Represents the number of trustees in equity compensation plan.

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Temporary Equity, Redemption Percentage

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Aggregate dividends paid during the period for each share of common stock outstanding.

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Aggregate dividends declared during the period for each share of common stock outstanding.

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Amount of paid and unpaid common stock dividends declared with the form of settlement in cash.

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The per share amount of a dividend declared, but not paid, as of the financial reporting date.

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Carrying value as of the balance sheet date of dividends declared but unpaid on equity securities issued by the entity and outstanding.

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The redemption (or callable) amount of currently redeemable preferred stock. Includes amounts representing dividends not currently declared or paid but which will be payable under the redemption features or for which ultimate payment is solely within the control of the issuer.

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The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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The weighted average fair value at grant date for nonvested equity-based awards issued during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan).

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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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No definition available.

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For net-share settlement of share-based awards when the employer settles employees' income tax withholding obligations, this element represents the number of shares the employees use to repay the employer.

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No definition available.

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Amount to be paid per share that is classified as temporary equity by entity upon redemption. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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The number of securities classified as temporary equity that have been issued and are held by the entity's shareholders. Securities outstanding equals securities issued minus securities held in treasury. Temporary equity is a security with redemption features that are outside the control of the issuer, is not classified as an asset or liability in conformity with GAAP, and is not mandatorily redeemable. Includes any type of security that is redeemable at a fixed or determinable price or on a fixed or determinable date or dates, is redeemable at the option of the holder, or has conditions for redemption which are not solely within the control of the issuer. If convertible, the issuer does not control the actions or events necessary to issue the maximum number of shares that could be required to be delivered under the conversion option if the holder exercises the option to convert the stock to another class of equity. If the security is a warrant or a rights issue, the warrant or rights issue is considered to be temporary equity if the issuer cannot demonstrate that it would be able to deliver upon the exercise of the option by the holder in all cases. Includes stock with put option held by ESOP and stock redeemable by holder only in the event of a change in control of the issuer.

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Total cost of shares repurchased divided by the total number of shares repurchased.

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Shareholders' Equity - Additional Information (Details) $ / shares in Units, $ in Thousands										1 Months Ended		9 Months Ended
	Oct. 18, 2018 USD ($) $ / shares	Sep. 24, 2018 $ / shares shares	Sep. 13, 2018 $ / shares shares	Aug. 20, 2018 USD ($) $ / shares	May 24, 2018 trustee $ / shares shares	May 21, 2018 USD ($) $ / shares	Apr. 03, 2018 $ / shares shares	Feb. 26, 2018 USD ($) $ / shares	Jan. 01, 2018 $ / shares shares	Sep. 30, 2018 shares	Sep. 30, 2017 shares	Sep. 30, 2018	May 01, 2018 USD ($) $ / shares shares
Share Awards
Cash distribution to common shareholders (in dollars per share)								$ 0.43
Distribution paid to common shareholders \| $				$ 42,641		$ 42,634		$ 42,632
Distribution payable to common shareholders (in dollars per share)						$ 0.43
Dividends declared (in dollars per share)				$ 0.43
Subsequent Event
Share Awards
Dividends declared (in dollars per share)	$ 0.43
Dividends declared \| $	$ 42,658
Officers and Other Employees
Share Awards
Shares paid for tax withholding (in shares) \| shares										18,875	13,636
Former Employee of RMR LLC
Share Awards
Shares paid for tax withholding (in shares) \| shares									617
Stock repurchased (in dollars per share)									$ 18.54
Trustees
Share Awards
Number of trustees \| trustee					1
Shares paid for tax withholding (in shares) \| shares					450
Stock repurchased (in dollars per share)					$ 14.10
Officers and Other Employees
Share Awards
Shares paid for tax withholding (in shares) \| shares		18,875
Stock repurchased (in dollars per share)		$ 11.35
Share Award Plan \| Common shares \| Trustees
Share Awards
Shares granted (in shares) \| shares					3,000		3,000
Shares granted (in dollars per share)					$ 14.10		$ 13.59
Number of trustees \| trustee					6
Share Award Plan \| Common shares \| Officers and Other Employees
Share Awards
Shares granted (in shares) \| shares			58,700
Shares granted (in dollars per share)			$ 16.95
Series A Cumulative Preferred Units
Share Awards
Temporary equity (in shares) \| shares													1,813,504
Redemption percentage												5.50%
Redemption price (in dollars per share)													$ 11.15
Redemption amount \| $													$ 20,310