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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 |  | $ 10,204,000 us-gaap_AmortizationOfIntangibleAssets |  | $ 9,365,000 us-gaap_AmortizationOfIntangibleAssets | $ 10,906,000 us-gaap_AmortizationOfIntangibleAssets |
Goodwill |  | 469,433,000 us-gaap_Goodwill |  | 337,438,000 us-gaap_Goodwill | 337,438,000 us-gaap_Goodwill | 469,433,000 us-gaap_Goodwill
Increase in goodwill | 132,000,000 us-gaap_GoodwillPeriodIncreaseDecrease |  |  |  |  |
Number of business divisions |  | 3 ewbc_NumberOfBusinessDivisions |  |  |  |
Number of operating segments |  | 3 us-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 |  | 0 us-gaap_GoodwillImpairmentLoss |  |  |  |
Changes in carrying amount of goodwill |  |  |  |  |  |
Beginning balance |  | 337,438,000 us-gaap_Goodwill |  | 337,438,000 us-gaap_Goodwill |  |
Additions from the MetroCorp acquisition |  | 131,995,000 us-gaap_GoodwillAcquiredDuringPeriod | [1] |  |  |
Ending Balance |  | 469,433,000 us-gaap_Goodwill |  | 337,438,000 us-gaap_Goodwill | 337,438,000 us-gaap_Goodwill | 469,433,000 us-gaap_Goodwill
Estimated Future Amortization Expense of Premiums on Acquired Deposits |  |  |  |  |  |
2015 |  | 9,234,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths |  |  |  | 9,234,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseNextTwelveMonths
2016 |  | 8,086,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo |  |  |  | 8,086,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearTwo
2017 |  | 6,935,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree |  |  |  | 6,935,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearThree
2018 |  | 5,883,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour |  |  |  | 5,883,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFour
2019 |  | 4,864,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive |  |  |  | 4,864,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseYearFive
Thereafter |  | 10,307,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive |  |  |  | 10,307,000 us-gaap_FiniteLivedIntangibleAssetsAmortizationExpenseAfterYearFive
Total |  | 45,309,000 us-gaap_FiniteLivedIntangibleAssetsNet |  |  |  | 45,309,000 us-gaap_FiniteLivedIntangibleAssetsNet
MetroCorp |  |  |  |  |  |
Premiums on Acquired Deposits |  |  |  |  |  |
Intangible recorded due to the acquisition of MetroCorp | 8,600,000 us-gaap_BusinessCombinationRecognizedIdentifiableAssetsAcquiredAndLiabilitiesAssumedIntangibles / us-gaap_BusinessAcquisitionAxis = ewbc_MetroCorpMember |  |  |  |  |
Additional tax adjustment in connection with a business combination |  | 11,000,000 us-gaap_GoodwillPurchaseAccountingAdjustments / us-gaap_BusinessAcquisitionAxis = ewbc_MetroCorpMember |  |  |  | 11,000,000 us-gaap_GoodwillPurchaseAccountingAdjustments / us-gaap_BusinessAcquisitionAxis = ewbc_MetroCorpMember
Goodwill | 121,000,000 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = ewbc_MetroCorpMember | 132,000,000 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = ewbc_MetroCorpMember |  |  |  | 132,000,000 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = ewbc_MetroCorpMember
Changes in carrying amount of goodwill |  |  |  |  |  |
Beginning balance | 121,000,000 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = ewbc_MetroCorpMember |  |  |  |  |
Ending Balance | 121,000,000 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = ewbc_MetroCorpMember | 132,000,000 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = ewbc_MetroCorpMember |  |  |  | 132,000,000 us-gaap_Goodwill / us-gaap_BusinessAcquisitionAxis = ewbc_MetroCorpMember
Premiums on acquired deposits |  |  |  |  |  |
Premiums on Acquired Deposits |  |  |  |  |  |
Gross carrying amount of premiums on acquired deposits |  | 108,800,000 us-gaap_FiniteLivedCoreDepositsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember |  | 100,200,000 us-gaap_FiniteLivedCoreDepositsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember |  | 108,800,000 us-gaap_FiniteLivedCoreDepositsGross / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember
Accumulated amortization for premiums on acquired deposits |  | 63,500,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember |  | 53,300,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember |  | 63,500,000 us-gaap_FiniteLivedIntangibleAssetsAccumulatedAmortization / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember
Amortization of premiums on deposits acquired |  | 10,200,000 us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember |  | 9,400,000 us-gaap_AmortizationOfIntangibleAssets / us-gaap_FiniteLivedIntangibleAssetsByMajorClassAxis = us-gaap_CoreDepositsMember | 10,900,000 us-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 | $ 8,600,000 us-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.

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