Condensed Consolidated Statements of Comprehensive Income (Parenthetical) - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Statement of Comprehensive Income [Abstract]
Unrealized gain on derivatives, tax	$ 251	$ 0	$ 251	$ 0
Less: unrealized gain on derivatives attributable to noncontrolling interest, tax	(117)	0	(117)	0
Other comprehensive income attributable to The RMR Group Inc., tax	$ 134	$ 0	$ 134	$ 0

Amount, after reclassification, of tax expense (benefit) for gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 220
-SubTopic 10
-Name Accounting Standards Codification
-Section 45
-Paragraph 12
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147482790/220-10-45-12

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Amount, after reclassification, of tax expense (benefit) for gain (loss) from derivative instrument designated and qualifying as cash flow hedge included in assessment of hedge effectiveness, attributable to noncontrolling interest.

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Amount of tax expense (benefit) allocated to other comprehensive income (loss) attributable to parent entity.

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-Topic 810
-SubTopic 10
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