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Commitments and Contingencies - Additional Information (Details) $ in Millions	12 Months Ended
	Dec. 31, 2020 USD ($)
Commitments Disclosure [Line Items]
Amount outstanding performance and financial standby letters of credit	$ 25.2
Minimum
Commitments Disclosure [Line Items]
Warranty period	1 year
Maximum
Commitments Disclosure [Line Items]
Warranty period	5 years
Property Lease Guarantee
Commitments Disclosure [Line Items]
Repurchase obligation, single year potential cash payments	$ 4.1
Repurchase obligation, maximum potential cash payments	$ 4.1

X

- Definition

Commitments Disclosure [Line Items]

+ References

No definition available.

+ Details

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Namespace Prefix:	fss_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Definition

Guarantor Obligations, Maximum Exposure, Undiscounted, Annual Amount

+ References

No definition available.

+ Details

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Namespace Prefix:	fss_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Definition

Term of standard product warranty.

+ References

No definition available.

+ Details

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Balance Type:	na
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X

- Definition

Maximum potential amount of future payments (undiscounted) the guarantor could be required to make under the guarantee or each group of similar guarantees before reduction for potential recoveries under recourse or collateralization provisions.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 460
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=121555522&loc=d3e12069-110248

+ Details

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Namespace Prefix:	us-gaap_
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Balance Type:	credit
Period Type:	instant

X

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

X

- Details

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- Details

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X

- Details

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