Fair Value of Assets and Liabilities (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2014 building property item	Dec. 31, 2013
Assets and liabilities measured at fair value
Investments in available for sale securities	$ 23,993us-gaap_AvailableForSaleSecurities	$ 29,078us-gaap_AvailableForSaleSecurities
Number of properties classified as held for sale	5
Number of Buildings Held For Sale	8snh_NumberOfBuildingsHeldForSale
Cumulative impairments of properties held for sale	17,753
Number of public issues of unsecured senior notes	6
Senior notes	1,743,628us-gaap_SeniorNotes	1,093,337us-gaap_SeniorNotes
Excess of fair value over aggregate book value	97,332
Secured Debt	611,369us-gaap_SecuredDebt
Excess of fair value over aggregate book value	67,138
CommonWealth REIT (EQC)
Assets and liabilities measured at fair value
Investments in available for sale securities	6,418	5,828
Investment in common shares	250,000
Five Star
Assets and liabilities measured at fair value
Investments in available for sale securities	17,575	23,250
Investment in common shares	4,235,000
Recurring and Nonrecurring \| Total
Assets and liabilities measured at fair value
Assets held for sale	3,395
Investments in available for sale securities	23,993
Recurring and Nonrecurring \| Quoted Prices in Active Markets for Identical Assets (Level 1)
Assets and liabilities measured at fair value
Investments in available for sale securities	23,993
Recurring and Nonrecurring \| Significant Other Observable Inputs (Level 2)
Assets and liabilities measured at fair value
Assets held for sale	$ 3,395

The cumulative amount of write-downs for impairments recognized during the period for long-lived assets held for sale.

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- 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.

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- Definition

Represents the number of public issues of unsecured senior notes.

+ References

No definition available.

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- 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.

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- Definition

The amount by which the fair value of secured debt exceeds the book value.

+ References

No definition available.

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The amount by which the fair value of senior notes exceeds the book value.

+ References

No definition available.

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

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- Definition

Balance held at close of period in number of shares.

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- 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.

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- Definition

Carrying value as of the balance sheet date, including the current and noncurrent portions, of collateralized debt obligations (with maturities initially due after one year or beyond the operating cycle, if longer). Such obligations include mortgage loans, chattel loans, and any other borrowings secured by assets of the borrower.

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Including the current and noncurrent portions, carrying value as of the balance sheet date of Notes with the highest claim on the assets of the issuer in case of bankruptcy or liquidation (with maturities initially due after one year or beyond the operating cycle if longer). Senior note holders are paid off in full before any payments are made to junior note holders.

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