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Basis of Presentation (Details) | Mar. 31, 2018 trust
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Organization, Consolidation and Presentation of Financial Statements [Abstract] |
Number of wholly-owned subsidiaries that are statutory business trusts (the Trusts) | 6

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- Definition Represents the number of wholly owned subsidiaries of the entity that are statutory business trusts, which are not consolidated. + References No definition available. + Details
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Namespace Prefix: | ewbc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- References No definition available. + Details
Name: | us-gaap_OrganizationConsolidationAndPresentationOfFinancialStatementsAbstract
Namespace Prefix: | us-gaap_
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Balance Type: | na
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