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Basis of Presentation and Summary of Significant Accounting Policies - Revenue Recognition (Details) $ in Millions	12 Months Ended
	Dec. 31, 2017 USD ($)
Accounting Policies [Abstract]
Revenue under percentage of completion	$ 255.5

X

- Definition

Represents the revenue recognized during the period using the percentage-of-completion method.

+ References

No definition available.

+ Details

Name:	spxc_RevenueUnderPercentageOfCompletionMethod
Namespace Prefix:	spxc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

X

- References

No definition available.

+ Details

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