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Income Taxes (Deferred Tax Assets and Liabilities) (Details) (USD $) In Millions, unless otherwise specified | Dec. 31, 2014 | Dec. 31, 2013
--- | --- | ---
Operating Loss Carryforwards [Line Items] |  |
Deferred Tax Assets, Operating Loss Carryforwards, Foreign | $ 5.4 us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsForeign |
Deferred Tax Assets, Operating Loss Carryforwards, State and Local | 15.0 us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsStateAndLocal |
Deferred tax assets |  |
Net operating loss carryforwards | 20.4 us-gaap_DeferredTaxAssetsOperatingLossCarryforwards | 20.7 us-gaap_DeferredTaxAssetsOperatingLossCarryforwards
Tax credit carryforwards | 40.4 us-gaap_DeferredTaxAssetsTaxCreditCarryforwards | 36.1 us-gaap_DeferredTaxAssetsTaxCreditCarryforwards
Restructuring and impairment charges | 0 wst_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsRestructuringAndImpairmentCharges | 0.1 wst_DeferredTaxAssetsTaxDeferredExpenseReservesAndAccrualsRestructuringAndImpairmentCharges
Pension and deferred compensation | 43.7 us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits | 51.2 us-gaap_DeferredTaxAssetsTaxDeferredExpenseCompensationAndBenefits
Other | 20.0 us-gaap_DeferredTaxAssetsOther | 19.8 us-gaap_DeferredTaxAssetsOther
Valuation allowance | (22.1)us-gaap_DeferredTaxAssetsValuationAllowance | (23.5)us-gaap_DeferredTaxAssetsValuationAllowance
Total deferred tax assets | 102.4 us-gaap_DeferredTaxAssetsNet | 104.4 us-gaap_DeferredTaxAssetsNet
Deferred tax liabilities: |  |
Accelerated depreciation | 36.8 us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment | 40.5 us-gaap_DeferredTaxLiabilitiesPropertyPlantAndEquipment
Other | 7.7 us-gaap_DeferredTaxLiabilitiesOther | 5.4 us-gaap_DeferredTaxLiabilitiesOther
Total deferred tax liabilities | 44.5 us-gaap_DeferredIncomeTaxLiabilities | 45.9 us-gaap_DeferredIncomeTaxLiabilities
Net deferred tax asset | 57.9 us-gaap_DeferredTaxAssetsLiabilitiesNet | 58.5 us-gaap_DeferredTaxAssetsLiabilitiesNet
State and Local Jurisdiction [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Operating loss carryforwards | 267.0 us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |
Foreign Tax Authority [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Operating loss carryforwards | 22.5 us-gaap_OperatingLossCarryforwards / us-gaap_IncomeTaxAuthorityAxis = us-gaap_ForeignCountryMember |
Deferred Tax Assets, Operating Loss Carryforwards, Not Subject to Expiration | 17.2 us-gaap_DeferredTaxAssetsOperatingLossCarryforwardsNotSubjectToExpiration / us-gaap_IncomeTaxAuthorityAxis = us-gaap_ForeignCountryMember |
Tax credit carryforwards | 22.6 us-gaap_TaxCreditCarryforwardAmount / us-gaap_IncomeTaxAuthorityAxis = us-gaap_ForeignCountryMember |
Year 2019 [Member] | Foreign Tax Authority [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 3.1 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2019Member / us-gaap_IncomeTaxAuthorityAxis = us-gaap_ForeignCountryMember |
Year 2024 [Domain] | Foreign Tax Authority [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 2.1 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2024Domain / us-gaap_IncomeTaxAuthorityAxis = us-gaap_ForeignCountryMember |
Year 2015 [Domain] | State and Local Jurisdiction [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Operating loss carryforwards | 8.3 us-gaap_OperatingLossCarryforwards / wst_ExpirationPeriodAxis = wst_Year2015Domain / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |
Year After 2015 [Domain] | State and Local Jurisdiction [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Operating loss carryforwards | 258.7 us-gaap_OperatingLossCarryforwards / wst_ExpirationPeriodAxis = wst_YearAfter2015Domain / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |
Year 2016 [Member] [Domain] | Foreign Tax Authority [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 0.4 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2016MemberDomain / us-gaap_IncomeTaxAuthorityAxis = us-gaap_ForeignCountryMember |
Year 2020 [Member] | State and Local Jurisdiction [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 1.5 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2020Member / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember |
Year 2020 [Member] | Foreign Tax Authority [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 3.2 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2020Member / us-gaap_IncomeTaxAuthorityAxis = us-gaap_ForeignCountryMember |
Year 2021 [Member] | Foreign Tax Authority [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 9.6 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2021Member / us-gaap_IncomeTaxAuthorityAxis = us-gaap_ForeignCountryMember |
Year 2017 [Member] | Foreign Tax Authority [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 2.4 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2017Member / us-gaap_IncomeTaxAuthorityAxis = us-gaap_ForeignCountryMember |
Year 2018 [Member] | Foreign Tax Authority [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 1.8 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2018Member / us-gaap_IncomeTaxAuthorityAxis = us-gaap_ForeignCountryMember |
