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

The number of buildings owned by the entity, which are classified as held for sale as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

This element represents the number of buildings sold by the entity.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of communities.

+ References

No definition available.

+ Details

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

- 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

- 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

- Definition

Represents the number of tenants.

+ References

No definition available.

+ Details

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

- Definition

Amount of cash received from agreement relating to settlement, termination of lease and transfer operations.

+ References

No definition available.

+ Details

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

- Definition

This element represents the aggregate sales price excluding closing costs, of real estate properties sold by the entity.

+ References

No definition available.

+ Details

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

- Definition

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=68055307&loc=d3e2420-110228

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

+ Details

Name:	us-gaap_AssetImpairmentCharges
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The difference between the carrying value and the sale price of real estate or properties that were intended to be sold or held for capital appreciation or rental income. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-URI http://asc.fasb.org/extlink&oid=66902209&loc=d3e3602-108585

+ Details

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

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_RealEstatePropertiesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DiscontinuedOperationsDisposedOfBySaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DiscontinuedOperationsHeldForSaleOrDisposedOfBySaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	snh_OperatingLeasesOfLessorLesseeAxis=snh_TaxableREITSubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ScenarioAdjustmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Real Estate Properties - Discontinued Operations and Properties Held for Sale (Details)	1 Months Ended					3 Months Ended				9 Months Ended
	Sep. 30, 2016 USD ($) community property	Jul. 31, 2016 USD ($) building	Jun. 30, 2016 USD ($) building property	Apr. 30, 2016 USD ($) tenant_agreement	Mar. 31, 2016 USD ($) land_parcel	Sep. 30, 2016 USD ($) community property	Jun. 30, 2016 USD ($) building property	Mar. 31, 2016 USD ($) operator building community land_parcel property	Sep. 30, 2015 USD ($)	Sep. 30, 2016 USD ($) community property	Sep. 30, 2015 USD ($)
Real estate properties
Impairment (reversal of impairment) of assets						$ 4,578,000			$ (98,000)	$ 16,930,000	$ (98,000)
Number of tenants \| tenant_agreement				1
Gain on sale of properties						0			$ 0	$ 4,061,000	$ 0
Discontinued Operations, Disposed of by Sale
Real estate properties
Impairment (reversal of impairment) of assets						2,191,000
Discontinued Operations, Held-for-sale or Disposed of by Sale
Real estate properties
Impairment (reversal of impairment) of assets						$ 2,394,000
Number of properties classified as held for sale \| community	1					1				1
Five Star \| Discontinued Operations, Disposed of by Sale
Real estate properties
Number of communities \| community	1
Sale price of property sold and agreed to be sold	$ 248,000
Gain on sale of properties						$ 0
Increase or decrease in annual lease rent payable						$ 25,000
Five Star \| TRS
Real estate properties
Proceeds from settlement agreement				$ 2,365,000
Triple Net Leased Senior Living Communities
Real estate properties
Impairment (reversal of impairment) of assets								$ 4,391,000
Number of communities \| community								2
Number of tenants \| operator								2
MOBs
Real estate properties
Impairment (reversal of impairment) of assets							$ 4,961,000
Number of properties classified as held for sale \| property	2		5			2	5			2
Number of buildings held for sale \| building			5				5
MOBs \| Discontinued Operations, Disposed of by Sale
Real estate properties
Number of properties sold \| building		4
Number of buildings sold \| building		4
Sale price of property sold and agreed to be sold		$ 20,150,000
Gain on sale of properties		$ 0
MOBs \| Discontinued Operations, Held-for-sale or Disposed of by Sale
Real estate properties
Number of properties classified as held for sale \| property	1					1				1
MOB and land parcel
Real estate properties
Impairment (reversal of impairment) of assets								$ 2,999,000
Number of properties sold \| property								1
Number of buildings sold \| building								1
Managed senior living communities \| Discontinued Operations, Held-for-sale or Disposed of by Sale
Real estate properties
Number of properties classified as held for sale \| community	1					1				1
Land parcel
Real estate properties
Number of properties classified as held for sale \| land_parcel					1			1
Land parcel \| Discontinued Operations, Disposed of by Sale
Real estate properties
Sale price of property sold and agreed to be sold					$ 700,000
Gain on sale of properties					$ 0
Skilled Nursing Facilities \| Discontinued Operations, Disposed of by Sale
Real estate properties
Impairment (reversal of impairment) of assets						$ 2,191,000
Number of properties classified as held for sale \| community	1					1				1
Skilled Nursing Facilities \| Discontinued Operations, Held-for-sale or Disposed of by Sale
Real estate properties
Number of properties sold \| building			1
Sale price of property sold and agreed to be sold			$ 9,100,000
Gain on sale of properties			$ 4,061,000
Scenario, Adjustment \| MOBs \| Discontinued Operations, Disposed of by Sale
Real estate properties
Impairment (reversal of impairment) of assets						$ (7,000)