Transactions with Controlled Companies - First Tower Finance Company LLC (Details) - USD ($) $ in Thousands	12 Months Ended
Jun. 30, 2024	Jun. 30, 2023	Jun. 30, 2022
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income	$ 770,312	$ 760,785	$ 584,685
Structuring Fee	27,666	18,131	43,683
Other Income	79,397	83,023	111,194
Interest Receivable	$ 26,936	22,701
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%
First Tower, LLC \| First Tower Finance Company LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	100.00%
Reportable Legal Entities \| Subsidiaries \| First Tower Holdings of Delaware LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Additions	$ 0	0	22,123
Interest Income Capitalized as PIK	29,385	40,688	20,546
Repayment of Loan Receivable	319	987	11,153
Interest Receivable	2,461	165
Other Receivables	1	1
Reportable Legal Entities \| Subsidiaries \| First Tower Finance Company LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income	62,675	63,364	74,501
Structuring Fee	0	0	7,898
Other Income	0	0	7,898
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	1,800
Reimbursement of Legal, Tax, etc.	$ 0	$ 0	$ 45
Reportable Legal Entities \| Subsidiaries \| First Tower Holdings of Delaware LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	100.00%

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