Number of shares delivered of equity interests owned of a related party to acquire an entity.

No definition available.

Name:	snh_BusinessAcquisitionEquityInterestsDelivered
Namespace Prefix:	snh_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of direct and indirect economic interest held in RMR LLC.

+ References

No definition available.

+ Details

Name:	snh_DirectAndIndirectEconomicInterestPercent
Namespace Prefix:	snh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of economic interest held in RMR Inc.

+ References

No definition available.

+ Details

Name:	snh_EconomicInterestPercent
Namespace Prefix:	snh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The ratio upon conversion of RMR Inc. class B-1 common stock into RMR Inc. class A common stock.

+ References

No definition available.

+ Details

Name:	snh_EquityInstrumentConvertibleConversionRatio
Namespace Prefix:	snh_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

The ratio upon conversion of RMR LLC class A membership units owned by RMR Trust into RMR Inc. class A common stock.

+ References

No definition available.

+ Details

Name:	snh_EquityInstrumentConvertibleConversionRatio1
Namespace Prefix:	snh_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of indirect economic interest held in RMR LLC.

+ References

No definition available.

+ Details

Name:	snh_IndirectEconomicInterestPercent
Namespace Prefix:	snh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of the company's common shares under a lock up and registration rights agreement that are not authorized to be transfered for a specified period of time.

+ References

No definition available.

+ Details

Name:	snh_LockUpAgreementTransferOfCommonShares
Namespace Prefix:	snh_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the period over which the company's common shares remain under a lock up and registration rights agreement and not authorized to be transfered.

+ References

No definition available.

+ Details

Name:	snh_LockUpAgreementTransferOfCommonSharesPeriod
Namespace Prefix:	snh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of management agreements the company would need to terminate for convenience before a termination fee is incurred.

+ References

No definition available.

+ Details

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

- Definition

presents the number of management agreements RMR LLC would need to terminate for good cause before a termination fee is incurred.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of management agreements the company would need to terminate for a performance reason before a termination fee is incurred.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of votes per equity interest.

+ References

No definition available.

+ Details

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

- Definition

Represents the cash purchase price paid to acquire common shares of beneficial interest of related party pursuant to the stock purchase agreement.

+ References

No definition available.

+ Details

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

- Definition

Represents the window or numbers of business days after any calendar year to provide notice for termination of property management agreement by the related party for performance reasons.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionNumberOfBusinessDayWindowAfterEndOfAnyCalendarYearPriorWrittenNoticeForTerminationOfPropertyManagementAgreementForPerformanceByRelatedParty
Namespace Prefix:	snh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of business days notice for termination of property management agreement by the related party for convenience.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionNumberOfBusinessDaysPriorWrittenNoticeForTerminationOfPropertyManagementAgreementForConvenienceByRelatedParty
Namespace Prefix:	snh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of business days notice for termination of property management agreement by the related party for performance, provided within a given window or numbers of days after any calendar year.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionNumberOfBusinessDaysPriorWrittenNoticeForTerminationOfPropertyManagementAgreementForPerformanceByRelatedParty
Namespace Prefix:	snh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the window after a change in control to provide notice for termination of property management agreement by the related party.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionWindowAfterChangeOfControlPriorWrittenNoticeForTerminationOfPropertyManagementAgreementByRelatedParty
Namespace Prefix:	snh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

epresents the remaining term assumption in years used to calculate the fee for termination of one or both of the company's amended management agreements for a performance reason.

+ References

No definition available.

+ Details

Name:	snh_TerminationFeeRemainingTermAssumption
Namespace Prefix:	snh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of voting power controlled by a given entity with outstanding capital stock in RMR Inc.

+ References

No definition available.

+ Details

Name:	snh_VotingPowerPercent
Namespace Prefix:	snh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of shares of equity interests issued or issuable to acquire entity.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 50

-Paragraph 1

-Subparagraph (b)(4)

-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

+ Details

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

- Definition

Balance held at close of period in number of shares.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 320

-Section S99

-Paragraph 4

-Subparagraph (SX 210.12-12C.Column B)

-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611225-123010

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 320

-Section S99

-Paragraph 6

-Subparagraph (SX 210.12-14.Column B)

-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611322-123010

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 946

-SubTopic 320

-Section S99

-Paragraph 1

-Subparagraph (SX 210.12-12.Column B)

-URI http://asc.fasb.org/extlink&oid=50485924&loc=d3e611133-123010

+ Details

Name:	us-gaap_InvestmentOwnedBalanceShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
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_RelatedPartyTransactionLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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

- Details

Name:	us-gaap_RelatedPartyTransactionAxis=snh_UpCTransactionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=snh_ReitManagementResearchTrustMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=snh_ReitManagementAndResearchLLCMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TransactionTypeAxis=snh_AmendedAndRestateBusinessManagementAgreementMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=snh_GovernmentPropertiesIncomeTrustMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=snh_HospitalityPropertiesTrustMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=snh_SelectIncomeReitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TitleOfIndividualAxis=snh_ManagementTrusteesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=snh_ReitManagementAndResearchIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EquityInterestIssuedOrIssuableByTypeAxis=us-gaap_CommonStockMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EquityInterestIssuedOrIssuableByTypeAxis=us-gaap_CommonClassAMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	dei_LegalEntityAxis=snh_ReitManagementAndResearchIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

Name:	us-gaap_EquityInterestIssuedOrIssuableByTypeAxis=us-gaap_CommonClassBMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EquityInterestIssuedOrIssuableByTypeAxis=snh_CommonClassB2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EquityInterestIssuedOrIssuableByTypeAxis=us-gaap_MemberUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EquityInterestIssuedOrIssuableByTypeAxis=snh_ClassBMemberUnitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Related Person Transactions - Up-C Transaction (Details) $ in Thousands		3 Months Ended	9 Months Ended
	Jun. 05, 2015 USD ($) agreement shares	Sep. 30, 2015 Vote shares	Sep. 30, 2015 shares
RMR LLC
Related person transactions
Shares issued in connection with acquisition			81,557
Up C Transaction
Related person transactions
Indirect economic interest in RMR LLC (as a percent)	17.00%
Up C Transaction \| RMR Trust
Related person transactions
Direct and indirect economic interest in RMR LLC (as a percent)	51.60%
Voting power of outstanding capital stock of RMR Inc. (as a percent)	91.40%
Up C Transaction \| RMR LLC \| Amended Agreement
Related person transactions
Number of business days notice for termination of property management agreement for convenience by the related party	60 days
Number of business days notice for termination of property management agreement for performance by the related party	60 days
Window for providing notice of termination of property management agreement for performance by the related party	60 days
Window for providing notice of termination of property management agreement for change of control by the related party	12 months
Number of terminated management agreements for convenience before termination fee is incurred \| agreement	1
Number of RMR LLC terminated management agreements for good cause before termination fee is incurred \| agreement	1
Number of terminated management agreements for a performance reason before termination fee is incurred \| agreement	1
Termination fee remaining term assumption	10 years
Up C Transaction \| GOV
Related person transactions
Indirect economic interest in RMR LLC (as a percent)	5.00%
Up C Transaction \| HPT
Related person transactions
Indirect economic interest in RMR LLC (as a percent)	16.20%
Up C Transaction \| SIR
Related person transactions
Indirect economic interest in RMR LLC (as a percent)	10.20%
Up C Transaction \| Managing Trustees Barry And Adam Portnoy \| RMR Trust
Related person transactions
Number of shares under lock up and registration agreement		2,345,000
Period over which shares remain under lock up and registration agreement		10 years
RMR Inc \| Up C Transaction
Related person transactions
Cash purchase price \| $	$ 13,967
Equity conversion ratio of RMR Inc class B-1 common stock		1
Equity conversion ratio of RMR LLC class A membership units		1
RMR Inc \| Up C Transaction \| RMR Trust
Related person transactions
Cash purchase price \| $	11,520
RMR Inc \| Up C Transaction \| GOV
Related person transactions
Cash purchase price \| $	3,917
RMR Inc \| Up C Transaction \| HPT
Related person transactions
Cash purchase price \| $	12,622
RMR Inc \| Up C Transaction \| SIR
Related person transactions
Cash purchase price \| $	$ 15,880
Common Shares \| RMR Inc \| Up C Transaction
Related person transactions
Shares issued in connection with acquisition	2,345,000
Common Shares \| RMR Inc \| Up C Transaction \| GOV
Related person transactions
Shares issued in connection with acquisition	700,000
Common Shares \| RMR Inc \| Up C Transaction \| HPT
Related person transactions
Shares issued in connection with acquisition	1,490,000
Common Shares \| RMR Inc \| Up C Transaction \| SIR
Related person transactions
Shares issued in connection with acquisition	880,000
Class A common shares \| Up C Transaction \| RMR Inc
Related person transactions
Shares issued in connection with acquisition	5,272,787
Class A common shares \| Up C Transaction \| GOV \| RMR Inc
Related person transactions
Shares issued in connection with acquisition	1,541,201
Class A common shares \| Up C Transaction \| HPT \| RMR Inc
Related person transactions
Shares issued in connection with acquisition	5,019,121
Class A common shares \| Up C Transaction \| SIR \| RMR Inc
Related person transactions
Shares issued in connection with acquisition	3,166,891
Class A common shares \| RMR Inc \| Up C Transaction
Related person transactions
Number of votes per equity interest \| Vote		1
Class B1 common shares \| Up C Transaction \| RMR Inc
Related person transactions
Shares issued in connection with acquisition	1,000,000
Class B1 common shares \| RMR Inc \| Up C Transaction
Related person transactions
Number of votes per equity interest \| Vote		10
Class B2 common shares \| Up C Transaction \| RMR Inc
Related person transactions
Shares issued in connection with acquisition	15,000,000
Class B2 common shares \| RMR Inc \| Up C Transaction
Related person transactions
Number of votes per equity interest \| Vote		10
Economic interest in RMR Inc (as a percent)		0.00%
Class A member units \| RMR Inc \| Up C Transaction \| RMR LLC \| RMR Trust
Related person transactions
Business acquisition related party equity interests delivered	15,000,000
Investment in common shares	30,000,000
Class B member units \| RMR Inc \| Up C Transaction \| RMR LLC
Related person transactions
Shares issued in connection with acquisition	1,000,000