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Pension Plan - Additional Information (Detail) (USD $) | 12 Months Ended
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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 | $ 872,000 us-gaap_PensionContributions | $ 788,000 us-gaap_PensionContributions | $ 716,000 us-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 | 57,000 us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear |  |
Accumulated benefit obligation | 1,762,000 us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation | 1,369,000 us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation | 1,332,000 us-gaap_DefinedBenefitPlanAccumulatedBenefitObligation
Estimated amortization of net gain from accumulated other comprehensive income into net periodic benefit cost over the next fiscal year | 26,000 us-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 | 1,052,000 us-gaap_DefinedBenefitPlansEstimatedFutureEmployerContributionsInNextFiscalYear / dei_LegalEntityAxis = simo_FciIncMember |  |
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 | $ 0 us-gaap_FairValueConcentrationOfRiskInvestments / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = simo_PlanAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member | $ 0 us-gaap_FairValueConcentrationOfRiskInvestments / us-gaap_DefinedBenefitPlansDisclosuresDefinedBenefitPlansAxis = simo_PlanAssetsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member |
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 / us-gaap_RangeAxis = us-gaap_MinimumMember |  |

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- Definition Defined Benefit Plan, Contributions, Percent of Compensation + References No definition available. + Details
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- Definition Percentage of Pension Payment to Employee Benefits + References No definition available. + Details
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- Definition For defined benefit pension plans, the actuarial present value of benefits (whether vested or nonvested) attributed by the pension benefit formula to employee service rendered before a specified date and based on employee service and compensation (if applicable) before that date. The accumulated benefit obligation differs from the projected benefit obligation in that it includes no assumption about future compensation levels. For plans with flat-benefit or nonpay-related pension benefit formulas, the accumulated benefit obligation and the projected benefit obligation are the same. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Accumulated Benefit Obligation -URI http://asc.fasb.org/extlink&oid=6503844 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 715 -SubTopic 20 -Section 50 -Paragraph 1 -Subparagraph (e) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition Amount included in accumulated other comprehensive income (AOCI) related to gain (loss) expected to be recognized as components of net periodic benefit cost for the fiscal year that follows the most recent annual statement of financial position. + References No definition available. + Details
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- Definition Amount of employer's best estimate of contributions expected to be paid to the plan during the next fiscal year beginning after the date of the latest statement of financial position. + 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 (g) -URI http://asc.fasb.org/extlink&oid=35743120&loc=d3e1928-114920 + Details
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- Definition This item represents disclosure of all significant concentrations of credit risk or market risk arising from the subject financial instrument (as defined), whether from an individual counterparty or groups of counterparties. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Available-for-Sale Securities -URI http://asc.fasb.org/extlink&oid=6505594 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 25 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph a, f, g -Article 7 + Details
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- Definition The amount of cash or cash equivalents contributed by the entity to fund its pension plans. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 25 -Subparagraph (g) -URI http://asc.fasb.org/extlink&oid=31042434&loc=d3e3536-108585 + Details
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