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O’Brien & Associates, LLC R.J. O’Brien & Associates, LLC [Member] R.J. 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Clearing Organizations And Counter Parties Non Segregated Cash And Other Non Cash Equivalent Assets Included With In Deposits And Receivables From Broker Dealers Clearing Organizations And Counter Parties Credit Facility [Axis] Credit Facility [Axis] Aggregate Available Trading Arrangement, Securities Aggregate Available Amount Total assets at fair value Assets, Fair Value Disclosure Website domains Internet Domain Names [Member] Name Measure Name Business Combination, Consideration Transferred, Equity Interest, Type [Domain] Business Combination, Consideration Transferred, Equity Interest, Type [Domain] Income Taxes Income Tax Disclosure [Text Block] Pay vs Performance Disclosure [Line Items] Fair Value, Measurements, Fair Value Hierarchy [Domain] Fair Value Hierarchy and NAV [Domain] Securities purchased under agreements to resell Securities purchased under agreements to resell, net Securities Purchased under Agreements to Resell Pay vs Performance Disclosure Pay vs Performance Disclosure [Table] Total merger consideration Business Combination, Consideration Transferred Additional Paid-in Capital Additional Paid-in Capital [Member] Entity Filer Category Entity Filer Category Indefinite-lived Intangible Assets [Axis] Intangible Asset, Indefinite-Lived, Class [Axis] Insurance General Insurance Expense Sales of physical commodities Revenue Not from Contract with Customer Impact of netting and collateral asset Derivative Asset, Subject to Master Netting Arrangement, Gross Liability and Collateral, Obligation to Return Cash, Offset Name Trading Arrangement, Individual Name Deposits and receivables from exchange clearing organizations [Domain] Deposits and Receivables from Exchange Clearing Organizations [Domain] Deposits and Receivables from Exchange Clearing Organizations [Domain] Cash and cash equivalents Cash and Cash Equivalent Position [Domain] Position [Domain] Raw materials Inventory, Raw Materials, Net of Reserves Over 90 Days Maturity Greater than 90 Days [Member] Concentration Risk Benchmark [Domain] Concentration Risk Benchmark [Domain] Company Selected Measure Amount Company Selected Measure Amount Derivative contracts not accounted for as hedges Not Designated as Hedging Instrument [Member] Income taxes receivable Income Taxes Receivable Fixed compensation and benefits Fixed Compensation And Benefits (Expense) Fixed Compensation And Benefits (Expense) Depreciation and amortization Depreciation, Depletion and Amortization Net income allocated to common stockholders, basic Net Income (Loss) from Continuing Operations Available to Common Shareholders, Basic Physical commodities inventory, net (including $413.5 million and $471.1 million at fair value at June 30, 2026 and September 30, 2025, respectively) Physical commodities inventory Inventory, Gross Number of employees Entity Number of Employees Deposits with and receivables from broker-dealers, clearing organizations and counterparties, net Receivables from Clearing Organizations Including Netting Adjustment Receivables from Clearing Organizations Including Netting Adjustment Securities sold under agreements to repurchase, offset Security Sold under Agreement to Repurchase, Subject to Master Netting Arrangement, Asset Offset Securities sold under agreements to repurchase Securities sold under agreements to repurchase, gross Security Sold under Agreement to Repurchase, Subject to Master Netting Arrangement, before Offset Entity Address, Address Line Two Entity Address, Address Line Two Fiscal 2030 and thereafter Finite-Lived Intangible Asset, Expected Amortization, Year Four and Thereafter Finite-Lived Intangible Asset, Expected Amortization, Year Four and Thereafter Sales of physical commodities Sales of Physical Commodities [Member] Sales of Physical Commodities Accounts Payable and Other Accrued Liabilities (Including Contingent Liabilities) [Axis] Accounts Payable and Other Accrued Liabilities (Including Contingent Liabilities) [Axis] Accounts payable and other accrued liabilities (including contingent liabilities) [Axis] Total