Assets and Liabilities, at Fair Value - Suriwongse Bonds (Details) $ in Millions	Sep. 30, 2016 USD ($)
Assets and Liabilities, at Fair Value [Abstract]
Suriwongse Debt Investment Balance	$ 3.0

Suriwongse Debt Investment Balance - Investment in Suriwongse hotel

No definition available.

Name:	intl_SuriwongseDebtInvestmentBalance
Namespace Prefix:	intl_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant