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Segment Reporting - Company's Revenue by Geographic Region (Detail) (USD $)
In Thousands, unless otherwise specified
 3 Months Ended
Apr. 30, 2015
Apr. 30, 2014
Revenue from External Customer [Line Items]    
Total revenue $ 71,013us-gaap_Revenues $ 40,921us-gaap_Revenues
Hong Kong [Member]    
Revenue from External Customer [Line Items]    
Total revenue 65,690us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= country_HK		 35,394us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= country_HK
Asia Pacific [Member]    
Revenue from External Customer [Line Items]    
Total revenue 484us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= us-gaap_AsiaPacificMember		 633us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= us-gaap_AsiaPacificMember
United States [Member]    
Revenue from External Customer [Line Items]    
Total revenue 1,206us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= country_US		 2,147us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= country_US
North America other than United States [Member]    
Revenue from External Customer [Line Items]    
Total revenue 1,443us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= amba_NorthAmericaOtherThanUnitedStatesMember		 1,271us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= amba_NorthAmericaOtherThanUnitedStatesMember
Europe [Member]    
Revenue from External Customer [Line Items]    
Total revenue $ 2,190us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= us-gaap_EuropeMember		 $ 1,476us-gaap_Revenues
/ us-gaap_StatementGeographicalAxis
= us-gaap_EuropeMember