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GOODWILL AND OTHER INTANGIBLE ASSETS (Details) (USD $)
 0 Months Ended 12 Months Ended 3 Months Ended
Jan. 17, 2014
Dec. 31, 2014
item
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2014
Premiums on Acquired Deposits          
Acquired Finite-lived Intangible Assets, Weighted Average Useful Life   8 years      
Amortization of premiums on deposits acquired   $ 10,204,000us-gaap_AmortizationOfIntangibleAssets $ 9,365,000us-gaap_AmortizationOfIntangibleAssets $ 10,906,000us-gaap_AmortizationOfIntangibleAssets  
Goodwill   469,433,000us-gaap_Goodwill 337,438,000us-gaap_Goodwill 337,438,000us-gaap_Goodwill 469,433,000us-gaap_Goodwill
Increase in goodwill 132,000,000us-gaap_GoodwillPeriodIncreaseDecrease        
Number of business divisions   3ewbc_NumberOfBusinessDivisions      
Number of operating segments   3us-gaap_NumberOfOperatingSegments      
Period for which the company provided a net income projection under the income approach to determine the fair value of the reporting units   3 years      
Goodwill impairment   0us-gaap_GoodwillImpairmentLoss      
Changes in carrying amount of goodwill          
Beginning balance   337,438,000us-gaap_Goodwill 337,438,000us-gaap_Goodwill    
Additions from the MetroCorp acquisition   131,995,000us-gaap_GoodwillAcquiredDuringPeriod [1]      
Ending Balance   469,433,000us-gaap_Goodwill 337,438,000us-gaap_Goodwill 337,438,000us-gaap_Goodwill 469,433,000us-gaap_Goodwill
Estimated Future Amortization Expense of Premiums on Acquired Deposits          
2015   9,234,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths     9,234,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths
2016   8,086,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo     8,086,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo
2017   6,935,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree     6,935,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree
2018   5,883,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour     5,883,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour
2019   4,864,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive     4,864,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive
Thereafter   10,307,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive     10,307,000us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive
Total   45,309,000us-gaap_FiniteLivedIntangibleAssetsNet     45,309,000us-gaap_FiniteLivedIntangibleAssetsNet
MetroCorp          
Premiums on Acquired Deposits          
Intangible recorded due to the acquisition of MetroCorp 8,600,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles
/ us-gaap_BusinessAcquisitionAxis
= ewbc_MetroCorpMember		        
Additional tax adjustment in connection with a business combination   11,000,000us-gaap_GoodwillPurchaseAccountingAdjustments
/ us-gaap_BusinessAcquisitionAxis
= ewbc_MetroCorpMember		     11,000,000us-gaap_GoodwillPurchaseAccountingAdjustments
/ us-gaap_BusinessAcquisitionAxis
= ewbc_MetroCorpMember
Goodwill 121,000,000us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= ewbc_MetroCorpMember		 132,000,000us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= ewbc_MetroCorpMember		     132,000,000us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= ewbc_MetroCorpMember
Changes in carrying amount of goodwill          
Beginning balance 121,000,000us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= ewbc_MetroCorpMember		        
Ending Balance 121,000,000us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= ewbc_MetroCorpMember		 132,000,000us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= ewbc_MetroCorpMember		     132,000,000us-gaap_Goodwill
/ us-gaap_BusinessAcquisitionAxis
= ewbc_MetroCorpMember
Premiums on acquired deposits          
Premiums on Acquired Deposits          
Gross carrying amount of premiums on acquired deposits   108,800,000us-gaap_FiniteLivedCoreDepositsGross
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CoreDepositsMember		 100,200,000us-gaap_FiniteLivedCoreDepositsGross
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CoreDepositsMember		   108,800,000us-gaap_FiniteLivedCoreDepositsGross
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CoreDepositsMember
Accumulated amortization for premiums on acquired deposits   63,500,000us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CoreDepositsMember		 53,300,000us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CoreDepositsMember		   63,500,000us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CoreDepositsMember
Amortization of premiums on deposits acquired   10,200,000us-gaap_AmortizationOfIntangibleAssets
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CoreDepositsMember		 9,400,000us-gaap_AmortizationOfIntangibleAssets
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CoreDepositsMember		 10,900,000us-gaap_AmortizationOfIntangibleAssets
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CoreDepositsMember		  
Premiums on acquired deposits | MetroCorp          
Premiums on Acquired Deposits          
Intangible recorded due to the acquisition of MetroCorp $ 8,600,000us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles
/ us-gaap_BusinessAcquisitionAxis
= ewbc_MetroCorpMember
/ us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis
= us-gaap_CoreDepositsMember		        
[1] Includes $11.0 million of deferred tax adjustments recorded in the fourth quarter of 2014.