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

No definition available.

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 during the period.

+ References

No definition available.

+ Details

Name:	snh_RealEstateAggregateSalesPrice
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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=51824106&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=56944662&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=56944662&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_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_DisposalGroupClassificationAxis=us-gaap_DiscontinuedOperationsHeldForSaleOrDisposedOfBySaleMember
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_LandParcelMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DiscontinuedOperationsDisposedOfBySaleMember
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:

Real Estate Properties - Discontinued Operations and Properties Held for Sale (Details) $ in Thousands	1 Months Ended				3 Months Ended		6 Months Ended
	Jul. 31, 2016 USD ($) building	Jun. 30, 2016 USD ($) building	Apr. 30, 2016 USD ($) item	Mar. 31, 2016 USD ($) property	Jun. 30, 2016 USD ($) building	Mar. 31, 2016 USD ($) community item property	Jun. 30, 2016 USD ($) building	Jun. 30, 2016 property
Real estate properties
Impairment of assets					$ 4,961		$ 12,351
Number of tenants \| item			1
Gain on sale of properties					4,061		$ 4,061
Five Star \| TRS
Real estate properties
Proceeds from settlement agreement			$ 2,365
Triple Net Leased Senior Living Communities
Real estate properties
Impairment of assets						$ 4,391
Number of communities \| community						2
Number of tenants \| item						2
MOBs
Real estate properties
Impairment of assets					$ 4,961
Number of Buildings Held For Sale		5			5		5	5
Number of buildings sold \| building	4
MOBs \| Discontinued Operations, Held-for-sale or Disposed of by Sale
Real estate properties
Number of properties sold \| building	4
Sale price of property sold and agreed to be sold	$ 20,150
MOB and land parcel
Real estate properties
Impairment of assets						$ 2,999
Land parcel
Real estate properties
Number of properties classified as held for sale \| property				1		1
Land parcel \| Discontinued Operations, Disposed of by Sale
Real estate properties
Sale price of property sold and agreed to be sold				$ 700
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
Gain on sale of properties		$ 4,061