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Goodwill - Schedule of Goodwill Reconciliation (Details) $ in Millions	12 Months Ended
	Sep. 30, 2025 USD ($)
Business Combination [Line Items]
Additional goodwill	$ 238.0
JBR | Commercial
Business Combination [Line Items]
Additional goodwill	4.8
Octo | Institutional
Business Combination [Line Items]
Additional goodwill	2.1
RJO | Commercial
Business Combination [Line Items]
Additional goodwill	75.0
RJO | Institutional
Business Combination [Line Items]
Additional goodwill	99.4
Benchmark | Institutional
Business Combination [Line Items]
Additional goodwill	55.7
Right | Commercial
Business Combination [Line Items]
Additional goodwill	$ 1.0

X

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Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

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