Credit Facilities - Credit Facilities (Details) - USD ($) $ in Millions	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	May 05, 2015	Jul. 31, 2013
Line of Credit Facility [Line Items]
Short-term Debt	$ 261.0		$ 180.0
Lenders under loans	263.4		182.8
Notes Payable to Bank	2.4		2.8
Senior unsecured notes	0.0		44.5		$ 45.5
Debt and Capital Lease Obligations	263.4		227.3
Debt Instrument, Interest Rate, Stated Percentage		8.50%
Main line of credit facilities [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Current Borrowing Capacity	200.0
Line of Credit Facility, Maximum Borrowing Capacity	447.0
HCO Syndicated line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	247.0
Lenders under loans	175.0		136.5
FCS Margin line of credit facility [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	75.0			$ 50.0
Lenders under loans	0.0		0.0
FCStone LLC [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	0.0
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, Maximum Borrowing Capacity	100.0
Lenders under loans	86.0		43.5
INTL FCStone Ltd [Member]
Line of Credit Facility [Line Items]
Line of Credit Facility, Maximum Borrowing Capacity	25.0
Lenders under loans	$ 0.0		$ 0.0