Condensed Consolidated Balance Sheets Parentheticals - USD ($) $ in Millions	Jun. 30, 2020	Sep. 30, 2019
Balance Sheet Parentheticals [Abstract]
Cash and Cash Equivalents, Fair Value Disclosure	$ 9.8	$ 306.0
Dep and rec -b/d - fair value	1,261.6	626.9
Physical commodities inventory at fair value	173.6	151.9
Collateral that can be sold or repledged	606.4	478.8
Accounts pay and other accrued - fair value	1.6	1.8
Payables to b/d - fair value	$ 8.8	$ 5.6
Preferred stock - par value	$ 0.01	$ 0.01
Preferred stock - authorized	1,000,000	1,000,000
Preferred stock - issued	0	0
Preferred stock - outstanding	0	0
Common stock - par value	$ 0.01	$ 0.01
Common stock - authorized	30,000,000	30,000,000
Common stock - issued	21,735,636	21,297,317
Common stock - outstanding	19,313,679	19,075,360
Treasury stock - shares	2,421,957	2,221,957

Accounts payable and other accrued liabilities - contingent consideration, fair value

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Deposits and receivables from b/ds and counterparties at fair value

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Payables to b/ds and counterparties at fair value

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Physical commodities inventory at fair value - precious metals

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Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

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Face amount or stated value per share of common stock.

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The maximum number of common shares permitted to be issued by an entity's charter and bylaws.

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Total number of common shares of an entity that have been sold or granted to shareholders (includes common shares that were issued, repurchased and remain in the treasury). These shares represent capital invested by the firm's shareholders and owners, and may be all or only a portion of the number of shares authorized. Shares issued include shares outstanding and shares held in the treasury.

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Number of shares of common stock outstanding. Common stock represent the ownership interest in a corporation.

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Face amount or stated value per share of preferred stock nonredeemable or redeemable solely at the option of the issuer.

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The maximum number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) permitted to be issued by an entity's charter and bylaws.

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Total number of nonredeemable preferred shares (or preferred stock redeemable solely at the option of the issuer) issued to shareholders (includes related preferred shares that were issued, repurchased, and remain in the treasury). May be all or portion of the number of preferred shares authorized. Excludes preferred shares that are classified as debt.

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Aggregate share number for all nonredeemable preferred stock (or preferred stock redeemable solely at the option of the issuer) held by stockholders. Does not include preferred shares that have been repurchased.

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Fair value of securities pledged as collateral against securities sold under agreement to repurchase.

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Number of common and preferred shares that were previously issued and that were repurchased by the issuing entity and held in treasury on the financial statement date. This stock has no voting rights and receives no dividends.

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