Condensed Consolidated Balance Sheets Parentheticals (USD $) In Millions, except Share data, unless otherwise specified	Mar. 31, 2015	Sep. 30, 2014
Balance Sheet Parentheticals [Abstract]
Securities and other assets segregated, fair value	$ 209.0	$ 15.3
Dep and rec -exch clear org - fair value	1,008.7	1,255.4
Dep and rec -b/d - fair value	(28.6)	(1.1)
Collateral that can be sold or repledged	183.4	0
Accounts pay and other accrued - fair value	3.1	5.5
Payables to b/d - fair value	$ 1.5	$ 0
Preferred stock - par value	$ 0.01	$ 0.01
Preferred stock - authorized	1,000,000us-gaap_PreferredStockSharesAuthorized	1,000,000us-gaap_PreferredStockSharesAuthorized
Preferred stock - issued	0us-gaap_PreferredStockSharesIssued	0us-gaap_PreferredStockSharesIssued
Preferred stock - outstanding	0us-gaap_PreferredStockSharesOutstanding	0us-gaap_PreferredStockSharesOutstanding
Common stock - par value	$ 0.01	$ 0.01
Common stock - authorized	30,000,000us-gaap_CommonStockSharesAuthorized	30,000,000us-gaap_CommonStockSharesAuthorized
Common stock - issued	20,132,970us-gaap_CommonStockSharesIssued	19,826,635us-gaap_CommonStockSharesIssued
Common stock - outstanding	18,965,488us-gaap_CommonStockSharesOutstanding	18,883,662us-gaap_CommonStockSharesOutstanding
Treasury stock - shares	1,167,482us-gaap_TreasuryStockShares	942,973us-gaap_TreasuryStockShares

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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Deposits and receivables from exchange clearing orgs, fair value

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Payables to b/ds and counterparties at fair value

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Securities and other assets segregated, fair value

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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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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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