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Summary Of Significant Accounting Policies - Additional Information (Detail) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 USD ($) Customer | Dec. 31, 2013 USD ($) Customer | Dec. 31, 2012 USD ($) Customer | Dec. 31, 2012 TWD | Dec. 31, 2014 Customers accounted for 10% or more Net revenue | Dec. 31, 2013 Customers accounted for 10% or more Net revenue | Dec. 31, 2012 Customers accounted for 10% or more Net revenue | Dec. 31, 2014 Amended in August 2012 TWD | Dec. 31, 2014 Minimum | Dec. 31, 2014 Maximum | Dec. 31, 2014 American Depositary Shares | Dec. 31, 2013 American Depositary Shares | Dec. 31, 2012 American Depositary Shares | Dec. 31, 2014 Ordinary Shares | Dec. 31, 2013 Ordinary Shares | Dec. 31, 2012 Ordinary Shares | Dec. 31, 2014 Software Minimum | Dec. 31, 2014 Software Maximum | Dec. 31, 2014 Core technology and customer relationship | Dec. 31, 2014 Buildings Minimum | Dec. 31, 2014 Buildings Maximum | Dec. 31, 2014 Machinery and Equipment Minimum | Dec. 31, 2014 Machinery and Equipment Maximum | Dec. 31, 2014 Furniture and Fixtures Minimum | Dec. 31, 2014 Furniture and Fixtures Maximum | Dec. 31, 2014 Leasehold And Building Improvement Minimum | Dec. 31, 2014 Leasehold And Building Improvement Maximum | Dec. 31, 2014 FCI
Significant Accounting Policies [Line Items] |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Consolidated interest acquire in subsidiary | 100.00%simo_PercentageOfOwnershipInterestAcquired |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 99.90%simo_PercentageOfOwnershipInterestAcquired / dei_LegalEntityAxis = simo_FciIncMember
Top ten customer sales in percentage | 76.00%simo_PercentageOfTotalRevenueAccountedForByTopTenCustomers | 76.00%simo_PercentageOfTotalRevenueAccountedForByTopTenCustomers | 75.00%simo_PercentageOfTotalRevenueAccountedForByTopTenCustomers | 75.00%simo_PercentageOfTotalRevenueAccountedForByTopTenCustomers |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Major customers percentage of net sales |  |  |  |  | 47.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember | 46.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember | 35.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = us-gaap_CustomerConcentrationRiskMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Number of customers accounted for 10% or more sales | 2 simo_NumberOfCustomersAccountingForTenPercentOrMoreOfConsolidatedRevenue | 2 simo_NumberOfCustomersAccountingForTenPercentOrMoreOfConsolidatedRevenue | 1 simo_NumberOfCustomersAccountingForTenPercentOrMoreOfConsolidatedRevenue | 1 simo_NumberOfCustomersAccountingForTenPercentOrMoreOfConsolidatedRevenue |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Short term investment maturity period |  |  |  |  |  |  |  |  | 3 months | 1 year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Property plant and equipment estimated useful life |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 1 year | 5 years |  | 25 years | 50 years | 3 years | 6 years | 3 years | 8 years | 2 years | 6 years |
Depreciation and amortization | $ 6,917 us-gaap_DepreciationDepletionAndAmortization | $ 6,429 us-gaap_DepreciationDepletionAndAmortization | $ 5,881 us-gaap_DepreciationDepletionAndAmortization |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Intangible asset amortized over estimated useful lives |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  | 4 years |  |  |  |  |  |  |  |  |
Warranty period for manufacturing defects of products | 1 year |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Evaluation of tax benefits realized upon settlement | 50.00%simo_PercentageOfIncomeTaxExaminationMinimumLikelihoodOfTaxBenefitsBeingRealizedUponUltimateSettlement |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Income tax under IBT act effective date | January 1, 2006 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Minimum Alternative Tax On Income under IBT act | 12.00%simo_MinimumAlternativeTaxOnIncomeAtForeignCountry |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Standard deduction tax amount |  |  |  | 1,000 us-gaap_IncomeTaxReconciliationDeductions |  |  |  | 500 us-gaap_IncomeTaxReconciliationDeductions / us-gaap_IncomeTaxAuthorityAxis = simo_AmendedMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Standard deduction tax rate |  |  | 10.00%us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsOther | 10.00%us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsOther |  |  |  | 12.00%us-gaap_EffectiveIncomeTaxRateReconciliationDeductionsOther / us-gaap_IncomeTaxAuthorityAxis = simo_AmendedMember |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
Amendment Effective Date |  |  |  |  |  |  |  | January 1, 2013 |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |  |
The effect of dilutive securities of employee stock options and restricted stock units |  |  |  |  |  |  |  |  |  |  | 546 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = simo_AmericanDepositaryShareMember | 577 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = simo_AmericanDepositaryShareMember | 1,311 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount / us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis = simo_AmericanDepositaryShareMember | 2,183 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember | 2,308 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember | 5,245 us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount / us-gaap_StatementEquityComponentsAxis = us-gaap_CommonStockMember |  |  |  |  |  |  |  |  |  |  |  |

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- Definition Percentage of the difference between reported income tax expense (benefit) and expected income tax expense (benefit) computed by applying the domestic federal statutory income tax rates to pretax income (loss) from continuing operations attributable to other deductions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 12 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32687-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SAB TOPIC 6.I) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330036-122817 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 13 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32698-109319 + Details
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