Transactions with Controlled Companies - First Tower Finance Company LLC (Details) - USD ($) $ in Thousands	12 Months Ended
Jun. 30, 2025	Jun. 30, 2024	Jun. 30, 2023
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income	$ 671,109	$ 770,312	$ 760,785
Structuring Fee	12,348	27,666	18,131
Total Other Income	28,949	79,397	83,023
Interest Receivable	$ 25,144	$ 26,936
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	$ 17,501	$ 0	0
Interest Income Capitalized as PIK	10,115	29,385	40,688
Repayment of Loan Receivable	437	319	987
Interest Receivable	189	2,461
Other Receivables	96	1
Reportable Legal Entities \| Subsidiaries \| First Tower Finance Company LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income	65,954	62,675	63,364
Structuring Fee	421	0	0
Total Other Income	421	0	0
Reportable Legal Entities \| Subsidiaries \| First Tower Finance Company LLC \| Prospect Administration
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Managerial Assistance	$ 2,400	$ 2,400	$ 2,400
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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