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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
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Schedule of Pension Plan Assets by Fair Value [Line Items] |  |  |  |
Fair value of FCI's pension plan assets | $ 2,556 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets | $ 2,319 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets | $ 1,925 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets | $ 1,376 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets
Total |  |  |  |
Schedule of Pension Plan Assets by Fair Value [Line Items] |  |  |  |
Fair value of FCI's pension plan assets | 1,605 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / simo_DefinedBenefitPensionPlanAxis = simo_TotalMember | 1,389 us-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 | 730 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / simo_DefinedBenefitPensionPlanAxis = simo_CompanyDMember / us-gaap_InformationByFinancialStatementLineItemAxis = simo_ContractMember | 534 us-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 | $ 875 us-gaap_DefinedBenefitPlanFairValueOfPlanAssets / simo_DefinedBenefitPensionPlanAxis = simo_CompanyEMember / us-gaap_InformationByFinancialStatementLineItemAxis = us-gaap_DepositsMember | $ 855 us-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 + Details
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