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Income Taxes - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Tax Credit Carryforward [Line Items] |  |  |
Change in valuation allowance | $ 515 us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount | $ 1,075 us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount | $ (3,271)us-gaap_ValuationAllowanceDeferredTaxAssetChangeInAmount
Income tax exemption term | 5 years |  |
Income tax holiday description | Profits generated from certain products of SMI Taiwan are exempted from income tax for five years beginning January 1, 2010 and January 1, 2012 |  |
Unrecognized tax benefits that would affect effective tax rate | 4,655 us-gaap_UnrecognizedTaxBenefitsThatWouldImpactEffectiveTaxRate |  |
Total amount of interest expense and penalties | 343 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense | 627 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense | 499 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestExpense
Total amount of accrued interest and penalties | 1,674 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued | 1,412 us-gaap_UnrecognizedTaxBenefitsIncomeTaxPenaltiesAndInterestAccrued |
Federal |  |  |
Tax Credit Carryforward [Line Items] |  |  |
Net operating loss carryforwards for income tax purposes | 7,794 us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = simo_FederalMember |  |
Federal net operating loss carryforwards expiration year | 2024 |  |
Research And Development | Federal |  |  |
Tax Credit Carryforward [Line Items] |  |  |
Deferred tax assets tax credit carryforwards | 2,391 us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsResearch / us-gaap_IncomeTaxAuthorityAxis = simo_FederalMember / us-gaap_TaxCreditCarryforwardAxis = simo_ResearchAndDevelopmentMember |  |
Tax credit carryforward expiration year for federal | 2023 |  |
Research And Development | State |  |  |
Tax Credit Carryforward [Line Items] |  |  |
Deferred tax assets tax credit carryforwards | 1,678 us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsResearch / us-gaap_IncomeTaxAuthorityAxis = simo_StateMember / us-gaap_TaxCreditCarryforwardAxis = simo_ResearchAndDevelopmentMember |  |
Tax credit carryforward expiration year for state | No expiration date |  |
FCI | Research And Development |  |  |
Tax Credit Carryforward [Line Items] |  |  |
Deferred tax assets tax credit carryforwards | $ 3,754 us-gaap_DeferredTaxAssetsTaxCreditCarryforwardsResearch / dei_LegalEntityAxis = simo_FciIncMember / us-gaap_TaxCreditCarryforwardAxis = simo_ResearchAndDevelopmentMember |  |
FCI | Research And Development | Minimum |  |  |
Tax Credit Carryforward [Line Items] |  |  |
Tax credit expiration period | 2015 |  |
FCI | Research And Development | Maximum |  |  |
Tax Credit Carryforward [Line Items] |  |  |
Tax credit expiration period | 2019 |  |

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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible research tax credit carryforwards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32621-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32632-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 + Details
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- Definition A description of the factual circumstances giving rise to an income tax exemption or special reduction received from a taxing jurisdiction. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SAB TOPIC 11.C) -URI http://asc.fasb.org/extlink&oid=34349781&loc=d3e330215-122817 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 35 -URI http://asc.fasb.org/extlink&oid=29652012&loc=d3e28937-109314 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Staff Accounting Bulletin (SAB) -Number Topic 11 -Section C + Details
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- Definition Amount of operating loss carryforward, before tax effects, available to reduce future taxable income under enacted tax laws. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 3 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32559-109319 + Details
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- Definition Amount accrued for interest on an underpayment of income taxes and penalties related to a tax position claimed or expected to be claimed in the tax return. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15 -Subparagraph (c) -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32718-109319 + Details
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- Definition The total amount of unrecognized tax benefits that, if recognized, would affect the effective tax rate. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 15A -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=6907707&loc=SL6600010-109319 + Details
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