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INDEBTEDNESS - Company-owned Life Insurance (Details) - USD ($) $ in Millions | 9 Months Ended |
--- | --- | ---
Sep. 27, 2025 | Sep. 28, 2024 | Dec. 31, 2024
Debt Disclosure [Abstract] |  |  |
Borrowing from life insurance policy during period |  | $ 41.2 |
Repayment of borrowing from life insurance policy | $ 37.4 |  |
Borrowings from life insurance policies | $ 0.0 |  | $ 39.0
Life insurance, corporate or bank owned, interest rate | 5.30% |  | 5.30%
Life insurance policy, maximum borrowing capacity | $ 35.0 |  |
Life insurance, corporate or bank owned, amount | $ 60.9 |  | $ 36.2

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- Definition Borrowing From Life Insurance Policy + References No definition available. + Details
Name: | spxc_BorrowingFromLifeInsurancePolicy
Namespace Prefix: | spxc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Borrowing From Life Insurance Policy During Period + References No definition available. + Details
Name: | spxc_BorrowingFromLifeInsurancePolicyDuringPeriod
Namespace Prefix: | spxc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Life Insurance, Corporate or Bank Owned, Interest Rate + References No definition available. + Details
Name: | spxc_LifeInsuranceCorporateOrBankOwnedInterestRate
Namespace Prefix: | spxc_
Data Type: | dtr-types:percentItemType
Balance Type: | na
Period Type: | instant

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- Definition Life Insurance Policy, Maximum Borrowing Capacity + References No definition available. + Details
Name: | spxc_LifeInsurancePolicyMaximumBorrowingCapacity
Namespace Prefix: | spxc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Repayment Of Borrowing From Life Insurance Policy + References No definition available. + Details
Name: | spxc_RepaymentOfBorrowingFromLifeInsurancePolicy
Namespace Prefix: | spxc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_DebtDisclosureAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition This item represents the amount that could be realized under a life insurance contract or contracts owned by the Entity as of the date of the statement of financial position. Such Entity-owned life insurance policies are commonly known as corporate-owned life insurance (COLI) or bank-owned life insurance (BOLI). + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Topic 210 -SubTopic 10 -Name Accounting Standards Codification -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02(12)) -Publisher FASB -URI https://asc.fasb.org/1943274/2147480566/210-10-S99-1 Reference 2: http://www.xbrl.org/2003/role/disclosureRef -Topic 325 -SubTopic 30 -Name Accounting Standards Codification -Section 25 -Paragraph 1 -Publisher FASB -URI https://asc.fasb.org/1943274/2147481612/325-30-25-1 + Details
Name: | us-gaap_LifeInsuranceCorporateOrBankOwnedAmount
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant