  |  |  |  | 36 months |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
SIR | Healthcare properties |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Related person transactions |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Sale price of properties under agreement to be sold |  |  |  |  | 539,000,000 snh_RealEstateAggregateSalesPrice / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_HealthcarePropertiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_SelectIncomeReitMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Debt disposed of from properties sold |  |  |  |  | $ 30,000,000 snh_RealEstateDebtDisposedOfInSaleOfPropertyTransactions / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_HealthcarePropertiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_SelectIncomeReitMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of properties agreed to be acquired |  |  |  |  | 23 snh_NumberOfPropertiesAgreedToBeAcquired / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_HealthcarePropertiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_SelectIncomeReitMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Area of real estate properties (in square feet) |  |  |  |  | 2,200,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_HealthcarePropertiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_SelectIncomeReitMember |  |  |  | 2,200,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_HealthcarePropertiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_SelectIncomeReitMember |  |  |  |  | 2,200,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_HealthcarePropertiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_SelectIncomeReitMember |  |  |  |  |  |  | 2,200,000 us-gaap_AreaOfRealEstateProperty / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_HealthcarePropertiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_SelectIncomeReitMember |  |  |  |  |  |  |  |  |  |
Number of states in which properties are located |  |  |  |  | 12 us-gaap_NumberOfStatesInWhichEntityOperates / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_HealthcarePropertiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_SelectIncomeReitMember |  |  |  | 12 us-gaap_NumberOfStatesInWhichEntityOperates / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_HealthcarePropertiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_SelectIncomeReitMember |  |  |  |  | 12 us-gaap_NumberOfStatesInWhichEntityOperates / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_HealthcarePropertiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_SelectIncomeReitMember |  |  |  |  |  |  | 12 us-gaap_NumberOfStatesInWhichEntityOperates / us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis = snh_HealthcarePropertiesMember / us-gaap_RelatedPartyTransactionsByRelatedPartyAxis = snh_SelectIncomeReitMember |  |  |  |  |  |  |  |  |  |

X
- Definition Represents the terms of additional insurance policy. + References No definition available. + Details
Name: | snh_AdditionalLiabilityInsurancePolicyTerm
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Amount of premium paid for combined and separate directors' and officers' liability insurance policy. + References No definition available. + Details
Name: | snh_CombinedAndSeparateDirectorsAndOfficersLiabilityInsurancePolicyPremiumPaid
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the amount of premium payable for combined directors' and officers' liability insurance policy. + References No definition available. + Details
Name: | snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPremiumPayable
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Aggregate additional coverage amount of combined directors' and officers' liability insurance policy, purchased by the related party. + References No definition available. + Details
Name: | snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPurchasedByRelatedPartyAdditionalAggregateCoverage
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Aggregate coverage amount of combined directors' and officers' liability insurance policy, purchased by the related party. + References No definition available. + Details
Name: | snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPurchasedByRelatedPartyAggregateCoverage
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Aggregate additional coverage amount of combined directors' and officers' liability insurance policy, purchased by the related party. + References No definition available. + Details
Name: | snh_CombinedDirectorsAndOfficersLiabilityInsurancePolicyPurchasedByRelatedPartyNonIndemnifiableCoverage
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the cash outflow for the early repayment of borrowing variable portion of debt. + References No definition available. + Details
Name: | snh_EarlyRepaymentOfSeniorSecuredDebtVariablePortion
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The entity owns less than this percentage of an equity method investment. + References No definition available. + Details
Name: | snh_EquityMethodInvestmentOwnershipPercentageHeld
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition This element represents the amount of annual premiums including taxes and fees for property insurance pursuant to an insurance program arranged by the equity method investee. + References No definition available. + Details
Name: | snh_EquityMethodInvestmentPropertyInsuranceAnnualPremiumAmount
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the amount of coverage provided for property insurance pursuant to an insurance program arranged by the equity method investee. + References No definition available. + Details
Name: | snh_EquityMethodInvestmentPropertyInsuranceCoverageAmount
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the increase or decrease on the annual rent the lessee is obligated to pay on an operating lease. + References No definition available. + Details
Name: | snh_IncreaseDecreaseOperatingLeasesAnnualRent
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the number of shares held as a percentage of the total shares outstanding at the end of the period. + References No definition available. + Details
Name: | snh_InvestmentOwnedPercentageOfTotalSharesOutstanding
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the percentage of common stock held in the investee. + References No definition available. + Details
Name: | snh_InvestmentOwnershipPercentage
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the terms of liability insurance policy. + References No definition available. + Details
Name: | snh_LiabilityInsurancePolicyTerm
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the minimum percentage of common stock held in the investee above which the entity would have the option to cancel all its rights. + References No definition available. + Details
Name: | snh_MinimumInvestmentOwnershipPercentageEligibleForOptionToCancelRightsOfLessee
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the number of business days before which the notice is required to be given for termination of property management agreement. + References No definition available. + Details
Name: | snh_NumberOfBusinessDaysBeforeWhichNoticeRequiredForTerminationOfPropertyManagementAgreementUponChangeInControl
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the information pertaining to number of communities that include assisted living units. + References No definition available. + Details
Name: | snh_NumberOfCommunitiesThatIncludeAssistedLivingUnits
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the information pertaining to number of communities that include independent living units. + References No definition available. + Details
Name: | snh_NumberOfCommunitiesThatIncludeIndependentLivingUnits
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of entities to which related party provides management services. + References No definition available. + Details
Name: | snh_NumberOfEntitiesToWhichRelatedPartyProvidesServices
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of pooling agreement. + References No definition available. + Details
Name: | snh_NumberOfPoolingAgreements
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition This element represents the number of properties acquired or agreed to be acquired by the entity during the period. + References No definition available. + Details
Name: | snh_NumberOfPropertiesAcquired
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of properties acquired or agreed to be acquired by the entity under purchase agreements, which are referred by the entity as leased properties. + References No definition available. + Details
Name: | snh_NumberOfPropertiesAcquiredLeasedProperties
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of properties acquired or agreed to be acquired by the entity during the period, which are referred by the entity as managed properties. + References No definition available. + Details
Name: | snh_NumberOfPropertiesAcquiredManagedProperties
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of properties agreed to be acquired by the entity during the period. + References No definition available. + Details
Name: | snh_NumberOfPropertiesAgreedToBeAcquired
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of properties pending acquisition. + References No definition available. + Details
Name: | snh_NumberOfPropertiesPendingAcquisition
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the number of properties previously agreed to be sold by the entity. + References No definition available. + Details
Name: | snh_NumberOfPropertiesPreviouslyAgreedToBeSold
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition This element represents the number of properties sold or agreed to be sold by the entity. + References No definition available. + Details
Name: | snh_NumberOfPropertiesSold
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition The number of real estate properties serving as collateral for debt as of the balance sheet date. + References No definition available. + Details
Name: | snh_NumberOfRealEstatePropertiesCollateralized
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of real estate properties owned by the entity, which are classified as held for sale as of the balance sheet date. + References No definition available. + Details
Name: | snh_NumberOfRealEstatePropertiesHeldForSale
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The number of real estate properties released from mortgage as collateral for debt as of the balance sheet date. + References No definition available. + Details
Name: | snh_NumberOfRealEstatePropertiesReleasedFromMortgageCollateral
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the service agreements entered into by the entity for availing services from other entities. + References No definition available. + Details
Name: | snh_NumberOfServiceAgreements
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the annual rent the lessee is obligated to pay on an operating lease. + References No definition available. + Details
Name: | snh_OperatingLeasesAnnualRent
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the amount of sublease rental revenue receivable under the agreement. + References No definition available. + Details
Name: | snh_OperatingLeasesIncomeStatementAnnualSubleaseRentalRevenueReceivable
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Represents the cash outflow associated with purchase of shares from a related party. + References No definition available. + Details
Name: | snh_PaymentsForSharesPurchasedToRelatedParty
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the period before which the written notice is required to be given for cancellation of service agreements. + References No definition available. + Details
Name: | snh_PeriodBeforeWhichWrittenNoticeRequiredForTerminationOfServiceAgreements
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the period by which the term of service agreements (i.e. business management and property management agreement) gets automatically renewed unless a notice for non-renewal is given. + References No definition available. + Details
Name: | snh_PeriodByWhichTermOfServiceAgreementsIsAutomaticallyRenewed
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the period for providing transition services under business management agreement and property management agreement. + References No definition available. + Details
Name: | snh_PeriodForProvidingTransitionServicesUnderServiceAgreements
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents period for which ARCP has agreed, among other things, not to make unsolicited proposals to acquire us, SIR or GOV for a period of 36 months. + References No definition available. + Details
Name: | snh_PeriodForWhichCompanyHasAgreedNotToMakeUnsolicitedProposalsToAcquire
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of months prior to the date of notice of nonrenewal or termination which is used for computing termination fee as an average of sum of the annual base management fee and the annual internal audit services expense. + References No definition available. + Details
Name: | snh_PeriodOnWhichTerminationFeesComputationIsBased
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the period within which property management agreement to be renewed or terminated. + References No definition available. + Details
Name: | snh_PeriodWithinWhichPropertyManagementAgreementToBeRenewedOrTerminated
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the term of property insurance policy. + References No definition available. + Details
Name: | snh_PropertyInsuranceProgramTerm
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition This element represents the aggregate purchase price excluding closing costs, of real estate properties acquired by the entity during the period. + References No definition available. + Details
Name: | snh_RealEstateAggregatePurchasePrice
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition This element represents the aggregate sales price excluding closing costs, of real estate properties sold by the entity during the period. + References No definition available. + Details
Name: | snh_RealEstateAggregateSalesPrice
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the debt disposed of in sale of property transactions. + References No definition available. + Details
Name: | snh_RealEstateDebtDisposedOfInSaleOfPropertyTransactions
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the amount of improvements to real estate properties made by lessees and purchased by the entity. + References No definition available. + Details
Name: | snh_RealEstateImprovementsByLesseePurchased
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the number of persons employed by a related party of the entity. + References No definition available. + Details
Name: | snh_RelatedPartyEmployeesNumber
Namespace Prefix: | snh_
Data Type: | xbrli:decimalItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the ratio of additional termination fee to the average monthly property management fee for certain period prior to the effective date of nonrenewal or termination. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionAdditionalTerminationFeeMultiple
Namespace Prefix: | snh_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the base management fee payable as a percentage of historical cost of other real estate investments, excluding transferred assets for investments after specified amount. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBaseBusinessManagementFeePayableAsPercentageOfHistoricalCostOfOtherRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsAfterTheSpecifiedAmount
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the base management fees payable as a percentage of aggregate book value of real estate assets or transferred assets. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAggregateBookValueOfRealEstateAssetsOrTransferredAssets
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the base management fee payable as a percentage of average closing price per share of common shares on NYSE. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageClosingStockPriceOnStockExchange
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the base management fees payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments exceeding specified amount. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageHistoricalCostOfRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsExceedingSpecifiedAmount
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the base management fees payable as a percentage of average historical cost of real estate investments, excluding transferred assets for investments up to specified amount. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageHistoricalCostOfRealEstateInvestmentsExcludingTransferredAssetsForInvestmentsUpToSpecifiedAmount
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the base management fee payable as a percentage of average market capitalization exceeding specified amount. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBaseManagementFeePayableAsPercentageOfAverageMarketCapitalizationExceedingSpecifiedAmount
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the amount of average market capitalization for payment of base management fee. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBaseManagementFeePayableAverageMarketCapitalization
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Represents the threshold amount of average market capitalization for payment of the base management fee. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfAverageMarketCapitalization
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Represents the threshold amount of other real estate investments for payment of base management fee. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfOtherRealEstateInvestments
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Represents the threshold amount of real estate investments for payment of base management fee. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBaseManagementFeePayableThresholdAmountOfRealEstateInvestments
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Represents the incentive fee earned from related parties under the business management agreement. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeeEarned
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition Represents the incentive fee payable to related parties under the business management agreement. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeePayable
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

X
- Definition Expenses recognized during the period resulting from business management transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionExpensesFromBusinessManagementAgreementTransactionsWithRelatedParty
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Expenses recognized during the period resulting from property management transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionExpensesFromPropertyManagementAgreementTransactionsWithRelatedParty
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the cap on the value of the incentive fee payable per share of our total shares outstanding. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionIncentiveFeePerShareMaximum
Namespace Prefix: | snh_
Data Type: | num:perShareItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the period of prior written notice for termination of the service agreements by the related party subject to approval by a majority vote of independent trustees. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionNoticePeriodForTerminationOfServiceAgreementByRelatedPartySubjectToApprovalByMajorityVoteOfIndepenentTrustees
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of equal annual installments for vesting of common shares. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionNumberOfEqualAnnualInstallmentsForVestingOfCommonShares
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of times registration rights exercisable by the eligible transferees whom common shares issued in payment of base management fee or incentive management fee. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionNumberOfTimesRegistrationRightCanBeExercisableByEligibleTransferee
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the incentive management fee payable as a percentage of the product of the entity's equity market capitalization and its share price appreciation plus dividends. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPercentageForLimitationAndAdjustmentsOfIncentiveManagementFeePayable
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the percentage of base business management fees payable in cash. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPercentageOfBaseBusinessManagementFeePayableInCash
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the percentage of base business management fees payable in common shares. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPercentageOfBaseBusinessManagementFeePayableInCommonShares
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the percentage of incentive fee payable. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPercentageOfIncentiveFeePayable
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the portion of remaining shares to be vested in equal annual installments. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPercentageOfRemainingSharesToBeVestedInEqualAnnualInstallments
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the portion of shares issued in payment of an incentive management fee. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPercentageOfSharesIssuedInPaymentOfIncentiveManagementFees
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the annual return as a percentage of the entity's invested surplus used to determine the incentive fee payable to related parties. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPropertyManagementAgreementAnnualReturnAsPercentageOfInvestedCapital
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the construction supervision fees payable to related parties under property management agreement expressed as a percentage of construction costs. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPropertyManagementAgreementConstructionSupervisionFeesAsPercentageOfConstructionCosts
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the incentive fee payable to related parties under property management agreement expressed as a percentage of the annual net operating income after the entity realizes an annual return equal to specified percentage of its invested capital. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPropertyManagementAgreementIncentiveFeeAsPercentageOfAnnualNetOperatingIncomeAfterRealizationOfSpecifiedPercentageOfAnnualReturn
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the management fees payable to related parties under property management agreement expressed as a percentage of gross revenues. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPropertyManagementAgreementManagementFeesAsPercentageOfGrossRevenues
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the number of consecutive renewal terms of agreement that the entity has the option to renew. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPropertyManagementAgreementNumberOfConsecutiveRenewalTerms
Namespace Prefix: | snh_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of years for which the entity has the option to renew the agreement. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPropertyManagementAgreementRenewalPeriod
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the number of consecutive period during which the entity must not receive the minimum return for the property management agreement to be subject to the pooling agreement. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionPropertyManagementAgreementSubjectToPoolingAgreementMinimumReturnNotReceivedPeriod
Namespace Prefix: | snh_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the pro rata share of the internal audit costs borne by the entity pursuant to arrangements with related parties. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionProRataShareOfInternalAuditCosts
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the number of shares purchased, from related party. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionSharesPurchased
Namespace Prefix: | snh_
Data Type: | xbrli:sharesItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the ratio of termination fee to the sum of the annual base management fee and the annual internal audit services expense if the property management agreement is terminated or not renewed other than for cause. + References No definition available. + Details
Name: | snh_RelatedPartyTransactionTerminalFeeRatio
Namespace Prefix: | snh_
Data Type: | xbrli:pureItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents rents receivable at the balance sheet date. + References No definition available. + Details
Name: | snh_RentsReceivable
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Aggregate coverage amount of separate directors' and officers' liability insurance policy, purchased by the company to cover the related entity with respect to services provided by the related entity. + References No definition available. + Details
Name: | snh_SeparateDirectorsAndOfficersLiabilityInsurancePolicyPurchasedByRelatedPartyAggregateCoverage
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition Represents the portion of awards granted which will vest on the grant date. + References No definition available. + Details
Name: | snh_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRightsPercentVestedOnGrantDate
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the portion of awards granted which will vest on each of the next four anniversaries of the grant date. + References No definition available. + Details
Name: | snh_ShareBasedCompensationArrangementByShareBasedPaymentAwardAwardVestingRightsToBeVestedOnEachOfNextFourAnniversaries
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | duration

