Cash Paid plus Assumed Debt, including closing costs plus other settlement adjustments

No definition available.

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

- Definition

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

+ References

No definition available.

+ Details

Name:	snh_NumberOfBuildingsAcquired
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

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

+ References

No definition available.

+ Details

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

- Definition

Represents the property plant and equipment assets recorded as part of the real estate acquisition.

+ References

No definition available.

+ Details

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

- Definition

Area of a real estate property.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Useful life of finite-lived intangible assets, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

No definition available.

+ Details

Name:	us-gaap_FiniteLivedIntangibleAssetUsefulLife
Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

+ Details

Name:	us-gaap_NoncashOrPartNoncashAcquisitionDebtAssumed1
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_RealEstateLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember
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:	srt_StatementGeographicalAxis=snh_KansasMissouriAndCaliforniaMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_LeaseAgreementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Real Estate Properties - Schedule of Purchase Price Allocations (Details) ft² in Thousands, $ in Thousands	1 Months Ended		9 Months Ended
	Mar. 31, 2018 USD ($) ft² building property	Jan. 31, 2018 USD ($) ft² building property	Sep. 30, 2018 USD ($) ft² building property	Sep. 30, 2017 USD ($)
Real Estate [Line Items]
Assumed Debt			$ 44,386	$ 0
Acquisition \| MOBs
Real Estate [Line Items]
Number of Properties \| property			4
Number of Buildings \| building			4
Area of real estate properties (in square feet) \| ft²			535
Cash Paid Plus Assumed Debt			$ 114,973
Acquired Real Estate Intangible Assets			29,527
Assumed Debt			11,050
Kansas, Missouri And California \| Acquisition \| MOBs
Real Estate [Line Items]
Number of Properties \| property		3
Number of Buildings \| building		3
Area of real estate properties (in square feet) \| ft²		400
Cash Paid Plus Assumed Debt		$ 91,698
Acquired Real Estate Intangible Assets		20,220
Assumed Debt		0
Virginia \| Acquisition \| MOBs
Real Estate [Line Items]
Number of Properties \| property	1
Number of Buildings \| building	1
Area of real estate properties (in square feet) \| ft²	135
Cash Paid Plus Assumed Debt	$ 23,275
Acquired Real Estate Intangible Assets	9,307
Assumed Debt	11,050
Land \| Acquisition \| MOBs
Real Estate [Line Items]
Real estate properties acquired, property plant and equipment			19,736
Land \| Kansas, Missouri And California \| Acquisition \| MOBs
Real Estate [Line Items]
Real estate properties acquired, property plant and equipment		16,873
Land \| Virginia \| Acquisition \| MOBs
Real Estate [Line Items]
Real estate properties acquired, property plant and equipment	2,863
Building and Improvements \| Acquisition \| MOBs
Real Estate [Line Items]
Real estate properties acquired, property plant and equipment			$ 65,710
Building and Improvements \| Kansas, Missouri And California \| Acquisition \| MOBs
Real Estate [Line Items]
Real estate properties acquired, property plant and equipment		$ 54,605
Building and Improvements \| Virginia \| Acquisition \| MOBs
Real Estate [Line Items]
Real estate properties acquired, property plant and equipment	$ 11,105
Lease Agreements \| Acquisition \| MOBs
Real Estate [Line Items]
Weighted average amortization period			5 years 9 months 18 days