Common shares owned accounted for as available for sale securities.

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

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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.

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No definition available.

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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.

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Represents the non-cash gain or loss recognized in connection with the distribution

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Represents the number of agreements with RMR LLC to provide management services to the company.

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Represents the number of other companies to whom management services will be provided by related party.

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Represents the aggregate market value at grant date for nonvested equity-based awards during the period on other than stock (or unit) options plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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No definition available.

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

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No definition available.

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

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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The cash outflow associated with the acquisition of business during the period. The cash portion only of the acquisition price.

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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.

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Amount of revenue, fees and commissions earned from transactions between (a) a parent company and its subsidiaries; (b) subsidiaries of a common parent; (c) an entity and trusts for the benefit of employees, for example, but not limited to, pension and profit-sharing trusts that are managed by or under the trusteeship of the entity's management; (d) an entity and its principal, owners, management, or members of their immediate families; and (e) affiliates.

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Percentage of vesting of share-based compensation awards.

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Number of new stock issued during the period.

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Related Party Transactions - Up-C Transaction (Details) $ in Thousands			3 Months Ended	12 Months Ended
	Dec. 14, 2015 shares	Jun. 05, 2015 USD ($) company shares	Dec. 31, 2015 USD ($)	Dec. 31, 2017 USD ($) agreement shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) shares
Related Party Transaction [Line Items]
Common shares held				99,145,921	71,177,906
Common shares owned in RMR Inc.				1,214,225
Up C Transaction \| Class A common shares
Related Party Transaction [Line Items]
Common shares owned in RMR Inc.				1,214,225
Up C Transaction \| RMR Inc \| Class A member units
Related Party Transaction [Line Items]
Shares issued in connection with acquisition	768,032
Up C Transaction \| RMR Inc \| Class A common shares
Related Party Transaction [Line Items]
Non-cash loss related to distribution of shares \| $			$ 12,368
Up C Transaction \| SIR \| Class A common shares
Related Party Transaction [Line Items]
Common shares held	441,056			441,056
RMR LLC
Related Party Transaction [Line Items]
Number of agreements with RMR LLC to provide management services \| agreement				2
Rental income earned \| $				$ 303	$ 366	$ 341
RMR Inc \| Up C Transaction
Related Party Transaction [Line Items]
Number of other companies to whom management services were provided by related party \| company		3
Shares issued in connection with acquisition		700,000
Cash consideration \| $		$ 3,917
RMR Inc \| Up C Transaction \| RMR Inc
Related Party Transaction [Line Items]
Shares issued in connection with acquisition		1,541,201
Managing Trustees Barry And Adam Portnoy Member \| Up C Transaction \| RMR Inc
Related Party Transaction [Line Items]
Number of shares under lock up and registration agreement		700,000
Period over which shares remain under lock up and registration agreement		10 years
Direct and indirect economic interest in RMR LLC as a percent				51.90%
Voting power of outstanding capital stock of RMR Inc				91.40%
Common Shares
Related Party Transaction [Line Items]
Number of shares granted to each trustee under the award plan				27,907,029		723,222
Common Shares \| Officers and Other Employees
Related Party Transaction [Line Items]
Number of shares granted to each trustee under the award plan				57,350	53,400	53,100
Aggregate market value of shares awarded \| $				$ 1,067	$ 1,183	$ 841
2009 Award Plan \| Common Shares \| Tranche One \| Officers and Other Employees
Related Party Transaction [Line Items]
Vesting percentage				20.00%
2009 Award Plan \| Common Shares \| Tranche Two \| Officers and Other Employees
Related Party Transaction [Line Items]
Vesting percentage				20.00%
2009 Award Plan \| Common Shares \| Tranche Three \| Officers and Other Employees
Related Party Transaction [Line Items]
Vesting percentage				20.00%
2009 Award Plan \| Common Shares \| Tranche Four \| Officers and Other Employees
Related Party Transaction [Line Items]
Vesting percentage				20.00%
2009 Award Plan \| Common Shares \| Tranche Five \| Officers and Other Employees
Related Party Transaction [Line Items]
Vesting percentage				20.00%