Organization (Details)	9 Months Ended
Jun. 30, 2026 real_estate_investment_trust shares
Related Party Transaction [Line Items]
Number of managed trusts \| real_estate_investment_trust	4
RMR LLC
Related Party Transaction [Line Items]
Ownership percentage	53.30%
Capital Unit Redeemable Class A Units \| Abp Trust
Related Party Transaction [Line Items]
Membership units (in shares)	15,000,000
Capital Unit Redeemable Class A Units \| RMR LLC \| Abp Trust
Related Party Transaction [Line Items]
Ownership percentage	46.70%
Class A Membership Units \| Class A Common Stock
Related Party Transaction [Line Items]
Membership units (in shares)	16,092,402
Class B Membership Units
Related Party Transaction [Line Items]
Membership units (in shares)	1,000,000

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