Represents the area of a real estate property, held for sale.

No definition available.

Name:	snh_AreaOfRealEstatePropertyHeldForSale
Namespace Prefix:	snh_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

Weighted average interest rate on debt during the period.

+ References

No definition available.

+ Details

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

- Definition

The amount of premium on assumed debt that an Entity assumes in acquiring a business or in consideration for an asset received in a noncash (or part noncash) acquisition.

+ References

No definition available.

+ Details

Name:	snh_NoncashOrPartNoncashAcquisitionPremiumOnDebtAssumed1
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Represents the number of buildings owned as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

The number of buildings owned by the entity, which are classified as held for sale as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

This element represents the number of buildings sold by the entity.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of communities.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of communities not yet acquired under the purchase agreement to acquire.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of operators or property managers.

+ References

No definition available.

+ Details

Name:	snh_NumberOfOperators
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 number of properties sold or agreed to be sold by the entity.

+ References

No definition available.

+ Details

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

- Definition

The number of real estate properties owned by the entity, which are classified as held for sale as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of states in which the comapnies property is located.

+ References

No definition available.

+ Details

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

- Definition

The number of units in a real estate property owned with an agreement for delayed closing as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

This element represents the aggregate purchase price excluding closing costs, of real estate properties acquired by the entity during the period.

+ References

No definition available.

+ Details

Name:	snh_RealEstateAggregatePurchasePrice
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

This element represents the aggregate sales price excluding closing costs, of real estate properties sold by the entity during the period.

+ References

No definition available.

+ Details

Name:	snh_RealEstateAggregateSalesPrice
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

Represents the intangible lease assets recorded as part of the real estate acquisition.

+ References

No definition available.

+ Details

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

- Definition

Represents the intangible lease liabilities recorded as part of the real estate acquisition.

+ References

No definition available.

+ Details

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

- Definition

Represents the property plant and equipment assets recorded as part of the real estate acquisition.

+ References

No definition available.

+ Details

Name:	snh_RealEstatePropertiesAcquiredPropertyPlantAndEquipment
Namespace Prefix:	snh_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Area of a real estate property.

+ References

No definition available.

+ Details

Name:	us-gaap_AreaOfRealEstateProperty
Namespace Prefix:	us-gaap_
Data Type:	num:areaItemType
Balance Type:	na
Period Type:	instant

- Definition

The difference between the carrying value and the sale price of real estate or properties that were intended to be sold or held for capital appreciation or rental income. This element refers to the gain (loss) included in earnings and not to the cash proceeds of the sale. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585

+ Details

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

- Definition

The amount of early contract termination fees included in liabilities subject to compromise.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 852

-SubTopic 10

-Section 55

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=34712771&loc=d3e56145-112766

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 852

-SubTopic 10

-Section 45

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6916575&loc=d3e55717-112764

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 852

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6918054&loc=d3e56015-112765

+ Details

Name:	us-gaap_LiabilitiesSubjectToCompromiseEarlyContractTerminationFees
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The amount of debt that an Entity assumes in acquiring a business or in consideration for an asset received in a noncash (or part noncash) acquisition. Noncash is defined as transactions during a period that affect recognized assets or liabilities but that do not result in cash receipts or cash payments in the period. "Part noncash" refers to that portion of the transaction not resulting in cash receipts or cash payments in the period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4332-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4313-108586

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 50

-Paragraph 3

-URI http://asc.fasb.org/extlink&oid=6367179&loc=d3e4304-108586

+ Details

Name:	us-gaap_NoncashOrPartNoncashAcquisitionDebtAssumed1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The number of real estate properties owned as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

The number of states the entity operates in as of the balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfStatesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
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

- Details

Name:	us-gaap_PropertyPlantAndEquipmentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of investments in land and buildings held for sale, excluding real estate considered to be inventory of the entity.

+ References

+ Details

Name:	us-gaap_RealEstateHeldforsale
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cumulative amount of depreciation for real estate property held for investment purposes.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 944

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.7-03.1(3))

-URI http://asc.fasb.org/extlink&oid=6879938&loc=d3e572229-122910

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 7

+ Details

Name:	us-gaap_RealEstateInvestmentPropertyAccumulatedDepreciation
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of real estate investment property which may include the following: (1) land available-for-sale; (2) land available-for-development; (3) investments in building and building improvements; (4) tenant allowances; (5) developments in-process; (6) rental properties; and (7) other real estate investments.

+ References

+ Details

Name:	us-gaap_RealEstateInvestmentPropertyAtCost
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Details

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=snh_IndependentLivingFacilityMember
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_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=snh_MemoryCareFacilityMember
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:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=snh_SkilledNursingFacilityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_BuildingImprovementsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_PropertyPlantAndEquipmentByTypeAxis=us-gaap_LandMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis=snh_AgreementToAcquireMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_SignificantAcquisitionsAndDisposalsByTransactionAxis=us-gaap_SeriesOfIndividuallyImmaterialBusinessAcquisitionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementGeographicalAxis=country_PA
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:

Real Estate Properties (Details) (USD $) In Thousands, unless otherwise specified	1 Months Ended	3 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended	0 Months Ended	1 Months Ended
	Feb. 28, 2015 property	Mar. 31, 2015 property building item	Mar. 31, 2014	Apr. 30, 2015 building property sqft	Dec. 31, 2014 community item	Jan. 31, 2015 property building sqft state	May 01, 2015	May 31, 2015 community item	Dec. 31, 2014 community state item
Real Estate Properties
Number of properties owned		392us-gaap_NumberOfRealEstateProperties
Number of buildings owned		419snh_NumberOfBuildings
Number of states in which properties are located		39
Real estate properties, at cost		$ 6,717,946			6,238,611				6,238,611
Accumulated depreciation		1,023,843			983,850				983,850
Assumption of mortgage notes payable		29,955
Number of properties classified as held for sale		4
Number of buildings classified as held for sale		7snh_NumberOfBuildingsHeldForSale
Number of properties to be sold	1snh_NumberOfPropertiesSold
Gain on the sale of property			156us-gaap_GainLossOnSaleOfProperties
Five Star
Real Estate Properties
Real estate improvements purchased		4,550	8,614
Increase or decrease in annual lease rent payable		367	689
MOBs
Real Estate Properties
Number of properties classified as held for sale		1	4
Number of buildings classified as held for sale		4	7
Property held for sale (in square feet)		323,541
Number of buildings sold				4
Sale price of property sold and agreed to be sold				1,500
Senior living communities
Real Estate Properties
Number of communities					5
Number of living units		192			395				395
Number of properties classified as held for sale		3
Real estate properties, held for sale		3,145
Senior living communities \| Five Star
Real Estate Properties
Number of properties acquired, referred to as managed properties		46
Number of communities					14
Number of living units					881				881
Fees paid to terminate the agreement					975				975
Independent living facility
Real Estate Properties
Number of living units					826				826
Assisted living facility
Real Estate Properties
Number of living units					1,860				1,860
Memory care facility
Real Estate Properties
Number of living units					744				744
Skilled nursing facilities
Real Estate Properties
Number of living units					36				36
Acquisition
Real Estate Properties
Number of properties acquired or agreed to be acquired		23
Assumption of mortgage notes payable		29,955
Acquisition \| MOBs
Real Estate Properties
Number of properties acquired or agreed to be acquired		23			2	23
Number of buildings acquired					3	23
Number of states in which property is located						12
Cash Paid plus Assumed Debt, excluding closing costs						539,000
Assumption of mortgage notes payable		(29,955)			15,630	(29,955)
Weighted average interest rate on debt (as a percent)						4.73%
Area of real estate properties (in square feet)		2,170,000				2,170,000
Cash Paid plus Assumed Debt, excluding closing costs plus other settlement adjustments		539,000				539,000
Premium on Assumed Debt		(1,074)				(1,074)
Intangible lease assets recorded		85,496				85,496
Intangible lease liabilities recorded		(3,298)				(3,298)
Acquisition \| Senior living communities
Real Estate Properties
Number of properties acquired or agreed to be acquired					2
Acquisition \| Senior living communities \| Subsequent event
Real Estate Properties
Number of living units							3,379
Number of living units with delayed closing							87
Cash Paid plus Assumed Debt, excluding closing costs							762,611
Acquisition \| Senior living communities \| Five Star
Real Estate Properties
Number of communities								14
Number of living units								881
Agreement to acquire \| Senior living communities
Real Estate Properties
Number of properties acquired or agreed to be acquired					38
Number of communities								37	38
Number of living units					3,466				3,466
Number of states in which property is located					16				16
Cash Paid plus Assumed Debt, excluding closing costs					790,000
Assumption of mortgage notes payable					153,000			139,181
Weighted average interest rate on debt (as a percent)					4.77%			4.59%
Agreement to acquire \| Senior living communities \| Leasing Member
Real Estate Properties
Number of communities					19
Number of living units					2,190				2,190
Number of communities not yet acquired					1
Number of operators					7
Agreement to acquire \| Senior living communities \| TRS \| Non Leasing Member
Real Estate Properties
Number of communities					19
Number of living units					1,276				1,276
Land \| Acquisition \| MOBs
Real Estate Properties
Property plant and equipment recorded		58,294				58,294
Buildings and improvements \| Acquisition \| MOBs
Real Estate Properties
Property plant and equipment recorded		399,582				399,582
GA \| Senior living communities \| Five Star
Real Estate Properties
Number of living units				40
Cash Paid plus Assumed Debt, excluding closing costs plus other settlement adjustments				9,750
GA \| Agreement to acquire \| Senior living communities
Real Estate Properties
Number of communities				1
Number of living units				40
Cash Paid plus Assumed Debt, excluding closing costs				9,750
Pennsylvania \| Senior living communities
Real Estate Properties
Sale price of property sold and agreed to be sold	250
Pennsylvania \| Sale \| Senior living communities \| Five Star
Real Estate Properties
Number of living units	120
Sale price of property sold and agreed to be sold	250
Increase or decrease in annual lease rent payable	23