Represents the number of entities to whom related party provides management services.

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- Definition

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

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Represents the number of common shares of beneficial interest of related party acquired pursuant to stock purchase agreement.

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No definition available.

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- Definition

This element represents the aggregate cost of investments accounted for under the equity method of accounting.

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- Definition

The percentage of ownership of common stock or equity participation in the investee accounted for under the equity method of accounting.

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This item represents the entity's proportionate share for the period of the net income (loss) of its investee (such as unconsolidated subsidiaries and joint ventures) to which the equity method of accounting is applied. This item includes income or expense related to stock-based compensation based on the investor's grant of stock to employees of an equity method investee.

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Amount of increase (decrease) in other comprehensive income, after tax, from changes classified as other.

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No definition available.

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- Definition

The percentage charged for managing real estate properties.

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No definition available.

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- Definition

Expenses recognized resulting from transactions (excluding transactions that are eliminated in consolidated or combined financial statements) with related party.

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- 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.

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No definition available.

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Related Party Transactions - REITs, for which RMR LLC provides Management Services (Details) $ in Thousands			12 Months Ended
	Mar. 05, 2015 shares	Mar. 04, 2015 USD ($) shares	Dec. 31, 2017 USD ($) company shares	Dec. 31, 2016 USD ($)	Dec. 31, 2015 USD ($)
Related Party Transaction [Line Items]
Recognized income (loss) related to investment			$ 21,571	$ 35,518	$ 18,640
Equity in unrealized gain (loss) of investees			$ 9,428	11,359	(5,513)
SIR
Related Party Transaction [Line Items]
Percentage of ownership interest			27.80%
Recognized income (loss) related to investment			$ 21,584	35,381	21,882
SIR
Related Party Transaction [Line Items]
Percentage of ownership interest			27.80%
SIR Common shares of beneficial interest acquired pursuant to stock purchase agreement \| shares			24,918,421
SIR \| Lakewood Capital Partners LP
Related Party Transaction [Line Items]
Percentage of ownership interest		3.90%
SIR Common shares of beneficial interest acquired pursuant to stock purchase agreement \| shares		3,418,421
Cash purchase price		$ 95,203
SIR \| Adam Portnoy \| Lakewood Capital Partners LP
Related Party Transaction [Line Items]
SIR Common shares of beneficial interest acquired pursuant to stock purchase agreement \| shares	2,429	87,606
SIR \| Barry Portnoy \| Lakewood Capital Partners LP
Related Party Transaction [Line Items]
SIR Common shares of beneficial interest acquired pursuant to stock purchase agreement \| shares		107,606
AIC
Related Party Transaction [Line Items]
Number of entities to whom RMR provides management services \| company			4
Amount invested in equity investee			$ 8,304	7,235	6,946
Recognized income (loss) related to investment			608	137	20
Equity in unrealized gain (loss) of investees			461	152	(20)
RMR LLC
Related Party Transaction [Line Items]
Related party transaction			$ 12,464	10,222	9,934
RMR LLC \| AIC
Related Party Transaction [Line Items]
Service fee percentage			3.00%
Property Insurance Premium Expense, June 2018 \| AIC
Related Party Transaction [Line Items]
Related party transaction			$ 757
Property Insurance Premium Expense, June 2017 \| AIC
Related Party Transaction [Line Items]
Related party transaction			1,032
Property Insurance Premium Expense, June 2016 \| AIC
Related Party Transaction [Line Items]
Related party transaction			1,277
Property Insurance Premium Expense
Related Party Transaction [Line Items]
Related party transaction			$ 91	$ 106	$ 316