Acquisitions Acquisitions (Notes)	3 Months Ended
Dec. 31, 2019
Acquisitions (Notes) [Abstract]
Business Combination Disclosure [Text Block]	Note 18 - Acquisitions UOB Bullion and Futures Limited On March 19, 2019, the Company’s subsidiary INTL FCStone Pte Ltd executed an asset purchase agreement to acquire the futures and options brokerage and clearing business of UOB Bullion and Futures Limited, a subsidiary of United Overseas Bank Limited. Closing was conditional upon receiving regulatory approval by the Monetary Authority of Singapore (“MAS”). This acquisition provides the Company access to an established institutional client base and also augments the Company’s global service capabilities in Singapore. The purchase price for the acquired assets was $5.0 million of which $2.5 million was due upon the execution of the asset purchase agreement and the remaining $2.5 million was due to the seller upon the closing of the acquisition, which occurred on October 7, 2019. The Company acquired certain client base intangible assets and property and equipment in connection with the acquisition. The Company has engaged a third-party valuation specialist to assist with the valuation of the acquired assets. As of December 31, 2019, the valuation of the acquired assets was not yet complete as the Company continues to acquire the information necessary to complete the valuation analysis. As of December 31, 2019, given the status of the valuation analysis, $0.7 million of the purchase price was allocated to the net book value of the property and equipment acquired and the excess consideration of $4.3 million was recorded as goodwill. Once the valuation analysis is complete, the Company will record measurement period adjustments to reclassify a portion of the purchase price recorded to goodwill to the fair value of the identifiable intangible assets acquired and to adjust the property and equipment to its fair market value on the acquisition date. The initial purchase price allocation resulted in the recognition of certain futures and options on futures client account balances of approximately $295.8 million as of the acquisition date, which was recorded within ‘payables to clients’ on the condensed consolidated balance sheet, and an equal and offsetting amount of assets. The business acquired has been assigned to the Company’s Clearing and Execution reportable segment. Quest Capital In August 2019, the Company’s subsidiary, SA Stone Wealth Management, executed an asset purchase agreement to acquire certain client accounts of Quest Capital Strategies, Inc. The asset purchase agreement was subject to FINRA approval and other conditions of closing. FINRA approval was obtained and the other conditions of closing were fulfilled with the closing of the transaction occurring on December 9, 2019. The cash purchase price for the acquired client accounts is equal to an amount not to exceed $1.7 million, which is reflected in an escrow account within ‘Other assets’ on the condensed consolidated balance sheet as of December 31, 2019. The final cash purchase price is dependent upon the value of the client accounts ultimately transferred to the Company following a conversion period of 60 days. This transaction will be accounted for as an asset acquisition at cost following the completion of the conversion period. Tellimer In December 2019, the Company executed a definitive purchase agreement to acquire the brokerage businesses of Tellimer Group (“Tellimer”). This transaction will involve the stock purchase of 100% of Exotix Partners, LLP, based in the U.K., the stock purchase of 100% of Tellimer Capital Ltd based in Nigeria, and the acquisition of the broking business assets of Tellimer Markets, Inc. based in the U.S. The closing of this transaction is subject to limited conditions including regulatory approval in the relevant jurisdictions. The purchase price will be equal to net tangible book value upon closing.

Note 18 - Acquisitions

UOB Bullion and Futures Limited

On March 19, 2019, the Company’s subsidiary INTL FCStone Pte Ltd executed an asset purchase agreement to acquire the futures and options brokerage and clearing business of UOB Bullion and Futures Limited, a subsidiary of United Overseas Bank Limited. Closing was conditional upon receiving regulatory approval by the Monetary Authority of Singapore (“MAS”). This acquisition provides the Company access to an established institutional client base and also augments the Company’s global service capabilities in Singapore. The purchase price for the acquired assets was $5.0 million of which $2.5 million was due upon the execution of the asset purchase agreement and the remaining $2.5 million was due to the seller upon the closing of the acquisition, which occurred on October 7, 2019.

The Company acquired certain client base intangible assets and property and equipment in connection with the acquisition. The Company has engaged a third-party valuation specialist to assist with the valuation of the acquired assets. As of December 31, 2019, the valuation of the acquired assets was not yet complete as the Company continues to acquire the information necessary to complete the valuation analysis. As of December 31, 2019, given the status of the valuation analysis, $0.7 million of the purchase price was allocated to the net book value of the property and equipment acquired and the excess consideration of $4.3 million was recorded as goodwill. Once the valuation analysis is complete, the Company will record measurement period adjustments to reclassify a portion of the purchase price recorded to goodwill to the fair value of the identifiable intangible assets acquired and to adjust the property and equipment to its fair market value on the acquisition date.

The initial purchase price allocation resulted in the recognition of certain futures and options on futures client account balances of approximately $295.8 million as of the acquisition date, which was recorded within ‘payables to clients’ on the condensed consolidated balance sheet, and an equal and offsetting amount of assets.

The business acquired has been assigned to the Company’s Clearing and Execution reportable segment.

Quest Capital

In August 2019, the Company’s subsidiary, SA Stone Wealth Management, executed an asset purchase agreement to acquire certain client accounts of Quest Capital Strategies, Inc. The asset purchase agreement was subject to FINRA approval and other conditions of closing. FINRA approval was obtained and the other conditions of closing were fulfilled with the closing of the transaction occurring on December 9, 2019. The cash purchase price for the acquired client accounts is equal to an amount not to exceed $1.7 million, which is reflected in an escrow account within ‘Other assets’ on the condensed consolidated balance sheet as of December 31, 2019. The final cash purchase price is dependent upon the value of the client accounts ultimately transferred to the Company following a conversion period of 60 days. This transaction will be accounted for as an asset acquisition at cost following the completion of the conversion period.

Tellimer

In December 2019, the Company executed a definitive purchase agreement to acquire the brokerage businesses of Tellimer Group (“Tellimer”). This transaction will involve the stock purchase of 100% of Exotix Partners, LLP, based in the U.K., the stock purchase of 100% of Tellimer Capital Ltd based in Nigeria, and the acquisition of the broking business assets of Tellimer Markets, Inc. based in the U.S. The closing of this transaction is subject to limited conditions including regulatory approval in the relevant jurisdictions. The purchase price will be equal to net tangible book value upon closing.