Related Person Transactions - Schedule of Tax Distributions (Details) - RMR LLC - USD ($) $ in Thousands	3 Months Ended	9 Months Ended
Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2026	Jun. 30, 2025
Related Party Transaction [Line Items]
Distributions paid	$ 2,267	$ 3,273	$ 6,802	$ 10,014
Abp Trust
Related Party Transaction [Line Items]
Distributions paid	1,999	2,951	5,997	8,889
ABP Trust and Managed REIT
Related Party Transaction [Line Items]
Distributions paid	$ 4,266	$ 6,224	$ 12,799	$ 18,903

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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+ Details