Name:	smp_DefinedContributionPensionAndOtherPostretirementPlansAbstract
Namespace Prefix:	smp_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Number of former union employees in the US covered by the plan.

No definition available.

Name:	smp_NumberOfFormerUnionEmployeesCoveredByThePlan
Namespace Prefix:	smp_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

Amount of discretionary contributions made by an employer to a defined contribution plan.

No definition available.

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

- References

No definition available.

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

The shares that, although not legally released, will be released by a future scheduled and committed debt service payment and will be allocated to employees for service rendered in the current accounting period. The ESOP documents typically define the period of service to which the shares relate. ESOP shares are released to compensate employees directly, to settle employer liabilities for other employee benefits, and to replace dividends on allocated shares that are used for debt service.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480489/718-40-50-1

Name:	us-gaap_EmployeeStockOwnershipPlanESOPNumberOfCommittedToBeReleasedShares
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	instant

This item represents the number of shares provided to the Employee Stock Ownership Plan (ESOP) during the period.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147480489/718-40-50-1

Name:	us-gaap_EmployeeStockOwnershipPlanESOPSharesContributedToESOP
Namespace Prefix:	us-gaap_
Data Type:	xbrli:sharesItemType
Balance Type:	na
Period Type:	duration

Sum of the allocated, committed-to-be-released and suspense shares of the entity held by the plan.