Note 4 - Balance Sheet Components (Details) - Other Long-Term Assets (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Other Long-Term Assets [Abstract]
Deferred compensation plan assets	$ 8,386us-gaap_DeferredCompensationPlanAssets	$ 6,084us-gaap_DeferredCompensationPlanAssets
Prepaid expense	1,348us-gaap_PrepaidExpenseNoncurrent	1,418us-gaap_PrepaidExpenseNoncurrent
Other	955	955
Total	$ 10,689us-gaap_OtherAssetsNoncurrent	$ 8,457us-gaap_OtherAssetsNoncurrent

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

Carrying amount as of the balance sheet date of assets held under deferred compensation agreements.

+ 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 210.5-02.17)

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

+ Details

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

- Definition

Amount of other miscellaneous assets expected to be realized or consumed after one year or normal operating cycle, if longer.

+ References

No definition available.

+ Details

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

- Definition

Aggregate carrying amount, as of the balance sheet date, of noncurrent assets not separately disclosed in the balance sheet. Noncurrent assets are expected to be realized or consumed after one year (or the normal operating cycle, if longer).

+ References

+ Details

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

- Definition

Sum of the carrying amounts as of the balance sheet date of amounts paid in advance for expenses which will be charged against earnings in periods after one year or beyond the operating cycle, if longer.

+ References

+ Details

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