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Retirement Benefit Plans - Amounts in Accumulated Other Comprehensive Loss Expected to be Recognized as Components of Net Periodic Benefit Costs (Details) $ in Thousands | 12 Months Ended
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Sep. 30, 2020 USD ($)
Retirement Benefits [Abstract] |
Net loss, plans in which assets exceed benefit obligations | $ 0
Net loss, plans in which benefit obligations exceed assets | $ 844

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- Definition Defined Benefit Plan, Future Amortization of Gain (Loss), Plans Which Assets Exceed Benefit Obligations + References No definition available. + Details
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Namespace Prefix: | sif_
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Balance Type: | credit
Period Type: | duration

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- Definition Defined Benefit Plan, Future Amortization of Gain (Loss), Plans Which Benefit Obligations Exceed Plan Assets + References No definition available. + Details
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Namespace Prefix: | sif_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_CompensationAndRetirementDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration