Represents the increase or decrease on the annual rent the lessee is obligated to pay on an operating lease.

No definition available.

Name:	snh_IncreaseDecreaseOperatingLeasesAnnualRent
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Represents the number of communities managed by a related party.

+ References

No definition available.

+ Details

Name:	snh_NumberOfCommunitiesManagedByRelatedParty
Namespace Prefix:	snh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of pre-existing management agreements.

+ References

No definition available.

+ Details

Name:	snh_NumberOfPreExistingManagementAgreements
Namespace Prefix:	snh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Pre-Existing Management Agreements Terminated

+ References

No definition available.

+ Details

Name:	snh_NumberOfPreExistingManagementAgreementsTerminated
Namespace Prefix:	snh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of properties acquired or agreed to be acquired by the entity.

+ References

No definition available.

+ Details

Name:	snh_NumberOfPropertiesAcquired
Namespace Prefix:	snh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of separate management agreements entered for communities acquired, upon termination of a pre-existing combined management agreement.

+ References

No definition available.

+ Details

Name:	snh_NumberOfSeparateManagementAgreements
Namespace Prefix:	snh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of Communities Included in Expansion and Development Project

+ References

No definition available.

+ Details

Name:	snh_NumberofCommunitiesIncludedinExpansionandDevelopmentProject
Namespace Prefix:	snh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Communities Leased by the Company

+ References

No definition available.

+ Details

Name:	snh_NumberofCommunitiesLeasedbytheCompany
Namespace Prefix:	snh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Number of Leases With Related Party

+ References

No definition available.

+ Details

Name:	snh_NumberofLeasesWithRelatedParty
Namespace Prefix:	snh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the aggregate purchase price excluding acquisition costs of real estate properties acquired or agreed to be acquired by the entity.

+ References

No definition available.

+ Details

Name:	snh_RealEstateAggregatePurchasePrice
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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

- Definition

Related Party Transaction, Annual Rent Increase Percentage in Addition to Rate Applicable on Outstanding Borrowings

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionAnnualRentIncreasePercentageInAdditiontoRateApplicableonOutstandingBorrowings
Namespace Prefix:	snh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Related Party Transaction, Annual Rents Due

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionAnnualRentsDue
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- 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

- 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

- 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

- Definition

Related Party Transaction, Property Management Agreement, Number of Communities Subject to Reset of Annual Minimum Return

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionPropertyManagementAgreementNumberofCommunitiesSubjecttoResetofAnnualMinimumReturn
Namespace Prefix:	snh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the payment of management capital expenditure as a percentage of amount funded by the company.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionPropertyManagementAgreementPaymentOfCapitalExpenditureAsPercentageOfFundedAmount
Namespace Prefix:	snh_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant

- 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

- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 18
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6351-108592

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13531-108611

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 275
-SubTopic 10
-Section 50
-Paragraph 20
-URI http://asc.fasb.org/extlink&oid=64851502&loc=d3e6404-108592

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 50
-Paragraph 21
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=73719730&loc=d3e13537-108611

+ Details

Name:	us-gaap_ConcentrationRiskPercentage1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of revenue recognized for the period from operating leases, including minimum lease revenue, contingent revenue, percentage revenue and sublease revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=7501430&loc=d3e39896-112707

+ Details

Name:	us-gaap_OperatingLeasesIncomeStatementLeaseRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=snh_FiveStarQualityCareIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=us-gaap_SalesRevenueServicesNetMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ConcentrationRiskByBenchmarkAxis=snh_RealEstateInvestmentPropertyAtCostMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	snh_RealEstateAgreementsByTypeAxis=snh_ALPoolingAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=snh_SeniorLivingCommunityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=snh_FourStatesMember
Namespace Prefix:
Data Type:	na
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Leases and Management Agreements with Five Star (Details) $ in Thousands		1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 29, 2016 community	Jun. 30, 2016 USD ($) pooling_agreement lease_agreement community	Jun. 30, 2017 USD ($) community	Jun. 30, 2016 USD ($) community	Jun. 30, 2017 USD ($) lease_agreement community	Jun. 30, 2016 USD ($) community	Dec. 31, 2016 USD ($)	May 31, 2015
Related party transaction, property management agreement, number of communities subject to reset of annual minimum return \| community		10		10		10
Five Star
Number of communities leased by the Company \| community		184	185	184	185	184
Number of leases with related party \| lease_agreement					5
Total rental income recognized			$ 51,123	$ 48,234	$ 102,108	$ 96,341
Related party transaction, annual rents due			1,392	1,388	2,837	2,861
Rents receivable			$ 17,044		17,044		$ 18,320
Real estate improvements purchased					19,308	11,836
Increase or decrease in annual lease rent payable					$ 1,547	949
Number of communities included in expansion and development project \| community			2		2
Related party transaction, annual rent increase percentage in addition to rate applicable on outstanding borrowings			2.00%		2.00%
Property management agreement expense			$ 3,554	$ 2,819	$ 7,117	$ 5,623
Number of pre-existing management agreements terminated \| pooling_agreement		3
Number of pre-existing management agreements \| lease_agreement		4
Five Star \| Rents from significant lessee \| Revenues
% of Total (as a percent)			19.30%		19.30%
Five Star \| Rents from significant lessee \| Investment
% of Total (as a percent)					27.50%
Five Star \| A L Pooling Agreements
Related party transaction, property management agreement, management fees as percentage of gross revenues	5.00%							3.00%
Related party transaction property management agreement, payment of capital expenditure as percentage of the funded amount		0.03		0.03		0.03
Related party transaction, property management agreement, incentive fee as percentage of annual net operating income after realization of specified percentage of annual return	20.00%							35.00%
Five Star \| A L Pooling Agreements \| Minimum
Related party transaction, property management agreement, management fees as percentage of gross revenues		3.00%		3.00%		3.00%
Five Star \| A L Pooling Agreements \| Maximum
Related party transaction, property management agreement, management fees as percentage of gross revenues		5.00%		5.00%		5.00%
Five Star \| Senior Living Communities
Number of communities managed by related party \| community					68	62
Number of separate management agreements \| pooling_agreement		10
Five Star \| Senior Living Communities \| Four States
Number of properties acquired \| community	7
Real estate aggregate purchase price		$ 112,350