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Note 4 - Fair Value Measurement (Details) - Discounted Cash Flow Assumptions
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Defined Benefit Plan Disclosure [Line Items]    
Time-to-liquidity (months) 24mpwr_CashFlowModelInputTimeToLiquidity 24mpwr_CashFlowModelInputTimeToLiquidity
Expected return 2.90%mpwr_CashFlowModelInputExpectedReturn 2.50%mpwr_CashFlowModelInputExpectedReturn
Discount rate 9.00%us-gaap_FairValueInputsDiscountRate  
Minimum [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 4.00%us-gaap_FairValueInputsDiscountRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember		 3.30%us-gaap_FairValueInputsDiscountRate
/ us-gaap_RangeAxis
= us-gaap_MinimumMember
Maximum [Member]    
Defined Benefit Plan Disclosure [Line Items]    
Discount rate 7.00%us-gaap_FairValueInputsDiscountRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember		 8.10%us-gaap_FairValueInputsDiscountRate
/ us-gaap_RangeAxis
= us-gaap_MaximumMember