CONDENSED CONSOLIDATED STATEMENTS OF INCOME (UNAUDITED) (USD $) In Millions, except Per Share data, unless otherwise specified	3 Months Ended
Mar. 31, 2015	Mar. 31, 2014
Income Statement [Abstract]
Net sales	$ 335.9us-gaap_SalesRevenueNet	$ 346.8us-gaap_SalesRevenueNet
Cost of goods and services sold	226.2us-gaap_CostOfGoodsAndServicesSold	240.4us-gaap_CostOfGoodsAndServicesSold
Gross profit	109.7us-gaap_GrossProfit	106.4us-gaap_GrossProfit
Research and development	7.5us-gaap_ResearchAndDevelopmentExpense	10.0us-gaap_ResearchAndDevelopmentExpense
Selling, general and administrative expenses	55.2	56.4
Other (income) expense (Note 11)	(0.8)wst_OtherIncomeExpense	0.7wst_OtherIncomeExpense
Operating profit	47.8us-gaap_OperatingIncomeLoss	39.3us-gaap_OperatingIncomeLoss
Interest expense	4.1us-gaap_InterestExpense	4.0us-gaap_InterestExpense
Interest income	0.4us-gaap_InvestmentIncomeNet	0.4us-gaap_InvestmentIncomeNet
Income before income taxes	44.1	35.7
Income tax expense	12.5us-gaap_IncomeTaxExpenseBenefit	9.8us-gaap_IncomeTaxExpenseBenefit
Equity in net income of affiliated companies	1.3	1.2
Net income	$ 32.9us-gaap_ProfitLoss	$ 27.1us-gaap_ProfitLoss
Net income per share:
Basic (in dollars per share)	$ 0.46us-gaap_EarningsPerShareBasic	$ 0.38us-gaap_EarningsPerShareBasic
Diluted (in dollars per share)	$ 0.45us-gaap_EarningsPerShareDiluted	$ 0.38us-gaap_EarningsPerShareDiluted
Weighted average shares outstanding:
Basic (in shares)	71.7	70.6
Diluted (in shares)	73.3	72.3
Dividends declared per share	$ 0.11	$ 0.10

Aggregate dividends declared during the period for each share of common stock outstanding.

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

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 04

-Article 3

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 505

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.3-04)

-URI http://asc.fasb.org/extlink&oid=27012166&loc=d3e187085-122770