Document and Entity Information (USD $)	12 Months Ended
	Sep. 30, 2012	Oct. 31, 2012	Mar. 31, 2012
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		23,193,584
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	FY
Document Type	10-K
Amendment Flag	false
Document Period End Date	Sep. 30, 2012