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AVAILABLE-FOR-SALE INVESTMENT SECURITIES (Details 4) (USD $) In Thousands, unless otherwise specified | Mar. 31, 2015 | Dec. 31, 2014
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Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position |  |
Continuous unrealized loss position less than 12 months, Fair Value | $ 296,465 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue | $ 414,390 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Continuous unrealized loss position less than 12 months, Unrealized Losses | (1,319)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss | (2,051)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Continuous unrealized loss position 12 months or more, Fair Value | 315,486 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue | 718,223 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Continuous unrealized loss position 12 months or more, Unrealized Losses | (5,234)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss | (11,917)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Continuous unrealized loss position total, Fair Value | 611,951 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue | 1,132,613 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
Continuous unrealized loss position total, Unrealized Losses | (6,553)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss | (13,968)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss
U.S. Treasury securities |  |
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position |  |
Continuous unrealized loss position less than 12 months, Fair Value | 61,684 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember | 170,260 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember
Continuous unrealized loss position less than 12 months, Unrealized Losses | (37)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember | (266)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember
Continuous unrealized loss position 12 months or more, Fair Value | 50,860 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember | 163,800 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember
Continuous unrealized loss position 12 months or more, Unrealized Losses | (124)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember | (1,371)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember
Continuous unrealized loss position total, Fair Value | 112,544 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember | 334,060 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember
Continuous unrealized loss position total, Unrealized Losses | (161)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember | (1,637)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USTreasurySecuritiesMember
U.S. government agency and U.S. government sponsored enterprise debt securities |  |
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position |  |
Continuous unrealized loss position less than 12 months, Fair Value | 144,114 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 69,438 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Continuous unrealized loss position less than 12 months, Unrealized Losses | (383)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | (504)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Continuous unrealized loss position 12 months or more, Fair Value | 24,927 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 124,104 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Continuous unrealized loss position 12 months or more, Unrealized Losses | (69)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | (889)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Continuous unrealized loss position total, Fair Value | 169,041 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | 193,542 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Continuous unrealized loss position total, Unrealized Losses | (452)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember | (1,393)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities |  |
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position |  |
Continuous unrealized loss position less than 12 months, Fair Value | 14,119 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | 45,405 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Continuous unrealized loss position less than 12 months, Unrealized Losses | (141)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | (257)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Continuous unrealized loss position 12 months or more, Fair Value | 13,541 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | 16,169 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Continuous unrealized loss position 12 months or more, Unrealized Losses | (196)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | (336)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Continuous unrealized loss position total, Fair Value | 27,660 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | 61,574 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Continuous unrealized loss position total, Unrealized Losses | (337)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | (593)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities |  |
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position |  |
Continuous unrealized loss position less than 12 months, Fair Value | 40,969 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | 81,927 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Continuous unrealized loss position less than 12 months, Unrealized Losses | (97)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | (270)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Continuous unrealized loss position 12 months or more, Fair Value | 103,488 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | 241,047 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Continuous unrealized loss position 12 months or more, Unrealized Losses | (1,514)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | (3,808)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Continuous unrealized loss position total, Fair Value | 144,457 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | 322,974 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Continuous unrealized loss position total, Unrealized Losses | (1,611)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | (4,078)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Percentage of the total available-for-sale investment securities portfolio | 26.00%ewbc_TotalInvestmentSecuritiesAvailableForSalePortfolio / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember | 30.00%ewbc_TotalInvestmentSecuritiesAvailableForSalePortfolio / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Municipal securities |  |
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position |  |
Continuous unrealized loss position less than 12 months, Fair Value | 26,905 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 6,391 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Continuous unrealized loss position less than 12 months, Unrealized Losses | (335)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | (26)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Continuous unrealized loss position 12 months or more, Fair Value | 15,783 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 61,107 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Continuous unrealized loss position 12 months or more, Unrealized Losses | (463)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | (1,136)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Continuous unrealized loss position total, Fair Value | 42,688 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 67,498 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Continuous unrealized loss position total, Unrealized Losses | (798)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | (1,162)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Percentage of the total available-for-sale investment securities portfolio | 7.00%ewbc_TotalInvestmentSecuritiesAvailableForSalePortfolio / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember | 10.00%ewbc_TotalInvestmentSecuritiesAvailableForSalePortfolio / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_USStatesAndPoliticalSubdivisionsMember
Other residential mortgage-backed securities | Investment grade |  |
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position |  |
Continuous unrealized loss position 12 months or more, Fair Value | 6,985 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | 7,217 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember
Continuous unrealized loss position 12 months or more, Unrealized Losses | (106)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | (135)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember
Continuous unrealized loss position total, Fair Value | 6,985 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | 7,217 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember
Continuous unrealized loss position total, Unrealized Losses | (106)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember | (135)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_ResidentialMortgageBackedSecuritiesMember
Corporate debt securities | Investment grade |  |
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position |  |
Continuous unrealized loss position less than 12 months, Fair Value |  | 25,084 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Continuous unrealized loss position less than 12 months, Unrealized Losses |  | (12)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Continuous unrealized loss position 12 months or more, Fair Value | 90,401 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | 90,098 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Continuous unrealized loss position 12 months or more, Unrealized Losses | (739)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | (1,042)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Continuous unrealized loss position total, Fair Value | 90,401 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | 115,182 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Continuous unrealized loss position total, Unrealized Losses | (739)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | (1,054)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Corporate debt securities | Non-investment grade |  |
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position |  |
Continuous unrealized loss position 12 months or more, Fair Value | 9,501 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | 14,681 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Continuous unrealized loss position 12 months or more, Unrealized Losses | (2,023)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | (3,200)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Continuous unrealized loss position total, Fair Value | 9,501 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | 14,681 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Continuous unrealized loss position total, Unrealized Losses | (2,023)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | (3,200)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Percentage of the total available-for-sale investment securities portfolio | 1.00%ewbc_TotalInvestmentSecuritiesAvailableForSalePortfolio / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember | 1.00%ewbc_TotalInvestmentSecuritiesAvailableForSalePortfolio / us-gaap_ExternalCreditRatingByGroupingAxis = us-gaap_ExternalCreditRatingNonInvestmentGradeMember / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_CorporateDebtSecuritiesMember
Other securities |  |
Gross unrealized losses and related fair values of individual securities in a continuous unrealized loss position |  |
Continuous unrealized loss position less than 12 months, Fair Value | 8,674 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember | 15,885 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember
Continuous unrealized loss position less than 12 months, Unrealized Losses | (326)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember | (716)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember
Continuous unrealized loss position total, Fair Value | 8,674 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember | 15,885 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember
Continuous unrealized loss position total, Unrealized Losses | $ (326)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember | $ (716)us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAccumulatedLoss / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = ewbc_OtherSecuritiesMember

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