Document and Entity Information (USD $)	3 Months Ended
	Dec. 31, 2014	Jan. 31, 2015	Mar. 31, 2014
Document and Entity Information [Abstract]
Entity Registrant Name	CABOT MICROELECTRONICS CORP
Entity Central Index Key	0001102934
Current Fiscal Year End Date	--09-30
Entity Well-known Seasoned Issuer	Yes
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Filer Category	Large Accelerated Filer
Entity Public Float			$ 1,030,587,000
Entity Common Stock, Shares Outstanding		24,074,291
Document Fiscal Year Focus	2015
Document Fiscal Period Focus	Q1
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Dec. 31, 2014