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Description of Business and Significant Accounting Policies - Notes Receivable - Participation (Details) | Sep. 30, 2017 | Sep. 30, 2016
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Minimum [Member] |  |
Short Term Notes Receivable Outstanding Balance Threshold, Percentage | 90.00% | 90.00%
Maximum [Member] |  |
Short Term Notes Receivable Outstanding Balance Threshold, Percentage | 98.00% | 98.00%

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- Definition Short Term Notes Receivable Outstanding Balance Threshold, Percentage + References No definition available. + Details
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Namespace Prefix: | intl_
Data Type: | num:percentItemType
Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |