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Investments - Gross Unrealized Gains and (Losses) Aggregated by Investment Category Short-Term and Long-Term Securities (Detail) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	$ 237,285us-gaap_AvailableForSaleSecuritiesAmortizedCost	$ 157,489us-gaap_AvailableForSaleSecuritiesAmortizedCost
Investments, Gross Unrealized Gains	121us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax	8us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Investments, Gross Unrealized (Losses)	(93)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax	(296)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Short-term investments, Estimated Fair Value	158,631us-gaap_AvailableForSaleSecuritiesCurrent	129,594us-gaap_AvailableForSaleSecuritiesCurrent
Long-term investments, Estimated Fair Value	237,313us-gaap_AvailableForSaleSecuritiesNoncurrent	157,201us-gaap_AvailableForSaleSecuritiesNoncurrent
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	90,128us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember	64,842us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember
Investments, Gross Unrealized Gains	44us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember	1us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember
Investments, Gross Unrealized (Losses)	(58)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember	(174)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember
U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	16,070us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	15,563us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Investments, Gross Unrealized Gains	8us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	2us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Investments, Gross Unrealized (Losses)	(1)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	(9)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Asset Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	129,209us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember	75,778us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Investments, Gross Unrealized Gains	66us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember	5us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Investments, Gross Unrealized (Losses)	(33)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember	(109)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_AssetBackedSecuritiesMember
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	1,878us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember	1,258us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember
Investments, Gross Unrealized Gains	3us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember
Investments, Gross Unrealized (Losses)	(1)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember	(4)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MunicipalBondsMember
Time Deposits And Certificates of Deposit [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	5,400us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = mksi_TimeDepositsAndCertificatesOfDepositMember	20,901us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = mksi_TimeDepositsAndCertificatesOfDepositMember
Investments, Gross Unrealized (Losses)		(1)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = mksi_TimeDepositsAndCertificatesOfDepositMember
Short-term investments, Estimated Fair Value	5,400us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_TimeDepositsAndCertificatesOfDepositMember	20,900us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_TimeDepositsAndCertificatesOfDepositMember
Long-term investments, Estimated Fair Value		48us-gaap_AvailableForSaleSecuritiesNoncurrent / us-gaap_InvestmentTypeAxis = mksi_TimeDepositsAndCertificatesOfDepositMember
Bankers Acceptance Drafts [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	327us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_BankersAcceptanceMember	82us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_BankersAcceptanceMember
Short-term investments, Estimated Fair Value	327us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_BankersAcceptanceMember	82us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_BankersAcceptanceMember
Commercial Paper [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	1,447us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_CommercialPaperMember
Short-term investments, Estimated Fair Value	1,447us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_CommercialPaperMember
Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments, Estimated Fair Value	58,331us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_CorporateObligationsMember	24,020us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = mksi_CorporateObligationsMember
Long-term investments, Estimated Fair Value	90,114us-gaap_AvailableForSaleSecuritiesNoncurrent / us-gaap_InvestmentTypeAxis = mksi_CorporateObligationsMember	64,669us-gaap_AvailableForSaleSecuritiesNoncurrent / us-gaap_InvestmentTypeAxis = mksi_CorporateObligationsMember
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Short-term investments, Estimated Fair Value	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 Available-for-sale Securities [Line Items]
Short-term investments, Estimated Fair Value	87,328us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	82,493us-gaap_AvailableForSaleSecuritiesCurrent / us-gaap_InvestmentTypeAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Long-term investments, Estimated Fair Value	16,077us-gaap_AvailableForSaleSecuritiesNoncurrent / us-gaap_InvestmentTypeAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	15,556us-gaap_AvailableForSaleSecuritiesNoncurrent / us-gaap_InvestmentTypeAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Asset Backed Securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Long-term investments, Estimated Fair Value	129,242us-gaap_AvailableForSaleSecuritiesNoncurrent / us-gaap_InvestmentTypeAxis = us-gaap_AssetBackedSecuritiesMember	75,674us-gaap_AvailableForSaleSecuritiesNoncurrent / us-gaap_InvestmentTypeAxis = us-gaap_AssetBackedSecuritiesMember
Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Long-term investments, Estimated Fair Value	1,880us-gaap_AvailableForSaleSecuritiesNoncurrent / us-gaap_InvestmentTypeAxis = us-gaap_MunicipalBondsMember	1,254us-gaap_AvailableForSaleSecuritiesNoncurrent / us-gaap_InvestmentTypeAxis = us-gaap_MunicipalBondsMember
Short-Term [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	158,621us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember	129,600us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember
Investments, Gross Unrealized Gains	34us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember	16us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember
Investments, Gross Unrealized (Losses)	(24)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember	(22)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember
Short-Term [Member] | Corporate Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	58,336us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember	24,029us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember
Investments, Gross Unrealized Gains	10us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember	2us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember
Investments, Gross Unrealized (Losses)	(15)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember	(11)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = mksi_CorporateObligationsMember
Short-Term [Member] | Municipal Bonds [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	5,800us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember	2,100us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Investments, Gross Unrealized Gains	1us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Investments, Gross Unrealized (Losses)	(3)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember	(1)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Short-Term [Member] | U.S. Agency Obligations [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost	87,311us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	82,488us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Investments, Gross Unrealized Gains	23us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	14us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Investments, Gross Unrealized (Losses)	(6)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember	(9)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax / us-gaap_InvestmentTypeAxis = us-gaap_ShortTermInvestmentsMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentAgenciesDebtSecuritiesMember
Time Deposits [Member]
Schedule of Available-for-sale Securities [Line Items]
Investments, Cost		$ 48us-gaap_AvailableForSaleSecuritiesAmortizedCost / us-gaap_InvestmentTypeAxis = us-gaap_BankTimeDepositsMember

X

- Definition

Amount before tax of unrealized gain in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (b)

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Amount before tax of unrealized loss in accumulated other comprehensive income (AOCI) on investments in debt and equity securities classified as available-for-sale.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

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- Definition

This item represents the cost of debt and equity securities, which are categorized neither as held-to-maturity nor trading, net of adjustments including accretion, amortization, collection of cash, previous other-than-temporary impairments recognized in earnings (less any cumulative-effect adjustments recognized, as defined), and fair value hedge accounting adjustments, if any.

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-Publisher FASB

-Name Accounting Standards Codification

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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

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-Publisher FASB

-Name Accounting Standards Codification

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Investments in debt and equity securities which are categorized neither as held-to-maturity nor trading and which are intended to be sold or mature more than one year from the balance sheet date or operating cycle, if longer. Such securities are reported at fair value; unrealized gains (losses) related to Available-for-sale Securities are excluded from earnings and reported in a separate component of shareholders' equity (other comprehensive income), unless the Available-for-sale security is designated as a hedge or is determined to have had an other than temporary decline in fair value below its amortized cost basis. All or a portion of the unrealized holding gain (loss) of an Available-for-sale security that is designated as being hedged in a fair value hedge is recognized in earnings during the period of the hedge, as are other than temporary declines in fair value below the cost basis for investments in equity securities and debt securities that an entity intends to sell or it is more likely than not that it will be required to sell before the recovery of its amortized cost basis. Other than temporary declines in fair value below the cost basis for debt securities categorized as Available-for-sale that an entity does not intend to sell and for which it is not more likely than not that the entity will be required to sell before the recovery of its amortized cost basis are bifurcated into credit losses and losses related to all other factors. Other than temporary declines in fair value below cost basis related to credit losses are recognized in earnings, and losses related to all other factors are recognized in other comprehensive income.

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