Basis of Presentation (Details)	6 Months Ended
	Mar. 31, 2022 company real_estate_investment_trust shares
Related Party Transaction [Line Items]
Number of managed trusts | real_estate_investment_trust	4
Number of real estate operating companies | company	3
RMR LLC
Related Party Transaction [Line Items]
Ownership percentage	52.40%
Class B membership units
Related Party Transaction [Line Items]
Membership units (in shares)	1,000,000
Class A Common Stock | Class A membership units
Related Party Transaction [Line Items]
Membership units (in shares)	15,501,536
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 | ABP Trust | RMR LLC
Related Party Transaction [Line Items]
Ownership percentage	47.60%