Transactions with Controlled Companies - First Tower Finance Company LLC (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Sep. 30, 2026	Sep. 30, 2025	Jun. 30, 2026
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income	$ 132,608	$ 152,394
Structuring Fee	10,605	1,299
Total Other Income	13,658	1,657
Interest Receivable	$ 23,039		$ 17,350
First Tower Finance Company LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	78.06%
First Tower Finance Company LLC \| First Tower Holdings of Delaware LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	80.10%		80.10%
First Tower, LLC \| First Tower Finance Company LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	100.00%		100.00%
Reportable Legal Entities \| Subsidiaries \| First Tower Holdings of Delaware LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Additions	$ 9,366	0
Interest Income Capitalized as PIK	0	31
Interest Receivable	209		$ 205
Other Receivables	4		$ 4
Reportable Legal Entities \| Subsidiaries \| First Tower Finance Company LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income	18,824	17,333
Structuring Fee	281	0
Royalty/Net Interest	2,798
Total Other Income	3,079	0
Reportable Legal Entities \| Subsidiaries \| First Tower Finance Company LLC \| Prospect Administration
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Managerial Assistance	1,000	600
Reimbursement of Legal, Tax, etc	$ 0	$ 6
Reportable Legal Entities \| First Tower Holdings of Delaware LLC \| Subsidiaries
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	100.00%		100.00%

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