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v3.20.4

Revenue - Voluntary Recall (Details) - USD ($) $ in Millions | 3 Months Ended | 12 Months Ended
--- | --- | ---
Dec. 31, 2018 | Dec. 31, 2019
Revenue from Contract with Customer [Abstract] |  |
Provision for product returns | $ 11.3 | $ 5.4

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- References No definition available. + Details
Name: | us-gaap_RevenueFromContractWithCustomerAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Provision for Product Returns + References No definition available. + Details
Name: | wst_ProvisionForProductReturns
Namespace Prefix: | wst_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | duration