Net Income Attributable to RMR Inc. (Details) - USD ($) $ in Thousands	12 Months Ended
	Sep. 30, 2025	Sep. 30, 2024	Sep. 30, 2023
Net Income Attributable to RMR Inc.
Income before income tax expense	$ 46,350	$ 64,448	$ 149,539
RMR Inc. franchise tax expense and interest income	(583)	(885)	(755)
Net income before noncontrolling interest	45,767	63,563	148,784
Net income attributable to noncontrolling interest in The RMR Group LLC	(21,910)	(30,039)	(70,624)
Net loss attributable to other noncontrolling interests	827	40	0
Net income attributable to RMR Inc. before income tax expense	24,684	33,564	78,160
Income tax expense attributable to RMR Inc.	(7,671)	(11,319)	(21,768)
RMR Inc. franchise tax expense and interest income	583	885	755
Net income attributable to The RMR Group Inc.	$ 17,596	$ 23,130	$ 57,147