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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
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 $ 0.0375us-gaap_CommonStockDividendsPerShareDeclared $ 0.0375us-gaap_CommonStockDividendsPerShareDeclared $ 0.0375us-gaap_CommonStockDividendsPerShareDeclared $ 0.0375us-gaap_CommonStockDividendsPerShareDeclared $ 0.0375us-gaap_CommonStockDividendsPerShareDeclared $ 0.0375us-gaap_CommonStockDividendsPerShareDeclared $ 0.0375us-gaap_CommonStockDividendsPerShareDeclared $ 0.0375us-gaap_CommonStockDividendsPerShareDeclared $ 0.15us-gaap_CommonStockDividendsPerShareDeclared $ 0.15us-gaap_CommonStockDividendsPerShareDeclared   $ 0us-gaap_CommonStockDividendsPerShareDeclared
Treasury stock, share repurchase program retire period                     2013-07  
American Depositary Shares                        
Retained Earnings Adjustments [Line Items]                        
ADSs repurchased during period, shares                   891us-gaap_StockRepurchasedAndRetiredDuringPeriodShares
/ us-gaap_StatementClassOfStockAxis
= simo_AmericanDepositaryShareMember		    
ADSs repurchased during period, cost                   $ 10.0us-gaap_StockRepurchasedAndRetiredDuringPeriodValue
/ us-gaap_StatementClassOfStockAxis
= simo_AmericanDepositaryShareMember		    
Average purchase price per ADS                   $ 11.24simo_StockRepurchasedAndRetiredDuringPeriodValuePerShare
/ us-gaap_StatementClassOfStockAxis
= simo_AmericanDepositaryShareMember		    
American Depositary Shares | Maximum                        
Retained Earnings Adjustments [Line Items]                        
Repurchase of shares                     40us-gaap_StockRepurchaseProgramAuthorizedAmount1
/ us-gaap_RangeAxis
= us-gaap_MaximumMember
/ us-gaap_StatementClassOfStockAxis
= simo_AmericanDepositaryShareMember