Related Person Transactions - Schedule of Amount Due from Related Parties (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Sep. 30, 2025
Related Party Transaction [Line Items]
Accounts receivable	$ 29,495	$ 30,725
Reimbursable costs	61,755	59,352
Total	91,250	90,077
Perpetual Capital
Related Party Transaction [Line Items]
Accounts receivable	20,924	21,192
Reimbursable costs	49,844	51,736
Total	70,768	72,928
Total Managed Equity REITs
Related Party Transaction [Line Items]
Accounts receivable	19,493	19,679
Reimbursable costs	48,170	48,464
Total	67,663	68,143
DHC
Related Party Transaction [Line Items]
Accounts receivable	4,939	4,806
Reimbursable costs	12,493	13,780
Total	17,432	18,586
ILPT
Related Party Transaction [Line Items]
Accounts receivable	4,468	4,011
Reimbursable costs	11,448	8,922
Total	15,916	12,933
OPI
Related Party Transaction [Line Items]
Accounts receivable	4,784	4,031
Reimbursable costs	17,257	15,819
Total	22,041	19,850
SVC
Related Party Transaction [Line Items]
Accounts receivable	5,302	6,831
Reimbursable costs	6,972	9,943
Total	12,274	16,774
SEVN
Related Party Transaction [Line Items]
Accounts receivable	1,431	1,513
Reimbursable costs	1,674	3,272
Total	3,105	4,785
Private Capital
Related Party Transaction [Line Items]
Accounts receivable	8,571	9,533
Reimbursable costs	11,911	7,616
Total	20,482	17,149
Sonesta
Related Party Transaction [Line Items]
Accounts receivable	19	51
Reimbursable costs	0	0
Total	19	51
RMR Residential
Related Party Transaction [Line Items]
Accounts receivable	6,756	6,117
Reimbursable costs	0	0
Total	6,756	6,117
Other private entities
Related Party Transaction [Line Items]
Accounts receivable	1,796	3,365
Reimbursable costs	11,911	7,616
Total	$ 13,707	$ 10,981