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Equity Incentive Plan - Additional Information (Detail) (USD $)
In Thousands, except Share data, unless otherwise specified
 1 Months Ended 12 Months Ended
Apr. 30, 2010
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2009
Dec. 31, 2006
Dec. 31, 2004
Dec. 31, 2011
Apr. 22, 2005
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Number of option outstanding   1,058,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber 1,410,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber 1,697,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber       1,849,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber  
Number of option exercisable   1,058,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber              
Stock option exchange for new stock option granted 4,369,000simo_StockOptionsSubjectToAndExchangedInOptionExchangeProgram                
Stock options exercise price $ 1.47simo_OptionsExchangedUnderOptionExchangeProgramExercisePricePerShare                
Eligible stock options exchanged for new stock options granted 3,785,000simo_NumberOfOptionsExchangedUnderOptionExchangeProgram                
Stock Option Granted   0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod 0us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriod          
Stock Option Granted Intrinsic Value   $ 1,565us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 $ 594us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1 $ 318us-gaap_SharebasedCompensationArrangementBySharebasedPaymentAwardOptionsExercisableIntrinsicValue1          
Total unrecognized compensation cost related to non-vested share-based compensation                   
Cash received from employee toward stock option exercise   514us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions 422us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions 224us-gaap_EmployeeServiceShareBasedCompensationCashReceivedFromExerciseOfStockOptions          
Tax effect for stock-based compensation benefit (expense)   (24)simo_ShareBasedCompensationTaxExpenseBenefit 343simo_ShareBasedCompensationTaxExpenseBenefit 631simo_ShareBasedCompensationTaxExpenseBenefit          
Minimum                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Stock option granted exercise price $ 1.85simo_ExercisePriceRangeOfStockOptionsSubjectToExchangeProgram
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		                
2005 Equity Incentive Plan                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Number of option exercisable                 10,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_PlanNameAxis
= simo_EquityIncentivePlanTwentyZeroFiveMember
Ordinary shares for issuance upon exercise of stock options and restricted stock units         15,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_PlanNameAxis
= simo_EquityIncentivePlanTwentyZeroFiveMember		 15,000,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfAdditionalSharesAuthorized
/ us-gaap_PlanNameAxis
= simo_EquityIncentivePlanTwentyZeroFiveMember		      
Conversion ratio of restricted stock unit to ordinary shares   One-for-one              
Employee Stock Option Plan, 2004                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Number of option outstanding             8,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsOutstandingNumber
/ us-gaap_AwardTypeAxis
= simo_EmployeeStockOptionPlanTwentyZeroFourMember		    
Number of option exercisable             1,000us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsExercisableNumber
/ us-gaap_AwardTypeAxis
= simo_EmployeeStockOptionPlanTwentyZeroFourMember		    
Option expiration period             6 years    
Employee stock option description   The options may be granted to qualified employees of the Company or any of its domestic or foreign subsidiaries and expire no later than six years from the date of grant. The options were granted at an exercise price not lower than the market value of SMI Taiwan's common stock at the date of the grant and vest over four years at certain percentages after two years from the date of grant. As part of the share exchange between the Company and the shareholders of SMI Taiwan effective on April 25, 2005, the Company agreed to assume the share options previously issued by SMI Taiwan. Subsequently on June 3, 2005, the Company amended the 2004 Plan such that options under the 2004 Plan are granted at an exercise price not lower than the market value of the Company's ordinary shares at the date of the grant and vest over four years at certain percentages after one year from the date of grant.              
Restricted Stock Units | 2005 Equity Incentive Plan                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Total unrecognized compensation cost related to non-vested share-based compensation   2,463us-gaap_EmployeeServiceShareBasedCompensationNonvestedAwardsTotalCompensationCostNotYetRecognized
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
/ us-gaap_PlanNameAxis
= simo_EquityIncentivePlanTwentyZeroFiveMember		              
Stock Options And Restricted Stock Units Exercised                  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]                  
Tax effect for stock-based compensation benefit (expense)   $ 1,231simo_ShareBasedCompensationTaxExpenseBenefit
/ us-gaap_AwardTypeAxis
= simo_StockOptionsAndRestrictedStockUnitsExercisedMember		 $ 1,599simo_ShareBasedCompensationTaxExpenseBenefit
/ us-gaap_AwardTypeAxis
= simo_StockOptionsAndRestrictedStockUnitsExercisedMember		 $ 1,560simo_ShareBasedCompensationTaxExpenseBenefit
/ us-gaap_AwardTypeAxis
= simo_StockOptionsAndRestrictedStockUnitsExercisedMember