Related Person Transactions - Management Fees and Reimbursements (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2016	Mar. 31, 2015
Related person transactions
Property management and construction supervision fees	$ 2,546	$ 2,438
Property management and construction supervision fees paid	2,128	1,387
RMR LLC
Related person transactions
Business management fees incurred	8,347	$ 8,869
Incentive fees payable	0
Common shares issued as payment for base business management fee		39,467
Accrual for RMR LLC employee share grants and internal audit costs	$ 585	$ 461

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 incentive fee payable in a related party transaction.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionIncentiveFeePayable
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

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