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Sale of Receivables (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2018 | Mar. 31, 2017
Sale of Receivables [Abstract] |  |
Sale of receivables to financial institutions | $ 157.5 | $ 179.7
Charge related to sale of receivables | $ 5.4 | $ 5.2

X
- Definition The amount of receivables sold during the period. + References No definition available. + Details
Name: | smp_SaleOfReceivables
Namespace Prefix: | smp_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

X
- Definition The amount of charges incurred relating to the sale of receivables during the reporting period. + References No definition available. + Details
Name: | smp_SaleOfReceivablesRelatedCharges
Namespace Prefix: | smp_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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