Retirement Plans (Notes)	12 Months Ended
Sep. 30, 2018
Retirement Benefits [Abstract]
Pension and Other Postretirement Benefits Disclosure [Text Block]	Note 15 – Retirement Plans Defined Benefit Retirement Plans The Company has a frozen qualified defined benefit pension plan (the “Qualified Plan”) and a nonqualified defined benefit pension plan (the “Nonqualified Plan”), and recognizes their funded status, measured as the difference between the fair value of the plan assets and the projected benefit obligation, in “other assets” or “accounts payable and other accrued liabilities” in the consolidated balance sheets, depending on the funded status of each plan. The Qualified Plan assets, which are managed in a third-party trust, primarily consist of a diversified blend of approximately 80% debt securities and 20% equity investments and had a total fair value of $35.6 million and $36.3 million as of September 30, 2018 and 2017, respectively. All Qualified Plan assets fall within Level 2 of the fair value hierarchy. The benefit obligation associated with the Qualified Plan will vary over time only as a result of changes in market interest rates, the life expectancy of the plan participants, and benefit payments, since the accrual of benefits was suspended when the Qualified Plan was frozen in 2006. The benefit obligation was $32.5 million and $34.7 million and the discount rate assumption used in the measurement of this obligation was 4.20% and 3.75% as of September 30, 2018 and 2017, respectively. Related to the Qualified Plan, the Company’s net liability for retirement costs had a funded status of $3.1 million and $1.6 million as of September 30, 2018 and 2017, respectively. The Nonqualified Plan assets had a total fair value of less than $0.1 million as of September 30, 2018 and 2017. The benefit obligation associated with the Nonqualified Plan will vary over time only as a result of changes in market interest rates, the life expectancy of the plan participants, and benefit payments. There are no active participants in the Nonqualified plan. The benefit obligation was $1.6 million and $1.8 million as of September 30, 2018 and 2017, respectively. Related to the Nonqualified Plan, the Company’s unfunded pension obligation was $1.6 million and $1.7 million as of September 30, 2018 and 2017, respectively. The Company recognized a net periodic benefit $0.2 million and $0.3 million for the year ended September 30, 2018 and 2017, respectively. The net periodic benefit cost associated with the plans was $0.2 million for the year ended September 30, 2016. The expected long-term return on plan assets assumption is 4.50% for 2018. The Company made contributions of $1.0 million and $2.0 million to the plans in the years ended September 30, 2018 and 2017, respectively. The Company complies with minimum funding requirements. The estimated undiscounted future benefit payments are expected to be $2.1 million in 2019, $2.0 million in 2020, $2.0 million in 2021, $2.0 million in 2022, $2.0 million in 2023 and $9.7 million in 2024 through 2028. Defined Contribution Retirement Plans The Company offers participation in the INTL FCStone Inc. 401(k) Plan (“401(k) Plan”), a defined contribution plan providing retirement benefits to all domestic full-time non-temporary employees who have reached 21 years of age. Employees may contribute from 1% to 80% of their annual compensation to the 401(k) Plan, limited to a maximum annual amount as set periodically by the Internal Revenue Service. The Company makes matching contributions to the 401(k) Plan in an amount equal to 62.5% of each participant’s eligible elective deferral contribution to the 401(k) Plan, up to 8% of employee compensation. Matching contributions vest, by participant, based on the following years of service schedule: less than two years – none, after two years – 33%, after three years – 66%, and after four years – 100%. U.K. based employees of INTL FCStone are eligible to participate in a defined contribution pension plan. The Company contributes double the employee’s contribution up to 10% of total base salary for this plan. For this plan, employees are 100% vested in both the employee and employer contributions at all times. For fiscal years ended September 30, 2018, 2017, and 2016, the Company’s contribution to these defined contribution plans were $6.8 million, $6.1 million and $5.3 million, respectively.

Note 15 – Retirement Plans

Defined Benefit Retirement Plans

The Company has a frozen qualified defined benefit pension plan (the “Qualified Plan”) and a nonqualified defined benefit pension plan (the “Nonqualified Plan”), and recognizes their funded status, measured as the difference between the fair value of the plan assets and the projected benefit obligation, in “other assets” or “accounts payable and other accrued liabilities” in the consolidated balance sheets, depending on the funded status of each plan.

The Qualified Plan assets, which are managed in a third-party trust, primarily consist of a diversified blend of approximately 80% debt securities and 20% equity investments and had a total fair value of $35.6 million and $36.3 million as of September 30, 2018 and 2017, respectively. All Qualified Plan assets fall within Level 2 of the fair value hierarchy. The benefit obligation associated with the Qualified Plan will vary over time only as a result of changes in market interest rates, the life expectancy of the plan participants, and benefit payments, since the accrual of benefits was suspended when the Qualified Plan was frozen in 2006. The benefit obligation was $32.5 million and $34.7 million and the discount rate assumption used in the measurement of this obligation was 4.20% and 3.75% as of September 30, 2018 and 2017, respectively. Related to the Qualified Plan, the Company’s net liability for retirement costs had a funded status of $3.1 million and $1.6 million as of September 30, 2018 and 2017, respectively.

The Nonqualified Plan assets had a total fair value of less than $0.1 million as of September 30, 2018 and 2017. The benefit obligation associated with the Nonqualified Plan will vary over time only as a result of changes in market interest rates, the life expectancy of the plan participants, and benefit payments. There are no active participants in the Nonqualified plan. The benefit obligation was $1.6 million and $1.8 million as of September 30, 2018 and 2017, respectively. Related to the Nonqualified Plan, the Company’s unfunded pension obligation was $1.6 million and $1.7 million as of September 30, 2018 and 2017, respectively.

The Company recognized a net periodic benefit $0.2 million and $0.3 million for the year ended September 30, 2018 and 2017, respectively. The net periodic benefit cost associated with the plans was $0.2 million for the year ended September 30, 2016. The expected long-term return on plan assets assumption is 4.50% for 2018. The Company made contributions of $1.0 million and $2.0 million to the plans in the years ended September 30, 2018 and 2017, respectively. The Company complies with minimum funding requirements. The estimated undiscounted future benefit payments are expected to be $2.1 million in 2019, $2.0 million in 2020, $2.0 million in 2021, $2.0 million in 2022, $2.0 million in 2023 and $9.7 million in 2024 through 2028.

Defined Contribution Retirement Plans

The Company offers participation in the INTL FCStone Inc. 401(k) Plan (“401(k) Plan”), a defined contribution plan providing retirement benefits to all domestic full-time non-temporary employees who have reached 21 years of age. Employees may contribute from 1% to 80% of their annual compensation to the 401(k) Plan, limited to a maximum annual amount as set periodically by the Internal Revenue Service. The Company makes matching contributions to the 401(k) Plan in an amount equal to 62.5% of each participant’s eligible elective deferral contribution to the 401(k) Plan, up to 8% of employee compensation. Matching contributions vest, by participant, based on the following years of service schedule: less than two years – none, after two years – 33%, after three years – 66%, and after four years – 100%.

U.K. based employees of INTL FCStone are eligible to participate in a defined contribution pension plan. The Company contributes double the employee’s contribution up to 10% of total base salary for this plan. For this plan, employees are 100% vested in both the employee and employer contributions at all times.

For fiscal years ended September 30, 2018, 2017, and 2016, the Company’s contribution to these defined contribution plans were $6.8 million, $6.1 million and $5.3 million, respectively.