This element represents the number of buildings acquired or agreed to be acquired by the entity during the period.

No definition available.

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

- Definition

Represents the number of communities.

+ References

No definition available.

+ Details

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

- Definition

This element represents the number of properties acquired or agreed to be acquired by the entity during the period.

+ References

No definition available.

+ Details

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

- Definition

This element represents the number of properties sold or agreed to be sold by the entity.

+ References

No definition available.

+ Details

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

- Definition

The aggregate revenue from residents fees and related services provided during the reporting period.

+ References

No definition available.

+ Details

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

- Definition

The pro forma net income or loss for the period as if the significant acquisitions or disposals had been completed at the beginning of the period.

+ References

No definition available.

+ Details

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

- Definition

The pro forma basic net income per share for a period as if the significant acquisitions or disposals had been completed at the beginning of the period.

+ References

No definition available.

+ Details

Name:	snh_SignificantAcquisitionsAndDisposalsProFormaEarningsPerShareBasic
Namespace Prefix:	snh_
Data Type:	num:perShareItemType
Balance Type:	na
Period Type:	duration

- References

No definition available.

+ Details

Name:	snh_SignificantAcquisitionsAndDisposalsProFormaInformationAbstract
Namespace Prefix:	snh_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The pro forma revenue for a period as if the significant acquisitions or disposals had been completed at the beginning of the period.

+ References

No definition available.

+ Details

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

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentBasisSpreadOnVariableRate1
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The reference rate for the variable rate of the debt instrument, such as LIBOR or the US Treasury rate and the maturity of the reference rate used, such as three months or six months LIBOR.

+ References

No definition available.

+ Details

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

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 55

-Paragraph 8

-URI http://asc.fasb.org/extlink&oid=34725769&loc=d3e28878-108400

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 835

-SubTopic 30

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6451184&loc=d3e28551-108399

+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.22(a)(1))

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 22

-Article 5

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average interest rate of debt outstanding.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtWeightedAverageInterestRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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=6367179&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=6367179&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=6367179&loc=d3e4304-108586

+ Details

Name:	us-gaap_NoncashOrPartNoncashAcquisitionDebtAssumed1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Generally recurring costs associated with normal operations except for the portion of these expenses which can be clearly related to production and included in cost of sales or services. Includes selling, general and administrative expense.

+ References

No definition available.

+ Details

Name:	us-gaap_OperatingExpenses
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The total amount of revenue recognized for the period from operating leases, including minimum lease revenue, contingent revenue, percentage revenue and sublease revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=7501430&loc=d3e39896-112707

+ Details

Name:	us-gaap_OperatingLeasesIncomeStatementLeaseRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash outflow associated with the acquisition of long-lived, physical assets that are used in the normal conduct of business to produce goods and services and not intended for resale; includes cash outflows to pay for construction of self-constructed assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Investing Activities

-URI http://asc.fasb.org/extlink&oid=6516133

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 13

-Subparagraph (c)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3213-108585

+ Details

Name:	us-gaap_PaymentsToAcquirePropertyPlantAndEquipment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The cash inflow from additional borrowings, net of cash paid to third parties in connection with debt origination.

+ References

No definition available.

+ Details

Name:	us-gaap_ProceedsFromDebtNetOfIssuanceCosts
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The cash inflow from the additional capital contribution to the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Financing Activities

-URI http://asc.fasb.org/extlink&oid=6513228

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 14

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3255-108585

+ Details

Name:	us-gaap_ProceedsFromIssuanceOfCommonStock
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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_SignificantAcquisitionsAndDisposalsLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of new stock issued during the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section 50

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6928386&loc=d3e21463-112644

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 02

-Paragraph 29, 30

-Article 5

+ Details

Name:	us-gaap_StockIssuedDuringPeriodSharesNewIssues
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementScenarioAxis=us-gaap_ProFormaMember
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_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=snh_TripleNetSeniorLivingCommunitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_DebtInstrumentAxis=snh_SeniorUnsecuredNotes3.25PercentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=snh_SeniorUnsecuredNotes4.75PercentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DebtInstrumentAxis=us-gaap_UnsecuredDebtMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Pro Forma Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended						3 Months Ended		4 Months Ended	6 Months Ended		12 Months Ended
	Jul. 31, 2015 property	May. 31, 2015 USD ($) property community	Feb. 28, 2015 USD ($) property shares	Jan. 31, 2015 USD ($) property building	May. 31, 2014 USD ($)	Apr. 30, 2014 USD ($) shares	Jun. 30, 2015 USD ($)	Jun. 30, 2014 USD ($)	Sep. 30, 2014	Jun. 30, 2015 USD ($) property community $ / shares	Jun. 30, 2014 USD ($) $ / shares	Dec. 31, 2014 USD ($) property building
Pro Forma Information
Number of properties to be sold \| property			1
Interest rate (as a percent)							1.58%			1.58%
Mortgage debt assumed										$ 169,136	$ 15,630
Residents fees and services							$ 91,856	$ 79,039		174,649	158,481
Common shares issued in public offering \| shares			31,050,000			15,525,000
Net proceeds from issuance of common shares issued in public offering			$ 659,502			$ 322,807				659,502	322,864
Net proceeds after underwriting discounts from sale of senior unsecured notes										644,889
Pro Forma
Pro forma results of operations
Total revenues										508,448	505,044
Net income										$ 77,822	$ 66,987
Net income per share (in dollars per share) \| $ / shares										$ 0.33	$ 0.29
Senior living communities
Pro Forma Information
Number of communities \| community										19
Number of properties to be sold \| property	1
Property operating expenses										$ 6,156
Residents fees and services										8,828
Triple Net Leased Net Senior Living Communities
Pro Forma Information
Number of communities \| community		18
Total rental income recognized										$ 5,644
Acquisition
Pro Forma Information
Number of properties acquired or agreed to be acquired \| property										23
Aggregate purchase price properties, excluding closing costs				$ 539,000
Mortgage debt assumed				$ 29,955
Weighted average interest rate on debt (as a percent)				4.73%
Property operating expenses										$ 2,591
Total rental income recognized										$ 17,208
Acquisition \| Senior living communities
Pro Forma Information
Number of properties acquired or agreed to be acquired		37										2
Aggregate purchase price properties, excluding closing costs		$ 762,611
Mortgage debt assumed		$ 139,181
Weighted average interest rate on debt (as a percent)		4.43%
Acquisition \| MOBs
Pro Forma Information
Number of properties acquired or agreed to be acquired \| property				23						23		2
Number of buildings acquired \| building				23								3
Aggregate purchase price properties, excluding closing costs												$ 1,204,393
Mortgage debt assumed				$ (29,955)						$ (29,955)		$ 15,630
Weighted average interest rate on debt (as a percent)												6.28%
Acquisition \| Triple Net Leased Net Senior Living Communities
Pro Forma Information
Number of properties acquired or agreed to be acquired \| property		18
Mortgage debt assumed		$ (44,395)
Senior unsecured notes 3.25%
Pro Forma Information
Interest rate (as a percent)						3.25%
Principal amount of debt						$ 400,000
Senior unsecured notes 4.75%
Pro Forma Information
Interest rate (as a percent)						4.75%
Principal amount of debt						$ 250,000
Unsecured Debt
Pro Forma Information
Principal amount of debt					$ 350,000		$ 350,000			$ 350,000		$ 350,000
Interest rate, description					LIBOR				LIBOR
Interest rate added to the base rate (as a percent)					1.40%							1.40%