Document and Entity Information - shares
9 Months Ended
Oct. 31, 2019
Dec. 02, 2019
Cover [Abstract]    
Document Type 10-Q  
Amendment Flag false  
Document Period End Date Oct. 31, 2019  
Document Fiscal Year Focus 2020  
Document Fiscal Period Focus Q3  
Trading Symbol AMBA  
Entity Registrant Name AMBARELLA INC  
Entity Central Index Key 0001280263  
Current Fiscal Year End Date --01-31  
Entity Filer Category Large Accelerated Filer  
Entity Small Business false  
Entity Emerging Growth Company false  
Entity Shell Company false  
Entity Current Reporting Status Yes  
Entity Common Stock, Shares Outstanding   33,544,802
Entity File Number 001-35667  
Entity Tax Identification Number 98-0459628  
Entity Address, Address Line One 3101 Jay Street  
Entity Address, City or Town Santa Clara  
Entity Address, State or Province CA  
Entity Address, Postal Zip Code 95054  
City Area Code 408  
Local Phone Number 734-8888  
Entity Incorporation, State or Country Code E9  
Document Quarterly Report true  
Document Transition Report false  
Title of 12(b) Security Ordinary Shares, $0.00045 Par Value Per Share  
Security Exchange Name NASDAQ  
Entity Interactive Data Current Yes