Name:	snh_DeferredCostsLeasingExpectedFutureAmortizationAbstract
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Period Type:	duration

Amount of amortization expense expected to be recognized after the fifth fiscal year following the latest fiscal year for deferred leasing costs.

+ References

No definition available.

+ Details

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

- Definition

Amount of amortization expense expected to be recognized during the fifth fiscal year following the latest fiscal year for deferred leasing costs.

+ References

No definition available.

+ Details

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

- Definition

Amount of amortization expense expected to be recognized during the fourth fiscal year following the latest fiscal year for deferred leasing costs.

+ References

No definition available.

+ Details

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

- Definition

Amount of amortization expense expected to be recognized during the next fiscal year following the latest fiscal year for deferred leasing costs.

+ References

No definition available.

+ Details

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

- Definition

Amount of amortization expense expected to be recognized during the third fiscal year following the latest fiscal year for deferred leasing costs.

+ References

No definition available.

+ Details

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

- Definition

Amount of amortization expense expected to be recognized during the second fiscal year following the latest fiscal year for deferred leasing costs.

+ References

No definition available.

+ Details

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

- Definition

Represents the weighted average amortization period for deferred leasing costs.

+ References

No definition available.

+ Details

Name:	snh_DeferredCostsLeasingWeightedAverageAmortizationPeriod
Namespace Prefix:	snh_
Data Type:	xbrli:durationItemType
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

- Details

Name:	snh_RevenueRecognitionLineItems
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Data Type:	xbrli:stringItemType
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Period Type:	duration

- Definition

For an unclassified balance sheet, the accumulated amortization, as of the reporting date, which represents the periodic charge to earnings of initial direct costs which have been deferred and are being allocated over the lease term in proportion to the recognition of rental income.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 35

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6453741&loc=d3e40879-112712

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 25

-Paragraph 16

-URI http://asc.fasb.org/extlink&oid=6748888&loc=d3e40588-112709

+ Details

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

- Definition

For an unclassified balance sheet, this element represents costs incurred by the lessor that are (a) costs to originate a lease incurred in transactions with independent third parties that (i) result directly from and are essential to acquire that lease and (ii) would not have been incurred had that leasing transaction not occurred and (b) certain costs directly related to specified activities performed by the lessor for that lease. Those activities are: evaluating the prospective lessee's financial condition; evaluating and recording guarantees, collateral, and other security arrangements; negotiating lease terms; preparing and processing lease documents; and closing the transaction. This amount is before considering accumulated amortization representing the periodic charge to earnings to recognize the deferred costs over the term of the related lease.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 25

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=6748888&loc=d3e40246-112709

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 840

-SubTopic 20

-Section 25

-Paragraph 16

-URI http://asc.fasb.org/extlink&oid=6748888&loc=d3e40588-112709

+ Details

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

- Details

Name:	us-gaap_DeferredCostsLeasingNetAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of operating segments. An operating segment is a component of an enterprise: (a) that engages in business activities from which it may earn revenues and incur expenses (including revenues and expenses relating to transactions with other components of the same enterprise), (b) whose operating results are regularly reviewed by the enterprise's chief operating decision maker to make decisions about resources to be allocated to the segment and assess its performance, and (c) for which discrete financial information is available. An operating segment may engage in business activities for which it has yet to earn revenues, for example, start-up operations may be operating segments before earning revenues.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfOperatingSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of segments reported by the entity. A reportable segment is a component of an entity for which there is an accounting requirement to report separate financial information on that component in the entity's financial statements.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfReportableSegments
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

This element represents the rental revenue earned during the period from lessee-operators based on revenues generated in their operations, generally in excess of a base amount. Such rental revenue is generally stipulated in the lease agreement, usually will provide for a fixed percentage of revenue to be paid as additional (or possibly only) rent due the lessor, and may be based on gross revenues, net revenues, or multiple variations thereof. Percentage rent is often required under leases with retail outlets located on premises owned by hoteliers, cruise lines, others in the hospitality industry, and shopping mall operators, among others.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1(e))

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

Name:	us-gaap_PercentageRent
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

- Details

Name:	us-gaap_SegmentReportingAbstract
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=snh_SeniorLivingCommunityMember
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Data Type:	na
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Period Type:

Summary of Significant Accounting Policies (Details 5) (USD $) In Thousands, unless otherwise specified	12 Months Ended			1 Months Ended		43 Months Ended
	Dec. 31, 2014 item	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2014 property item	May 31, 2011 property	Dec. 31, 2014 property item
DEFERRED LEASING COSTS
Unamortized gross balance of deferred leasing costs	$ 14,844us-gaap_DeferredCostsLeasingGross	$ 3,722us-gaap_DeferredCostsLeasingGross		14,844us-gaap_DeferredCostsLeasingGross		14,844us-gaap_DeferredCostsLeasingGross
Accumulated amortization	10,542	2,687		10,542		10,542
Weighted average amortization period for deferred leasing cost	7 years 6 months
Expected amortization expense for the five years
Expected amortization expense, 2015	1,945			1,945		1,945
Expected amortization expense, 2016	1,789			1,789		1,789
Expected amortization expense, 2017	1,527			1,527		1,527
Expected amortization expense, 2018	1,358			1,358		1,358
Expected amortization expense, 2019	1,180			1,180		1,180
Expected amortization expense, thereafter	3,183			3,183		3,183
Revenue Recognition
Percentage rents earned	$ 10,155us-gaap_PercentageRent	$ 9,226us-gaap_PercentageRent	$ 10,859us-gaap_PercentageRent
Segment Reporting
Number of Operating Segments	4us-gaap_NumberOfOperatingSegments
Number of Reportable Segments	3us-gaap_NumberOfReportableSegments
Senior living communities \| Five Star
Revenue Recognition
Number of properties acquired or agreed to be acquired	46			2	6	36
Number of properties acquired, referred to as managed properties	46
Number of real estate properties leased	10			10		10