Other (Income) Expense (Details) (USD $) In Millions, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Other Income and Expenses [Abstract]
Development income	$ (0.4)wst_DevelopmentIncome	$ (0.4)wst_DevelopmentIncome
Acquisition-related contingencies	0.2	0.4
Foreign exchange and other	(0.6)us-gaap_OtherOperatingIncomeExpenseNet	0.7us-gaap_OtherOperatingIncomeExpenseNet
Other (income) expense	$ (0.8)wst_OtherIncomeExpense	$ 0.7wst_OtherIncomeExpense

Amount of increase (decrease) in the value of a contingent consideration liability, including, but not limited to, differences arising upon settlement.

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 805

-SubTopic 30

-Section 50

-Paragraph 4

-Subparagraph (a)(1)

-URI http://asc.fasb.org/extlink&oid=35744584&loc=d3e7008-128479

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

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- Definition

The net amount of other operating income and expenses, the components of which are not separately disclosed on the income statement, from items that are associated with the entity's normal revenue producing operations.

+ References

No definition available.

+ Details

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

- Definition

The amount of consideration recognized during the period under a development, licensing and supply agreement entered into with a customer.

+ References

No definition available.

+ Details

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Namespace Prefix:	wst_
Data Type:	xbrli:monetaryItemType
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Period Type:	duration

- Definition

The total amount of other income and expense items that are associated with the entity's normal revenue producing operation.

+ References

No definition available.

+ Details

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