| Cover Page | Oct. 01, 2019 |
| Cover page. | |
| Title of 12(b) Security | Common Stock |
| Entity Incorporation, State or Country Code | DE |
| Entity Registrant Name | COMMVAULT SYSTEMS, INC. |
| Document Type | 8-K/A |
| Entity Central Index Key | 0001169561 |
| Amendment Flag | false |
| Entity File Number | 1-33026 |
| Entity Tax Identification Number | 22-3447504 |
| Trading Symbol | CVLT |
| Security Exchange Name | NASDAQ |
| Document Period End Date | Oct. 1, 2019 |
| Entity Address, Address Line One | 1 Commvault Way |
| Entity Address, City or Town | Tinton Falls |
| Entity Address, State or Province | NJ |
| Entity Address, Postal Zip Code | 07724 |
| City Area Code | 732 |
| Local Phone Number | 870-4000 |
| Written Communications | false |
| Soliciting Material | false |
| Pre-commencement Tender Offer | false |
| Pre-commencement Issuer Tender Offer | false |
| Entity Emerging Growth Company | false |
