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Loans Receivable and Allowance for Credit Losses (Loans Held-for-Sale Narrative) (Details) - USD ($) $ in Thousands | Dec. 31, 2017 | Dec. 31, 2016
--- | --- | ---
Loans Held for Sale |  |
Loans held-for-sale, including loans pending sale | $ 78,200 |
Branch assets held-for-sale | 91,318 | $ 0
Loans held-for-sale | 85 | $ 23,076
Loans held-for-sale |  |
Loans Held for Sale |  |
Branch assets held-for-sale | $ 78,100 |

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- Definition Branch Assets Held-for-sale as part of the branch purchase agreement. + References No definition available. + Details
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Namespace Prefix: | ewbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Loans Receivable Held-For-Sale, Net, Excluded From Discontinued Operations + References No definition available. + Details
Name: | ewbc_LoansReceivableHeldForSaleNetExcludedFromDiscontinuedOperations
Namespace Prefix: | ewbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- 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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- Definition Amount, after allowance for bad debt, of loan receivables held-for-sale that are not part of a disposal group. Excludes loans and leases covered under loss sharing agreements and loans classified as debt securities. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 310 -SubTopic 10 -Section 45 -Paragraph 2 -URI http://asc.fasb.org/extlink&oid=82891408&loc=d3e4428-111522 + Details
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Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Details
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Balance Type: |
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