Employee Benefits (Details) $ in Millions	3 Months Ended
Mar. 31, 2019 USD ($) Employee shares
Benefit Plan [Abstract]
Number of former union employees covered by the plan \| Employee	19
Supplemental Executive Retirement Plan [Member]
Defined Contribution Pension and Other Postretirement Plans Disclosure [Abstract]
Employer discretionary contribution amount \| $	$ 0.3
Employee Stock Ownership Plan and Trust (ESOP) [Member]
Employee Stock Ownership Plan (ESOP), Debt Structure [Abstract]
Additional shares contributed to ESOP (in shares)	49,100
Shares released from trust (in shares)	49,100
Total remaining balance of shares in the ESOP (in shares)	200

No definition available.

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

- Definition

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

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

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

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Definition

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.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

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

- Definition

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

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 718
-SubTopic 40
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=109244661&loc=d3e17540-113929

+ Details

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

- Definition

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

+ References

+ Details

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

- Details

Name:	us-gaap_RetirementPlanTypeAxis=us-gaap_SupplementalEmployeeRetirementPlanDefinedBenefitMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EmployeeStockOwnershipPlanESOPDisclosuresByPlanAxis=smp_EmployeeStockOwnershipPlanAndTrustEsopMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: