Disposal Group, Including Discontinued Operation, Increase (Decrease) From Sale Of Annual Rental Income

No definition available.

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

- 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

Number Of Properties Included In Joint Venture

+ References

No definition available.

+ Details

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

- 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

Number Of Real Estate Properties Sold

+ References

No definition available.

+ Details

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

- Definition

Number of Buildings Included In Joint Venture

+ References

No definition available.

+ Details

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

- Definition

Number of Real Estate Properties Under Agreement

+ References

No definition available.

+ Details

Name:	snh_NumberofRealEstatePropertiesUnderAgreement
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 sold.

+ References

No definition available.

+ Details

Name:	snh_SquareFootageOfPropertiesSold
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 before tax of gain (loss) recognized on the sale or disposal of a disposal group. Excludes discontinued operations.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=109226348&loc=d3e2443-110228

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-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 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 360
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=109226691&loc=d3e2941-110230

+ Details

Name:	us-gaap_DisposalGroupNotDiscontinuedOperationGainLossOnDisposal
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_SeniorHousingPropertiesMember
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:

- Details

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

Real Estate Properties - Narrative (Details) $ in Thousands	1 Months Ended				3 Months Ended		6 Months Ended
Real Estate Properties - Narrative (Details) $ in Thousands	Aug. 08, 2019 USD ($) property	Jun. 30, 2019 USD ($) state building property	May 31, 2019 USD ($) building community	Mar. 31, 2019 USD ($) building	Jun. 30, 2019 USD ($) state building property	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) ft² state building property	Jun. 30, 2018 USD ($)
Real Estate Properties
Impairment of assets					$ 2,213	$ 548	$ 8,419	$ 548
Skilled Nursing Facility
Real Estate Properties
Number of real estate properties held for sale \| property		15			15		15
Impairment of assets					$ 2,117		$ 8,323
Discontinued Operations, Held-for-sale
Real Estate Properties
Number of real estate properties \| property		456			456		456
Number of real estate properties held for sale \| property		22			22		22
Number of states in which properties are located \| state		42			42		42
Discontinued Operations, Held-for-sale \| MOBs
Real Estate Properties
Number of real estate properties held for sale \| property		5			5		5
Aggregate purchase price							$ 9,926
Amount under agreement to sell		$ 10,072			$ 10,072		$ 10,072
Discontinued Operations, Held-for-sale \| Skilled Nursing Facility
Real Estate Properties
Number of real estate properties held for sale \| property		17			17		17
Aggregate purchase price							$ 17,000
Amount under agreement to sell		$ 34,246			$ 34,246		$ 34,246
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Real Estate Properties
Number of real estate properties \| building		13			13		13
Aggregate purchase price							$ 35,107
Gain on disposal of assets							$ 17,710
Disposal Group, Disposed of by Sale, Not Discontinued Operations \| MOBs
Real Estate Properties
Number of properties sold \| property							10
Rentable space (in sqft) \| ft²							244,564
Aggregate purchase price							$ 13,607
Decrease in annual rental income					$ (589)		$ (1,599)
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
Decrease in annual rental income			$ 831
Senior Housing Properties
Real Estate Properties
Number of buildings \| building		2			2		2
Senior Housing Properties \| MOBs
Real Estate Properties
Number of properties included in joint venture \| property		1			1		1
Joint Venture
Real Estate Properties
Ownership percentage		55.00%			55.00%		55.00%
California \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| Skilled Nursing Facility
Real Estate Properties
Number of real estate properties \| building			3
Aggregate purchase price			$ 21,500
Gain on disposal of assets			$ 15,207
Massachusetts \| MOBs
Real Estate Properties
Impairment of assets					$ 96
Number of properties sold \| property					3
Massachusetts \| Discontinued Operations, Held-for-sale \| MOBs
Real Estate Properties
Number of properties sold \| property		3
Aggregate purchase price		$ 4,955
Massachusetts \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| MOBs
Real Estate Properties
Number of real estate properties \| building		7		1	7		7
Aggregate purchase price		$ 8,042		$ 75
Gain on disposal of assets		$ 1,590		$ (58)
Subsequent Event \| Massachusetts \| Discontinued Operations, Held-for-sale \| Senior Living Communities
Real Estate Properties
Aggregate purchase price	$ 135,000
Number of real estate properties under agreement \| property	15