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 measurement periods ending with the year for which the incentive management fee is being calculated, with periods applicable in the case of calculation of the incentive management fee.

+ References

No definition available.

+ Details

Name:	snh_PeriodApplicableInCaseOfCalculationOfIncentiveManagementFeeFor2015
Namespace Prefix:	snh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the measurement periods ending with the year for which the incentive management fee is being calculated.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of amortization of the liability recorded during the period.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionAmortizationOfLiability
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 common shares issued for incentive fees during the period.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionCommonStockIssuedForIncentiveFee
Namespace Prefix:	snh_
Data Type:	xbrli:sharesItemType
Balance Type:	na
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 number of equal annual installments for vesting of common shares.

+ References

No definition available.

+ Details

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

- Definition

Represents the incentive management fee payable as a percentage of the product of the entity's equity market capitalization and its share price appreciation plus dividends.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionPercentageForLimitationAndAdjustmentsOfIncentiveManagementFeePayable
Namespace Prefix:	snh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage of base business management fees payable in cash.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionPercentageOfBaseBusinessManagementFeePayableInCash
Namespace Prefix:	snh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the percentage of base business management fees payable in common shares.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionPercentageOfBaseBusinessManagementFeePayableInCommonShares
Namespace Prefix:	snh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the portion of remaining shares to be vested in equal annual installments.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionPercentageOfRemainingSharesToBeVestedInEqualAnnualInstallments
Namespace Prefix:	snh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the portion of shares issued in payment of an incentive management fee.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionPercentageOfSharesIssuedInPaymentOfIncentiveManagementFees
Namespace Prefix:	snh_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Represents the construction supervision fees payable to related parties under property management agreement expressed as a percentage of construction costs.

+ References

No definition available.

+ Details

Name:	snh_RelatedPartyTransactionPropertyManagementAgreementConstructionSupervisionFeesAsPercentageOfConstructionCosts
Namespace Prefix:	snh_
Data Type:	num:percentItemType
Balance Type:	na
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

Represents the portion of awards granted which will vest on the grant date.

+ References

No definition available.

+ Details

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

- Definition

Represents the portion of awards granted which will vest on each of the next four anniversaries of the grant date.

+ References

No definition available.

+ Details

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

- Definition

Represents the aggregate fair value of the equity instruments other than options granted during the period.

+ References

No definition available.

+ Details

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

- Definition

Represents the measurement periods ending with the year for which the incentive management fee is being calculated, with shorter periods applicable in the case of calculation of the incentive management fee.

+ References

No definition available.

+ Details

Name:	snh_ShorterPeriodApplicableInCaseOfCalculationOfIncentiveManagementFeeFor2014
Namespace Prefix:	snh_
Data Type:	xbrli:durationItemType
Balance Type:	na
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

Period which an employee's right to exercise an award is no longer contingent on satisfaction of either a service condition, market condition or a performance condition, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents the reported fact of one year, five months, and thirteen days.

+ References

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

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target 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
-Subparagraph (c)(2)(iii)(1)
-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

+ Details

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

- Definition

Number of shares that have been repurchased during the period and have not been retired and are not held in treasury. Some state laws may govern the circumstances under which an entity may acquire its own stock and prescribe the accounting treatment therefore. This element is used when state law does not recognize treasury stock.

+ 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 SEC
-Name Regulation S-X (SX)
-Number 210
-Section 04
-Article 3

Reference 3: 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_StockRepurchasedDuringPeriodShares
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:

- Details

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

- Details

Name:	us-gaap_PlanNameAxis=snh_RestrictedSharesMember
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_TransactionTypeAxis=snh_AmendedAndRestateBusinessManagementAgreementMember
Namespace Prefix:
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Related Person Transactions - RMR LLC Management Fees and Reimbursements (Details) $ in Thousands		1 Months Ended		5 Months Ended	12 Months Ended
	Dec. 23, 2013 installment	Sep. 30, 2015 shares	Mar. 31, 2013 shares	Jun. 05, 2015 shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2014 USD ($) shares	Dec. 31, 2013 USD ($) shares
Related person transactions
Portion of shares issued in payment of an incentive management fee (as a percent)	33.33%
Property management and construction supervision fees					$ 10,342	$ 8,259	$ 6,568
Property management and construction supervision fees paid					7,021	5,289	4,705
RMR LLC
Related person transactions
Business management fees incurred					34,949	30,794	27,013
Incentive fees payable					0	$ 0	0
Recognized amortization of the liability					1,743
Common shares issued for the incentive fees \| shares			21,968	68,983		123,462
Repurchase of common shares (in shares) \| shares		13,113
Accrual for RMR LLC employee share grants and internal audit costs					$ 1,340	$ 1,835	$ 1,877
RMR LLC \| MOBs
Related person transactions
Base business management fee payable in cash (as a percent)					3.00%
Construction supervision fees payable under property management agreement as a percentage of construction costs					5.00%
Restricted shares \| RMR LLC
Related person transactions
Number of shares granted under the award plan \| shares					84,000,000	81,700,000	82,600,000
Aggregate value of awards granted during the period					$ 1,321	$ 1,750	$ 1,888
Portion of the awards granted that vested on grant date (as a percent)					2.00%
Portion of the awards granted which will vest on each of the next four anniversaries of the grant date					2.00%
Restricted shares \| RMR Inc \| RMR LLC
Related person transactions
Award vesting period					4 years
Amended Agreement \| RMR LLC
Related person transactions
Incentive management fee payable (as a percent)	12.00%
Period of measurement	3 years
Shorter period applicable in the case of calculation of the incentive management fee for 2014	1 year
Period applicable in the case of calculation of the incentive management fee for 2015	2 years
Base business management fee payable in cash (as a percent)	90.00%
Base business management fee payable in common shares (as a percent)	10.00%
Portion of remaining shares to be vested in equal annual installments (as a percent)	66.66%
Number of equal annual installments for vesting of common shares \| installment	2