Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2015
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation: The consolidated financial statements include the accounts of West Pharmaceutical Services, Inc. and its majority-owned subsidiaries (which may be referred to as “West”, the “Company”, “we”, “us” or “our”) after the elimination of intercompany transactions. We have no participation or other rights in variable interest entities.
Use of Estimates	Use of Estimates: The financial statements are prepared in conformity with U.S. GAAP. These principles require management to make estimates and assumptions that affect the reported amounts of assets, liabilities, revenues and expenses and the disclosure of contingencies in the financial statements. Actual amounts realized may differ from these estimates.
Cash and Cash Equivalents	Cash and Cash Equivalents: Cash equivalents include time deposits, certificates of deposit and all highly liquid debt instruments with maturities of three months or less at the time of purchase.
Accounts Receivable	Accounts Receivable: Our accounts receivable balance was net of an allowance for doubtful accounts of $0.6 million and $0.9 million at December 31, 2015 and 2014, respectively. We record the allowance based on a specific identification methodology.
Inventories	Inventories: Inventories are valued at the lower of cost (on a first-in, first-out basis) or market.
Property, Plant and Equipment	Property, Plant and Equipment: Property, plant and equipment assets are carried at cost. Maintenance and minor repairs and renewals are charged to expense as incurred. Costs incurred for computer software developed or obtained for internal use are capitalized for application development activities and immediately expensed for preliminary project activities or post-implementation activities. Upon sale or retirement of depreciable assets, costs and related accumulated depreciation are eliminated, and gains or losses are recognized in other (income) expense. Depreciation and amortization are computed principally using the straight-line method over the estimated useful lives of the assets, or the remaining term of the lease, if shorter.
Impairment of Goodwill and Other Intangible Assets	Impairment of Goodwill and Other Intangible Assets: Goodwill and indefinite-lived intangible assets are tested for impairment at least annually, following the completion of our annual budget and long-range planning process, or whenever circumstances indicate that the carrying value of these assets may not be recoverable. Goodwill is tested for impairment at the reporting unit level, which is the same as, or one level below, our operating segments. Recent accounting guidance allows entities to first assess qualitative factors, including macroeconomic conditions, industry and market considerations, cost factors, and overall financial performance, to determine whether it is necessary to perform the first step of the two-step quantitative goodwill impairment test. We considered this guidance when performing our annual impairment testing, but elected to continue utilizing the two-step quantitative impairment test. The first step in the two-step analysis is to compare the fair value of each reporting unit to its carrying amount, including goodwill. If the carrying amount exceeds fair value, the second step must be performed. The second step requires the comparison of the carrying amount of the goodwill to its implied fair value, which is calculated as if the reporting unit had just been acquired as of the testing date. Any excess of the carrying amount of goodwill over the implied fair value would represent an impairment loss. Certain trademarks have been determined to have indefinite lives and, therefore, are not subject to amortization. Similar to the impairment testing for goodwill, there is an option to first assess qualitative factors as a basis for determining whether it is necessary to perform a quantitative impairment test. We considered this option when performing our impairment testing, but elected to continue utilizing a quantitative test, comparing the fair value and carrying value of the asset. Any excess carrying value would represent an impairment loss. Fair values are determined using discounted cash flow analyses. Intangible assets with finite lives are amortized using the straight-line method over their estimated useful lives of 5 to 25 years, and reviewed for impairment whenever circumstances indicate that the carrying value of these assets may not be recoverable.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets: Long-lived assets, including property, plant and equipment, are tested for impairment whenever circumstances indicate that the carrying value of these assets may not be recoverable. An asset is considered impaired if the carrying value of the asset exceeds the sum of the future expected undiscounted cash flows to be derived from the asset. Once an asset is considered impaired, an impairment loss is recorded within other (income) expense for the difference between the asset's carrying value and its fair value. For assets held and used in the business, management determines fair value using estimated future cash flows to be derived from the asset, discounted to a net present value using an appropriate discount rate. For assets held for sale or for investment purposes, management determines fair value by estimating the proceeds to be received upon sale of the asset, less disposition costs.
Employee Benefits	Employee Benefits: The measurement of the obligations under our defined benefit pension and postretirement medical plans are subject to a number of assumptions. These include the rate of return on plan assets (for funded plans) and the rate at which the future obligations are discounted to present value. U.S. GAAP requires the recognition of an asset or liability for the funded status of a defined benefit postretirement plan, as measured by the difference between the fair value of plan assets, if any, and the benefit obligation. For a pension plan, the benefit obligation is the projected benefit obligation; for any other postretirement plan, such as a retiree health plan, the benefit obligation is the accumulated postretirement benefit obligation. See Note 13, Benefit Plans, for a more detailed discussion of our pension and other retirement plans.
Financial Instruments	Financial Instruments: All derivatives are recognized as either assets or liabilities in the balance sheet and recorded at their fair value. For a derivative designated as hedging the exposure to variable cash flows of a forecasted transaction (referred to as a cash flow hedge), the effective portion of the derivative's gain or loss is initially reported as a component of other comprehensive income, net of tax, and subsequently reclassified into earnings when the forecasted transaction affects earnings. For a derivative designated as hedging the exposure to changes in the fair value of a recognized asset or liability or a firm commitment (referred to as a fair value hedge), the derivative's gain or loss is recognized in earnings in the period of change together with the offsetting loss or gain on the hedged item. For a derivative designated as hedging the foreign currency exposure of a net investment in a foreign operation, the gain or loss is reported in other comprehensive income, net of tax, as part of the cumulative translation adjustment. The ineffective portion of any derivative used in a hedging transaction is recognized immediately into earnings. Derivative financial instruments that are not designated as hedges are also recorded at fair value, with the change in fair value recognized immediately into earnings. We do not purchase or hold any derivative financial instrument for investment or trading purposes.
Foreign Currency Translation	Foreign Currency Translation: Foreign currency transaction gains and losses are recognized in the determination of net income. Foreign currency translation adjustments of subsidiaries and affiliates operating outside of the U.S. are accumulated in other comprehensive income, a separate component of equity.
Revenue Recognition	Revenue Recognition: Revenue is recognized when persuasive evidence of a sales arrangement exists, title and risk of loss have transferred, the selling price is fixed or determinable, and collectability is reasonably assured. Generally, sales are recognized upon shipment or upon delivery to our customers' site, based upon shipping terms or legal requirements. Some customers receive pricing rebates upon attaining established sales volumes. We record rebate costs when sales occur based on our assessment of the likelihood that the required volumes will be attained. We also maintain an allowance for product returns, as we believe that we are able to reasonably estimate the amount of returns based on our substantial historical experience.
Shipping and Handling Costs	Shipping and Handling Costs: Shipping and handling costs are included in cost of goods and services sold. Shipping and handling costs billed to customers in connection with the sale are included in net sales.
Research and Development	Research and Development: Research and development expenditures are for the creation, engineering and application of new or improved products and processes. Expenditures include primarily salaries and outside services for those directly involved in research and development activities and are expensed as incurred.
Environmental Remediation and Compliance Costs	Environmental Remediation and Compliance Costs: Environmental remediation costs are accrued when such costs are probable and reasonable estimates are determinable. Cost estimates include investigation, cleanup and monitoring activities; such estimates are adjusted, if necessary, based on additional findings. Environmental compliance costs are expensed as incurred as part of normal operations.
Litigation	Litigation: From time to time, we are involved in legal proceedings, investigations and claims generally incidental to our normal business activities. In accordance with U.S. GAAP, we accrue for loss contingencies when it is probable that a liability has been incurred and the amount of the loss can be reasonably estimated. These estimates are based on an analysis made by internal and external legal counsel considering information known at the time. Legal costs in connection with loss contingencies are expensed as incurred.
Income Taxes	Income Taxes: Deferred income taxes are recognized by applying enacted statutory tax rates, applicable to future years, to temporary differences between the tax basis and financial statement carrying values of our assets and liabilities. Valuation allowances are established when it is more likely than not that all or a portion of a deferred tax asset will not be realized. No provision is made for the U.S. income taxes on the undistributed earnings of wholly-owned foreign subsidiaries as such earnings are intended to be permanently reinvested. We recognize interest costs related to income taxes in interest expense and penalties within other (income) expense. The tax law ordering approach is used for purposes of determining whether an excess tax benefit has been realized during the year.
Stock-based Compensation	Stock-Based Compensation: Under the fair value provisions of U.S. GAAP, stock-based compensation cost is measured at the grant date based on the value of the award and is recognized as expense over the vesting period. In order to determine the fair value of stock options on the grant date, the company uses the Black-Scholes valuation model.
Net Income Per Share	Net Income Per Share: Basic net income per share is computed by dividing net income attributable to common shareholders by the weighted average number of shares of common stock outstanding during each period. Net income per share assuming dilution considers the dilutive effect of outstanding stock options and other stock awards based on the treasury stock method, as well as convertible debt based on the if-converted method. The treasury stock method assumes the use of exercise proceeds to repurchase common stock at the average fair market value in the period. The if-converted method assumes conversion of the debt at the beginning of the reporting period (or at time of issuance, if later). In addition, interest charges applicable to the convertible debt, net of tax, are added back to net income for the purpose of this calculation.
New Accounting Standards	Recently Adopted Standards In November 2015, the FASB issued guidance regarding the balance sheet classification of deferred taxes. This guidance requires that deferred tax assets and liabilities be classified as noncurrent. The current requirement that deferred tax assets and liabilities of a tax-paying component of an entity be offset and presented as a single amount is not affected by these amendments. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2016. Early adoption is permitted and the amendments may be applied either prospectively to all deferred tax assets and liabilities or retrospectively to all periods presented. We adopted this guidance in the fourth quarter of 2015, on a prospective basis. The adoption did not have a material impact on our financial statements. In April 2015, the FASB issued guidance regarding the classification of debt issuance costs. This guidance requires debt issuance costs related to a recognized debt liability to be presented in the balance sheet as a direct deduction from the carrying amount of that debt. Subsequently, in August 2015, the FASB issued additional guidance which addressed the presentation of debt issuance costs associated with lines of credit, whereby these costs may be presented as an asset and amortized ratably over the term of the line of credit arrangement, regardless of whether there are any outstanding borrowings. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2015. Early adoption is permitted for financial statements that have not been previously issued, and retrospective application is required for each balance sheet presented. We adopted this guidance in the fourth quarter of 2015. Debt issuance costs previously recorded as an asset, in the amount of $1.0 million and $1.2 million as of December 31, 2015 and 2014, respectively, have been reclassified as a reduction to long-term debt within our consolidated balance sheets. In April 2014, the FASB issued guidance for the reporting of discontinued operations, which also contained new disclosure requirements for both discontinued operations and other disposals that do not meet the definition of a discontinued operation. We adopted this guidance as of January 1, 2015, on a prospective basis. The adoption did not have a material impact on our financial statements. Standards Issued Not Yet Adopted In September 2015, the FASB issued guidance that simplifies the accounting for measurement-period adjustments in business combinations, by eliminating the requirement to account for those adjustments retrospectively. Instead, the acquirer will be required to recognize measurement-period adjustments in the reporting period in which the amounts are determined. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2015. Management believes that the adoption of this guidance will not have a material impact on our financial statements. In July 2015, the FASB issued guidance regarding the subsequent measurement of inventory. This guidance requires inventory measured using any method other than last-in, first-out or the retail inventory method to be measured at the lower of cost and net realizable value. Net realizable value represents estimated selling prices in the ordinary course of business, less reasonably predictable costs of completion, disposal and transportation. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2016. Management believes that the adoption of this guidance will not have a material impact on our financial statements. In April 2015, the FASB issued guidance on the accounting for fees paid by a customer in a cloud computing arrangement. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2015. Management is currently evaluating the impact that this guidance will have on our financial statements, if any. In January 2015, the FASB issued guidance which removes the concept of extraordinary items from U.S. GAAP. This guidance eliminates the requirement for companies to spend time assessing whether items meet the criteria of being both unusual and infrequent. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2015. Management believes that the adoption of this guidance will not have a material impact on our financial statements. In August 2014, the FASB issued guidance which defines management's responsibility to evaluate whether there is substantial doubt about an entity's ability to continue as a going concern and to provide related footnote disclosures. This guidance is effective for the annual period ending after December 15, 2016, and for annual periods and interim periods thereafter. Early adoption is permitted. Management believes that the adoption of this guidance will not have a material impact on our financial statements. In June 2014, the FASB issued guidance that clarifies the accounting for share-based payments in which the terms of the award provide that a performance target that affects vesting could be achieved after the requisite service period. In this case, the performance target would be required to be treated as a performance condition, and should not be reflected in estimating the grant-date fair value of the award. The guidance also addresses when to recognize the related compensation cost. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2015. Management believes that the adoption of this guidance will not have a material impact on our financial statements. In May 2014, the FASB issued guidance on the accounting for revenue from contracts with customers that will supersede most existing revenue recognition guidance, including industry-specific guidance. The core principle requires an entity to recognize revenue to depict the transfer of goods or services to customers in an amount that reflects the consideration to which the entity expects to be entitled in exchange for those goods or services. In addition, the guidance requires enhanced disclosures regarding the nature, timing and uncertainty of revenue and cash flows arising from an entity's contracts with customers. This guidance is effective for interim and annual reporting periods beginning on or after December 15, 2017. Early adoption is permitted as of one year prior to the current effective date. Entities can choose to apply the guidance using either a full retrospective approach or a modified retrospective approach. Management is currently evaluating the impact that this guidance will have on our financial statements, if any, including the transition method which it will adopt.