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Shareholders' Equity - Additional Information (Detail) (USD $) In Millions, except Share data in Thousands, unless otherwise specified | 3 Months Ended | 12 Months Ended
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Dec. 31, 2014 | Sep. 30, 2014 | Jun. 30, 2014 | Mar. 31, 2014 | Dec. 31, 2013 | Sep. 30, 2013 | Jun. 30, 2013 | Mar. 31, 2013 | Dec. 31, 2014 | Dec. 31, 2013 | Jan. 21, 2013 | Dec. 31, 2012
Retained Earnings Adjustments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Dividend distribution allowance description |  |  |  |  |  |  |  |  | SMI Taiwan subsidiary may only distribute dividends after it has made allowances as determined under ROC GAAP at each year-end for: a. Payment of taxes; b. Recovery of prior years’ deficits, if any; c. 10% of remaining balance after deduction for a and b as legal reserve; d. Special reserve based on relevant laws or regulations or 10% of remaining balance for deduction from above a to c as special reserve when necessary; e. Cash or stock bonus to employees at 0.01% of any remaining earnings after the above reserves have been appropriated, based on a resolution of the board of directors. If bonus to employees is in the form of stock, the bonus may also be appropriated to employees of subsidiaries under the board of directors’ approval; |  |  |
Dividend declared | $ 0.0375 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.0375 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.0375 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.0375 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.0375 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.0375 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.0375 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.0375 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.15 us-gaap_CommonStockDividendsPerShareDeclared | $ 0.15 us-gaap_CommonStockDividendsPerShareDeclared |  | $ 0 us-gaap_CommonStockDividendsPerShareDeclared
Treasury stock, share repurchase program retire period |  |  |  |  |  |  |  |  |  |  | 2013-07 |
American Depositary Shares |  |  |  |  |  |  |  |  |  |  |  |
Retained Earnings Adjustments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
ADSs repurchased during period, shares |  |  |  |  |  |  |  |  |  | 891 us-gaap_StockRepurchasedAndRetiredDuringPeriodShares / us-gaap_StatementClassOfStockAxis = simo_AmericanDepositaryShareMember |  |
ADSs repurchased during period, cost |  |  |  |  |  |  |  |  |  | $ 10.0 us-gaap_StockRepurchasedAndRetiredDuringPeriodValue / us-gaap_StatementClassOfStockAxis = simo_AmericanDepositaryShareMember |  |
Average purchase price per ADS |  |  |  |  |  |  |  |  |  | $ 11.24 simo_StockRepurchasedAndRetiredDuringPeriodValuePerShare / us-gaap_StatementClassOfStockAxis = simo_AmericanDepositaryShareMember |  |
American Depositary Shares | Maximum |  |  |  |  |  |  |  |  |  |  |  |
Retained Earnings Adjustments [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Repurchase of shares |  |  |  |  |  |  |  |  |  |  | 40 us-gaap_StockRepurchaseProgramAuthorizedAmount1 / us-gaap_RangeAxis = us-gaap_MaximumMember / us-gaap_StatementClassOfStockAxis = simo_AmericanDepositaryShareMember |

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- Definition Aggregate dividends declared during the period for each share of common stock outstanding. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 04 -Article 3 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 505 -SubTopic 10 -Section S99 -Paragraph 1 -Subparagraph (SX 210.3-04) -URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770 + Details
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