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Stock-Based Compensation - Effect of Recording Stock-Based Compensation (Detail) (USD $) In Thousands, except Per Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	$ 11,315us-gaap_AllocatedShareBasedCompensationExpense	$ 13,992us-gaap_AllocatedShareBasedCompensationExpense	$ 13,031us-gaap_AllocatedShareBasedCompensationExpense
Tax effect on stock-based compensation	(331)us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense	(495)us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense	(1,862)us-gaap_EmployeeServiceShareBasedCompensationTaxBenefitFromCompensationExpense
Net effect on net income	10,984us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax	13,497us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax	11,169us-gaap_AllocatedShareBasedCompensationExpenseNetOfTax
Basic	$ 0.21mksi_AllocatedShareBasedCompensationEffectOnEarningPerShareBasic	$ 0.25mksi_AllocatedShareBasedCompensationEffectOnEarningPerShareBasic	$ 0.21mksi_AllocatedShareBasedCompensationEffectOnEarningPerShareBasic
Diluted	$ 0.21mksi_AllocatedShareBasedCompensationEffectOnEarningPerShareDiluted	$ 0.25mksi_AllocatedShareBasedCompensationEffectOnEarningPerShareDiluted	$ 0.21mksi_AllocatedShareBasedCompensationEffectOnEarningPerShareDiluted
Restricted Stock Units (RSUs) [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	10,203us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember	12,982us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember	11,836us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = us-gaap_RestrictedStockUnitsRSUMember
Employee Stock Purchase Plan [Member]
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Total stock-based compensation	$ 1,112us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = mksi_EmployeeStockPurchasePlanMember	$ 1,010us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = mksi_EmployeeStockPurchasePlanMember	$ 1,195us-gaap_AllocatedShareBasedCompensationExpense / us-gaap_AwardTypeAxis = mksi_EmployeeStockPurchasePlanMember

X

- Definition

Allocated share based compensation effect on earning per share basic.

+ References

No definition available.

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- Definition

Allocated share based compensation effect on earning per share diluted.

+ References

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- Definition

Represents the expense recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 1

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5047-113901



Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SAB TOPIC 14.F)

-URI http://asc.fasb.org/extlink&oid=27013229&loc=d3e301413-122809



Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901



Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Staff Accounting Bulletin (SAB)

-Number Topic 14

-Section F

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- Definition

The amount of expense, net of income tax, recognized during the period arising from equity-based compensation arrangements (for example, shares of stock, unit, stock options or other equity instruments) with employees, directors and certain consultants qualifying for treatment as employees.

+ References

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- Definition

The total recognized tax benefit related to compensation cost for equity-based payment arrangements recognized in income during the period.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 718

-SubTopic 10

-Section 50

-Paragraph 2

-Subparagraph (h)(1)(i)

-URI http://asc.fasb.org/extlink&oid=6415400&loc=d3e5070-113901

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