Credit Facilities - Number of Credit Facilities (Details)	12 Months Ended
	Sep. 30, 2018 USD ($) Rate	May 05, 2015 USD ($)
Line of Credit Facility [Line Items]
Number of credit facilities	4
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 150.0
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage | Rate	0.625%
Line of Credit Facility, Interest Rate at Period End | Rate	5.17%
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 262,000,000
HCO Syndicated line of credit facility [Member] | Eurodollar Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	3.00%
HCO Syndicated line of credit facility [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%
INTL FCStone, Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 25,000,000
INTL FCStone, Ltd [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.50%
INTL FCStone Financial Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage | Rate	0.50%
Line of Credit Facility, Interest Rate at Period End | Rate	7.25%
Line of Credit Facility, Maximum Borrowing Capacity | $	$ 75,000,000	$ 75,000,000
INTL FCStone Financial Margin line of credit facility [Member] | Base Rate [Member]
Line of Credit Facility [Line Items]
Debt Instrument, Basis Spread on Variable Rate	2.00%