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

No definition available.

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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

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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 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

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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://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_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
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- Details

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

- Details

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

- Details

Name:	us-gaap_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_RelatedPartyTransactionsByRelatedPartyAxis=snh_FiveStarQualityCareIncMember
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:
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- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_AZ
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:

- Details

Name:	us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis=us-gaap_LeaseAgreementsMember
Namespace Prefix:
Data Type:	na
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Real Estate Properties - Acquisitions (Details) $ in Thousands	1 Months Ended				2 Months Ended	3 Months Ended
	Mar. 31, 2018 USD ($) ft² building property	Feb. 28, 2018 USD ($) living_unit community property	Jan. 31, 2018 USD ($) ft² living_unit building community property	Nov. 30, 2017 property	Feb. 28, 2018 USD ($) living_unit property	Mar. 31, 2018 USD ($) ft² building property	Mar. 31, 2017 USD ($)
Real Estate Properties
Assumed Debt						$ 27,798	$ 0
Acquisition \| MOBs
Real Estate Properties
Number of properties \| property						4
Number of buildings acquired \| building						4
Area of real estate properties (in square feet) \| ft²	535,000					535,000
Cash Paid plus Assumed Debt						$ 114,973
Acquired Real Estate Intangible Assets	$ 29,527					29,527
Assumed Debt						$ 11,050
Acquisition \| Kansas, Missouri And California \| MOBs
Real Estate Properties
Number of properties \| property			3
Number of buildings acquired \| building			3
Area of real estate properties (in square feet) \| ft²			400,000
Cash Paid plus Assumed Debt			$ 91,698
Acquired Real Estate Intangible Assets			20,220
Assumed Debt			0
Acquisition \| Virginia \| MOBs
Real Estate Properties
Number of properties \| property	1
Number of buildings acquired \| building	1
Area of real estate properties (in square feet) \| ft²	135,000					135,000
Cash Paid plus Assumed Debt	$ 23,275
Acquired Real Estate Intangible Assets	9,307					$ 9,307
Assumed Debt	11,050
Acquisition \| Land \| MOBs
Real Estate Properties
Real estate properties acquired, property plant and equipment						19,736
Acquisition \| Land \| Kansas, Missouri And California \| MOBs
Real Estate Properties
Real estate properties acquired, property plant and equipment			16,873
Acquisition \| Land \| Virginia \| MOBs
Real Estate Properties
Real estate properties acquired, property plant and equipment	2,863
Acquisition \| Building and Improvements \| MOBs
Real Estate Properties
Real estate properties acquired, property plant and equipment						$ 65,710
Acquisition \| Building and Improvements \| Kansas, Missouri And California \| MOBs
Real Estate Properties
Real estate properties acquired, property plant and equipment			$ 54,605
Acquisition \| Building and Improvements \| Virginia \| MOBs
Real Estate Properties
Real estate properties acquired, property plant and equipment	$ 11,105
Five Star \| Senior Living Communities
Real Estate Properties
Number of properties \| property				6
Five Star \| Tennessee \| Senior Living Communities
Real Estate Properties
Number of properties \| community			1
Number of acquired private pay independent living units \| living_unit			88
Five Star \| Arizona \| Senior Living Communities
Real Estate Properties
Number of properties \| community		1
Number of acquired private pay independent living units \| living_unit		127
Assumed Debt		$ 16,748
Five Star \| Acquisition \| Senior Living Communities
Real Estate Properties
Number of properties \| property					2
Number of acquired private pay independent living units \| living_unit					215
Cash Paid plus Assumed Debt					$ 42,490
Acquired Real Estate Intangible Assets		$ 7,646			7,646
Assumed Debt					16,748
Premium on Assumed Debt					(1,359)
Five Star \| Acquisition \| Tennessee \| Senior Living Communities
Real Estate Properties
Number of properties \| property			1
Cash Paid plus Assumed Debt			$ 19,868
Acquired Real Estate Intangible Assets			3,195
Assumed Debt			0
Premium on Assumed Debt			0
Five Star \| Acquisition \| Arizona \| Senior Living Communities
Real Estate Properties
Number of properties \| property		1
Cash Paid plus Assumed Debt		$ 22,622
Acquired Real Estate Intangible Assets		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					2,597
Five Star \| Acquisition \| Land \| Tennessee \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment			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					32,007
Five Star \| Acquisition \| Building and Improvements \| Tennessee \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment			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					$ 1,599
Five Star \| Acquisition \| FF&E \| Tennessee \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment			$ 1,209
Five Star \| Acquisition \| FF&E \| Arizona \| Senior Living Communities
Real Estate Properties
Real estate properties acquired, property plant and equipment		$ 390
Lease Agreements \| Acquisition \| MOBs
Real Estate Properties
Weighted average amortization period						5 years 9 months 18 days