Organization (Details)	12 Months Ended
Sep. 30, 2020 real_estate_investment_trust shares
Related Party Transaction [Line Items]
Number of managed trusts \| real_estate_investment_trust	4
Class A membership units
Related Party Transaction [Line Items]
Anti-dilutive securities (in shares)	15,000,000
Class A common shares \| Class A membership units
Related Party Transaction [Line Items]
Membership units (in units)	15,395,641
Class B-1 common shares
Related Party Transaction [Line Items]
Membership units (in units)	1,000,000
ABP Trust \| Class A membership units
Related Party Transaction [Line Items]
Membership units (in units)	15,000,000
RMR LLC
Related Party Transaction [Line Items]
Ownership percentage	52.20%
RMR LLC \| ABP Trust \| Redeemable Class A membership units
Related Party Transaction [Line Items]
Ownership percentage	47.80%

Number Of Managed Real Estate Investment Trusts

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- Definition

Securities (including those issuable pursuant to contingent stock agreements) that could potentially dilute basic earnings per share (EPS) or earnings per unit (EPU) in the future that were not included in the computation of diluted EPS or EPU because to do so would increase EPS or EPU amounts or decrease loss per share or unit amounts for the period presented.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 260
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257

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+ References

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+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 272
-SubTopic 10
-Section 50
-Paragraph 3
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=6373374&loc=d3e70478-108055

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+ References

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