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

No definition available.

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

- Definition

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

+ References

No definition available.

+ Details

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

- Definition

Represents the percentage of common stock held in the investee.

+ References

No definition available.

+ Details

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

- 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 under purchase agreements, which are referred by the entity as leased properties.

+ References

No definition available.

+ Details

Name:	snh_NumberOfPropertiesAcquiredLeasedProperties
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 serving as collateral for debt as of the balance sheet date.

+ References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- 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 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

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

- 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 Statement of Financial Accounting Standard (FAS)

-Number 13

-Paragraph 19

-Subparagraph b

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: 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=6453417&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

- Details

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

Related Person Transactions (Details 2) (USD $) In Thousands, unless otherwise specified	1 Months Ended	2 Months Ended				12 Months Ended			1 Months Ended			12 Months Ended	1 Months Ended						12 Months Ended	1 Months Ended	12 Months Ended				3 Months Ended	1 Months Ended	2 Months Ended	3 Months Ended	1 Months Ended			12 Months Ended	1 Months Ended
	Nov. 30, 2009 Property	Jun. 30, 2011 Property	Dec. 31, 2011 state	Dec. 31, 2011 TRS	May 31, 2011 TRS	Dec. 31, 2011 Five Star Property	Dec. 31, 2010 Five Star	Dec. 31, 2009 Five Star	Feb. 29, 2012 Five Star Senior living communities Property unit	Dec. 31, 2011 Five Star Senior living communities Property unit	Dec. 31, 2011 Five Star Rehabilitation hospitals Property	Dec. 31, 2011 Acquisition Senior living communities Property	May 31, 2011 Acquisition Senior living communities Illinois Property unit	Aug. 31, 2011 Acquisition Senior living communities Five States, Southeast Property	Jul. 31, 2011 Acquisition Senior living communities Five States, Southeast Property	Jun. 30, 2011 Acquisition Senior living communities Five States, Southeast Property	Dec. 31, 2011 Acquisition Senior living communities Six states Property	Dec. 31, 2011 Acquisition Senior living communities Six states TRS Property	Dec. 31, 2011 Acquisition Five Star Senior living communities Five States, Southeast Property	May 31, 2011 Acquisition Five Star Five Star Lease No. 1 Senior living communities Illinois	Dec. 31, 2011 Sale	Dec. 31, 2011 Sale Skilled nursing facilities Property	Dec. 31, 2010 Sale Skilled nursing facilities Property	Dec. 31, 2011 Sale Assisted living community Property	Jun. 30, 2011 Sale Assisted living community Pennsylvania Property	May 31, 2011 Sale Five Star	Jun. 30, 2011 Sale Five Star	Feb. 29, 2012 Agreement to acquire	Mar. 31, 2011 Agreement to acquire Senior living communities Five States, Southeast Property state	Jul. 31, 2011 Agreement to acquire Senior living communities Six states Property state unit	May 31, 2011 Agreement to acquire Five Star Senior living communities Five States, Southeast Property	Dec. 31, 2011 Agreement to acquire Five Star Senior living communities Five States, Southeast Property	May 31, 2011 Agreement to acquire Five Star Senior living communities Five States, Southeast TRS Property	Jan. 31, 2011 Agreement to acquire Five Star Assisted living community Pennsylvania Property unit	Nov. 30, 2010 Agreement to sell Senior living communities Georgia unit	Nov. 30, 2010 Agreement to sell Skilled nursing facilities Georgia Property	Aug. 31, 2011 Agreement to sell Five Star Assisted living community Pennsylvania Property unit
Related person transactions
Number of real estate properties leased										188	2
Minimum annual rent payable to entity						$ 195,228														$ 608
Total rent recognized						195,400	189,682	178,909
Number of properties mortgaged						28
Real estate improvements purchased						33,269	31,894
Increase or decrease in annual lease rent payable						2,665	2,555												6,923							(72)	(1,792)
Number of properties sold or agreed to be sold	1	2																				4	4	1	1									1		3	1
Number of properties acquired or agreed to be acquired									1	1		28	1	1	3	14	8		18										20	9
Number of units									92	57			73																	2,226				70	329		103
Aggregate sale price																					39,460		1,450											800	18,000
Number of states in which properties are located			38																										5	6
Aggregate purchase price of properties acquired, excluding closing costs									$ 11,300	$ 11,300			$ 7,500	$ 17,158	$ 44,671	$ 196,594	$ 379,000											$ 144,750	$ 304,000	$ 478,000
Number of properties acquired, or agreed to be acquired, referred to as managed properties																			13														15
Investment ownership (as a percent)				100.00%	100.00%
Number of properties agreed to be acquired, or agreed to be acquired, referred as leased properties																		7	5												5	2
Increase or decrease in annual lease rent payable (as a percent)																																					9.00%