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

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

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

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 real estate properties impaired.

+ References

No definition available.

+ Details

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

- 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

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 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

Amount of write-down of assets recognized in the income statement. Includes, but is not limited to, losses from tangible assets, intangible assets and goodwill.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 28

-Subparagraph (b)

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

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 360

-SubTopic 10

-Section 45

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=8077374&loc=d3e2420-110228

+ Details

Name:	us-gaap_AssetImpairmentCharges
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- 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 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

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(f))

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

+ Details

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

Real Estate Properties (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	9 Months Ended		1 Months Ended	9 Months Ended				1 Months Ended		1 Months Ended			9 Months Ended		1 Months Ended			9 Months Ended		1 Months Ended		9 Months Ended		9 Months Ended		1 Months Ended
	Sep. 30, 2013	Sep. 30, 2014 property building item	Sep. 30, 2013	Aug. 31, 2014 MOBs property	Sep. 30, 2014 MOBs item property building sqft	Dec. 31, 2013 MOBs building sqft property	Sep. 30, 2014 Senior living communities item	Dec. 31, 2013 Senior living communities item	Aug. 31, 2013 Senior living communities Five Star property	Sep. 30, 2014 Senior living communities Five Star item	Sep. 30, 2014 Sale MOBs building property sqft	Jun. 30, 2014 Sale MOBs property building sqft	Apr. 30, 2014 Sale MOBs building property sqft	Sep. 30, 2014 Sale MOBs property sqft	Sep. 30, 2014 Sale Senior living communities property	Jun. 30, 2014 Sale Senior living communities Five Star property item	Jan. 31, 2014 Sale Senior living communities Five Star item	Aug. 31, 2013 Sale Senior living communities Five Star item	Sep. 30, 2014 Acquisition MOBs property sqft	Aug. 31, 2014 Acquisition MOBs sqft state	Sep. 30, 2014 Acquisition Senior living communities property item	Jul. 31, 2014 Acquisition Senior living communities property	Sep. 30, 2014 Acquisition Senior living communities property item	Jul. 31, 2014 Acquisition Senior living communities Subsequent event item	Sep. 30, 2014 Land Acquisition MOBs	Sep. 30, 2014 Buildings and improvements Acquisition MOBs	May 31, 2014 MA Acquisition MOBs property building sqft	May 31, 2014 MA Land Acquisition MOBs	May 31, 2014 MA Buildings and improvements Acquisition MOBs	Jan. 31, 2014 Texas Sale Senior living communities Five Star item	Apr. 30, 2014 Texas Acquisition MOBs building property sqft	Apr. 30, 2014 Texas Land Acquisition MOBs	Apr. 30, 2014 Texas Buildings and improvements Acquisition MOBs	Oct. 31, 2014 Virginia Sale Senior living communities Five Star item	Oct. 31, 2014 Virginia Sale Senior living communities Five Star Subsequent event property item	Oct. 31, 2014 Arizona Sale Senior living communities Five Star item	Oct. 31, 2014 Arizona Sale Senior living communities Five Star Subsequent event property item
Real Estate Properties
Number of properties owned		371
Number of buildings owned		398
Number of states in which properties are located		38
Number of properties acquired or agreed to be acquired		2		23															2		1	1	2				1				1
Number of buildings acquired																											2				1
Number of living units							552	744								156	36	112			176		176	52											70		177
Number of states in which property is located																				12
Cash Paid plus Assumed Debt, excluding closing costs				$ 539,000																	$ 40,430	$ 7,000	$ 47,430				$ 1,125,420				$ 32,658
Cash Paid plus Assumed Debt, excluding closing costs plus other settlement adjustments																			1,156,963								1,124,031				32,932
Mortgage debt assumed in connection with real estate acquisitions		15,630	12,266	30,000															15,630												15,630
Area of real estate properties (in square feet)											62,000	235,079	210,879	62,000					1,776	2,200,000							1,651,037				125,240
Impairment of asset charges recorded			5,675		117
Number of properties classified as held for sale		8			1	4	7	10		4
Number of buildings classified as held for sale		11			5	7
Property held for sale (in square feet)					323,541	831,499
Number of properties impaired					4
Real estate properties, held for sale							12,924	27,888
Number of properties sold									1		1	1	1	3	3	2														36				70	1	177	2
Number of buildings sold											1	1	1
Sale price of property sold and agreed to be sold											675	6,000	5,000			4,500	2,400	2,550												2,400				2,850	2,850	5,900	5,900
Gain on the sale of property	1,141	2,552	1,141								0	0	0			2,396	156
Premium on Assumed Debt																			1,013												1,013
Intangible lease assets recorded																			249,904								245,511				4,393
Intangible lease liabilities recorded																			118,495								118,485				10
Property plant and equipment recorded																									$ 55,784	$ 970,783		$ 52,643	$ 944,362			$ 3,141	$ 26,421