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v3.21.1

Subsequent Events - Additional Information (Detail) $ in Thousands, $ in Thousands | May 31, 2021 TWD ($) | May 31, 2021 USD ($) | Feb. 18, 2021 TWD ($) | Feb. 18, 2021 USD ($)
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Subsequent Event [Line Items] |  |  |  |
Property development construction required to complete with in period |  |  | 3 years | 3 years
Subsequent Event | Property Development Agreement [Member] |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Property development administrative Fee | $ 30,000 | $ 1,051 |  |
Subsequent Event | Performance Bond Secured By A Certificate Of Deposit [Member] | Property Development Agreement [Member] |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Property development surety amount | $ 150,000 | $ 5,257 |  |
Subsequent Event | Taipei [Member] | Office Building [Member] |  |  |  |
Subsequent Event [Line Items] |  |  |  |
Amount paid for bid bond |  |  | $ 30,000 | $ 1,051

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- Definition Amount paid for bid bond. + References No definition available. + Details
Name: | simo_AmountPaidForBidBond
Namespace Prefix: | simo_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration

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- Definition Property development administrative fee. + References No definition available. + Details
Name: | simo_PropertyDevelopmentAdministrativeFee
Namespace Prefix: | simo_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Property development construction required to completed with in period. + References No definition available. + Details
Name: | simo_PropertyDevelopmentConstructionRequiredToCompleteWithInPeriod
Namespace Prefix: | simo_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Property development surety amount. + References No definition available. + Details
Name: | simo_PropertyDevelopmentSuretyAmount
Namespace Prefix: | simo_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Detail information of subsequent event by type. User is expected to use existing line items from elsewhere in the taxonomy as the primary line items for this disclosure, which is further associated with dimension and member elements pertaining to a subsequent event. + References No definition available. + Details
Name: | us-gaap_SubsequentEventLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_SubsequentEventTypeAxis=us-gaap_SubsequentEventMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_TypeOfArrangementAxis=simo_PropertyDevelopmentAgreementMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | simo_BidSuretyBondAxis=simo_PerformanceBondSecuredByACertificateOfDepositMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | srt_StatementGeographicalAxis=simo_TaipeiMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

X
- Details
Name: | simo_BidBondAxis=srt_OfficeBuildingMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |