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Revenue Supply Chain Financing (Details) $ in Millions | Sep. 30, 2018 USD ($)
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Supply Chain Financing [Abstract] |
Transfer of Financial Assets Accounted for as Sales, Cash Proceeds Received for Assets Derecognized, Amount | $ 2.3

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- Definition Amount, before counterparty netting, of cash proceeds received in transfers of derecognized financial assets from transactions which comprise an initial transfer and an agreement entered into in contemplation of the initial transfer resulting in retention of substantially all of the exposure to the economic return throughout the term of the transaction. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 860 -SubTopic 20 -Section 50 -Paragraph 4D -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=109247956&loc=SL51823488-111719 + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Supply Chain Financing [Abstract] + References No definition available. + Details
Name: | wst_SupplyChainFinancingAbstract
Namespace Prefix: | wst_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration