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Revenue Supply Chain Financing (Details) - USD ($) $ in Millions | Mar. 31, 2020 | Mar. 31, 2019
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Supply Chain Financing [Abstract] |  |
Sales of certain accounts receivable | $ 3.3 | $ 1.8

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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=118948506&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
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Namespace Prefix: | wst_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration