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Refund Liabilities - Summary of Change in Refund Liabilities (Detail) - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2020 | Dec. 31, 2019
Other Liabilities [Abstract] |  |
Balance, beginning of year | $ 2,260 | $ 2,093
Additions | 10,576 | 5,076
Actual sales return and discount | (10,731) | (4,909)
Balance, end of year | $ 2,105 | $ 2,260

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- Definition Additions charged to expense net. + References No definition available. + Details
Name: | simo_AdditionsChargedToExpenseNet
Namespace Prefix: | simo_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Customer refund liability current beginning balance. + References No definition available. + Details
Name: | simo_CustomerRefundLiabilityCurrentBeginningBalance
Namespace Prefix: | simo_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Customer refund liability current ending balance. + References No definition available. + Details
Name: | simo_CustomerRefundLiabilityCurrentEndingBalance
Namespace Prefix: | simo_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Sales return and discounts. + References No definition available. + Details
Name: | simo_SalesReturnAndDiscounts
Namespace Prefix: | simo_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- References No definition available. + Details
Name: | us-gaap_OtherLiabilitiesAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration