Segment and Geographic Information - Reportable Segments (Details)	12 Months Ended
Sep. 30, 2013
Segment Analysis [Abstract]
Number of different types of foreign currencies	130

Number of different types of foreign currencies the company trades

No definition available.

Name:	intl_NumberOfDifferentTypesOfForeignCurrencies
Namespace Prefix:	intl_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration