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Subsequent Event - Additional Information (Detail) (Subsequent Event, Shannon, USD $)
In Millions, unless otherwise specified
1 Months Ended
Apr. 30, 2015
Subsequent Event | Shannon
 
Subsequent Event [Line Items]  
Business acquisition consideration transferred $ 57.5us-gaap_BusinessCombinationConsiderationTransferred1
/ us-gaap_BusinessAcquisitionAxis
= simo_ShannonSystemsMember
/ us-gaap_SubsequentEventTypeAxis
= us-gaap_SubsequentEventMember