Transactions with Controlled Companies - NMMB, Inc. (Details) - USD ($) $ in Thousands	6 Months Ended	12 Months Ended
Dec. 31, 2025	Jun. 30, 2026	Jun. 30, 2025	Jun. 30, 2024
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Interest Income		$ 581,932	$ 671,109	$ 770,312
Dividend Income		46,967	19,378	11,953
Net realized gains (losses)		(223,719)	(518,682)	(417,443)
Interest Receivable		$ 17,350	$ 25,144
NMMB, Inc. \| NMMB Holdings, Inc.
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	92.77%	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%	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		$ 3,820	$ 4,039	4,255
Dividend Income		2,112	0	657
Net realized gains (losses)		2,108	6,366	1,040
Interest Receivable		10	11
Other Receivables		1	10
Reportable Legal Entities \| Subsidiaries \| NMMB, Inc. \| Prospect Administration
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Managerial Assistance		400	400	400
Reimbursement of Legal, Tax, etc		$ 17	$ 9	$ 1
Reportable Legal Entities \| Subsidiaries \| NMMB Holdings, Inc.
Subsidiary of Limited Liability Company or Limited Partnership [Line Items]
Ownership interest	100.00%	100.00%

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