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
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

Defined Benefit Plan, Future Amortization of Gain (Loss), Plans Which Benefit Obligations Exceed Plan Assets

No definition available.

Name:	sif_DefinedBenefitPlanFutureAmortizationofGainLossPlansWhichBenefitObligationsExceedPlanAssets
Namespace Prefix:	sif_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration