Document and Entity Information - shares
6 Months Ended
Sep. 30, 2017
Oct. 23, 2017
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  
Document Type 10-Q  
Document Period End Date Sep. 30, 2017  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q2  
Amendment Flag false  
Entity Common Stock, Shares Outstanding   46,185,364