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Stock Plans - Weighted Average Risk Assumptions (Details) (USD $)
3 Months Ended
Mar. 31, 2015
Stock Option  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Fair value per option (dollars per share) $ 15.63us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Risk-free interest rate 1.77%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Expected dividend yield 2.32%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Expected volatility 38.94%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Expected life (years) 6 years 8 months 16 days
Performance Stock Unit  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Fair value per unit (dollars per share) $ 40.06us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardEquityInstrumentsOtherThanOptionsGrantsInPeriodWeightedAverageGrantDateFairValue
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Risk-free interest rate 0.93%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Expected dividend yield 2.32%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
Expected volatility 27.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember
MSA stock beta 1.132msa_SharebasedCompensationArrangementbySharebasedPaymentAwardFairValueAssumptionsStockBeta
/ us-gaap_AwardTypeAxis
= us-gaap_PerformanceSharesMember