Document and Entity Information (USD $)	6 Months Ended
	Mar. 31, 2013	Apr. 30, 2013	Mar. 31, 2012
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			$ 892,790,000
Entity Common Stock, Shares Outstanding		23,271,925
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q2
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Mar. 31, 2013