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Securities - Additional Information (Detail) (USD $)
In Millions, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Schedule of Available-for-Sale Securities [Line Items]    
Securities, carrying value $ 286.6us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral $ 399.0us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral
Debt Securities [Member]    
Schedule of Available-for-Sale Securities [Line Items]    
Number of securities, Total 340abcb_NumberOfSecuritiesInSecurityPortfolio
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		  
Number of securities in unrealized loss position 66us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_DebtSecuritiesMember		  
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises [Member]    
Schedule of Available-for-Sale Securities [Line Items]    
Number of securities in unrealized loss position 37us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember		  
State, County and Municipal Securities [Member]    
Schedule of Available-for-Sale Securities [Line Items]    
Number of securities in unrealized loss position 26us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		  
U.S. Government Sponsored Agencies [Member]    
Schedule of Available-for-Sale Securities [Line Items]    
Number of securities in unrealized loss position 3us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember