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Fair Value of Assets (Details) $ in Thousands	Sep. 30, 2017 USD ($) shares
RMR Inc | Class A common shares
Recurring Fair Value Measurements
Investment in common shares (in shares) | shares	2,637,408
Five Star
Recurring Fair Value Measurements
Investment in common shares (in shares) | shares	4,235,000
Five Star | Common Shares
Recurring Fair Value Measurements
Investment in common shares (in shares) | shares	4,235,000
Recurring
Recurring Fair Value Measurements
Investments in available for sale securities	$ 141,995
Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1)
Recurring Fair Value Measurements
Investments in available for sale securities	141,995
Recurring | Significant Other Observable Inputs (Level 2)
Recurring Fair Value Measurements
Investments in available for sale securities	0
Recurring | Significant Unobservable Inputs (Level 3)
Recurring Fair Value Measurements
Investments in available for sale securities	$ 0

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

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