Regulatory Requirements and Subsidiary Dividend Restrictions - Minimum net capital (Details)	Sep. 30, 2012
Capital and Other Regulatory Requirements [Abstract]
Ratio of Indebtedness to Net Capital	15
Ratio of Indebtedness to Net Capital - Equity Withdrawal Limitation	10

Ratio of Indebtedness is Indebtedness divided by net capital. This ratio represents the minimum allowable in case of an equity withdrawal.

No definition available.

Name:	intl_RatioOfIndebtednessToNetCapitalEquityWithdrawal
Namespace Prefix:	intl_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	instant