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FAIR VALUE MEASUREMENT AND FAIR VALUE OF FINANCIAL INSTRUMENTS (Details) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014
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Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | $ 2,841,085 us-gaap_AvailableForSaleSecurities |  | $ 2,626,365 us-gaap_AvailableForSaleSecurities |
U.S. Treasury securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 1,172,226 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember |  | 873,435 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember |
U.S. government agency and U.S. government sponsored enterprise debt securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 411,966 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |  | 311,024 us-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 |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 95,235 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |  | 141,420 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 727,356 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |  | 791,088 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |
Municipal securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 191,246 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |  | 250,448 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Other residential mortgage-backed securities | Investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 51,501 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [1] | 53,918 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | [1]
Other commercial mortgage-backed securities | Investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities |  |  | 34,053 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember | [1]
Corporate debt securities | Investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 140,401 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | [1] | 115,182 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | [1]
Corporate debt securities | Non-investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 9,501 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | [1] | 14,681 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | [1]
Other securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 41,653 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember |  | 41,116 us-gaap_AvailableForSaleSecurities / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember |
Fair Value, Measurements, Recurring |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 2,841,085 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 2,626,365 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Foreign exchange options |  |  |  |
Derivative |  |  |  |
Derivative assets | 3,683 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeOptionMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 6,136 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeOptionMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Interest rate swaps on certificates of deposits |  |  |  |
Derivative |  |  |  |
Derivative liabilities | (6,370)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapsOnCertificatesOfDepositsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (9,922)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapsOnCertificatesOfDepositsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Interest rate swaps and caps |  |  |  |
Derivative |  |  |  |
Derivative assets | 66,060 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapAndCapMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 41,534 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapAndCapMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Derivative liabilities | (66,914)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapAndCapMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (41,779)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapAndCapMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Foreign exchange contracts |  |  |  |
Derivative |  |  |  |
Derivative assets | 13,340 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 8,123 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Derivative liabilities | (13,080)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (9,171)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeContractMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Embedded derivative liabilities |  |  |  |
Derivative |  |  |  |
Derivative liabilities | (3,412)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_EmbeddedDerivativeFinancialInstrumentsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (3,392)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_EmbeddedDerivativeFinancialInstrumentsMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | U.S. Treasury securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 1,172,226 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember |  | 873,435 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember |
Fair Value, Measurements, Recurring | U.S. government agency and U.S. government sponsored enterprise debt securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 411,966 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |  | 311,024 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |
Fair Value, Measurements, Recurring | U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 95,235 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |  | 141,420 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |
Fair Value, Measurements, Recurring | U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 727,356 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |  | 791,088 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |
Fair Value, Measurements, Recurring | Municipal securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 191,246 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |  | 250,448 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Fair Value, Measurements, Recurring | Other residential mortgage-backed securities | Investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 51,501 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  | 53,918 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |
Fair Value, Measurements, Recurring | Other commercial mortgage-backed securities | Investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities |  |  | 34,053 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |
Fair Value, Measurements, Recurring | Corporate debt securities | Investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 140,401 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember |  | 115,182 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember |
Fair Value, Measurements, Recurring | Corporate debt securities | Non-investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 9,501 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember |  | 14,681 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember |
Fair Value, Measurements, Recurring | Other securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 41,653 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember |  | 41,116 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 1,204,703 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 905,540 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | U.S. Treasury securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 1,172,226 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember |  | 873,435 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember |
Fair Value, Measurements, Recurring | Quoted Prices in Active Markets for Identical Assets (Level 1) | Other securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 32,477 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember |  | 32,105 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel1Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 1,636,382 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 1,714,297 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign exchange options |  |  |  |
Derivative |  |  |  |
Derivative assets | 3,683 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeOptionMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 6,136 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeOptionMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swaps on certificates of deposits |  |  |  |
Derivative |  |  |  |
Derivative liabilities | (6,370)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapsOnCertificatesOfDepositsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (9,922)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapsOnCertificatesOfDepositsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Interest rate swaps and caps |  |  |  |
Derivative |  |  |  |
Derivative assets | 66,060 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapAndCapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 41,534 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapAndCapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Derivative liabilities | (66,914)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapAndCapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (41,779)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = ewbc_InterestRateSwapAndCapMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Foreign exchange contracts |  |  |  |
Derivative |  |  |  |
Derivative assets | 13,340 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | 8,123 us-gaap_DerivativeAssets / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Derivative liabilities | (13,080)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (9,171)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_ForeignExchangeContractMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. government agency and U.S. government sponsored enterprise debt securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 411,966 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |  | 311,024 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 95,235 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |  | 141,420 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 727,356 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |  | 791,088 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Municipal securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 191,246 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |  | 250,448 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other residential mortgage-backed securities | Investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 51,501 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |  | 53,918 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other commercial mortgage-backed securities | Investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities |  |  | 34,053 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CommercialMortgageBackedSecuritiesMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt securities | Investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 140,401 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember |  | 115,182 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Corporate debt securities | Non-investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 9,501 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember |  | 8,153 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember |
Fair Value, Measurements, Recurring | Significant Other Observable Inputs (Level 2) | Other securities |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities | 9,176 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember |  | 9,011 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel2Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities |  |  | 6,528 us-gaap_AvailableForSaleSecurities / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Embedded derivative liabilities |  |  |  |
Derivative |  |  |  |
Derivative liabilities | (3,412)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_EmbeddedDerivativeFinancialInstrumentsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |  | (3,392)us-gaap_DerivativeLiabilities / us-gaap_DerivativeInstrumentRiskAxis = us-gaap_EmbeddedDerivativeFinancialInstrumentsMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember |
Fair Value, Measurements, Recurring | Significant Unobservable Inputs (Level 3) | Corporate debt securities | Non-investment grade |  |  |  |
Available-for-sale investment securities |  |  |  |
Total available-for-sale investment securities |  |  | $ 6,528 us-gaap_AvailableForSaleSecurities / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_FairValueByFairValueHierarchyLevelAxis = us-gaap_FairValueInputsLevel3Member / us-gaap_FairValueByMeasurementFrequencyAxis = us-gaap_FairValueMeasurementsRecurringMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember |
[1] | Available-for-sale investment securities rated BBB- or higher by S&P or Baa3 or higher by Moody's are considered investment grade. Conversely, available-for-sale investment securities rated lower than BBB- by S&P or lower than Baa3 by Moody's are considered non-investment grade.

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