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Investments - Fair Value of Short-Term Available-for-Sale and Trading Investments (Detail) (USD $) In Thousands, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
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Schedule of Investments [Line Items] |  |
Fair value of short-term available-for-sale investments | $ 129,594 us-gaap_AvailableForSaleSecuritiesCurrent | $ 299,715 us-gaap_AvailableForSaleSecuritiesCurrent
Fair value of short-term securities | 129,594 us-gaap_ShortTermInvestments | 300,715 us-gaap_ShortTermInvestments
Time Deposits and Certificates of Deposit [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of short-term available-for-sale investments | 20,900 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_CommercialPaperCertificatesOfDepositTimeDepositsAndOtherMoneyMarketInstrumentsMember | 64,989 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_CommercialPaperCertificatesOfDepositTimeDepositsAndOtherMoneyMarketInstrumentsMember
Bankers Acceptance Drafts [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of short-term available-for-sale investments | 82 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_BankersAcceptanceMember | 491 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 |  | 53,434 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 | 24,020 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_CorporateObligationsMember | 18,351 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 | 2,099 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_MunicipalBondsMember |
U.S. Agency Obligations [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of short-term available-for-sale investments | 82,493 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember | 162,450 us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Mutual Funds [Member] |  |
Schedule of Investments [Line Items] |  |
Fair value of short-term securities |  | $ 1,000 us-gaap_TradingSecurities / us-gaap_InvestmentTypeAxis = us-gaap_EquityFundsMember

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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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- Definition Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy. + 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 210.5-02.2) -URI http://asc.fasb.org/extlink&oid=6877327&loc=d3e13212-122682 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 03 -Paragraph 1 -Subparagraph g -Article 7 + Details
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- Definition Amount of investments in debt and equity securities and other forms of securities that provide ownership interests classified as trading. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 320 -SubTopic 10 -Section 45 -Paragraph 1 -URI http://asc.fasb.org/extlink&oid=6871852&loc=d3e26610-111562 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 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Glossary Trading Securities -URI http://asc.fasb.org/extlink&oid=6526789 Reference 4: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 210 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-03.4) -URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878 + Details
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