Credit Facilities - Senior Secured Notes (Details) - Senior Secured Notes due 2025 - USD ($)	1 Months Ended
Jun. 30, 2021	Dec. 31, 2021	Jun. 11, 2020
Line of Credit Facility [Line Items]
Debt instrument, face amount			$ 350,000,000
Debt instrument, interest rate, stated percentage		8.625%	8.625%
Debt instrument offering price, percentage		8.625%	98.50%
Repayment of senior secured notes	$ 1,600,000
Debt instrument purchase percentage	103.00%
Debt issuance costs, gross		$ 9,500,000

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

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

+ References

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+ Details

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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

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

- Definition

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

+ References

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+ Details

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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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Balance Type:	debit
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

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

- 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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Balance Type:	credit
Period Type:	duration

- Details

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Period Type: