Number Of Properties Included In Joint Venture

No definition available.

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

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

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_MedicalOfficeBuildingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- 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:	us-gaap_DisposalGroupClassificationAxis=us-gaap_DisposalGroupHeldforsaleNotDiscontinuedOperationsMember
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_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:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Real Estate Properties - Narrative (Details) $ in Thousands		1 Months Ended						3 Months Ended		9 Months Ended
Real Estate Properties - Narrative (Details) $ in Thousands	Nov. 06, 2019 USD ($) property	Nov. 06, 2019 USD ($) property	Sep. 30, 2019 USD ($) state building property	Aug. 31, 2019 USD ($) building	Jul. 31, 2019 USD ($) building	Jun. 30, 2019 USD ($) building property	Mar. 31, 2019 USD ($) building	Sep. 30, 2019 USD ($) state building property	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) state building property	Sep. 30, 2018 USD ($)
Real Estate Properties
Impairment of assets \| $								$ 33,099	$ 4,525	$ 41,518	$ 5,073
MOBs
Real Estate Properties
Number of real estate properties			7					7		7
Number of real estate properties held for sale			4					4		4
Impairment of assets \| $								$ 26,037		$ 26,133
Number of real estate properties sold						4
Senior Living Communities
Real Estate Properties
Number of real estate properties			16					16		16
Number of real estate properties held for sale			4					4		4
Impairment of assets \| $								$ 7,062		$ 15,385
SNF
Real Estate Properties
Number of real estate properties sold			15
Discontinued Operations, Held-for-sale
Real Estate Properties
Number of real estate properties			436					436		436
Number of real estate properties held for sale			8					8		8
Number of states in which properties are located \| state			41					41		41
Amount under agreement to sell \| $			$ 136,231					$ 136,231		$ 136,231
Disposal Group, Held-for-sale, Not Discontinued Operations \| MOBs
Real Estate Properties
Number of real estate properties held for sale			2			3		2		2
Impairment of assets \| $										$ 2,661
Disposal Group, Disposed of by Sale, Not Discontinued Operations
Real Estate Properties
Number of real estate properties sold \| building										33
Aggregate sale price \| $										$ 53,033
Disposal Group, Disposed of by Sale, Not Discontinued Operations \| SNF
Real Estate Properties
Number of real estate properties sold										18
Aggregate sale price \| $										$ 29,500
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			1					1		1
Joint Venture
Real Estate Properties
Ownership percentage			55.00%					55.00%		55.00%
Massachusetts \| Disposal Group, Disposed of by Sale, Not Discontinued Operations \| MOBs
Real Estate Properties
Number of real estate properties sold \| building			1	1	3	7	1
Aggregate sale price \| $			$ 2,750	$ 2,221	$ 4,955	$ 8,042	$ 75
Subsequent Event
Real Estate Properties
Aggregate sale price \| $	$ 452,804
Amount under agreement to sell	40	40
Subsequent Event \| Disposal Group, Disposed of by Sale, Not Discontinued Operations
Real Estate Properties
Number of real estate properties sold		4
Aggregate sale price \| $		$ 58,000
Fair Value, Measurements, Nonrecurring \| Senior Living Communities
Real Estate Properties
Number of real estate properties			1					1		1
Impairment of assets \| $										$ 6,344
Fair Value, Measurements, Nonrecurring \| Disposal Group, Held-for-sale, Not Discontinued Operations \| MOBs
Real Estate Properties
Number of real estate properties held for sale			3					3		3
Impairment of assets \| $										$ 26,037