Document and Entity Information - shares
 3 Months Ended
Mar. 31, 2018
Jun. 05, 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 Mar. 31, 2018  
Amendment Flag false  
Current Fiscal Year End Date --12-31  
Entity Current Reporting Status No  
Entity Filer Category Non-accelerated Filer  
Entity Common Stock, Shares Outstanding   67,545,281
Document Fiscal Year Focus 2018  
Document Fiscal Period Focus Q1