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Pension Plan - Additional Information (Detail) (USD $)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Contributions and Recognized Pension Costs under Labor Pension Act $ 872,000us-gaap_PensionContributions $ 788,000us-gaap_PensionContributions $ 716,000us-gaap_PensionContributions
Contributions Based on Percentage Employee Salaries under Labor Standards Law 2.00%simo_DefinedBenefitPlanContributionsPercentOfCompensation    
Estimated Future Contributions under Labor Standards Law in 2015 57,000us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear    
Accumulated benefit obligation 1,762,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation 1,369,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation 1,332,000us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Estimated amortization of net gain from accumulated other comprehensive income into net periodic benefit cost over the next fiscal year 26,000us-gaap_DefinedBenefitPlanFutureAmortizationOfGainLoss    
FCI      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Estimated Future Contributions under Labor Standards Law in 2015 1,052,000us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear
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Fair Value, Inputs, Level 2 | FCI's Pension Plan Assets      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Concentration of risk $ 0us-gaap_FairValueConcentrationOfRiskInvestments
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$ 0us-gaap_FairValueConcentrationOfRiskInvestments
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Minimum      
Defined Benefit Plans and Other Postretirement Benefit Plans Table Text Block [Line Items]      
Percentage of Contribution by an Employer to Employees Pension 6.00%simo_PercentageOfPensionPaymentToEmployeeBenefits
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