| Document and Entity Information | Jul. 06, 2022 |
| Cover [Abstract] | |
| Document Type | 8-K |
| Amendment Flag | false |
| Document Period End Date | Jul. 06, 2022 |
| Current Fiscal Year End Date | --09-30 |
| Entity Registrant Name | CMC Materials, Inc. |
| Entity Incorporation, State or Country Code | DE |
| Entity File Number | 000-30205 |
| 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 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
| Entity Central Index Key | 0001102934 |
| Title of 12(b) Security | Common Stock, $0.001 par value per share |
| Trading Symbol | CCMP |
| Security Exchange Name | NASDAQ |
