Document and Entity Information	3 Months Ended
	Mar. 31, 2019 shares
Document and Entity Information [Abstract]
Entity Registrant Name	WEST PHARMACEUTICAL SERVICES INC
Entity Central Index Key	0000105770
Current Fiscal Year End Date	--12-31
Entity Filer Category	Large Accelerated Filer
Entity Emerging Growth Company	false
Entity Small Business	false
Document Type	10-Q
Document Period End Date	Mar. 31, 2019
Document Fiscal Year Focus	2019
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding	73,483,687
Entity Current Reporting Status	Yes