revenues Business Combination, Pro Forma Information, Pro Forma Revenue Non-PEO NEO Non-PEO NEO [Member] Senior Notes Senior Notes [Member] Accounts Payable and Other Accrued Liabilities (Including Contingent Liabilities) [Domain] Accounts Payable and Other Accrued Liabilities (Including Contingent Liabilities) [Domain] Accounts Payable and Other Accrued Liabilities (Including Contingent Liabilities) [Domain] Entity Address, Address Line One Entity Address, Address Line One Write off amortized intangible assets Intangible Asset, Finite-Lived, Impairment Loss Deposits and Receivables from Exchange Clearing Organizations [Axis] Deposits and Receivables from Exchange Clearing Organizations [Axis] Deposits and Receivables from Exchange Clearing Organizations [Axis] Income tax expense Income Tax Expense (Benefit) Total compensation and other expenses Noninterest Expense Other Expenses Other Income and Other Expense Disclosure [Text Block] Non-variable expenses Non-Variable Expenses Non-Variable Expenses Dilutive potential common shares outstanding: Dilutive Securities, Effect on Basic Earnings Per Share [Abstract] Customer Concentration Risk Customer Concentration Risk [Member] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] SEC Schedule, 12-09, Movement in Valuation Allowances and Reserves [Roll Forward] Award Timing Method Award Timing Method [Text Block] StoneX Financial Pte. Ltd. StoneX Financial Pte. Ltd. StoneX Financial Pte Ltd [Member] StoneX Financial Pte Ltd Derivative, remaining maturity Derivative, Remaining Maturity Consolidation Consolidation, Policy [Policy Text Block] Net increase in cash, segregated cash, cash equivalents, and segregated cash equivalents Cash, Cash Equivalent, Restricted Cash, and Restricted Cash Equivalent, Period Increase (Decrease), Including Exchange Rate Effect and Discontinued Operation Forgone Recovery, Explanation of Impracticability Forgone Recovery, Explanation of Impracticability [Text Block] Client account fees Client Account Fees [Member] Client Account Fees [Member] AOCI Attributable to Parent, Net of Tax [Roll Forward] AOCI Attributable to Parent, Net of Tax [Roll Forward] Net income Net income Net income Net Income (Loss) Attributable to Parent Long-term Debt, Type [Axis] Long-Term Debt, Type [Axis] Erroneous Compensation Analysis Erroneous Compensation Analysis [Text Block] Balance Sheet Location [Axis] Location, Statement of Financial Position, Balance [Axis] Statement [Table] Statement [Table] Restatement Determination Date: Restatement Determination Date [Axis] Exercise of stock options Proceeds from Stock Options Exercised Schedule of Changes in Accumulated Other Comprehensive Loss Schedule of Accumulated Other Comprehensive Income (Loss) [Table Text Block] Amounts receivable from sellers Business Combination, Consideration Transferred, Amounts Receivable From Sellers Business Combination, Consideration Transferred, Amounts Receivable From Sellers Certificates of deposit Certificates of Deposit [Member] Compensatory damages awarded to other party Litigation Settlement, Amount Awarded to Other Party Derivative Instruments and Hedging Activities Disclosure [Line Items] Derivative Instruments and Hedging Activities Disclosures [Line Items] Security Owned and Sold, Not yet Purchased, at Fair Value [Table] Security Owned and Sold, Not yet Purchased, at Fair Value [Table] Derivative asset, fair value, gross asset Asset Derivatives Derivative Asset, Subject to Master Netting Arrangement, before Offset Net income Income (Loss) from Continuing Operations, Net of Tax, Attributable to Parent Bad debt expense (reversal) SEC Schedule, 12-09, Valuation Allowances and Reserves, Credit Loss Expense (Reversal) Not Included in Allowance SEC Schedule, 12-09, Valuation Allowances and Reserves, Credit Loss Expense (Reversal) Not Included in Allowance Cash and Cash Equivalents [Axis] Cash and Cash Equivalents [Axis] Income taxes payable Accrued Income Taxes Revenues: Revenues [Abstract] Commission and clearing fees Total commission and clearing fees Commission and Clearing Fees [Member] Commission and Clearing Fees [Member] Pension Benefits Adjustments, Footnote Pension Benefits Adjustments, Footnote [Text Block]