Basis of Presentation (Details)	9 Months Ended
	Jun. 30, 2020 shares
RMR LLC
Related Party Transaction [Line Items]
Ownership percentage	52.10%
Class B membership units
Related Party Transaction [Line Items]
Membership units (in units)	1,000,000
Class A Common Stock | Class A membership units
Related Party Transaction [Line Items]
Membership units (in units)	15,315,445
Capital Unit Redeemable Class A Units | ABP Trust
Related Party Transaction [Line Items]
Membership units (in units)	15,000,000
Capital Unit Redeemable Class A Units | ABP Trust | RMR LLC
Related Party Transaction [Line Items]
Ownership percentage	47.90%