Credit Facilities - Credit Facilities (Details) - USD ($) $ in Millions	3 Months Ended	6 Months Ended
	Mar. 31, 2016	Mar. 31, 2016	Mar. 15, 2016	Sep. 30, 2015	May. 05, 2015
Line of Credit Facility [Line Items]
Short-term Debt	$ 148.3	$ 148.3		$ 38.0
Proceeds from note payable		4.0
Lenders under loans	151.5	151.5		41.6
Notes Payable to Bank	3.2	3.2		3.6
Senior unsecured notes	45.5	45.5		45.5
Debt and Capital Lease Obligations	$ 197.0	$ 197.0		87.1
Debt Instrument, Interest Rate, Stated Percentage	8.50%	8.50%
Debt Instrument, Call Feature, Redemption Price Percentage of Principal	100.00%	100.00%
Debt Issuance Cost	$ 1.8	$ 1.7
Main line of credit facilities [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	165.0	165.0
Line of Credit Facility, Maximum Borrowing Capacity	370.0	370.0
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	205.0	205.0
Lenders under loans	105.9	105.9		28.0
FCS Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	75.0	75.0			$ 50.0
Lenders under loans	0.0	0.0		0.0
FCStone LLC [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	0.0	0.0
Lenders under loans	0.0	0.0		0.0
FMS Sub-note commodity line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	65.0	65.0	$ 40.0
Lenders under loans	42.4	42.4		10.0
INTL FCStone Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	25.0	25.0
Lenders under loans	$ 0.0	$ 0.0		$ 0.0