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Net Income Per Ordinary Share - Weighted-Average Potentially Dilutive Securities Excluded from Computation of Diluted Net Income Per Ordinary Share (Detail)
 3 Months Ended
Apr. 30, 2015
Apr. 30, 2014
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive shares excluded from computation of earnings per share 84,917us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount 192,864us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
Stock options [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive shares excluded from computation of earnings per share 71,433us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember		 119,467us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_EmployeeStockOptionMember
Restricted stock units [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive shares excluded from computation of earnings per share 0us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember		 31,355us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AwardTypeAxis
= us-gaap_RestrictedStockUnitsRSUMember
Employee stock purchase plan [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive shares excluded from computation of earnings per share 13,428us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= amba_EmployeeStockPurchasePlanMember		 31,443us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= amba_EmployeeStockPurchasePlanMember
Early exercised options subject to repurchase [Member]    
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]    
Antidilutive shares excluded from computation of earnings per share 56us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= amba_EarlyExercisedOptionsSubjectToRepurchaseMember		 10,599us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareAmount
/ us-gaap_AntidilutiveSecuritiesExcludedFromComputationOfEarningsPerShareByAntidilutiveSecuritiesAxis
= amba_EarlyExercisedOptionsSubjectToRepurchaseMember