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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
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	$ 158,631us-gaap_AvailableForSaleSecuritiesCurrent	$ 129,594us-gaap_AvailableForSaleSecuritiesCurrent
Time Deposits And Certificates of Deposit [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	5,400us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_TimeDepositsAndCertificatesOfDepositMember	20,900us-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	327us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_BankersAcceptanceMember	82us-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	1,447us-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	58,331us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_CorporateObligationsMember	24,020us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_CorporateObligationsMember
Municipal Bonds [Member]
Schedule of Investments [Line Items]
Fair value of short-term available-for-sale investments	5,798us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember	2,099us-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	$ 87,328us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	$ 82,493us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember

X

- 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

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