Document and Entity Information - shares	9 Months Ended
	Oct. 31, 2017	Nov. 30, 2017
Document And Entity Information [Line Items]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Oct. 31, 2017
Document Fiscal Year Focus	2018
Document Fiscal Period Focus	Q3
Trading Symbol	BOX
Entity Registrant Name	BOX INC
Entity Central Index Key	0001372612
Current Fiscal Year End Date	--01-31
Entity Filer Category	Large Accelerated Filer
Class A Common Stock
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		120,976,520
Class B Common Stock
Document And Entity Information [Line Items]
Entity Common Stock, Shares Outstanding		15,165,697