Summary of Significant Accounting Policies (Policies)	12 Months Ended
Summary of Significant Accounting Policies (Policies)	Dec. 31, 2017
Accounting Policies [Abstract]
Principles of Consolidation	Principles of Consolidation: The consolidated financial statements include the accounts of West after the elimination of intercompany transactions. We have no participation or other rights in variable interest entities. As of April 1, 2017, our consolidated financial statements exclude the results of our Venezuelan subsidiary. Please refer to Note 14, Other Expense, for further discussion.
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 $0.5 million and $0.4 million at December 31, 2017 and 2016, 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) and net realizable value.
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. In January 2017, the FASB issued guidance which removes the second step of the quantitative goodwill impairment test. A goodwill impairment charge will now be the amount by which a reporting unit's carrying amount exceeds its fair value, not to exceed the total amount of goodwill allocated to that reporting unit. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2019. Early adoption is permitted. We adopted this guidance as of January 1, 2017, on a prospective basis. Recent accounting guidance also 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 quantitative goodwill impairment test. As each of our reporting units had a fair value in excess of its carrying value of at least 180% within our 2016 annual impairment test, we elected to follow this guidance for our 2017 annual impairment test. Based upon our assessment, we determined that it was not more likely than not that the fair value of each of our reporting units was less than its carrying amount and determined that it was not necessary to perform the quantitative goodwill impairment test in 2017. At December 31, 2015, a trademark had been determined to have an indefinite life and, therefore, was not subject to amortization. During 2016, as part of our restructuring plan, we recorded within other expense a $10.0 million non-cash asset write-down associated with the discontinued use of this trademark. 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. During 2016, as part of our restructuring plan, we recorded within other expense a $2.8 million non-cash asset write-down associated with the discontinued use of a patent.
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. During 2016, as part of our restructuring plan, we recorded within other expense a $4.5 million non-cash asset write-down associated with the discontinued use of certain equipment.
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 (“OCI”), 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 OCI, 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 loss, 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. In response to the 2017 Tax Act, we reevaluated our position regarding permanent reinvestment of foreign subsidiary earnings and profits through 2017 (with the exception of China and Mexico, both of which will remain permanently reinvested) and elected to include in our provision for income taxes for the year ended December 31, 2017 an estimated liability of $9.8 million related to foreign withholding taxes and state income taxes that will be incurred upon the distribution of those foreign earnings and profits to the U.S. at a future date. Please refer to Note 15, Income Taxes, for discussion of the undistributed earnings of our China and Mexico entities at December 31, 2017. 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, we use 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. The treasury stock method assumes the use of exercise proceeds to repurchase common stock at the average fair market value in the period.
New Accounting Standards	Recently Adopted Standards In January 2017, the FASB issued guidance which removes the second step of the goodwill impairment test. A goodwill impairment charge will now be the amount by which a reporting unit's carrying amount exceeds its fair value, not to exceed the total amount of goodwill allocated to that reporting unit. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2019. Early adoption is permitted. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did not have a material impact on our financial statements. In January 2017, the FASB issued guidance which clarifies the definition of a business to assist entities with evaluating whether transactions should be accounted for as acquisitions (or disposals) of assets or businesses. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did not have a material impact on our financial statements. In October 2016, the FASB issued guidance which requires companies to recognize the income tax consequences of an intra-entity transfer of an asset other than inventory when the transfer occurs. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. We adopted this guidance as of January 1, 2017, on a modified retrospective basis. As a result of the adoption, a cumulative-effect adjustment of $4.1 million was recorded within retained earnings in our consolidated balance sheet as of January 1, 2017, for unamortized tax expense previously deferred and previously unrecognized deferred tax assets. In March 2016, the FASB issued guidance that simplifies several aspects of the accounting for share-based payment transactions, including income tax consequences, classification of awards as either equity or liabilities, and classification on the statement of cash flows. We adopted this guidance as of January 1, 2017, on a prospective basis as it relates to the timing or recognition and classification of share-based compensation award-related income tax effects. For the year ended December 31, 2017, we recorded a tax benefit of $33.1 million within income tax expense in our consolidated statement of income. These tax benefits were recorded within capital in excess of par value in our consolidated balance sheet in the prior-year period. Also per the amended guidance, we classified the $33.1 million of excess tax benefits within net cash provided by operating activities in our consolidated statement of cash flows for the year ended December 31, 2017, rather than net cash used in financing activities, which included the excess tax benefits for the year ended December 31, 2016. The amended guidance allows entities to account for award forfeitures as they occur, however, we have elected to continue to estimate forfeitures expected to occur to determine the amount of compensation cost to be recognized in each period. The adoption of the amended guidance may result in increased volatility in our effective tax rate. In March 2016, the FASB issued guidance that simplifies the transition to the equity method of accounting. This guidance eliminates the requirement to retroactively adopt the equity method of accounting when there is an increase in the level of ownership interest or degree of influence. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did 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. We adopted this guidance as of January 1, 2017, on a prospective basis. The adoption did not have a material impact on our financial statements. Standards Issued Not Yet Adopted In August 2017, the FASB issued guidance which expands and refines hedge accounting for both nonfinancial and financial risk components and aligns the recognition and presentation of the effects of the hedging instrument and the hedged item in the financial statements. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018. Early adoption is permitted. We are currently evaluating our adoption timing and the impact that this guidance will have on our financial statements. In May 2017, the FASB issued guidance which amends the scope of modification accounting for share-based payment arrangements. The guidance focuses on changes to the terms or conditions of share-based payment awards that would require the application of modification accounting and specifies that an entity would not apply modification accounting if its fair value, vesting conditions and classification of the awards are the same immediately before and after the modification. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. We are currently evaluating the impact that this guidance will have on our financial statements. In March 2017, the FASB issued guidance on the presentation of net periodic pension and postretirement benefit cost (net benefit cost). The guidance requires the bifurcation of net benefit cost. The service cost component will be presented with other employee compensation costs in operating income (or capitalized in assets) and the other components will be reported separately outside of operations, and will not be eligible for capitalization. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. Upon adoption, we will apply the income statement classification provisions of this guidance retrospectively, and will reclassify net benefit cost components other than service cost from operating income to outside of operations. Net periodic benefit cost for the year ended December 31, 2017 was $7.3 million, of which $10.4 million related to service cost. This guidance has no impact on net income. In November 2016, the FASB issued guidance on the classification and presentation of restricted cash in the statement of cash flows. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. As of December 31, 2017, we had no restricted cash. In August 2016, the FASB issued guidance to reduce the diversity in how certain cash receipts and cash payments are presented and classified in the statement of cash flows. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. Early adoption is permitted. We believe that the adoption of this guidance will not have a material impact on our financial statements. In February 2016, the FASB issued guidance on the accounting for leases. This guidance requires lessees to recognize lease assets and lease liabilities on the balance sheet and to expand disclosures about leasing arrangements, both qualitative and quantitative. In terms of transition, the guidance requires adoption based upon a modified retrospective approach. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2018. As of December 31, 2017, future minimum rental payments under non-cancelable operating leases were $79.1 million. In January 2016, the FASB issued guidance that addresses certain aspects of recognition, measurement, presentation, and disclosure of financial instruments. This guidance is effective for fiscal years, and interim periods within those years, beginning after December 15, 2017. We believe 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. The FASB subsequently issued additional clarifying standards to address issues arising from implementation of the new revenue recognition standard. 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. Based on the results of the procedures performed through December 31, 2017, which included a review of a representative sample of our contracts across our reportable segments and revenue streams, we believe that the adoption of this guidance will not have a material impact on our financial statements, particularly as the majority of our net sales relates to the sale of packaging components. We expect to record a cumulative-effect adjustment within retained earnings in our consolidated balance sheet as of January 1, 2018 for the impact of the guidance on the remaining unearned income for the nonrefundable customer payment received in June 2013 in return for the exclusive use of the SmartDose technology platform within a specific therapeutic area, as well as our Contract-Manufactured Products product sales, certain Proprietary Products product sales, and our development and tooling agreements. We continue to review the impact that the adoption of this guidance will have on our financial statement disclosures, accounting policies, business processes, and internal controls. We will apply the guidance using the modified retrospective approach.