Related Person Transactions - Amount Due from Related Parties (Details) - USD ($) $ in Thousands	Dec. 31, 2022	Sep. 30, 2022
Related Party Transaction [Line Items]
Accounts receivable	$ 25,948	$ 21,084
Reimbursable costs	112,330	102,294
Total	138,278	123,378
Perpetual Capital
Related Party Transaction [Line Items]
Accounts receivable	21,318	19,299
Reimbursable costs	101,546	94,554
Total	122,864	113,853
Managed Equity REITs
Related Party Transaction [Line Items]
Accounts receivable	19,302	17,295
Reimbursable costs	84,851	81,165
Total	104,153	98,460
DHC
Related Party Transaction [Line Items]
Accounts receivable	4,917	8,098
Reimbursable costs	12,896	14,148
Total	17,813	22,246
ILPT
Related Party Transaction [Line Items]
Accounts receivable	3,498	3,235
Reimbursable costs	9,066	13,717
Total	12,564	16,952
OPI
Related Party Transaction [Line Items]
Accounts receivable	6,544	335
Reimbursable costs	53,206	47,943
Total	59,750	48,278
SVC
Related Party Transaction [Line Items]
Accounts receivable	4,343	5,627
Reimbursable costs	9,683	5,357
Total	14,026	10,984
SEVN
Related Party Transaction [Line Items]
Accounts receivable	1,844	1,768
Reimbursable costs	1,148	1,262
Total	2,992	3,030
ALR
Related Party Transaction [Line Items]
Accounts receivable	86	112
Reimbursable costs	526	492
Total	612	604
TA
Related Party Transaction [Line Items]
Accounts receivable	86	124
Reimbursable costs	15,021	11,635
Total	15,107	11,759
Private Capital
Related Party Transaction [Line Items]
Accounts receivable	4,630	1,785
Reimbursable costs	10,784	7,740
Total	15,414	9,525
Sonesta
Related Party Transaction [Line Items]
Accounts receivable	702	127
Reimbursable costs	234	290
Total	936	417
Other private entities
Related Party Transaction [Line Items]
Accounts receivable	3,928	1,658
Reimbursable costs	10,550	7,450
Total	$ 14,478	$ 9,108