Summary of Significant Accounting Policies - Revenue Recognition (Details) - USD ($) $ in Thousands		12 Months Ended
	May 15, 2023	Sep. 30, 2023	Sep. 30, 2022	Sep. 30, 2021
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		$ 962,316	$ 832,503	$ 607,238
Percent of gross collected rents		3.00%
Percent of construction supervision		5.00%
Property management fees revenue		$ 63,153	59,667	47,377
Property management fee		$ 18,443	16,743	8,476
Total Managed Equity REITs
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Percentage of historical cost of transferred real estate assets		0.50%
Percentage of average invested capital below threshold limit		0.70%
Threshold amount, maximum		$ 250,000
Percentage of average invested capital above threshold limit		0.50%
Threshold limit, minimum		$ 250,000
Percentage of average market capitalization below threshold limit		0.70%
Percentage of average market capitalization above threshold limit		0.50%
Aggregate annual base business management fees		$ 85,603	96,031	93,153
Incentive management fee percentage		12.00%
Aggregate incentive business management fees		$ 0	0	0
Revenues		$ 787,506	715,440	532,365
Managed Operating Companies
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Business management fee percent based on management agreements		0.60%
SEVN
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		$ 10,053	10,222	4,927
Managed Public Real Estate Capital
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Aggregate annual business management fees		36,815	39,653	30,105
Revenues		$ 856,249	743,648	557,191
Tremont Advisors
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Incentive fee percentage condition 1		20.00%
Incentive fee percentage condition 2		7.00%
Minimum | Tremont Advisors
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Advisory fee percentage based on aggregate principal amounts of loan originated		0.50%
Maximum | Tremont Advisors
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Advisory fee percentage based on aggregate principal amounts of loan originated		1.00%
Advisory services
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		$ 4,520	4,530	3,956
Advisory services | Tremont Advisors
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Business management fee percent based on management agreements		1.50%
Revenues		$ 4,520	4,530	3,956
Management services
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		185,702	195,450	171,102
Management services | Tremont Advisors
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		131	99	467
Termination and incentive business management fees
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues	$ 45,282
Termination and incentive business management fees | Tremont Advisors
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Revenues		$ 660	$ 0	$ 620