Credit Facilities - Number of Credit Facilities (Details) $ in Millions	Jun. 30, 2019 USD ($)	Mar. 31, 2019	Dec. 31, 2018 USD ($)
Number of credit facilities		4
HCO Syndicated line of credit facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 350.0		$ 262.0
Line of Credit Facility, Remaining Borrowing Capacity	345.6
FCS Margin line of credit facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	75.0
FMS Sub-note commodity line of credit facility [Member]
Line of Credit Facility, Maximum Borrowing Capacity	232.5
INTL FCStone Ltd [Member]
Line of Credit Facility, Maximum Borrowing Capacity	100.0
INTL FCStone Ltd [Member]
Line of Credit Facility, Maximum Borrowing Capacity	$ 50.0		$ 25.0