Note 11 - Fair Value Measurements (Details) - Financial Assets and Liabilities, Fair Value (USD $) In Thousands, unless otherwise specified	Sep. 30, 2014	Dec. 31, 2013
Note 11 - Fair Value Measurements (Details) - Financial Assets and Liabilities, Fair Value [Line Items]
Money market funds	$ 29,103	$ 35,588
U.S. treasuries and government agency bonds	126,849	128,126
Total	165,747	173,574
Contingent consideration	2,507
Total	2,507
Money Market Funds [Member] \| Fair Value, Inputs, Level 1 [Member]
Note 11 - Fair Value Measurements (Details) - Financial Assets and Liabilities, Fair Value [Line Items]
Money market funds	29,103	35,588
Money Market Funds [Member]
Note 11 - Fair Value Measurements (Details) - Financial Assets and Liabilities, Fair Value [Line Items]
Money market funds	29,103	35,588
US Government Agencies Short-term Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Note 11 - Fair Value Measurements (Details) - Financial Assets and Liabilities, Fair Value [Line Items]
U.S. treasuries and government agency bonds	126,849	128,126
US Government Agencies Short-term Debt Securities [Member]
Note 11 - Fair Value Measurements (Details) - Financial Assets and Liabilities, Fair Value [Line Items]
U.S. treasuries and government agency bonds	126,849	128,126
Auction Rate Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Note 11 - Fair Value Measurements (Details) - Financial Assets and Liabilities, Fair Value [Line Items]
Auction-rate securities backed by student-loan notes	9,795	9,860
Auction Rate Securities [Member]
Note 11 - Fair Value Measurements (Details) - Financial Assets and Liabilities, Fair Value [Line Items]
Auction-rate securities backed by student-loan notes	9,795	9,860
Fair Value, Inputs, Level 1 [Member]
Note 11 - Fair Value Measurements (Details) - Financial Assets and Liabilities, Fair Value [Line Items]
Total	29,103	35,588
Fair Value, Inputs, Level 2 [Member]
Note 11 - Fair Value Measurements (Details) - Financial Assets and Liabilities, Fair Value [Line Items]
Total	126,849	128,126
Fair Value, Inputs, Level 3 [Member]
Note 11 - Fair Value Measurements (Details) - Financial Assets and Liabilities, Fair Value [Line Items]
Total	9,795	9,860
Contingent consideration	2,507
Total	$ 2,507

Name:	mpwr_Note11FairValueMeasurementsDetailsFinancialAssetsandLiabilitiesFairValueLineItems
Namespace Prefix:	mpwr_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 820

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (a)

-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt and equity securities categorized neither as trading securities nor held-to-maturity securities and intended be sold or mature one year or operating cycle, if longer.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=28360136&loc=d3e22054-111558

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26626-111562

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesCurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of liability recognized arising from contingent consideration in a business combination.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 25

-Paragraph 6

-URI http://asc.fasb.org/extlink&oid=6911189&loc=d3e6408-128476

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 35

-Paragraph 1

-Subparagraph b

-URI http://asc.fasb.org/extlink&oid=6911338&loc=d3e6819-128478

+ Details

Name:	us-gaap_BusinessCombinationContingentConsiderationLiability
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Fair value of financial and nonfinancial obligations.

+ References

+ Details

Name:	us-gaap_LiabilitiesFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Investment in short-term money-market instruments (such as commercial paper, banker's acceptances, repurchase agreements, government securities, certificates of deposit, and so forth) which are highly liquid (that is, readily convertible to known amounts of cash) and so near their maturity that they present an insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify as cash equivalents by definition. Original maturity means an original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

+ Details

Name:	us-gaap_MoneyMarketFundsAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Debt (bills, notes or bonds) that are issued by the government of the United States which are short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates. Generally, only investments with original maturities of three months or less qualify under that definition. Original maturity means original maturity to the entity holding the investment. For example, both a three-month US Treasury bill and a three-year Treasury note purchased three months from maturity qualify as cash equivalents. However, a Treasury note purchased three-years ago does not become a cash equivalent when its remaining maturity is three months.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

-URI http://asc.fasb.org/extlink&oid=6507016

+ Details

Name:	us-gaap_USGovernmentSecuritiesAtCarryingValue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant