Related Person Transactions - Amount Due from Related Parties (Details) - USD ($) $ in Thousands	Sep. 30, 2025	Sep. 30, 2024
Related Party Transaction [Line Items]
Accounts Receivable	$ 30,725	$ 38,597
Reimbursable Costs	59,352	104,783
Total	90,077	143,380
Perpetual Capital:
Related Party Transaction [Line Items]
Accounts Receivable	21,192	24,449
Reimbursable Costs	51,736	50,650
Total	72,928	75,099
Total Managed Equity REITs
Related Party Transaction [Line Items]
Accounts Receivable	19,679	21,898
Reimbursable Costs	48,464	48,049
Total	68,143	69,947
DHC
Related Party Transaction [Line Items]
Accounts Receivable	4,806	6,307
Reimbursable Costs	13,780	11,358
Total	18,586	17,665
ILPT
Related Party Transaction [Line Items]
Accounts Receivable	4,011	4,244
Reimbursable Costs	8,922	7,968
Total	12,933	12,212
OPI
Related Party Transaction [Line Items]
Accounts Receivable	4,031	5,877
Reimbursable Costs	15,819	20,132
Total	19,850	26,009
SVC
Related Party Transaction [Line Items]
Accounts Receivable	6,831	5,470
Reimbursable Costs	9,943	8,591
Total	16,774	14,061
SEVN
Related Party Transaction [Line Items]
Accounts Receivable	1,513	2,551
Reimbursable Costs	3,272	2,601
Total	4,785	5,152
Private Capital:
Related Party Transaction [Line Items]
Accounts Receivable	9,533	14,148
Reimbursable Costs	7,616	54,133
Total	17,149	68,281
AlerisLife
Related Party Transaction [Line Items]
Accounts Receivable	529	570
Reimbursable Costs	0	0
Total	529	570
Sonesta
Related Party Transaction [Line Items]
Accounts Receivable	51	82
Reimbursable Costs	0	0
Total	51	82
RMR Residential
Related Party Transaction [Line Items]
Accounts Receivable	6,117	9,587
Reimbursable Costs	0	0
Total	6,117	9,587
Other private entities
Related Party Transaction [Line Items]
Accounts Receivable	2,836	3,909
Reimbursable Costs	7,616	54,133
Total	$ 10,452	$ 58,042