X
- Definition Represents the aggregate fair value of the equity instruments other than options granted during the period. + References No definition available. + Details
Name: | snh_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodFairValue
Namespace Prefix: | snh_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

X
- Definition Represents the maximum percentage of the equity shares of the entity which any single person or group can acquire without obtaining approval. + References No definition available. + Details
Name: | snh_ShareOwnershipRestrictionsMaximumPercentageOfEquitySharesThatCanBeAcquiredWithoutApproval
Namespace Prefix: | snh_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the area of the real estate property subject to an operating lease. + References No definition available. + Details
Name: | snh_SquareFootageOfRealEstatePropertyLeased
Namespace Prefix: | snh_
Data Type: | num:areaItemType
Balance Type: | na
Period Type: | duration

X
- Definition Area of a real estate property. + References No definition available. + Details
Name: | us-gaap_AreaOfRealEstateProperty
Namespace Prefix: | us-gaap_
Data Type: | num:areaItemType
Balance Type: | na
Period Type: | instant

X
- Definition This element represents the aggregate cost of investments accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 02 -Paragraph 12 -Article 5 + Details
Name: | us-gaap_EquityMethodInvestmentAggregateCost
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- Definition The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a)(1) -URI http://asc.fasb.org/extlink&oid=6382943&loc=d3e33918-111571 + Details
Name: | us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix: | us-gaap_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

X
- Definition This item represents the carrying amount on the entity's balance sheet of its investment in common stock of an equity method investee. This is not an indicator of the fair value of the investment, rather it is the initial cost adjusted for the entity's share of earnings and losses of the investee, adjusted for any distributions (dividends) and other than temporary impairment (OTTI) losses recognized. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 323 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=35755396&loc=d3e33749-111570 + Details
Name: | us-gaap_EquityMethodInvestments
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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