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Major customers representing at least 10% of net sales (Detail) (Net revenue, USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Samsung
Receivables From Major Customers [Line Items]
Revenue major customer	$ 30,065us-gaap_Revenues / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = simo_SamsungMember	$ 36,037us-gaap_Revenues / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = simo_SamsungMember	$ 98,368us-gaap_Revenues / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = simo_SamsungMember
Major customers percentage of net sales	10.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = simo_SamsungMember	16.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = simo_SamsungMember	35.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = simo_SamsungMember
SK Hynix
Receivables From Major Customers [Line Items]
Revenue major customer	$ 107,227us-gaap_Revenues / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = simo_SkHynixMember	$ 67,977us-gaap_Revenues / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = simo_SkHynixMember		[1]
Major customers percentage of net sales	37.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = simo_SkHynixMember	30.00%us-gaap_ConcentrationRiskPercentage1 / us-gaap_ConcentrationRiskByBenchmarkAxis = us-gaap_SalesRevenueNetMember / us-gaap_ConcentrationRiskByTypeAxis = simo_SkHynixMember		[1]
[1] Less than 10%

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- Definition

For an entity that discloses a concentration risk in relation to quantitative amount, which serves as the "benchmark" (or denominator) in the equation, this concept represents the concentration percentage derived from the division.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 21

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13537-108611



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6404-108592



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 20

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13531-108611



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 275

-SubTopic 10

-Section 50

-Paragraph 18

-URI http://asc.fasb.org/extlink&oid=6927468&loc=d3e6351-108592

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- Definition

Amount of revenue recognized from goods sold, services rendered, insurance premiums, or other activities that constitute an earning process. Includes, but is not limited to, investment and interest income before deduction of interest expense when recognized as a component of revenue, and sales and trading gain (loss).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.1)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Article 5

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