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Unrealized Gain / Loss on Investments (Details) (USD $) | 3 Months Ended
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Mar. 31, 2015
CommonWealth REIT (EQC) |
Unrealized gain on investments |
Investment in common shares | 250,000 us-gaap_InvestmentOwnedBalanceShares / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = snh_CommonWealthREITMember
Quoted market prices (in dollars per share) | $ 26.55 snh_InvestmentQuotedMarketPricePerShare / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = snh_CommonWealthREITMember
Weighted average costs (in dollars per share) | $ 26.00 snh_InvestmentWeightedAverageCostPerShare / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = snh_CommonWealthREITMember
Five Star |
Unrealized gain on investments |
Investment in common shares | 4,235,000 us-gaap_InvestmentOwnedBalanceShares / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = snh_FiveStarQualityCareIncMember
Quoted market prices (in dollars per share) | $ 4.44 snh_InvestmentQuotedMarketPricePerShare / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = snh_FiveStarQualityCareIncMember
Weighted average costs (in dollars per share) | $ 3.36 snh_InvestmentWeightedAverageCostPerShare / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = snh_FiveStarQualityCareIncMember

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- 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=34726532&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=34726532&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=34726532&loc=d3e611133-123010 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12C -Paragraph Column B -Article 12 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12 -Paragraph Column B -Article 12 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 14 -Paragraph Column B -Article 12 + Details
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