Number of Management Agreements

No definition available.

Name:	snh_NumberofManagementAgreements
Namespace Prefix:	snh_
Data Type:	xbrli:integerItemType
Balance Type:	na
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- Definition

Represents the number of persons employed by a related party of the entity.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyEmployeesNumber
Namespace Prefix:	snh_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Related Party Transaction, Business Management Agreement Annual Incentive Fee Estimate Included in Management Fees

+ References

No definition available.

+ Details

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

- Definition

Related Party Transaction Business Management Agreement Incentive Fee Paid

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionBusinessManagementAgreementIncentiveFeePaid
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

Related Party Transaction Business Management Fees Related to Subsidiary Level Management

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No definition available.

+ Details

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

- Definition

Related Party Transaction, Period Of Actual Amount Of Incentive Fees

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No definition available.

+ Details

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

- Definition

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

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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

- Details

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

- Details

Name:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=snh_SeniorLivingCommunityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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- Details

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Business and Property Management Agreements with RMR LLC (Details)	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) employee management_agreement	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) employee management_agreement	Sep. 30, 2018 USD ($)	Dec. 31, 2019
Related person transactions
Number of employees \| employee		0		0
Related party transaction business management agreement incentive fee paid	$ 40,642,000
Property management and construction supervision fees		$ 3,289,000	$ 3,025,000	$ 9,844,000	$ 8,829,000
Property management and construction supervision fees paid		3,419,000	3,440,000	10,145,000	9,391,000
RMR LLC
Related person transactions
Business management fees incurred		6,616,000	28,306,000	20,917,000	78,119,000
Related party transaction business management fees related to subsidiary level management		725,000	725,000	2,175,000	2,175,000
Related party transaction business management agreement, annual incentive fee estimate included in management fees		$ 0	$ 18,751,000	$ 0	$ 50,708,000
Senior Living Communities \| RMR Inc
Related person transactions
Number of management agreements \| management_agreement		2		2
Subsequent Event \| Scenario, Forecast \| RMR LLC
Related person transactions
Period of actual amount of incentive fees						3 years