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Subsequent Events - Additional Information (Detail) $ in Thousands, $ in Thousands	May 31, 2021 TWD ($)	May 31, 2021 USD ($)	Feb. 18, 2021 TWD ($)	Feb. 18, 2021 USD ($)
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

X

- 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

X

- 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

X

- 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

X

- 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

X

- 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

X

- Details

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

X

- Details

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

X

- 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: