Document and Entity Information - shares
3 Months Ended
Apr. 30, 2019
Jun. 03, 2019
Document Information [Abstract]    
Entity Registrant Name MongoDB, Inc.  
Entity Central Index Key 0001441816  
Current Fiscal Year End Date --01-31  
Entity Filer Category Large Accelerated Filer  
Entity Emerging Growth Company false  
Entity Small Business false  
Document Type 10-Q  
Document Period End Date Apr. 30, 2019  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q1  
Amendment Flag false  
Class A Common Stock    
Entity Common Stock, Shares Outstanding   41,955,411
Class B Common Stock    
Entity Common Stock, Shares Outstanding   13,373,252