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INVESTMENT SECURITIES (Details) (USD $)
In Thousands, unless otherwise specified
Dec. 31, 2014
Dec. 31, 2013
Schedule of Available-for-sale Securities    
Amortized Cost $ 2,619,205us-gaap_AvailableForSaleSecuritiesAmortizedCost $ 2,786,490us-gaap_AvailableForSaleSecuritiesAmortizedCost
Gross Unrealized Gains 21,128us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax 12,203us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Gross Unrealized Losses (13,968)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax (64,896)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Fair Value 2,626,365us-gaap_AvailableForSaleSecurities 2,733,797us-gaap_AvailableForSaleSecurities
U.S. Treasury securities    
Schedule of Available-for-sale Securities    
Amortized Cost 873,101us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 495,053us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Gross Unrealized Gains 1,971us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 201us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Gross Unrealized Losses (1,637)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 (3,622)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Fair Value 873,435us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 491,632us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
U.S. government agency and U.S. government sponsored enterprise debt securities    
Schedule of Available-for-sale Securities    
Amortized Cost 311,927us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 406,807us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Gross Unrealized Gains 490us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 242us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Gross Unrealized Losses (1,393)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 (12,726)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Fair Value 311,024us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 394,323us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities    
Schedule of Available-for-sale Securities    
Amortized Cost 140,957us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 182,257us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Gross Unrealized Gains 1,056us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 1,062us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Gross Unrealized Losses (593)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 (4,449)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Fair Value 141,420us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 178,870us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities    
Schedule of Available-for-sale Securities    
Amortized Cost 785,412us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 892,435us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Gross Unrealized Gains 9,754us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 7,729us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Gross Unrealized Losses (4,078)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 (14,927)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Fair Value 791,088us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 885,237us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Municipal securities    
Schedule of Available-for-sale Securities    
Amortized Cost 245,408us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 297,390us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Gross Unrealized Gains 6,202us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 1,122us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Gross Unrealized Losses (1,162)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 (17,533)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Fair Value 250,448us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 280,979us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Other residential mortgage-backed securities | Investment grade    
Schedule of Available-for-sale Securities    
Amortized Cost 52,694us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1] 48,129us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1]
Gross Unrealized Gains 1,359us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1]  
Gross Unrealized Losses (135)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1] (1,802)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1]
Fair Value 53,918us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1] 46,327us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1]
Other commercial mortgage-backed securities | Investment grade    
Schedule of Available-for-sale Securities    
Amortized Cost 34,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		 [1] 51,000us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		 [1]
Gross Unrealized Gains 53us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		 [1] 617us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		 [1]
Fair Value 34,053us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		 [1] 51,617us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CommercialMortgageBackedSecuritiesMember		 [1]
Corporate debt securities | Investment grade    
Schedule of Available-for-sale Securities    
Amortized Cost 116,236us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] 312,726us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Gross Unrealized Gains   613us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Gross Unrealized Losses (1,054)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] (3,344)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Fair Value 115,182us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] 309,995us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Corporate debt securities | Non-investment grade    
Schedule of Available-for-sale Securities    
Amortized Cost 17,881us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] 20,668us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Gross Unrealized Gains   62us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Gross Unrealized Losses (3,200)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] (5,629)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Fair Value 14,681us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] 15,101us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Other securities    
Schedule of Available-for-sale Securities    
Amortized Cost 41,589us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember		 80,025us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember
Gross Unrealized Gains 243us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember		 555us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember
Gross Unrealized Losses (716)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember		 (864)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember
Fair Value $ 41,116us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember		 $ 79,716us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember
[1] Investment securities rated BBB- or higher by S&P, or Baa3 or higher by Moody are considered investment grade. Conversely, investment securities rated below BBB- by S&P, or below Baa3 by Moody are considered non-investment grade.