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Summary of Plan Includes Stock Options and Restricted Stock Units (Detail) (Stock Option And Restricted Stock Unit Plans) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012
Stock Option And Restricted Stock Unit Plans |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |
Available for grant at beginning date | 3,566 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember | 5,336 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember | 6,506 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember
Restricted stock units granted | (1,923)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember | (1,893)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember | (1,461)us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriod / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember
Option and restricted stock units forfeited | 44 simo_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeitedOrCancelledInPeriod / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember | 123 simo_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeitedOrCancelledInPeriod / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember | 291 simo_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrantForfeitedOrCancelledInPeriod / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember
Available for grant at ending balance | 1,687 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember | 3,566 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember | 5,336 us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardNumberOfSharesAvailableForGrant / us-gaap_PlanNameAxis = simo_StockOptionAndRestrictedStockUnitPlansMember

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- Definition Share Based Compensation Arrangement By Share Based Payment Award Number Of Shares Available For Grant Forfeited Or Cancelled In Period + References No definition available. + Details
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- Definition The number of grants made during the period on other than stock (or unit) option plans (for example, phantom stock or unit plan, stock or unit appreciation rights plan, performance target plan). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -Subparagraph (c)(2)(iii)(1) -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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- Details
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- Definition The difference between the maximum number of shares (or other type of equity) authorized for issuance under the plan (including the effects of amendments and adjustments), and the sum of: 1) the number of shares (or other type of equity) already issued upon exercise of options or other equity-based awards under the plan; and 2) shares (or other type of equity) reserved for issuance on granting of outstanding awards, net of cancellations and forfeitures, if applicable. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 718 -SubTopic 10 -Section 50 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901 + Details
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