Debt - Credit Facility (Details) $ in Millions	1 Months Ended
Mar. 31, 2022 USD ($) instance fiscal_quarter	Dec. 31, 2021 USD ($)
Line of Credit Facility [Line Items]
Long-term debt, gross	$ 252.9	$ 253.5
Long-term debt	$ 208.3	208.8
Base Rate \| Minimum
Line of Credit Facility [Line Items]
Debt instrument, stated interest rate	0.00%
Base Rate \| Maximum
Line of Credit Facility [Line Items]
Debt instrument, stated interest rate	0.375%
Revolving Credit Facility, Due 2024
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity	$ 500.0
Credit available for the issuance of letters of credit	50.0
Line of credit facility, additional borrowing capacity	$ 929.0
Preceding period	12 months
Number of instances not to exceed \| instance	3
Number of quarters following acquisition \| fiscal_quarter	4
Line of credit facility, unused commitment level	$ 497.6
Revolving Credit Facility, Due 2024 \| Minimum
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity	$ 300.0
Ratio of debt to EBITDA	3.5
Revolving Credit Facility, Due 2024 \| Maximum
Line of Credit Facility [Line Items]
Line of credit facility, current borrowing capacity	$ 500.0
Ratio of debt to EBITDA	4.0
Revolving Credit Facility, Due 2024 \| Domestic Line of Credit
Line of Credit Facility [Line Items]
Credit facility is available for swing-line loans	$ 50.0
Revolving Credit Facility, Due 2024 \| Foreign Line of Credit
Line of Credit Facility [Line Items]
Credit facility is available for swing-line loans	$ 40.0
Revolving Credit Facility, Due 2024 \| SOFR
Line of Credit Facility [Line Items]
Debt instrument, stated interest rate	0.10%
Revolving Credit Facility, Due 2024 \| Federal Funds Effective Rate Plus
Line of Credit Facility [Line Items]
Debt instrument, stated interest rate	0.50%
Revolving Credit Facility, Due 2024 \| LIBOR
Line of Credit Facility [Line Items]
Debt instrument, stated interest rate	1.00%
Revolving Credit Facility, Due 2024 \| LIBOR \| Minimum
Line of Credit Facility [Line Items]
Debt instrument, stated interest rate	0.875%
Revolving Credit Facility, Due 2024 \| LIBOR \| Maximum
Line of Credit Facility [Line Items]
Debt instrument, stated interest rate	1.375%
Revolving Credit Facility, Due 2024 \| Letter of Credit
Line of Credit Facility [Line Items]
Long-term line of credit	$ 2.4
Term Loan Due 2024
Line of Credit Facility [Line Items]
Long-term debt, gross	84.9	$ 85.5
Long-term debt, current	2.2
Long-term debt	$ 82.7

Amount of short-term debt and current maturity of long-term debt and capital lease obligations due within one year or the normal operating cycle, if longer.

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Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Percentage points added to the reference rate to compute the variable rate on the debt instrument.

+ References

No definition available.

+ Details

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Period Type:	duration

- Definition

Amount, before unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but is not limited to, notes payable, bonds payable, commercial loans, mortgage loans, convertible debt, subordinated debt and other types of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 470
-SubTopic 20
-Section 50
-Paragraph 4
-Subparagraph (b)(1)
-URI http://asc.fasb.org/extlink&oid=123466204&loc=SL6031897-161870

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

+ Details

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

- Definition

The carrying value as of the balance sheet date of the current and noncurrent portions of long-term obligations drawn from a line of credit, which is a bank's commitment to make loans up to a specific amount. Examples of items that might be included in the application of this element may consist of letters of credit, standby letters of credit, and revolving credit arrangements, under which borrowings can be made up to a maximum amount as of any point in time conditional on satisfaction of specified terms before, as of and after the date of drawdowns on the line. Includes short-term obligations that would normally be classified as current liabilities but for which (a) postbalance sheet date issuance of a long term obligation to refinance the short term obligation on a long term basis, or (b) the enterprise has entered into a financing agreement that clearly permits the enterprise to refinance the short-term obligation on a long term basis and the following conditions are met (1) the agreement does not expire within 1 year and is not cancelable by the lender except for violation of an objectively determinable provision, (2) no violation exists at the BS date, and (3) the lender has entered into the financing agreement is expected to be financially capable of honoring the agreement.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(22))
-URI http://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(16))
-URI http://asc.fasb.org/extlink&oid=120398452&loc=d3e534808-122878

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 944
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.7-03(16))
-URI http://asc.fasb.org/extlink&oid=120400017&loc=d3e572229-122910

+ Details

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

- Definition

Amount of current borrowing capacity under the credit facility considering any current restrictions on the amount that could be borrowed (for example, borrowings may be limited by the amount of current assets), but without considering any amounts currently outstanding under the facility.

+ References

+ Details

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

- 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

- Definition

Amount of borrowing capacity currently available under the credit facility (current borrowing capacity less the amount of borrowings outstanding).

+ References

+ Details

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

- Definition

Amount after unamortized (discount) premium and debt issuance costs of long-term debt classified as noncurrent and excluding amounts to be repaid within one year or the normal operating cycle, if longer. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

+ References

+ Details

Name:	us-gaap_LongTermDebtNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

this refers to Credit available for the issuance of letters of credit

+ References

No definition available.

+ Details

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Namespace Prefix:	wst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

This refers to credit facility is available for swing-line loans

+ References

No definition available.

+ Details

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Namespace Prefix:	wst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Debt Instrument, Increase In Facility, Preceding Period

+ References

No definition available.

+ Details

Name:	wst_DebtInstrumentIncreaseInFacilityPrecedingPeriod
Namespace Prefix:	wst_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Number Of Fiscal Quarters Following Acquisition

+ References

No definition available.

+ Details

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Namespace Prefix:	wst_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Number Of Instances Ratio Of Debt To EBITDA Exceeded

+ References

No definition available.

+ Details

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Namespace Prefix:	wst_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Debt Instrument, Ratio Of Debt To EBITDA

+ References

No definition available.

+ Details

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Namespace Prefix:	wst_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Line Of Credit Facility Additional Borrowing Capacity

+ References

No definition available.

+ Details

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Namespace Prefix:	wst_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

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Namespace Prefix:
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Balance Type:
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- Details

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Namespace Prefix:
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- Details

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Namespace Prefix:
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Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_DomesticLineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_ForeignLineOfCreditMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_SecuredOvernightFinancingRateSofrOvernightIndexSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_CreditFacilityAxis=us-gaap_FederalFundsEffectiveSwapRateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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