Document and Entity Information - $ / shares
9 Months Ended
Sep. 30, 2018
Oct. 22, 2018
Document and Entity Information [Abstract]    
Entity Registrant Name Carbon Black, Inc.  
Entity Central Index Key 0001366527  
Document Type 10-Q  
Document Period End Date Sep. 30, 2018  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status Yes  
Entity Filer Category Non-accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company true  
Entity Ex Transition Period true  
Entity Common Stock, Shares Outstanding   67,917,331
Entity Listing, Par Value Per Share $ 0.001  
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q3