Special Charges, Net - Narrative (Details) $ in Millions	12 Months Ended
Dec. 31, 2021 USD ($) employee	Dec. 31, 2020 USD ($) employee	Dec. 31, 2019 USD ($) employee
Special charges, net
Special charges, net \| $	$ 1.0	$ 2.4	$ 1.5
Period for selling an asset	1 year
Period for settling liabilities	1 year
HVAC reportable segment \| Employee Termination Costs
Special charges, net
Number of employees terminated	6	11	19
Detection and Measurement reportable segment \| Employee Termination Costs
Special charges, net
Number of employees terminated	44	5

Period within which the entity expects to sell an asset (in years) in order to qualify as a discontinued operation.

No definition available.

Name:	spxc_PeriodWithinWhichAssetWillBeSold
Namespace Prefix:	spxc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Represents the period within which the liabilities related to restructuring actions will be settled.

+ References

No definition available.

+ Details

Name:	spxc_PeriodWithinWhichLiabilitiesWillBeSettled
Namespace Prefix:	spxc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount charged against earnings in the period for incurred and estimated costs associated with an exit from business activities or restructuring pursuant to a duly authorized plan, excluding asset retirement obligations. Such costs include charges associated with employee terminations, lease terminations, asset impairments, etc.

+ References

No definition available.

+ Details

Name:	spxc_SpecialCharges
Namespace Prefix:	spxc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of positions eliminated during the period as a result of restructuring activities.

+ References

No definition available.

+ Details

Name:	us-gaap_RestructuringAndRelatedCostNumberOfPositionsEliminated
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- 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_RestructuringCostAndReserveLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=spxc_HVACReportableSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RestructuringCostAndReserveAxis=us-gaap_OneTimeTerminationBenefitsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=spxc_DetectionandMeasurementReportableSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: