Credit Facilities - Credit Facilities (Details) (USD $) In Millions, unless otherwise specified	6 Months Ended
	Mar. 31, 2015	Sep. 30, 2015	Sep. 30, 2014	May 05, 2015	Apr. 21, 2015
Line of Credit Facility [Line Items]
Line of Credit Facility, Amount Outstanding	$ 45.8		$ 22.5
Senior unsecured notes	45.5	45.5	45.5
Debt and Capital Lease Obligations	91.3		68.0
Debt Instrument, Interest Rate, Stated Percentage	8.50%
Debt Instrument, Call Feature, Redemption Price Percentage of Principal	100.00%
Debt Issuance Cost	1.7
Main line of credit facilities [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	270.0
Line of Credit Facility, Current Borrowing Capacity	140
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	140.0
Line of Credit Facility, Amount Outstanding	25.0		15.0
FCS Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	75.0			50.0
Line of Credit Facility, Amount Outstanding	0		0
FMS Sub-note commodity line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	30.0				40.0
Line of Credit Facility, Amount Outstanding	20.8		7.5
INTL FCStone Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	25.0
Line of Credit Facility, Amount Outstanding	$ 0		$ 0