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Equity Investments with Carrying Value (Detail) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Schedule of Cost-method Investments [Line Items] |  |
Long-term investments | $ 133 us-gaap_LongTermInvestments | $ 133 us-gaap_LongTermInvestments
Cashido Corp. (Cashido) |  |
Schedule of Cost-method Investments [Line Items] |  |
Long-term investments | 104 us-gaap_LongTermInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyAMember | 104 us-gaap_LongTermInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyAMember
Equity Investments Percentage of Ownership | 2.10%simo_CostMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyAMember | 2.10%simo_CostMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyAMember
Vastview Technology, Corp. (Vastview) |  |
Schedule of Cost-method Investments [Line Items] |  |
Long-term investments | $ 29 us-gaap_LongTermInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember | $ 29 us-gaap_LongTermInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember
Equity Investments Percentage of Ownership | 2.90%simo_CostMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember | 2.90%simo_CostMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember

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- Definition Cost Method Investment, Ownership Percentage + References No definition available. + Details
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- Definition The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle). + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 210 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.5-02.12) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 + Details
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- Details
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