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Acquisitions - Narrative (Details) $ in Millions | Oct. 04, 2021 USD ($)
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Ground Force |
Business Acquisition [Line Items] |
Purchase price, inclusive of preliminary closing adjustments | $ 43.1

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- Definition Acquisition purchase price, inclusive of preliminary closing adjustments. + References No definition available. + Details
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Namespace Prefix: | fss_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
Name: | us-gaap_BusinessAcquisitionLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_BusinessAcquisitionAxis=fss_GroundForceMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |