Document and Entity Information - USD ($)
$ in Billions
12 Months Ended
Mar. 31, 2019
May 01, 2019
Sep. 30, 2018
Document And Entity Information [Abstract]      
Trading Symbol CVLT    
Entity Registrant Name COMMVAULT SYSTEMS INC    
Entity Central Index Key 0001169561    
Current Fiscal Year End Date --03-31    
Entity Filer Category Large Accelerated Filer    
Entity Emerging Growth Company false    
Entity Small Business false    
Entity Shell Company false    
Document Type 10-K    
Document Period End Date Mar. 31, 2019    
Document Fiscal Year Focus 2019    
Document Fiscal Period Focus FY    
Amendment Flag false    
Entity Common Stock, Shares Outstanding   45,679,184  
Entity Well-known Seasoned Issuer Yes    
Entity Voluntary Filers No    
Entity Current Reporting Status Yes    
Entity Public Float     $ 3.0