v3.19.3
Cover Page - USD ($)
12 Months Ended
Sep. 30, 2019
Oct. 31, 2019
Mar. 31, 2019
Cover page.      
Document Type 10-K    
Document Annual Report true    
Document Period End Date Sep. 30, 2019    
Document Transition Report false    
Entity File Number 000-30205    
Entity Registrant Name CABOT MICROELECTRONICS CORPORATION    
Entity Incorporation, State or Country Code DE    
Entity Tax Identification Number 36-4324765    
Entity Address, Address Line One 870 North Commons Drive    
Entity Address, City or Town Aurora    
Entity Address, State or Province IL    
Entity Address, Postal Zip Code 60504    
City Area Code 630    
Local Phone Number 375-6631    
Title of 12(b) Security Common Stock, $0.001 par value    
Trading Symbol CCMP    
Security Exchange Name NASDAQ    
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Interactive Data Current Yes    
Entity Filer Category Large Accelerated Filer    
Entity Small Business false    
Entity Emerging Growth Company false    
Entity Shell Company false    
Entity Public Float     $ 3,221,306,626
Entity Common Stock, Shares Outstanding   29,104,190  
Entity Central Index Key 0001102934    
Current Fiscal Year End Date --09-30    
Amendment Flag false    
Document Fiscal Year Focus 2019    
Document Fiscal Period Focus FY