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AVAILABLE-FOR-SALE INVESTMENT SECURITIES (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Schedule of Available-for-sale Investment Securities    
Amortized Cost $ 2,817,847us-gaap_AvailableForSaleSecuritiesAmortizedCost $ 2,619,205us-gaap_AvailableForSaleSecuritiesAmortizedCost
Gross Unrealized Gains 29,791us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax 21,128us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
Gross Unrealized Losses (6,553)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax (13,968)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
Fair Value 2,841,085us-gaap_AvailableForSaleSecurities 2,626,365us-gaap_AvailableForSaleSecurities
U.S. Treasury securities    
Schedule of Available-for-sale Investment Securities    
Amortized Cost 1,162,801us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 873,101us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Gross Unrealized Gains 9,586us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 1,971us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Gross Unrealized Losses (161)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 (1,637)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember
Fair Value 1,172,226us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USTreasurySecuritiesMember		 873,435us-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 Investment Securities    
Amortized Cost 411,275us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 311,927us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Gross Unrealized Gains 1,143us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 490us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Gross Unrealized Losses (452)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 (1,393)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Fair Value 411,966us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember		 311,024us-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 Investment Securities    
Amortized Cost 94,330us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 140,957us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Gross Unrealized Gains 1,242us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 1,056us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Gross Unrealized Losses (337)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 (593)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Fair Value 95,235us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_CommercialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 141,420us-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 Investment Securities    
Amortized Cost 717,693us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 785,412us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Gross Unrealized Gains 11,274us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 9,754us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Gross Unrealized Losses (1,611)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 (4,078)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Fair Value 727,356us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember		 791,088us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_ResidentialMortgageBackedSecuritiesIssuedByUsGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Municipal securities    
Schedule of Available-for-sale Investment Securities    
Amortized Cost 187,244us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 245,408us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Gross Unrealized Gains 4,800us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 6,202us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Gross Unrealized Losses (798)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 (1,162)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Fair Value 191,246us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember		 250,448us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_USStatesAndPoliticalSubdivisionsMember
Other residential mortgage-backed securities | Investment grade    
Schedule of Available-for-sale Investment Securities    
Amortized Cost 50,297us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1] 52,694us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1]
Gross Unrealized Gains 1,310us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1] 1,359us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1]
Gross Unrealized Losses (106)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1] (135)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1]
Fair Value 51,501us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_ResidentialMortgageBackedSecuritiesMember		 [1] 53,918us-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 Investment Securities    
Amortized Cost   34,000us-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]
Fair Value   34,053us-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 Investment Securities    
Amortized Cost 141,140us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] 116,236us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Gross Unrealized Losses (739)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] (1,054)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Fair Value 140,401us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] 115,182us-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 Investment Securities    
Amortized Cost 11,524us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] 17,881us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Gross Unrealized Losses (2,023)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] (3,200)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Fair Value 9,501us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1] 14,681us-gaap_AvailableForSaleSecurities
/ us-gaap_ExternalCreditRatingByGroupingAxis
= us-gaap_ExternalCreditRatingNonInvestmentGradeMember
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_CorporateDebtSecuritiesMember		 [1]
Other securities    
Schedule of Available-for-sale Investment Securities    
Amortized Cost 41,543us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember		 41,589us-gaap_AvailableForSaleSecuritiesAmortizedCost
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember
Gross Unrealized Gains 436us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember		 243us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedGainBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember
Gross Unrealized Losses (326)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember		 (716)us-gaap_AvailableForSaleSecuritiesAccumulatedGrossUnrealizedLossBeforeTax
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember
Fair Value $ 41,653us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember		 $ 41,116us-gaap_AvailableForSaleSecurities
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= ewbc_OtherSecuritiesMember
[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.