Name:	snh_NoncashOrPartNoncashAcquisitionPremiumOnDebtAssumed1
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

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

No definition available.

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

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

No definition available.

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

Represents the intangible lease assets recorded as part of the real estate acquisition.

No definition available.

Name:	snh_RealEstatePropertiesAcquiredIntangibleLeaseAssets
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

The amount of debt that an Entity assumes in acquiring a business or in consideration for an asset received in a noncash (or part noncash) acquisition. Noncash is defined as transactions during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
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Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
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Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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The number of units in a real estate property owned as of the balance sheet date.

No definition available.

Name:	us-gaap_NumberOfUnitsInRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

Amount of real estate investment property, net of accumulated depreciation, which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
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-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

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Data Type:	xbrli:monetaryItemType
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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.

No definition available.

Name:	us-gaap_RealEstateLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
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Period Type:	duration

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=snh_SeniorLivingCommunityMember
Namespace Prefix:
Data Type:	na
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Name:	srt_StatementGeographicalAxis=snh_FourStatesMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	srt_StatementGeographicalAxis=stpr_IL
Namespace Prefix:
Data Type:	na
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Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	srt_StatementGeographicalAxis=stpr_TN
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_LeaseArrangementTypeAxis=snh_NonLeasingMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	srt_StatementGeographicalAxis=stpr_AZ
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	srt_StatementGeographicalAxis=snh_TwoStatesMember
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	srt_StatementGeographicalAxis=stpr_GA
Namespace Prefix:
Data Type:	na
Balance Type:
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Name:	us-gaap_LeaseArrangementTypeAxis=snh_LeasingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_LandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingAndBuildingImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: