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Summary of Significant Accounting Policies, Concentrations of Credit Risk and Foreign Cash Balances (Details) $ in Millions | 12 Months Ended |
--- | --- | ---
Dec. 31, 2021 USD ($) Customer | Dec. 31, 2020 USD ($)
Foreign Cash Balances [Abstract] |  |
Foreign cash balance | $ | $ 16.8 | $ 16.4
Customer Concentration Risk [Member] |  |
Concentration Risk [Abstract] |  |
Number of largest individual customers | Customer | 3 |

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- Definition Cash balances held in foreign currencies. + References No definition available. + Details
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Namespace Prefix: | smp_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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

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- Definition Represents the number of largest individual customers, including members of a marketing group. + References No definition available. + Details
Name: | smp_NumberOfLargestIndividualCustomers
Namespace Prefix: | smp_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | duration

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

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- Details
Name: | us-gaap_ConcentrationRiskByTypeAxis=us-gaap_CustomerConcentrationRiskMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |