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

The amount of premium on assumed debt that an Entity assumes in acquiring a business or in consideration for an asset received in a noncash (or part noncash) acquisition.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of private pay independent living units within communities acquired.

+ References

No definition available.

+ Details

Name:	snh_NumberOfAcquiredPrivatePayIndependentLivingUnits
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

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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

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://www.xbrl.org/2003/role/presentationRef
-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

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-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://www.xbrl.org/2003/role/presentationRef
-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

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

- Details

Name:	us-gaap_RelatedPartyTransactionsByRelatedPartyAxis=snh_FiveStarQualityCareIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=snh_SeniorLivingCommunityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_TN
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_AZ
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_PropertyPlantAndEquipmentByTypeAxis=snh_FurnitureFixturesAndEquipmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Real Estate Properties - Acquisitions (Details) $ in Thousands	1 Months Ended										6 Months Ended
	Jun. 30, 2018 USD ($) living_unit community property	Feb. 28, 2018 USD ($) living_unit	Feb. 28, 2018 USD ($)	Feb. 28, 2018 USD ($) community	Feb. 28, 2018 USD ($) property	Jan. 31, 2018 USD ($) living_unit	Jan. 31, 2018 USD ($)	Jan. 31, 2018 USD ($) community	Jan. 31, 2018 USD ($) property	Nov. 30, 2017 property	Jun. 30, 2018 USD ($) living_unit property	Jun. 30, 2017 USD ($)
Real Estate Properties
Assumed Debt											$ 44,386	$ 0
Five Star \| Acquisition \| Senior Living Communities
Real Estate Properties
Number of Properties	2									6	4
Units \| living_unit											366
Cash Paid Plus Assumed Debt											$ 66,350
Acquired Real Estate Intangible Assets	$ 11,489										11,489
Assumed Debt	$ 16,588										33,336
Premium on Assumed Debt											(1,845)
Five Star \| Acquisition \| Tennessee \| Senior Living Communities
Real Estate Properties
Number of Properties	2							1	1
Units \| living_unit	151					88
Cash Paid Plus Assumed Debt	$ 23,860						$ 19,868
Acquired Real Estate Intangible Assets	3,843					$ 3,195	3,195	$ 3,195	$ 3,195		3,843
Assumed Debt	16,588						0
Premium on Assumed Debt	(486)						0
Five Star \| Acquisition \| Arizona \| Senior Living Communities
Real Estate Properties
Number of Properties				1	1
Units \| living_unit		127
Cash Paid Plus Assumed Debt			$ 22,622
Acquired Real Estate Intangible Assets		$ 4,451	4,451	$ 4,451	$ 4,451
Assumed Debt			16,748
Premium on Assumed Debt			(1,359)
Five Star \| Acquisition \| Land \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment											3,562
Five Star \| Acquisition \| Land \| Tennessee \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment	965						580
Five Star \| Acquisition \| Land \| Arizona \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment			2,017
Five Star \| Acquisition \| Building and Improvements \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment											49,917
Five Star \| Acquisition \| Building and Improvements \| Tennessee \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment	17,910						14,884
Five Star \| Acquisition \| Building and Improvements \| Arizona \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment			17,123
Five Star \| Acquisition \| FF&E \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment											$ 3,227
Five Star \| Acquisition \| FF&E \| Tennessee \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment	$ 1,628						$ 1,209
Five Star \| Acquisition \| FF&E \| Arizona \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment			$ 390