Represents the deferred estimated percentage rent payments received during the period.

No definition available.

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

- Definition

Represents the increase or decrease on the annual rent the lessee is obligated to pay on an operating lease.

+ References

No definition available.

+ Details

Name:	snh_IncreaseDecreaseOperatingLeasesAnnualRent
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the number of shares held as a percentage of the total shares outstanding at the end of the period.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of private pay independent living units within communities acquired.

+ References

No definition available.

+ Details

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

- Definition

This element represents the number of properties acquired or agreed to be acquired by the entity during the period.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of properties acquired or agreed to be acquired by the entity during the period, which are referred by the entity as managed properties.

+ References

No definition available.

+ Details

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

- Definition

This element represents the aggregate purchase price of real estate properties acquired by the entity during the period. This amount includes cash paid plus debt assumed, if any, and other settlement adjustments but excludes closing costs.

+ References

No definition available.

+ Details

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

- Definition

Represents the amount of improvements to real estate properties made by lessees and purchased by the entity.

+ References

No definition available.

+ Details

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

- Definition

Expenses recognized during the period resulting from property management transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party during the period.

+ References

No definition available.

+ Details

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

- Definition

Represents rents receivable at the balance sheet date.

+ References

No definition available.

+ Details

Name:	snh_RentsReceivable
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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

The number of units in a real estate property owned as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfUnitsInRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The total amount of revenue recognized for the period from operating leases, including minimum lease revenue, contingent revenue, percentage revenue and sublease revenue.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 840
-SubTopic 20
-Section 25
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=7501430&loc=d3e39896-112707

+ Details

Name:	us-gaap_OperatingLeasesIncomeStatementLeaseRevenue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The number of units (items of property) under operating lease arrangements.

+ References

No definition available.

+ Details

Name:	us-gaap_PropertySubjectToOrAvailableForOperatingLeaseNumberOfUnits
Namespace Prefix:	us-gaap_
Data Type:	xbrli:decimalItemType
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_FiveStarQualityCareIncMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BalanceSheetLocationAxis=us-gaap_OtherAssetsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	snh_OperatingLeasesOfLessorLesseeAxis=snh_TaxableREITSubsidiariesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_NC
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_AL
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RealEstateAndAccumulatedDepreciationDescriptionOfPropertyAxis=us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember
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_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=stpr_GA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Related Person Transactions - Five Star (Details) $ in Thousands	1 Months Ended		3 Months Ended					12 Months Ended
	May. 31, 2016 USD ($) community property	Jan. 31, 2015 property	Mar. 31, 2016 USD ($) community item shares	Mar. 31, 2016 USD ($) community shares	Mar. 31, 2016 USD ($) community property shares	Mar. 31, 2016 USD ($) community shares	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($) item community	Apr. 30, 2016 item	Dec. 31, 2001
Five Star
Related person transactions
Percentage of total shares outstanding			8.60%	8.60%	8.60%	8.60%				100.00%
Investment in common shares \| shares			4,235,000	4,235,000	4,235,000	4,235,000
Number of real estate properties leased \| community			177	177	177	177
Total rental income recognized						$ 48,108	$ 47,691
Estimated percentage rent payments received						1,473	1,456
Real estate improvements purchased						5,755	4,060
Increase or decrease in annual lease rent payable			$ 462	$ 462	$ 462	462	328
Five Star \| Other assets
Related person transactions
Rents receivable			$ 16,022	$ 16,022	$ 16,022	16,022		$ 17,466
Five Star \| Senior Living Communities
Related person transactions
Number of properties acquired, referred to as managed properties			60	60				46
Property management agreement expense						$ 2,804	$ 2,523
Five Star \| Senior Living Communities \| TRS \| North Carolina
Related person transactions
Number of living units \| item								87
Five Star \| Senior Living Communities \| TRS \| Alabama
Related person transactions
Number of living units \| item									163
Acquisition
Related person transactions
Number of properties acquired or agreed to be acquired \| property					1
Acquisition \| MOBs
Related person transactions
Number of properties acquired or agreed to be acquired \| property		23
Subsequent event \| Five Star \| Senior Living Communities \| TRS \| Georgia
Related person transactions
Number of private pay independent living units \| community	38
Purchase price excluding closing costs and working capital adjustments	$ 8,400
Subsequent event \| Acquisition \| MOBs
Related person transactions
Number of properties acquired or agreed to be acquired \| property	1
Purchase price excluding closing costs and working capital adjustments	$ 45,000
Subsequent event \| Acquisition \| Five Star \| Georgia
Related person transactions
Number of private pay independent living units \| property	38
Subsequent event \| Acquisition \| Five Star \| Senior Living Communities \| TRS \| Georgia
Related person transactions
Purchase price excluding closing costs and working capital adjustments	$ 8,400