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Equity Investments with Carrying Value (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013
Schedule of Cost-method Investments [Line Items]
Long-term investments	$ 133us-gaap_LongTermInvestments	$ 133us-gaap_LongTermInvestments
Cashido Corp. (Cashido)
Schedule of Cost-method Investments [Line Items]
Long-term investments	104us-gaap_LongTermInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyAMember	104us-gaap_LongTermInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyAMember
Equity Investments Percentage of Ownership	2.10%simo_CostMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyAMember	2.10%simo_CostMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyAMember
Vastview Technology, Corp. (Vastview)
Schedule of Cost-method Investments [Line Items]
Long-term investments	$ 29us-gaap_LongTermInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember	$ 29us-gaap_LongTermInvestments / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember
Equity Investments Percentage of Ownership	2.90%simo_CostMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember	2.90%simo_CostMethodInvestmentOwnershipPercentage / us-gaap_ScheduleOfEquityMethodInvestmentEquityMethodInvesteeNameAxis = simo_CompanyBMember

X

- Definition

Cost Method Investment, Ownership Percentage

+ References

No definition available.

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- Definition

The total amount of investments that are intended to be held for an extended period of time (longer than one operating cycle).

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.12)

-URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682

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