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Derivatives (Hedged Items Currently Designated) (Details) - Certificates of deposits - Fair Value Hedges - Interest rate swaps - Derivatives designated as hedging instruments $ in Thousands | Mar. 31, 2018 USD ($)
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Derivative [Line Items] |
Carrying Amount of the Hedged Assets/(Liabilities) | $ (29,779)
Cumulative Amount of Fair Value Hedging Adjustment Included in the Carrying Amount of the Hedged Assets (Liabilities) | $ 6,024

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- Definition Carrying amount of hedged liabilities in fair value hedging relationship recognized in the statement of financial position. + References No definition available. + Details
Name: | ewbc_HedgedLiabilityFairValueHedge
Namespace Prefix: | ewbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition The cumulative amount of fair value hedging adjustments to hedged liabilities included in the carrying amount of the hedged liabilities. + References No definition available. + Details
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Namespace Prefix: | ewbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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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
Name: | us-gaap_DerivativeLineItems
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Details
Name: | us-gaap_CashAndCashEquivalentsAxis=us-gaap_CertificatesOfDepositMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
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Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |

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- Details
Name: | us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |