Transactions with Controlled Companies - NMMB, Inc. (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
Dividend Income	5,475	3,573
Realized (Loss) Gain	(71,607)	(1,891)
Interest Receivable	$ 23,039		$ 17,350
NMMB, Inc. \| NMMB Holdings, Inc.
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	92.77%		92.77%
NMMB, Inc. \| Refuel Agency, Inc.
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	100.00%		100.00%
Armed Forces Communications, Inc. \| NMMB, Inc.
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	100.00%		100.00%
Reportable Legal Entities \| Subsidiaries \| NMMB, Inc.
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income	$ 949	991
Dividend Income	1,351	0
Realized (Loss) Gain	(1,351)	842
Interest Receivable	11		$ 10
Other Receivables	1		$ 1
Reportable Legal Entities \| Subsidiaries \| NMMB, Inc. \| Prospect Administration
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Managerial Assistance	$ 100	$ 100
Reportable Legal Entities \| Subsidiaries \| NMMB Holdings, Inc.
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	100.00%		100.00%

Amount of realized gain (loss) on investment in debt and equity securities.

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