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Business Segment, Geographic Area, and Significant Customer Information - Summary of Goodwill Associated with Reportable Segments (Detail) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020	Dec. 31, 2019
Segment Reporting Information [Line Items]
Goodwill	$ 1,226.2	$ 1,066.4	$ 1,058.5
Vacuum & Analysis [Member]
Segment Reporting Information [Line Items]
Goodwill	195.2	196.2
Light & Motion [Member]
Segment Reporting Information [Line Items]
Goodwill	556.3	395.3
Equipment & Solutions [Member]
Segment Reporting Information [Line Items]
Goodwill	$ 474.7	$ 474.9

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://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(10)(1))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 2: 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=120320667&loc=SL49117168-202975

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 852
-SubTopic 10
-Section 55
-Paragraph 10
-URI http://asc.fasb.org/extlink&oid=84165509&loc=d3e56426-112766

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-Name Accounting Standards Codification
-Topic 350
-SubTopic 20
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-Paragraph 1
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+ Details

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Balance Type:	debit
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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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- Details

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X

- Details

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- Details

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