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Earnings Per Share (Details) (USD $) In Thousands, except Share data, unless otherwise specified | 3 Months Ended
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Mar. 31, 2015 | Mar. 31, 2014
Basic Net Earnings Per Common Shares [Abstract] |  |
Earnings from continuing operations | $ 9,339 us-gaap_IncomeLossFromContinuingOperations | $ 12,407 us-gaap_IncomeLossFromContinuingOperations
Loss from discontinued operation | (391)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | (682)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity
Net earnings available to common stockholders | 8,948 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic | 11,725 us-gaap_NetIncomeLossAvailableToCommonStockholdersBasic
Weighted average common shares outstanding (in shares) | 22,910,889 us-gaap_WeightedAverageNumberOfSharesOutstandingBasic | 22,947,241 us-gaap_WeightedAverageNumberOfSharesOutstandingBasic
Earnings from continuing operations per common share (in dollars per share) | $ 0.41 us-gaap_IncomeLossFromContinuingOperationsPerBasicShare | $ 0.54 us-gaap_IncomeLossFromContinuingOperationsPerBasicShare
Loss from discontinued operations per common share (in dollars per share) | $ (0.02)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare | $ (0.03)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerBasicShare
Net earnings per common share - Basic (in dollars per share) | $ 0.39 us-gaap_EarningsPerShareBasic | $ 0.51 us-gaap_EarningsPerShareBasic
Diluted Net Earnings Per Common Share [Abstract] |  |
Earnings from continuing operations | 9,339 us-gaap_IncomeLossFromContinuingOperations | 12,407 us-gaap_IncomeLossFromContinuingOperations
Loss from discontinued operation | (391)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity | (682)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxAttributableToReportingEntity
Net earnings available to common stockholders | $ 8,948 us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted | $ 11,725 us-gaap_NetIncomeLossAvailableToCommonStockholdersDiluted
Plus incremental shares from assumed conversions [Abstract] |  |
Dilutive effect of restricted stock and performance stock (in shares) | 323,000 smp_IncrementalCommonSharesAttributableToRestrictedAndPerformanceStock | 272,000 smp_IncrementalCommonSharesAttributableToRestrictedAndPerformanceStock
Dilutive effect of stock options (in shares) | 4,000 us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements | 6,000 us-gaap_IncrementalCommonSharesAttributableToShareBasedPaymentArrangements
Weighted average common shares outstanding - Diluted (in shares) | 23,238,050 us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding | 23,224,698 us-gaap_WeightedAverageNumberOfDilutedSharesOutstanding
Earnings from continuing operations per common share (in dollars per share) | $ 0.40 us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare | $ 0.53 us-gaap_IncomeLossFromContinuingOperationsPerDilutedShare
Loss from discontinued operations per common share (in dollars per share) | $ (0.01)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare | $ (0.03)us-gaap_IncomeLossFromDiscontinuedOperationsNetOfTaxPerDilutedShare
Net earnings per common share - Diluted (in dollars per share) | $ 0.39 us-gaap_EarningsPerShareDiluted | $ 0.50 us-gaap_EarningsPerShareDiluted
Stock Options [Member] |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |
Antidilutive securities excluded from computation of earnings per share (in shares) | 3,000 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember | 6,000 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = us-gaap_EmployeeStockOptionMember
Restricted and Performance Shares [Member] |  |
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items] |  |
Antidilutive securities excluded from computation of earnings per share (in shares) | 358,000 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = smp_RestrictedAndPerformanceBasedSharesMember | 308,000 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = smp_RestrictedAndPerformanceBasedSharesMember

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- Definition The amount of net income (loss) for the period per each share of common stock or unit outstanding during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1252-109256 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 55 -Paragraph 52 -URI http://asc.fasb.org/extlink&oid=32703322&loc=d3e4984-109258 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.21) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 944 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.7-04.19) -URI http://asc.fasb.org/extlink&oid=6879464&loc=d3e573970-122913 Reference 6: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04.23) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 7: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 18 -Article 7 Reference 8: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 20 -Article 5 Reference 9: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 21 -Article 9 + Details
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- Definition The amount of net income (loss) for the period available to each share of common stock or common unit outstanding during the reporting period and to each share or unit that would have been outstanding assuming the issuance of common shares or units for all dilutive potential common shares or units outstanding during the reporting period. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=7655603&loc=d3e1252-109256 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.21) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 18 -Article 7 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 20 -Article 5 Reference 5: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Paragraph 21 -Article 9 + Details
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- Definition Amount of income (loss) from continuing operations attributable to the parent. Also defined as revenue less expenses and taxes from ongoing operations before extraordinary items but after deduction of those portions of income or loss from continuing operations that are allocable to noncontrolling interests. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3602-108585 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 260 -SubTopic 10 -Section 50 -Paragraph 1 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6371337&loc=d3e3550-109257 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 810 -SubTopic 10 -Section 45 -Paragraph 18 -URI http://asc.fasb.org/extlink&oid=7656940&loc=SL4613673-111683 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.13) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 + Details
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