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Investments - Fair Value of Short-Term Available-for-Sale Investments (Detail) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014
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Schedule of Investments [Line Items] |  |
Fair value of short-term available-for-sale investments | $ 158,631 us-gaap_AvailableForSaleSecuritiesCurrent | $ 129,594 us-gaap_AvailableForSaleSecuritiesCurrent
Time Deposits And Certificates of Deposit [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of short-term available-for-sale investments | 5,400 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_TimeDepositsAndCertificatesOfDepositMember | 20,900 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_TimeDepositsAndCertificatesOfDepositMember
Bankers Acceptance Drafts [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of short-term available-for-sale investments | 327 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_BankersAcceptanceMember | 82 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_BankersAcceptanceMember
Commercial Paper [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of short-term available-for-sale investments | 1,447 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_CommercialPaperMember |
Corporate Obligations [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of short-term available-for-sale investments | 58,331 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_CorporateObligationsMember | 24,020 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_CorporateObligationsMember
Municipal Bonds [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of short-term available-for-sale investments | 5,798 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 2,099 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
U.S. Agency Obligations [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of short-term available-for-sale investments | $ 87,328 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | $ 82,493 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember

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- 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
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