LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES (Details 2) (Loans Receivable, USD $) In Billions, unless otherwise specified	3 Months Ended
Mar. 31, 2015 item	Dec. 31, 2014
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Loans receivable pledged to secure borrowings and to provide additional borrowing capacity from the FHLB and the Federal Reserve Bank	14.79us-gaap_LoansPledgedAsCollateral	$ 14.66us-gaap_LoansPledgedAsCollateral
Number of grades in the risk rating system utilized by the company to rate credit risk of loans receivable	8ewbc_NumberOfGradesRiskRatingSystem
Residential \| Single-family \| Minimum
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Number of units of residential property securing fixed and adjustable rate first mortgage loans	1
Adjustable rate mortgage, term of initial fixed interest rates	1 year
Residential \| Single-family \| Maximum
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Number of units of residential property securing fixed and adjustable rate first mortgage loans	4
Adjustable rate mortgage, term of initial fixed interest rates	3 years
Residential \| Multifamily \| Minimum
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Adjustable rate mortgage, term of initial fixed interest rates	6 months
Residential \| Multifamily \| Maximum
LOANS RECEIVABLE AND ALLOWANCE FOR LOAN LOSSES
Adjustable rate mortgage, term of initial fixed interest rates	3 years

The term for an initial interest rate period of an adjustable rate mortgage.

No definition available.

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- Definition

The number of grades in the risk rating system utilized by the company to rate credit risk of loans receivable. Loans are risk rated based on analysis of the current state of the borrower's credit quality. Higher grades represent a higher level of credit risk.

+ References

No definition available.

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

The number of units in residential property that secures both fixed and adjustable rate first mortgage loans.

+ References

No definition available.

+ Details

Name:	ewbc_NumberOfUnitsForWhichBothFixedAndAdjustableRateFirstMortgageLoansSecured
Namespace Prefix:	ewbc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	us-gaap_AccountsNotesAndLoansReceivableLineItems
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Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Carrying amount as of the balance sheet date of loans that have been pledged as collateral for borrowings. If the secured party has the right by contract or custom to sell or re-pledge the collateral, then the debtor reclassifies that asset and report that asset in its statement of financial position separately from other assets not so encumbered.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 5

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5086-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 860

-SubTopic 30

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6467456&loc=d3e113888-111728

+ Details

Name:	us-gaap_LoansPledgedAsCollateral
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	ewbc_FinancingReceivableInformationByPortfolioSegmentsAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: