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Subsequent events - Narrative (Details) - IAM National Pension Fund - Subsequent event $ in Thousands | Nov. 26, 2019 USD ($) union
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Subsequent Event [Line Items] |
Number of unions | union | 1
Withdrawal liability | $ | $ 745
Payment period | 20 years

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- Definition Multiemployer Plans, Number Of Unions, Ratified Collective Bargaining Agreement + References No definition available. + Details
Name: | sif_MultiemployerPlansNumberOfUnionsRatifiedCollectiveBargainingAgreement
Namespace Prefix: | sif_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Definition Multiemployer Plans, Withdrawal Obligation, Payment Period + References No definition available. + Details
Name: | sif_MultiemployerPlansWithdrawalObligationPaymentPeriod
Namespace Prefix: | sif_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Amount of the obligation recognized by withdrawing from a pension or postretirement benefit plan to which two or more unrelated employers contribute where assets contributed by one participating employer may be used to provide benefits to employees of other participating employers. + References No definition available. + Details
Name: | us-gaap_MultiemployerPlansWithdrawalObligation
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_MultiemployerPlanNameAxis=sif_IAMNationalPensionFundMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |