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Fair Values Of FCI's Pension Plan Assets (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of FCI's pension plan assets	$ 2,556us-gaap_DefinedBenefitPlanFairValueOfPlanAssets	$ 2,319us-gaap_DefinedBenefitPlanFairValueOfPlanAssets	$ 1,925us-gaap_DefinedBenefitPlanFairValueOfPlanAssets	$ 1,376us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
Total
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of FCI's pension plan assets	1,605us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / simo_DefinedBenefitPensionPlanAxis = simo_TotalMember	1,389us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / simo_DefinedBenefitPensionPlanAxis = simo_TotalMember
Guaranteed interest contract | Kyobo Life Insurance Co. Ltd.
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of FCI's pension plan assets	730us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / simo_DefinedBenefitPensionPlanAxis = simo_CompanyDMember / us-gaap_InformationByFinancialStatementLineItemAxis = simo_ContractMember	534us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / simo_DefinedBenefitPensionPlanAxis = simo_CompanyDMember / us-gaap_InformationByFinancialStatementLineItemAxis = simo_ContractMember
Fixed Deposit | Industrial Bank of Korea
Schedule of Pension Plan Assets by Fair Value [Line Items]
Fair value of FCI's pension plan assets	$ 875us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / simo_DefinedBenefitPensionPlanAxis = simo_CompanyEMember / us-gaap_InformationByFinancialStatementLineItemAxis = us-gaap_DepositsMember	$ 855us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / simo_DefinedBenefitPensionPlanAxis = simo_CompanyEMember / us-gaap_InformationByFinancialStatementLineItemAxis = us-gaap_DepositsMember

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- Definition

Assets, usually stocks, bonds, and other investments, that have been segregated and restricted (usually in a trust) to provide benefits, at their fair value as of the measurement date. Plan assets include amounts contributed by the employer (and by employees for a contributory plan) and amounts earned from investing the contributions, less benefits paid. If a plan has liabilities other than for benefits, those non-benefit obligations may be considered as reductions of plan assets.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 20

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 715

-SubTopic 30

-Section 35

-Paragraph 50

-URI http://asc.fasb.org/extlink&oid=29635418&loc=d3e12355-114930

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