The number of buildings owned as of the balance sheet date.

No definition available.

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

- Definition

Represents the number of communities sold.

+ References

No definition available.

+ Details

Name:	snh_NumberOfCommunitiesSold
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

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

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

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

- 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2420-110228

+ Details

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

- Definition

Amount of rental income attributable to disposal group, including, but not limited to, discontinued operation.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 205
-SubTopic 20
-Section 50
-Paragraph 5B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109222650&loc=SL51721673-107760

+ Details

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

- 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://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 323
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=114001798&loc=d3e33918-111571

+ Details

Name:	us-gaap_EquityMethodInvestmentOwnershipPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

The number of states the entity operates in as of the balance sheet date.

+ References

No definition available.

+ Details

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

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

- Definition

Carrying amount as of the balance sheet date of investments in land and buildings held for sale, excluding real estate considered to be inventory of the entity.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03.1(f))
-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

+ Details

Name:	us-gaap_RealEstateHeldforsale
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=snh_SkilledNursingFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=snh_MedicalOfficeBuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_OwnershipAxis=snh_JointVentureMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=stpr_CA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=stpr_MA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Real Estate Properties - Narrative (Details) $ in Thousands	1 Months Ended		3 Months Ended
Real Estate Properties - Narrative (Details) $ in Thousands	May 09, 2019 USD ($) community	Mar. 31, 2019 USD ($) state building property	Mar. 31, 2019 USD ($) ft² state building community property	Mar. 31, 2018 USD ($)
Real Estate Properties
Impairment of assets			$ 6,206	$ 0
Skilled Nursing Facility
Real Estate Properties
Impairment of assets			$ 6,206
Number of properties acquired \| property			15
Discontinued Operations, Held-for-sale
Real Estate Properties
Number of real estate properties \| building		467	467
Number of real estate properties held for sale \| property		30	30
Number of states in which properties are located \| state		42	42
Discontinued Operations, Held-for-sale \| MOBs
Real Estate Properties
Number of communities sold \| community			10
Aggregate purchase price			$ 15,609
Amount under agreement to sell		$ 17,347	$ 17,347
Discontinued Operations, Held-for-sale \| Skilled Nursing Facility
Real Estate Properties
Number of communities sold \| community			20
Aggregate purchase price			$ 40,500
Amount under agreement to sell		$ 44,342	$ 44,342
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Real Estate Properties
Number of real estate properties \| building		2	2
Aggregate purchase price			$ 2,975
Disposal Group, Disposed of by Sale, Not Discontinued Operations \| MOBs
Real Estate Properties
Number of communities sold \| community			2
Square footage of real estate property \| ft²			64,796
Aggregate purchase price			$ 2,975
Rental income			$ 123
Joint Venture
Real Estate Properties
Number of buildings \| building		2	2
Ownership percentage		55.00%	55.00%
Joint Venture \| MOBs
Real Estate Properties
Number of real estate properties held for sale \| property		1	1
California \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Skilled Nursing Facility
Real Estate Properties
Number of communities sold \| community			3
Aggregate purchase price			$ 21,500
Massachusetts \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| MOBs
Real Estate Properties
Number of real estate properties \| building		1	1
Aggregate purchase price		$ 75
Subsequent Event \| Massachusetts \| Discontinued Operations, Held-for-sale \| MOBs
Real Estate Properties
Number of communities sold \| community	3
Aggregate purchase price	$ 4,955