Represents the expense amount accrued for employee share grants and internal audit costs to RMR LLC employees.

No definition available.

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

- Definition

Represents the business management fees incurred pursuant to business management agreement with related parties.

+ References

No definition available.

+ Details

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

- Definition

Represents the property management and construction supervision fees incurred pursuant to business and property management agreements with related parties.

+ References

No definition available.

+ Details

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

- Definition

Represents the property management and construction supervision fees paid to related parties.

+ References

No definition available.

+ Details

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

- Definition

Number of share instruments newly issued under a share-based compensation plan.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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

- Definition

For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

+ References

No definition available.

+ Details

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

- Definition

Number of shares issued in lieu of cash for services contributed to the entity. Number of shares includes, but is not limited to, shares issued for services contributed by vendors and founders.

+ References

No definition available.

+ Details

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

- Details

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

- Details

Name:	us-gaap_AwardTypeAxis=us-gaap_StockCompensationPlanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Related Person Transactions - Management Fees and Reimbursements (Details) - USD ($) $ in Thousands		3 Months Ended		5 Months Ended	9 Months Ended
	Sep. 26, 2016	Sep. 30, 2016	Sep. 30, 2015	May 31, 2016	Sep. 30, 2016	Sep. 30, 2015
Related person transactions
Property management and construction supervision fees		$ 2,961	$ 2,533		$ 8,193	$ 7,554
Property management and construction supervision fees paid		2,482	1,954		6,781	5,189
Shares paid for tax withholding for share based compensation (in shares)	17,667
RMR LLC
Related person transactions
Business management fees incurred		9,609	8,682		27,199	26,644
Common shares issued as payment for base business management fee (in shares)				68,983
Accrual for RMR LLC employee share grants and internal audit costs		$ 901	$ 302		$ 2,075	$ 1,337
Stock Compensation Plan \| RMR LLC
Related person transactions
Share-based compensation arrangement shares issued in period (in shares)					79,650	84,000
Shares paid for tax withholding for share based compensation (in shares)					17,667