Debt Instrument, Discount Rate at Issuance of Face Value

No definition available.

Name:	intl_DebtInstrumentDiscountRateAtIssuanceOfFaceValue
Namespace Prefix:	intl_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Debt Instrument Remaining Outstanding

+ References

No definition available.

+ Details

Name:	intl_DebtInstrumentRemainingOutstanding
Namespace Prefix:	intl_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Face (par) amount of debt instrument at time of issuance.

+ References

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-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
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+ Details

Name:	us-gaap_DebtInstrumentFaceAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Contractual interest rate for funds borrowed, under the debt agreement.

+ References

+ Details

Name:	us-gaap_DebtInstrumentInterestRateStatedPercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

Name:	us-gaap_DebtInstrumentLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage price of original principal amount of debt at which debt can be redeemed by the issuer.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
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-Section 50
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+ Details

Name:	us-gaap_DebtInstrumentRedemptionPricePercentage
Namespace Prefix:	us-gaap_
Data Type:	dtr-types:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount, before accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The cash outflow for a long-term debt where the holder has highest claim on the entity's asset in case of bankruptcy or liquidation during the period.

+ References

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+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LongtermDebtTypeAxis=us-gaap_SeniorNotesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_BusinessAcquisitionAxis=intl_GainCapitalHoldingsIncMember
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Credit Facilities - Senior Secured Notes due 2025 (Details) - USD ($)	12 Months Ended
	Sep. 30, 2022	Sep. 30, 2021	Sep. 30, 2020	Jun. 30, 2020
Debt Instrument [Line Items]
Repayments of senior secured notes	$ 500,000	$ 1,600,000	$ 92,100,000
Senior Notes Due Twenty Twenty Five
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage	8.625%
Senior Notes Due Twenty Twenty Five \| Senior Notes
Debt Instrument [Line Items]
Debt instrument, face amount				$ 350,000,000
Debt instrument, interest rate, stated percentage	8.625%			8.625%
Debt instrument offering price, percentage				98.50%
Debt issuance costs, gross	$ 9,500,000
Debt instrument, redemption price, percentage		103.00%
Repayments of senior secured notes		$ 1,600,000
Senior Notes Due Twenty Twenty Five \| Senior Notes \| Gain Capital Holdings Inc
Debt Instrument [Line Items]
Debt instrument, interest rate, stated percentage				5.00%
Debt instrument remaining outstanding	$ 500,000