Acquisitions Acquisitions (Notes)	9 Months Ended
Jun. 30, 2020
Acquisitions (Notes) [Abstract]
Business Combination Disclosure [Text Block]	Note 18 - Acquisitions The Company’s condensed consolidated financial statements include the operating results of the businesses acquired during the nine months ended June 30, 2020, from the dates of acquisition. On an aggregate basis, the businesses acquired during the reporting period, contributed $5.0 million and $12.7 million of total revenues for the three and nine months ended June 30, 2020. The earnings contributed by the acquired businesses from the dates of acquisition for the three and nine months ended June 30, 2020, were not material to the Company’s condensed consolidated income statements. UOB Bullion and Futures Limited On March 19, 2019, the Company’s subsidiary StoneX Financial 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 June 30, 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 June 30, 2020, the valuation of the acquired intangible assets and property and equipment was not yet complete as the Company is completing its final review of the valuation analysis. During the three months ended June 30, 2020, the Company recorded certain measurement period adjustments, which resulted in an increase in the purchase price allocated to the property and equipment acquired and the client base intangible assets acquired of $0.1 million and $1.0 million, respectively, with a corresponding decrease to the excess purchase price assigned to goodwill. As of June 30, 2020, given the status of the valuation analysis, $0.8 million of the purchase price was preliminarily allocated to the property and equipment acquired and $4.2 million was allocated to the client base intangible assets acquired. Once the valuation analysis is complete, the Company will record additional measurement period adjustments, if any, to reflect the final determination of 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 preliminarily been assigned a useful life of 5 years. 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 to closing. FINRA approval was obtained and the other conditions to closing were fulfilled and the closing of the transaction occurred 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 involved 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 was subject to limited conditions including regulatory approval in the relevant jurisdictions. The cash purchase price was 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, and the transaction closed on April 1, 2020. The cash purchase price for the acquisition of Exotix Partners, LLP, was $4.7 million. The final allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed resulted in the recognition of $1.0 million in cash and cash equivalents, $1.0 million in receivables from clients, net, $0.3 million in property and equipment, net, $3.4 million in other assets, and $1.0 million in liabilities assumed. Regulatory approval for the acquisition of Tellimer Capital Ltd was obtained during the three months ending June 30, 2020, and the transaction closed on June 1, 2020. The cash purchase price for the acquisition of Tellimer Capital Ltd was not material to the Company’s condensed consolidated financial statements. The acquired businesses have been assigned to the Company’s Securities reportable segment. 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 the equity interests 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 StoneX Financial 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. GIROXX In January 2020, the Company’s wholly owned subsidiary, StoneX Financial Ltd, executed a stock purchase agreement to acquire 100% of GIROXX based in Germany. Through its digital platform, GIROXX 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 restructurings 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 and the transaction closed on May 1, 2020. The cash purchase price was $4.4 million. The preliminary allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed resulted in the recognition of cash and cash equivalents of $6.5 million, property and equipment of $0.1 million, accounts payables and other accrued liabilities of $0.6 million, and payables to clients of $5.8 million as of the acquisition date. The excess purchase price over tangible net book value on the acquisition date of $4.2 million has been preliminarily allocated to goodwill. The Company acquired certain intangible assets in connection with the acquisition of GIROXX, primarily related to a business license permitting the Company to facilitate payment transactions in the European Union. The Company is in the process of gathering the information necessary to complete a valuation analysis of the intangible assets acquired. Once the valuation analysis is complete, the Company will record measurement period adjustments to reflect the final determination of the fair value of the intangible assets acquired with any remaining excess consideration allocated to goodwill. The acquired business has been assigned to the Company’s Global Payments reportable segment. Gain Capital On February 26, 2020, the Company entered into a definitive merger agreement to acquire Gain. The Company agreed to acquire Gain for $6.00 per share in an all-cash transaction representing approximately $236.2 million in equity value. Gain is a global provider of trading services and solutions to institutional and retail investors, specializing in both 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. As discussed in Note 11, on June 11, 2020, the Company completed the issuance and sale of $350 million in aggregate principal amount of the Company’s 8.625% Notes. The Company had deposited the gross proceeds from the sale of the Senior Secured Notes, as well as escrow agency fees and interest on the Senior Secured Notes to (but not including) the date that is two months from the date of the closing of the offering of the Senior Secured Notes, into a segregated escrow account until the date that certain escrow release conditions were satisfied, which included the consummation of the merger of the Company’s wholly-owned subsidiary with Gain. As of June 30, 2020, the total amount held in escrow was $349.8 million and is included within ‘Restricted cash held in escrow’ on the Company’s condensed consolidated balance sheet. The merger closed on July 31, 2020 subsequent to approval by Gain’s shareholders, approval by regulators, and the completion of customary closing conditions. In connection with the closing of the merger and the satisfaction of the escrow release conditions, the proceeds from the issuance of the Senior Secured Notes were released from escrow. The Company used the net proceeds from the sale of the Senior Secured Notes to fund the preliminary cash consideration for the merger of Gain on the closing date and to pay certain related transactions fees and expenses. The Company intends to utilize the remaining proceeds to fund the repayment of $92 million of Gain’s 5.00% Convertible Senior Notes due 2022 (“the Gain Notes”). The consummation of the merger with Gain constituted a fundamental change and make-whole fundamental change under the terms of the Gain Notes’ indenture. As a result, the holders of the Gain Notes are entitled to require the Company to repurchase the Gain Notes at a repurchase price equal to $1,002.36 per $1,000 principal amount on September 1, 2020. Alternatively, the holders of the Gain Notes may continue to hold such notes without exercising the repurchase right, in which case the Gain Notes will continue to bear interest at 5.00% and the notes will be convertible into the right to convert the principal amount of the Senior Secured Notes solely into cash in an amount equal to the conversion rate in effect on the conversion date multiplied by $6.00. If any holder of the Gain Notes neither exercises such holder's fundamental change repurchase right or make-whole fundamental change conversion right, such holder's Gain Notes will remain outstanding. To the extent that any Gain Notes remain outstanding following the fundamental change repurchase date, the Company will be required to redeem the Senior Secured Notes in an amount equal to the aggregate principal amount of the Gain Notes that remain outstanding after the fundamental change repurchase date, at a redemption price equal to 100% of the principal amount of the Senior Secured Notes redeemed, plus accrued and unpaid interest, if any, to the redemption date. The preliminary allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed has not yet been completed. The Company incurred acquisition related costs related to the merger for the three and nine months ended June 30, 2020, of $1.4 million and $1.9 million, respectively, that are included within ‘Professional fees’ on the condensed consolidated income statements.

The Company’s condensed consolidated financial statements include the operating results of the businesses acquired during the nine months ended June 30, 2020, from the dates of acquisition. On an aggregate basis, the businesses acquired during the reporting period, contributed $5.0 million and $12.7 million of total revenues for the three and nine months ended June 30, 2020. The earnings contributed by the acquired businesses from the dates of acquisition for the three and nine months ended June 30, 2020, were not material to the Company’s condensed consolidated income statements.

On March 19, 2019, the Company’s subsidiary StoneX Financial 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 June 30, 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 June 30, 2020, the valuation of the acquired intangible assets and property and equipment was not yet complete as the Company is completing its final review of the valuation analysis.

During the three months ended June 30, 2020, the Company recorded certain measurement period adjustments, which resulted in an increase in the purchase price allocated to the property and equipment acquired and the client base intangible assets acquired of $0.1 million and $1.0 million, respectively, with a corresponding decrease to the excess purchase price assigned to goodwill. As of June 30, 2020, given the status of the valuation analysis, $0.8 million of the purchase price was preliminarily allocated to the property and equipment acquired and $4.2 million was allocated to the client base intangible assets acquired. Once the valuation analysis is complete, the Company will record additional measurement period adjustments, if any, to reflect the final determination of the fair value of the property and equipment and intangible assets acquired on the acquisition date.

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 to closing. FINRA approval was obtained and the other conditions to closing were fulfilled and the closing of the transaction occurred 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.

In December 2019, the Company executed a definitive purchase agreement to acquire the brokerage businesses of Tellimer Group. This transaction involved 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 was subject to limited conditions including regulatory approval in the relevant jurisdictions. The cash purchase price was 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, and the transaction closed on April 1, 2020. The cash purchase price for the acquisition of Exotix Partners, LLP, was $4.7 million. The final allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed resulted in the recognition of $1.0 million in cash and cash equivalents, $1.0 million in receivables from clients, net, $0.3 million in property and equipment, net, $3.4 million in other assets, and $1.0 million in liabilities assumed.

Regulatory approval for the acquisition of Tellimer Capital Ltd was obtained during the three months ending June 30, 2020, and the transaction closed on June 1, 2020. The cash purchase price for the acquisition of Tellimer Capital Ltd was not material to the Company’s condensed consolidated financial statements.

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 the equity interests 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 StoneX Financial 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.

In January 2020, the Company’s wholly owned subsidiary, StoneX Financial Ltd, executed a stock purchase agreement to acquire 100% of GIROXX based in Germany. Through its digital platform, GIROXX 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 restructurings 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 and the transaction closed on May 1, 2020. The cash purchase price was $4.4 million. The preliminary allocation of the cash purchase price to the fair value of assets acquired and liabilities assumed resulted in the recognition of cash and cash equivalents of $6.5 million, property and equipment of $0.1 million, accounts payables and other accrued liabilities of $0.6 million, and payables to clients of $5.8 million as of the acquisition date. The excess purchase price over tangible net book value on the acquisition date of $4.2 million has been preliminarily allocated to goodwill.

The Company acquired certain intangible assets in connection with the acquisition of GIROXX, primarily related to a business license permitting the Company to facilitate payment transactions in the European Union. The Company is in the process of gathering the information necessary to complete a valuation analysis of the intangible assets acquired. Once the valuation analysis is complete, the Company will record measurement period adjustments to reflect the final determination of the fair value of the intangible assets acquired with any remaining excess consideration allocated to goodwill.

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.

As discussed in Note 11, on June 11, 2020, the Company completed the issuance and sale of $350 million in aggregate principal amount of the Company’s 8.625% Notes. The Company had deposited the gross proceeds from the sale of the Senior Secured Notes, as well as escrow agency fees and interest on the Senior Secured Notes to (but not including) the date that is two months from the date of the closing of the offering of the Senior Secured Notes, into a segregated escrow account until the date that certain escrow release conditions were satisfied, which included the consummation of the merger of the Company’s wholly-owned subsidiary with Gain. As of June 30, 2020, the total amount held in escrow was $349.8 million and is included within ‘Restricted cash held in escrow’ on the Company’s condensed consolidated balance sheet.

The merger closed on July 31, 2020 subsequent to approval by Gain’s shareholders, approval by regulators, and the completion of customary closing conditions. In connection with the closing of the merger and the satisfaction of the escrow release conditions, the proceeds from the issuance of the Senior Secured Notes were released from escrow. The Company used the net proceeds from the sale of the Senior Secured Notes to fund the preliminary cash consideration for the merger of Gain on the closing date and to pay certain related transactions fees and expenses.

The Company intends to utilize the remaining proceeds to fund the repayment of $92 million of Gain’s 5.00% Convertible Senior Notes due 2022 (“the Gain Notes”). The consummation of the merger with Gain constituted a fundamental change and make-whole fundamental change under the terms of the Gain Notes’ indenture. As a result, the holders of the Gain Notes are entitled to require the Company to repurchase the Gain Notes at a repurchase price equal to $1,002.36 per $1,000 principal amount on September 1, 2020. Alternatively, the holders of the Gain Notes may continue to hold such notes without exercising the repurchase right, in which case the Gain Notes will continue to bear interest at 5.00% and the notes will be convertible into the right to convert the principal amount of the Senior Secured Notes solely into cash in an amount equal to the conversion rate in effect on the conversion date multiplied by $6.00.

If any holder of the Gain Notes neither exercises such holder's fundamental change repurchase right or make-whole fundamental change conversion right, such holder's Gain Notes will remain outstanding. To the extent that any Gain Notes remain outstanding following the fundamental change repurchase date, the Company will be required to redeem the Senior Secured Notes in an amount equal to the aggregate principal amount of the Gain Notes that remain outstanding after the fundamental change repurchase date, at a redemption price equal to 100% of the principal amount of the Senior Secured Notes redeemed, plus accrued and unpaid interest, if any, to the redemption date.