Number of shares delivered of equity interests owned of a related party to acquire an entity.

No definition available.

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- Definition

Aggregate dividends received during the period for each share of common stock held.

+ References

No definition available.

+ Details

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of direct and indirect economic interest held in RMR LLC.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of economic interest held in RMR Inc.

+ References

No definition available.

+ Details

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Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

The ratio upon conversion of RMR Inc. class B-1 common stock into RMR Inc. class A common stock.

+ References

No definition available.

+ Details

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Data Type:	xbrli:pureItemType
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Period Type:	duration

- Definition

The ratio upon conversion of RMR LLC class A membership units owned by RMR Trust into RMR Inc. class A common stock.

+ References

No definition available.

+ Details

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Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the number of the company's common shares under a lock up and registration rights agreement that are not authorized to be transfered for a specified period of time.

+ References

No definition available.

+ Details

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the period over which the company's common shares remain under a lock up and registration rights agreement and not authorized to be transfered.

+ References

No definition available.

+ Details

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Namespace Prefix:	snh_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of non cash loss, which represents difference between our carrying value and the fair value of the RMR Inc. shares on the distribution date.

+ References

No definition available.

+ Details

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

- Definition

Represents the number of votes per equity interest.

+ References

No definition available.

+ Details

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

- Definition

Represents the cash purchase price paid to acquire common shares of beneficial interest of related party pursuant to the stock purchase agreement.

+ References

No definition available.

+ Details

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

- Definition

Number of shares distributed to the shareholders.

+ References

No definition available.

+ Details

Name:	snh_SharesDistributedToStockholders
Namespace Prefix:	snh_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the percentage of voting power controlled by a given entity with outstanding capital stock in RMR Inc.

+ References

No definition available.

+ Details

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

- Definition

Number of shares of equity interests issued or issuable to acquire entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 805
-SubTopic 30
-Section 50
-Paragraph 1
-Subparagraph (b)(4)
-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e6927-128479

+ Details

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Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

- 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

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

- Definition

Dividends received on equity and other investments during the current period.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 25
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=56944662&loc=d3e3536-108585

+ Details

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

- 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

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

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Name:	dei_LegalEntityAxis=snh_GovernmentPropertiesIncomeTrustMember
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Data Type:	na
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Related Person Transactions - Up-C Transaction (Details) $ in Thousands				3 Months Ended	12 Months Ended
	Dec. 15, 2015 USD ($) shares	Dec. 14, 2015 shares	Jun. 05, 2015 USD ($) Vote shares	Dec. 31, 2015 USD ($) shares	Dec. 31, 2015 USD ($) shares
Related person transactions
Loss on distribution to common shareholders of The RMR Group Inc. common stock \| $					$ (38,437)
RMR LLC
Related person transactions
Shares issued in connection with acquisition					81,557
Up C Transaction \| RMR Inc
Related person transactions
Direct and indirect economic interest in RMR LLC (as a percent)			51.60%
Voting power of outstanding capital stock of RMR Inc. (as a percent)			91.40%
Up C Transaction \| Managing Trustees Barry And Adam Portnoy \| RMR Inc
Related person transactions
Number of shares under lock up and registration agreement					2,345,000
Period over which shares remain under lock up and registration agreement					10 years
RMR Inc \| Up C Transaction
Related person transactions
Cash purchase price \| $			$ 13,967
Equity conversion ratio of RMR Inc class B-1 common stock			1
Equity conversion ratio of RMR LLC class A membership units			1
RMR Inc \| Up C Transaction \| ABP Trust formerly known as RMR Trust
Related person transactions
Cash purchase price \| $			$ 11,520
RMR Inc \| Up C Transaction \| GOV
Related person transactions
Cash purchase price \| $			3,917
RMR Inc \| Up C Transaction \| HPT
Related person transactions
Cash purchase price \| $			12,622
RMR Inc \| Up C Transaction \| SIR
Related person transactions
Cash purchase price \| $			$ 15,880
Common Shares \| RMR Inc \| Up C Transaction
Related person transactions
Shares issued in connection with acquisition			2,345,000
Common Shares \| RMR Inc \| Up C Transaction \| GOV
Related person transactions
Shares issued in connection with acquisition			700,000
Common Shares \| RMR Inc \| Up C Transaction \| HPT
Related person transactions
Shares issued in connection with acquisition			1,490,000
Common Shares \| RMR Inc \| Up C Transaction \| SIR
Related person transactions
Shares issued in connection with acquisition			880,000
Class A common shares \| RMR Inc
Related person transactions
Share distributed to the shareholders		2,635,379
Class A common shares \| RMR Inc
Related person transactions
Loss on distribution to common shareholders of The RMR Group Inc. common stock \| $				$ 38,437
Cash dividend received (per share)	0.5260
Proceeds from dividends received \| $	$ 2,773
Class A common shares \| RMR Inc \| Up C Transaction
Related person transactions
Number of votes per equity interest \| Vote			1
Class A common shares \| RMR Inc \| Up C Transaction \| GOV
Related person transactions
Investment in common shares			1,214,225
Class A common shares \| RMR Inc \| Up C Transaction \| HPT
Related person transactions
Investment in common shares			2,503,777
Class A common shares \| RMR Inc \| Up C Transaction \| SIR
Related person transactions
Shares issued in connection with acquisition			3,166,891
Investment in common shares			1,586,836
Class B1 common shares \| RMR Inc
Related person transactions
Cash dividend received (per share)	0.5260
Class B1 common shares \| RMR Inc \| Up C Transaction
Related person transactions
Number of votes per equity interest \| Vote			10
Class B1 common shares \| RMR Inc \| Up C Transaction \| SIR
Related person transactions
Shares issued in connection with acquisition			1,000,000
Class B2 common shares \| RMR Inc \| Up C Transaction
Related person transactions
Number of votes per equity interest \| Vote			10
Economic interest in RMR Inc (as a percent)			0.00%
Class B2 common shares \| RMR Inc \| Up C Transaction \| RMR Inc
Related person transactions
Shares issued in connection with acquisition			5,272,787
Class B2 common shares \| RMR Inc \| Up C Transaction \| ABP Trust formerly known as RMR Trust
Related person transactions
Shares issued in connection with acquisition			15,000,000
Class B2 common shares \| RMR Inc \| Up C Transaction \| GOV
Related person transactions
Shares issued in connection with acquisition			1,541,201
Class B2 common shares \| RMR Inc \| Up C Transaction \| HPT
Related person transactions
Shares issued in connection with acquisition			5,019,121
Class A member units \| Up C Transaction \| RMR LLC \| ABP Trust formerly known as RMR Trust
Related person transactions
Investment in common shares			30,000,000
Class A member units \| RMR Inc \| Up C Transaction \| RMR LLC \| ABP Trust formerly known as RMR Trust
Related person transactions
Business acquisition related party equity interests delivered			15,000,000
Class B member units \| RMR Inc \| Up C Transaction \| RMR LLC
Related person transactions
Shares issued in connection with acquisition			1,000,000
Class A common shares \| The RMR Group Inc
Related person transactions
Investment in common shares				2,637,408	2,637,408