INCOME TAXES (Details) - USD ($)	3 Months Ended	6 Months Ended
Jun. 29, 2019	Jun. 30, 2018	Jun. 29, 2019	Jun. 30, 2018
Uncertain Tax Benefits
Gross unrecognized tax benefits	$ 20,200,000		$ 20,200,000
Net unrecognized tax benefits	13,700,000		13,700,000
Net unrecognized tax benefits that would impact effective tax rate if recognized	10,300,000		10,300,000
Gross accrued interest	4,300,000		4,300,000
Net accrued interest	3,300,000		3,300,000
Penalties accrued	0		0
Other Tax Matters
Income tax provision	4,100,000	$ 400,000	8,700,000	$ 4,500,000
Pre-tax income (loss) from continuing operations	$ 23,500,000	$ 20,100,000	$ 28,700,000	$ 36,600,000
Effective income tax rate (as a percent)	17.40%	2.00%	30.30%	12.30%
Tax benefits related to U.S. tax credits and incentives	$ 1,300,000		$ 1,300,000
Excess tax benefits from stock-based compensation awards vested	400,000		1,600,000	$ 900,000
Tax benefit related to reductions in valuation allowances		$ 1,700,000		$ 1,700,000
Tax Cuts and Jobs Act of 2017, provisional charges		$ 1,100,000
Maximum
Uncertain Tax Benefits
Reasonably possible amount that unrecognized tax benefits could decrease within next 12 months, high end of range	$ 10,000,000.0		$ 10,000,000.0

Income Tax Expense (Benefit) Related To Valuation Allowances

No definition available.

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

- Definition

Represents the net (net of applicable income tax effect) amount of interest expense accrued as of the date of statement of financial position for underpayment of income taxes, computed by applying the applicable statutory rate of interest to the difference between a tax position recognized for financial reporting purposes and the amount previously taken or expected to be taken in a tax return of the entity.

+ References

No definition available.