Document and Entity Information - USD ($)
$ in Billions
12 Months Ended
Jan. 31, 2018
Mar. 23, 2018
Jul. 31, 2017
Document And Entity Information [Abstract]      
Document Type 10-K    
Amendment Flag false    
Document Period End Date Jan. 31, 2018    
Document Fiscal Year Focus 2018    
Document Fiscal Period Focus FY    
Trading Symbol AMBA    
Entity Registrant Name AMBARELLA INC    
Entity Central Index Key 0001280263    
Current Fiscal Year End Date --01-31    
Entity Well-known Seasoned Issuer Yes    
Entity Current Reporting Status Yes    
Entity Voluntary Filers No    
Entity Filer Category Large Accelerated Filer    
Entity Common Stock, Shares Outstanding   33,635,312  
Entity Public Float     $ 1.5