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Fair Value Measurement and Fair Value of Financial Instruments (Non-PCI Impaired Loans) (Details) | 12 Months Ended
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Dec. 31, 2017
Non-PCI Impaired Loans |
Fair Values of Derivative Instruments |
Period for updated appraisals and evaluations | 12 months

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- Definition Period within which updated appraisals and evaluations of impaired loans have generally been obtained. + References No definition available. + Details
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Namespace Prefix: | ewbc_
Data Type: | xbrli:durationItemType
Balance Type: | na
Period Type: | duration

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- Definition Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_FairValueByAssetClassAxis=ewbc_ReceivablesOriginatedOrAcquiredWithoutDeterioratedCreditQualityMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |