Physical Commodities Inventory - Physical Commodities Inventory (Details) - USD ($) $ in Millions	Dec. 31, 2022	Sep. 30, 2022
Inventory [Line Items]
Physical Ag & Energy	$ 274.8	$ 223.6
Precious metals - held by broker-dealer subsidiary	360.3	359.8
Physical commodities inventory, net	612.7	513.5
Physical Commodities Inventory - Precious Metals
Inventory [Line Items]
Precious metals - held by broker-dealer subsidiary	85.5	136.3
Precious metals - held by non-broker-dealer subsidiaries	$ 252.4	$ 153.6

Physical commodities inventory at fair value - precious metals

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Carrying amount, net of valuation reserves and adjustments, as of the balance sheet date of merchandise or goods held by the company that are readily available for sale.

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