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Transactions with Controlled Companies - R-V Industries, Inc. (Details) - USD ($) $ in Thousands	3 Months Ended		12 Months Ended
	Sep. 30, 2026	Sep. 30, 2025	Jun. 30, 2026	Dec. 15, 2020
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income	$ 132,608	$ 152,394
Dividend Income	5,475	3,573
Interest Receivable	$ 23,039		$ 17,350
Senior Subordinated Notes
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Restructured debt				$ 28,622
First Lien Note
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Principal amount				$ 28,622
R-V Industries, Inc. \| R-V Holdings of Delaware, LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	90.01%		90.28%
R-V Industries, Inc. \| Members of R-V Industries Management
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	9.99%
Reportable Legal Entities \| Subsidiaries \| R-V Industries, Inc.
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income	$ 1,828	1,456
Dividend Income	0	877
Interest Receivable	0		$ 0
Other Receivables	10		$ 10
Reportable Legal Entities \| Subsidiaries \| R-V Industries, Inc. \| Prospect Administration
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Managerial Assistance	$ 45	$ 45
Reportable Legal Entities \| Subsidiaries \| R-V Holdings of Delaware, LLC
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	100.00%		100.00%