Document and Entity Information Document - shares	9 Months Ended
	Oct. 31, 2017	Dec. 11, 2017
Document Information [Abstract]
Entity Registrant Name	MongoDB, Inc.
Entity Central Index Key	0001441816
Current Fiscal Year End Date	--01-31
Entity Filer Category	Non-accelerated Filer
Document Type	10-Q
Document Period End Date	Oct. 31, 2017
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Amendment Flag	false
Class A Common Stock
Entity Common Stock, Shares Outstanding		9,326,098
Class B Common Stock
Entity Common Stock, Shares Outstanding		41,255,576