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Shareholders' Equity - Compensation (Details) - $ / shares							1 Months Ended
	Oct. 02, 2018	Sep. 24, 2018	Sep. 13, 2018	May 22, 2018	Mar. 29, 2018	Jan. 01, 2018	Sep. 30, 2018	Sep. 30, 2017	Dec. 29, 2017
Employees Of RMR LLC
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, shares issued in period (in shares)			105,800				105,800	88,100
Shares purchased to satisfy tax withholding and payment obligations, price per share (in dollars per share)		$ 17.56	$ 19.11
Shares purchased to satisfy tax withholding and payment obligations (in shares)		18,121					18,121	16,654
Former Employees Of RMR LLC
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares purchased to satisfy tax withholding and payment obligations, price per share (in dollars per share)									$ 19.15
Shares purchased to satisfy tax withholding and payment obligations (in shares)						4,628
Trustees
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Share-based compensation, shares issued in period (in shares)				3,000	3,000
Share-based compensation, equity instruments other than options, nonvested closing price (in dollars per share)					$ 15.66
Shares purchased to satisfy tax withholding and payment obligations, price per share (in dollars per share)				$ 16.56
Subsequent Event | Employees Of RMR LLC
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Shares purchased to satisfy tax withholding and payment obligations, price per share (in dollars per share)	$ 17.05
Shares purchased to satisfy tax withholding and payment obligations (in shares)	250

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The weighted average of per share prices paid for shares purchased on the open market for issuance to employees under the plan.

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