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Revenue Voluntary Recall (Details) - USD ($) $ in Millions | 3 Months Ended
--- | ---
Mar. 31, 2019 | Dec. 31, 2018
Voluntary Recall [Abstract] |  |
Provision for Product Returns | $ 4.5 | $ 11.3

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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

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- Definition Voluntary Recall + References No definition available. + Details
Name: | wst_VoluntaryRecallAbstract
Namespace Prefix: | wst_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration