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Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
Share data in Millions, unless otherwise specified
 12 Months Ended
Jan. 03, 2015
segment
Dec. 28, 2013
Dec. 29, 2012
Summary Of Significant Accounting Policies [Line Items]      
Short-term investments $ 0us-gaap_ShortTermInvestments $ 0us-gaap_ShortTermInvestments  
Cash balance 92,900,000us-gaap_Cash 67,700,000us-gaap_Cash  
Cash equivalents 41,600,000us-gaap_CashEquivalentsAtCarryingValue 27,800,000us-gaap_CashEquivalentsAtCarryingValue  
Time Deposits 40,500,000us-gaap_TimeDepositsAtCarryingValue    
U.S. Treasury bills   26,000,000us-gaap_USGovernmentAgenciesSecuritiesAtCarryingValue  
Money market funds 1,100,000us-gaap_MoneyMarketFundsAtCarryingValue 1,800,000us-gaap_MoneyMarketFundsAtCarryingValue  
Accounts receivable, net of allowance for doubtful accounts 71,017,000us-gaap_AccountsReceivableNet 76,759,000us-gaap_AccountsReceivableNet  
Accumulated depreciation and amortization on property and equipment 9,100,000us-gaap_Depreciation 8,300,000us-gaap_Depreciation 7,300,000us-gaap_Depreciation
Accumulated amortization 13,015,000us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization 9,814,000us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization  
Amortization of Intangible Assets     2,100,000us-gaap_AmortizationOfIntangibleAssets
Cost of patents, Gross 6,400,000masi_FiniteLivedPatentsGrossNotAmortized 6,700,000masi_FiniteLivedPatentsGrossNotAmortized  
Cost of trademarks, Gross 800,000masi_FiniteLivedTrademarksGrossNotAmortized 700,000masi_FiniteLivedTrademarksGrossNotAmortized  
Capitalized Software Development Costs for Software Sold to Customers 500,000us-gaap_CapitalizedSoftwareDevelopmentCostsForSoftwareSoldToCustomers 0us-gaap_CapitalizedSoftwareDevelopmentCostsForSoftwareSoldToCustomers  
Product life estimate 7 years    
Amount amortized by company 200,000masi_AmountAmortizedByCompany 200,000masi_AmountAmortizedByCompany 200,000masi_AmountAmortizedByCompany
Unamortized cost by company 600,000masi_UnamortizedCostByCompany 300,000masi_UnamortizedCostByCompany  
Impairment of goodwill, intangible assets and other long-lived assets 0us-gaap_GoodwillAndIntangibleAssetImpairment 0us-gaap_GoodwillAndIntangibleAssetImpairment 0us-gaap_GoodwillAndIntangibleAssetImpairment
Number of Sources of Product Revenue 4masi_NumberofSourcesofProductRevenue    
Number of days royalty revenue is adjusted subsequent to quarter end 60 days    
Advertising costs 10,700,000us-gaap_AdvertisingExpense 9,600,000us-gaap_AdvertisingExpense 9,600,000us-gaap_AdvertisingExpense
Foreign currency transaction gain (loss) 1,000,000us-gaap_ForeignCurrencyTransactionGainLossBeforeTax 4,000,000us-gaap_ForeignCurrencyTransactionGainLossBeforeTax 1,600,000us-gaap_ForeignCurrencyTransactionGainLossBeforeTax
Options to purchase of shares of common stock 5.7us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount 7.2us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount 6.4us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Number of reportable segments 1us-gaap_NumberOfReportableSegments    
Patents      
Summary Of Significant Accounting Policies [Line Items]      
Estimated life maximum 10 years    
Accumulated amortization 6,649,000us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_PatentsMember		 5,679,000us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_PatentsMember		  
Total renewal costs capitalized 600,000us-gaap_FiniteLivedIntangibleAssetsCostIncurredToRenewOrExtend
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_PatentsMember		    
Weighted average number of years until the next renewal 1 year    
Trademarks      
Summary Of Significant Accounting Policies [Line Items]      
Estimated life maximum 17 years    
Accumulated amortization 866,000us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_TrademarksMember		 653,000us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_TrademarksMember		  
Total renewal costs capitalized   500,000us-gaap_FiniteLivedIntangibleAssetsCostIncurredToRenewOrExtend
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_TrademarksMember		  
Weighted average number of years until the next renewal 5 years    
Patents and trademarks      
Summary Of Significant Accounting Policies [Line Items]      
Accumulated amortization $ 3,700,000us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= masi_PatentsAndTrademarksMember		 $ 3,100,000us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= masi_PatentsAndTrademarksMember		  
Minimum      
Summary Of Significant Accounting Policies [Line Items]      
Product life estimate 3 years    
Warranty period for defects in material and workmanship 6 months    
Maximum      
Summary Of Significant Accounting Policies [Line Items]      
Product life estimate 6 years    
Warranty period for defects in material and workmanship 15 months