Document and Entity Information Document - USD ($) $ in Millions	12 Months Ended
	Jan. 31, 2018	Mar. 26, 2018
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-K
Document Period End Date	Jan. 31, 2018
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	FY
Amendment Flag	false
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Public Float	$ 359.3
Class A Common Stock
Entity Common Stock, Shares Outstanding		13,325,834
Class B Common Stock
Entity Common Stock, Shares Outstanding		37,250,011