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Loans Receivable and Allowance for Credit Losses (Summary of Activities in Allowance for Unfunded Credit Reserves) (Details) - Allowance for Unfunded Credit Reserve - USD ($) $ in Thousands | 12 Months Ended
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Dec. 31, 2017 | Dec. 31, 2016 | Dec. 31, 2015
Allowance for unfunded credit reserves |  |  |
Beginning balance | $ 16,121 | $ 20,360 | $ 12,712
(Reversal of) provision for unfunded credit reserves | (2,803) | (4,239) | 7,648
Ending balance | $ 13,318 | $ 16,121 | $ 20,360

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- Definition Allowance For Unfunded Credit Reserves [Roll Forward] + References No definition available. + Details
Name: | ewbc_AllowanceForUnfundedCreditReservesRollForward
Namespace Prefix: | ewbc_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration

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- Definition Reflects the Allowance for Unfunded Loan Commitments and Letters of Credit + References No definition available. + Details
Name: | ewbc_AllowanceforUnfundedLoanCommitmentsandLettersofCredit
Namespace Prefix: | ewbc_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Amount of expense related to credit loss from transactions other than loan and lease transactions. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 942 -SubTopic 225 -Section S99 -Paragraph 1 -Subparagraph (SX 210.9-04(11)) -URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 230 -SubTopic 10 -Section 45 -Paragraph 28 -Subparagraph (a) -URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585 + Details
Name: | us-gaap_ProvisionForOtherCreditLosses
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Details
Name: | us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_UnfundedLoanCommitmentMember
Namespace Prefix: |
Data Type: | na
Balance Type: |
Period Type: |