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Business Segment, Geographic Area, Product and Significant Customer Information - Summary of Goodwill Associated with Reportable Segments (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018	Dec. 31, 2017
Segment Reporting Information [Line Items]
Goodwill	$ 1,058,667	$ 586,996	$ 591,047
Vacuum & Analysis [Member]
Segment Reporting Information [Line Items]
Goodwill	196,777	197,126
Light & Motion [Member]
Segment Reporting Information [Line Items]
Goodwill	389,539	$ 389,870
Equipment & Solutions [Member]
Segment Reporting Information [Line Items]
Goodwill	$ 472,351

X

- Definition

Amount after accumulated impairment loss of an asset representing future economic benefits arising from other assets acquired in a business combination that are not individually identified and separately recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=77989000&loc=SL49117168-202975

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=99380562&loc=d3e13770-109266

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

X

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

X

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=mksi_LightAndMotionSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

X

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=mksi_EquipmentAndSolutionsMember
Namespace Prefix:
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Period Type: