Credit Facilities (Details) - USD ($) $ in Millions	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2013	May. 05, 2015
Line of Credit Facility [Line Items]
Short-term Debt	$ 38.0
Proceeds from notes payable	4.0	$ 0.0	$ 0.0
Payables to lenders under loans	41.6	22.5
Notes Payable to Bank	3.6	0.0
Senior Notes	$ 45.5	45.5
Debt Instrument, Interest Rate, Stated Percentage	8.50%
Debt Instrument, Call Feature, Redemption Price Percentage of Principal	100.00%
Debt Issuance Cost	$ 1.7
Debt and Capital Lease Obligations	$ 87.1	68.0
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	5.25%
Line of Credit Facility, Maximum Borrowing Capacity	$ 140.0
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.625%
Payables to lenders under loans	$ 28.0	15.0
Debt Issuance Cost	$ 1.5
INTL FCStone Financial Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	5.25%
Line of Credit Facility, Maximum Borrowing Capacity	$ 75.0			$ 50.0
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.50%
Payables to lenders under loans	$ 0.0	0.0
INTL FCStone Financial [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	0.0
Payables to lenders under loans	$ 0.0	0.0
FMS Sub-note commodity line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Interest Rate at Period End	4.25%
Line of Credit Facility, Maximum Borrowing Capacity	$ 40.0
Line of Credit Facility, Unused Capacity, Commitment Fee Percentage	0.50%
Payables to lenders under loans	$ 10.0	7.5
INTL FCStone, Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	25.0
Payables to lenders under loans	0.0	$ 0.0
Main line of credit facilities [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	280.0
Line of Credit Facility, Current Borrowing Capacity	$ 255.0