Research Tax Credit Carryforward [Member] | State and Local Jurisdiction [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 3.3 us-gaap_TaxCreditCarryforwardAmount / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |
Research Tax Credit Carryforward [Member] | Internal Revenue Service (IRS) [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 7.6 us-gaap_TaxCreditCarryforwardAmount / us-gaap_IncomeTaxAuthorityAxis = us-gaap_InternalRevenueServiceIRSMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |
Research Tax Credit Carryforward [Member] | Year 2032 [Member] | Internal Revenue Service (IRS) [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 1.4 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2032Member / us-gaap_IncomeTaxAuthorityAxis = us-gaap_InternalRevenueServiceIRSMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |
Research Tax Credit Carryforward [Member] | Year After 2032 [Domain] | Internal Revenue Service (IRS) [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 4.0 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_YearAfter2032Domain / us-gaap_IncomeTaxAuthorityAxis = us-gaap_InternalRevenueServiceIRSMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |
Research Tax Credit Carryforward [Member] | Year After 2022 [Member] | State and Local Jurisdiction [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 2.0 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_YearAfter2022Member / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |
Research Tax Credit Carryforward [Member] | Year 2029 [Domain] | Internal Revenue Service (IRS) [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 0.2 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2029Domain / us-gaap_IncomeTaxAuthorityAxis = us-gaap_InternalRevenueServiceIRSMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |
Research Tax Credit Carryforward [Member] | Year 2030 [Domain] | Internal Revenue Service (IRS) [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 1.0 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2030Domain / us-gaap_IncomeTaxAuthorityAxis = us-gaap_InternalRevenueServiceIRSMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |
Research Tax Credit Carryforward [Member] | Year 2031 [Member] | Internal Revenue Service (IRS) [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 1.0 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2031Member / us-gaap_IncomeTaxAuthorityAxis = us-gaap_InternalRevenueServiceIRSMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |
Research Tax Credit Carryforward [Member] | Year 2021 [Member] | State and Local Jurisdiction [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | 0.5 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2021Member / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |
Research Tax Credit Carryforward [Member] | Year 2022 [Member] | State and Local Jurisdiction [Member] |  |
Operating Loss Carryforwards [Line Items] |  |
Tax credit carryforwards | $ 0.8 us-gaap_TaxCreditCarryforwardAmount / wst_ExpirationPeriodAxis = wst_Year2022Member / us-gaap_IncomeTaxAuthorityAxis = us-gaap_StateAndLocalJurisdictionMember / us-gaap_TaxCreditCarryforwardAxis = us-gaap_ResearchMember |

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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible operating loss carryforwards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32621-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32632-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 20 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=29652012&loc=d3e28680-109314 + Details
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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible foreign operating loss carryforwards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32621-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32632-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 20 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=29652012&loc=d3e28680-109314 + Details
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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible state and local operating loss carryforwards. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32621-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32632-109319 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 20 -Subparagraph (b) -URI http://asc.fasb.org/extlink&oid=29652012&loc=d3e28680-109314 + Details
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- Definition Amount before allocation of valuation allowances of deferred tax asset attributable to deductible temporary differences not separately disclosed. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 6 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32621-109319 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 25 -Paragraph 20 -URI http://asc.fasb.org/extlink&oid=29652012&loc=d3e28680-109314 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 740 -SubTopic 10 -Section 50 -Paragraph 8 -URI http://asc.fasb.org/extlink&oid=6907707&loc=d3e32632-109319 + Details
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