Document and Entity Information	3 Months Ended
	Mar. 31, 2018 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
Document Type	10-Q
Document Period End Date	Mar. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q1
Amendment Flag	false
Entity Common Stock, Shares Outstanding	73,577,883
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes