Acquisitions Acquisitions (Notes)	6 Months Ended
Mar. 31, 2020
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. 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 upon the closing of the acquisition, which occurred on October 7, 2019. The purchase price allocation resulted in the recognition of liabilities assumed related to the futures and options on futures client account balances of approximately $351.8 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 acquired. The allocation of the purchase price to the client accounts is considered final as of March 31, 2020. The Company also 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 intangible assets and property and equipment. As of March 31, 2020, the valuation of the acquired intangible assets and property and equipment was not yet complete as the Company continues to acquire the information necessary to complete the valuation analysis. As of March 31, 2020, given the status of the valuation analysis, $0.7 million of the purchase price was preliminary allocated to the net book value of the property and equipment acquired, $3.2 million was allocated to the client base intangible assets acquired, and the remaining excess purchase price of $1.1 million was allocated to goodwill. Once the valuation analysis is complete, the Company will record measurement period adjustments to reflect the fair value of the property and equipment and intangible assets acquired on the acquisition date. The business acquired has been assigned to the Company’s Clearing and Execution reportable segment. The client base intangible assets have preliminary been assigned a useful life of 5 years. The revenues and net income contributed by the acquired business during the three and six months ended March 31, 2020, were not material to the Company’s condensed consolidated financial results. 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 was equal to $1.7 million. This transaction was accounted for as an asset acquisition at cost. The cash purchase price was allocated to the fair value of the client lists and relationships obtained and has been assigned, and will be amortized, over a useful life of seven years. Tellimer In December 2019, the Company executed a definitive purchase agreement to acquire the brokerage businesses of Tellimer Group. This transaction involves the stock purchase of 100% of Exotix Partners, LLP, based in the United Kingdom, and the stock purchase of 100% of Tellimer Capital Ltd based in Nigeria. The closing of this transaction is subject to limited conditions including regulatory approval in the relevant jurisdictions. The cash purchase price is equal to the net tangible book value of the acquired entities upon closing. Regulatory approval for the acquisition of Exotix Partners, LLP, was obtained during the three months ended March 31, 2020, with the transaction closing on April 1, 2020. The cash purchase price for the acquisition of Exotix Partners, LLP, was $4.7 million. The preliminary allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed has not yet been completed. IFCM Commodities On January 2, 2020, the Company’s wholly owned subsidiary, INTL Netherlands B.V., executed and closed on a stock purchase agreement to acquire 100% of IFCM Commodities GmbH (“IFCM”) based in Germany. IFCM specializes in providing commodity price risk management solutions for base metals serving clients across Germany and continental Europe and historically introduced clients to INTL FCStone Ltd. This purchase is part of the Company’s overall strategic plan to expand the Company’s footprint in Germany and continental Europe in order to handle European clients and regional metals business following Brexit. The cash purchase price of $1.9 million was equal to net tangible book value upon closing plus a premium of $1.0 million. The excess of the cash consideration over the fair value of the net tangible assets acquired on the closing date was allocated to the fair value of IFCM’s client relationships. This client base intangible asset has been assigned, and will be amortized over, a useful of five years. The acquired business has been assigned to the Company’s Commercial Hedging reportable segment. The revenues and net income contributed by the acquired business during the three months ended March 31, 2020, were not material to the Company’s condensed consolidated financial results. GIROXX In January 2020, the Company’s wholly owned subsidiary, INTL FCStone Ltd, executed a stock purchase agreement to acquire 100% of GIROXX Gmbh based in Germany. Through its digital platform, GIROXX Gmbh provides online payment and foreign exchange hedging services to small and medium sized enterprises in Germany, Austria, and Switzerland. The Company offers a wide range of financial services including advisory and execution services in commodities, which will be offered to GIROXX’s institutional client base. This purchase completes a series of acquisitions and restructuring to ensure that all clients of the Company are secure with their continuity of service and market access following Brexit. The closing of the transaction was conditional upon the approval of financial services regulators in Germany, which was obtained in April 2020 with the transaction closing in May 2020. The preliminary cash purchase price was approximately $4.4 million. The preliminary allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed has not yet been completed. Gain Capital On February 26, 2020, the Company entered into an definitive agreement to acquire Gain Capital Holdings, Inc. (“Gain”). The Company agreed to acquire Gain for $6.00 per share in an all-cash transaction representing approximately $236.3 million in equity value. Gain is a global provider of trading services and solutions to institutional and retail investors, specializing in both over-the-counter (“OTC”) products and exchange-traded futures and options on futures. Gain provides its clients with access to a diverse range of global OTC financial markets, including spot foreign exchange, precious metals, and contracts for a difference. As a result of the acquisition, the Company will add a new digital platform to its global financial network, significantly expand its offerings to retail clients, as well as add a complementary exchange-traded futures and options on futures business. The acquisition of Gain will also accelerate the digitization of the Company’s trading platforms. The transaction is expected to close in the second half of calendar year 2020, subject to approval by Gain’s shareholders, regulatory approvals, and customary closing conditions. In connection with the agreement, the Company has obtained commitments for up to $350.0 million in debt financing for the acquisition.

