INFORMATION ON REPORTABLE AND OTHER OPERATING SEGMENTS (Details) $ in Millions	3 Months Ended
Mar. 28, 2020 USD ($) country	Mar. 30, 2019 USD ($)
Information on reportable segments and other operating segments
Number of countries in which entity operates (over 15 countries) \| country	17
Revenues:
Revenues	$ 369.3	$ 343.6
Income (loss):
Consolidated operating income	32.7	3.0
Special charges, net	(0.3)	(0.1)
Other operating income (expense)	0.4	(1.8)
Operating Segments
Income (loss):
Consolidated operating income	47.2	20.8
Corporate
Income (loss):
Corporate expense	(11.1)	(12.4)
Special charges, net	0.0	0.0
Segment Reconciling Items
Income (loss):
Long-term incentive compensation expense	(3.5)	(3.5)
Special charges, net	(0.3)	(0.1)
Other operating income (expense)	0.4	(1.8)
HVAC reportable segment
Revenues:
Revenues	118.5	128.4
Income (loss):
Special charges, net	(0.1)	(0.1)
HVAC reportable segment \| Operating Segments
Income (loss):
Consolidated operating income	15.0	18.4
Detection and Measurement reportable segment
Revenues:
Revenues	91.9	85.1
Income (loss):
Special charges, net	0.0	0.0
Detection and Measurement reportable segment \| Operating Segments
Income (loss):
Consolidated operating income	18.2	17.0
Engineered Solutions reportable segment
Revenues:
Revenues	154.9	138.0
Income (loss):
Special charges, net	0.0	0.0
Engineered Solutions reportable segment \| Operating Segments
Income (loss):
Consolidated operating income	17.9	8.0
All Other
Revenues:
Revenues	4.0	(7.9)
Income (loss):
Consolidated operating income	(3.9)	(22.6)
Special charges, net	$ (0.2)	0.0
Minimum
Information on reportable segments and other operating segments
Number of countries in which entity sells its products and services (over 100 countries) \| country	100
Contracts Accounted for under Percentage of Completion \| South Africa \| Large Power Projects \| All Other \| Operating Segments
Revenues:
Revenues	$ 0.3	$ (17.5)

Represents the number of countries in which the entity sells its products and services.

No definition available.

Name:	spxc_NumberOfCountriesInWhichEntitySellsItsProductsAndServices
Namespace Prefix:	spxc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The amount of expenses at the corporate level which are not otherwise separately disclosed and are not allocated to the reportable segments or other operating segments for reporting purposes.

+ References

No definition available.

+ Details

Name:	spxc_OperatingExpense
Namespace Prefix:	spxc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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

Amount of expense for award under share-based payment arrangement. Excludes amount capitalized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5047-113901

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SAB Topic 14.F)
-URI http://asc.fasb.org/extlink&oid=115993241&loc=d3e301413-122809

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (h)(1)(i)
-URI http://asc.fasb.org/extlink&oid=116856206&loc=d3e5070-113901

+ Details

Name:	us-gaap_AllocatedShareBasedCompensationExpense
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The number of countries in which the entity operates as of balance sheet date.

+ References

No definition available.

+ Details

Name:	us-gaap_NumberOfCountriesInWhichEntityOperates
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The net result for the period of deducting operating expenses from operating revenues.

+ References

No definition available.

+ Details

Name:	us-gaap_OperatingIncomeLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

The net amount of other operating income and expenses, the components of which are not separately disclosed on the income statement, from items that are associated with the entity's normal revenue producing operations.

+ References

No definition available.

+ Details

Name:	us-gaap_OtherOperatingIncomeExpenseNet
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130543-203045

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118956577&loc=SL49130545-203045

+ Details

Name:	us-gaap_RevenueFromContractWithCustomerExcludingAssessedTax
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_SegmentReportingInformationLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_OperatingSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_CorporateNonSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_ConsolidationItemsAxis=us-gaap_MaterialReconcilingItemsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=spxc_HVACReportableSegmentMember
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:

- Details

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

- Details

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

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ChangeInAccountingEstimateByTypeAxis=us-gaap_ContractsAccountedForUnderPercentageOfCompletionMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_StatementGeographicalAxis=country_ZA
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_TypeOfArrangementAxis=spxc_LargePowerProjectsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: