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Long-term Investment - Additional Information (Detail) (USD $) | 12 Months Ended | 3 Months Ended | 12 Months Ended | 36 Months Ended | 48 Months Ended
--- | --- | --- | --- | --- | ---
Dec. 31, 2014 | Dec. 31, 2013 | Dec. 31, 2012 | Feb. 28, 2007 | Dec. 31, 2009 | Dec. 31, 2010 | Dec. 31, 2014
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |  |
Cost method investment impairments other than temporary | $ 0 us-gaap_CostmethodInvestmentsOtherThanTemporaryImpairment | $ 0 us-gaap_CostmethodInvestmentsOtherThanTemporaryImpairment | $ 0 us-gaap_CostmethodInvestmentsOtherThanTemporaryImpairment |  |  |  |
Vastview Technology, Corp. (Vastview) |  |  |  |  |  |  |
Schedule of Cost-method Investments [Line Items] |  |  |  |  |  |  |
Invested in common stock |  |  |  | 3,360,000 us-gaap_PaymentsToAcquireLongtermInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember |  |  |
Cost method investment capital return |  | 46,000 simo_CostMethodInvestmentReturnOfCapital / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember |  |  | 808,000 simo_CostMethodInvestmentReturnOfCapital / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember |  |
Recognized an impairment charges |  |  |  |  |  | $ 2,462,000 us-gaap_CostMethodInvestmentsRealizedGainLoss / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember | $ 0 us-gaap_CostMethodInvestmentsRealizedGainLoss / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember

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- Definition This item represents an other than temporary decline in value that has been recognized against an investment accounted for under the cost method of accounting. The excess of the carrying amount over the fair value of the investment represents the amount of the write down which is or was reflected in earnings. The written down value is a new cost basis with the adjusted value of the investment becoming its new carrying value. Evidence of a loss in value might include, but would not necessarily be limited to, absence of an ability to recover the carrying amount of the investment or inability of the investee to sustain an earnings capacity which would justify the carrying amount of the investment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 325 -SubTopic 20 -Section 50 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6872867&loc=d3e40691-111596 + Details
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- Definition This item represents the gain (loss) realized during the period from the sale of investments accounted for under the cost method of accounting and any losses recognized thereon for impairments of other than a temporary nature. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 9 -Article 5 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 225 -SubTopic 10 -Section S99 -Paragraph 2 -Subparagraph (SX 210.5-03.7(c),9(a)) -URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 7 -Subparagraph c, d -Article 5 + Details
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- Definition The cash outflow for securities or other assets acquired, which qualify for treatment as an investing activity and are to be liquidated, if necessary, beyond the current operating cycle. Includes cash flows from securities classified as trading securities that were acquired for reasons other than sale in the long-term. + References No definition available. + Details
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