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. 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 upon the closing of the acquisition, which occurred on October 7, 2019.

The purchase price allocation resulted in the recognition of liabilities assumed related to the futures and options on futures client account balances of approximately $351.8 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 acquired. The allocation of the purchase price to the client accounts is considered final as of March 31, 2020.

The Company also 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 intangible assets and property and equipment. As of March 31, 2020, the valuation of the acquired intangible assets and property and equipment was not yet complete as the Company continues to acquire the information necessary to complete the valuation analysis. As of March 31, 2020, given the status of the valuation analysis, $0.7 million of the purchase price was preliminary allocated to the net book value of the property and equipment acquired, $3.2 million was allocated to the client base intangible assets acquired, and the remaining excess purchase price of $1.1 million was allocated to goodwill. Once the valuation analysis is complete, the Company will record measurement period adjustments to reflect the fair value of the property and equipment and intangible assets acquired on the acquisition date.

The business acquired has been assigned to the Company’s Clearing and Execution reportable segment. The client base intangible assets have preliminary been assigned a useful life of 5 years. The revenues and net income contributed by the acquired business during the three and six months ended March 31, 2020, were not material to the Company’s condensed consolidated financial results.

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 was equal to $1.7 million. This transaction was accounted for as an asset acquisition at cost. The cash purchase price was allocated to the fair value of the client lists and relationships obtained and has been assigned, and will be amortized, over a useful life of seven years.

Tellimer

In December 2019, the Company executed a definitive purchase agreement to acquire the brokerage businesses of Tellimer Group. This transaction involves the stock purchase of 100% of Exotix Partners, LLP, based in the United Kingdom, and the stock purchase of 100% of Tellimer Capital Ltd based in Nigeria. The closing of this transaction is subject to limited conditions including regulatory approval in the relevant jurisdictions. The cash purchase price is equal to the net tangible book value of the acquired entities upon closing. Regulatory approval for the acquisition of Exotix Partners, LLP, was obtained during the three months ended March 31, 2020, with the transaction closing on April 1, 2020. The cash purchase price for the acquisition of Exotix Partners, LLP, was $4.7 million. The preliminary allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed has not yet been completed.

IFCM Commodities

On January 2, 2020, the Company’s wholly owned subsidiary, INTL Netherlands B.V., executed and closed on a stock purchase agreement to acquire 100% of IFCM Commodities GmbH (“IFCM”) based in Germany. IFCM specializes in providing commodity price risk management solutions for base metals serving clients across Germany and continental Europe and historically introduced clients to INTL FCStone Ltd. This purchase is part of the Company’s overall strategic plan to expand the Company’s footprint in Germany and continental Europe in order to handle European clients and regional metals business following Brexit.

The cash purchase price of $1.9 million was equal to net tangible book value upon closing plus a premium of $1.0 million. The excess of the cash consideration over the fair value of the net tangible assets acquired on the closing date was allocated to the fair value of IFCM’s client relationships. This client base intangible asset has been assigned, and will be amortized over, a useful of five years.

The acquired business has been assigned to the Company’s Commercial Hedging reportable segment. The revenues and net income contributed by the acquired business during the three months ended March 31, 2020, were not material to the Company’s condensed consolidated financial results.

GIROXX

In January 2020, the Company’s wholly owned subsidiary, INTL FCStone Ltd, executed a stock purchase agreement to acquire 100% of GIROXX Gmbh based in Germany. Through its digital platform, GIROXX Gmbh provides online payment and foreign exchange hedging services to small and medium sized enterprises in Germany, Austria, and Switzerland. The Company offers a wide range of financial services including advisory and execution services in commodities, which will be offered to GIROXX’s institutional client base. This purchase completes a series of acquisitions and restructuring to ensure that all clients of the Company are secure with their continuity of service and market access following Brexit. The closing of the transaction was conditional upon the approval of financial services regulators in Germany, which was obtained in April 2020 with the transaction closing in May 2020. The preliminary cash purchase price was approximately $4.4 million. The preliminary allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed has not yet been completed.

Gain Capital

On February 26, 2020, the Company entered into an definitive agreement to acquire Gain Capital Holdings, Inc. (“Gain”). The Company agreed to acquire Gain for $6.00 per share in an all-cash transaction representing approximately $236.3 million in equity value.

Gain is a global provider of trading services and solutions to institutional and retail investors, specializing in both over-the-counter (“OTC”) products and exchange-traded futures and options on futures. Gain provides its clients with access to a diverse range of global OTC financial markets, including spot foreign exchange, precious metals, and contracts for a difference. As a result of the acquisition, the Company will add a new digital platform to its global financial network, significantly expand its offerings to retail clients, as well as add a complementary exchange-traded futures and options on futures business. The acquisition of Gain will also accelerate the digitization of the Company’s trading platforms.

The transaction is expected to close in the second half of calendar year 2020, subject to approval by Gain’s shareholders, regulatory approvals, and customary closing conditions. In connection with the agreement, the Company has obtained commitments for up to $350.0 million in debt financing for the acquisition.