Carrying amount as of the balance sheet date of interest earned on loans receivable but not received.

Name:	ewbc_AccruedInterestOnLoansReceivable
Namespace Prefix:	ewbc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Total amount of acquired residential mortgage loans that offer the borrower variable payment option features as of the balance sheet date.

+ Details

Name:	ewbc_AcquiredResidentialMortgageLoansWithVariablePaymentOptionFeatures
Namespace Prefix:	ewbc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ Details

Name:	ewbc_AdjustableRateMortgageInitialInterestRatePeriodMaximum
Namespace Prefix:	ewbc
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ Details

Name:	ewbc_AdjustableRateMortgageInitialInterestRatePeriodMidrange
Namespace Prefix:	ewbc
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

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

+ Details

Name:	ewbc_AdjustableRateMortgageInitialInterestRatePeriodMinimum
Namespace Prefix:	ewbc
Data Type:	us-types:durationStringItemType
Balance Type:	na
Period Type:	duration

- Definition

The allowance for noncovered loan losses represents the reserve to cover probable credit losses related to specifically identified loans, as well as probable credit losses inherent in the remainder of the loan portfolio as of the balance sheet date.

+ Details

Name:	ewbc_AllowanceForNoncoveredLoansReceivable
Namespace Prefix:	ewbc
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The carrying amount of student loans acquired during the reporting period.

+ Details

Name:	ewbc_CarryingAmountOfStudentLoansAcquired
Namespace Prefix:	ewbc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Details

Name:	ewbc_CreditRiskAndConcentrationsAbstract
Namespace Prefix:	ewbc
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Total amount of new first mortgage loans on multifamily residential properties during the reporting period.

+ Details

Name:	ewbc_FirstMortgageLoansOnMultifamilyRealEstateNewMortgageLoans
Namespace Prefix:	ewbc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Total amount of new first mortgage loans on single-family residential properties during the reporting period.

+ Details

Name:	ewbc_FirstMortgageLoansOnSingleFamilyRealEstateNewMortgageLoans
Namespace Prefix:	ewbc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Loans acquired during the reporting period.

+ Details

Name:	ewbc_LoansAcquiredDuringPeriod
Namespace Prefix:	ewbc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

The net gain (loss) resulting from sale of loans classified as held-for-sale for investment purposes.

+ Details

Name:	ewbc_NetGainOrLossOnSaleOfLoansHeldForSale
Namespace Prefix:	ewbc
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Reflects the gross carrying amount of all categories of noncovered loans held in portfolio.

+ Details

Name:	ewbc_NoncoveredLoansReceivableGross
Namespace Prefix:	ewbc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Reflects the aggregate carrying amount of all categories of noncovered loans held in portfolio, net of unearned income and the allowance for losses on loans.

+ Details

Name:	ewbc_NoncoveredLoansReceivableNet
Namespace Prefix:	ewbc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

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

+ Details

Name:	ewbc_NumberOfUnitsOfWhichResidentialPropertySecuringFixedAndAdjustableRateFirstMortgageLoansConsistMaximum
Namespace Prefix:	ewbc
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

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

+ Details

Name:	ewbc_NumberOfUnitsOfWhichResidentialPropertySecuringFixedAndAdjustableRateFirstMortgageLoansConsistMinimum
Namespace Prefix:	ewbc
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of loans held for sale that were student loans held for investment reclassified to loans held for sale.

+ Details

Name:	ewbc_PercentageOfLoansHeldForSaleStudentLoans
Namespace Prefix:	ewbc
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of non-covered loans secured by real property located in the state of California as of the balance sheet date.

+ Details

Name:	ewbc_PercentageOfNoncoveredLoansSecuredWithRealPropertiesInCalifornia
Namespace Prefix:	ewbc
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Details

Name:	ewbc_PurchasedLoansAbstract
Namespace Prefix:	ewbc
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The ratio of residential mortgage loans that offer the borrower variable payment option features to total residential mortgage loans as of the balance sheet date.

+ Details

Name:	ewbc_RatioOfResidentialMortgageLoansWithVariablePaymentOptionFeaturesToTotalResidentialMortgageLoans
Namespace Prefix:	ewbc
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The ratio of single-family loans that offer the borrower interest-only features to total single-family loans as of the balance sheet date.

+ Details

Name:	ewbc_RatioOfSingleFamilyMortgageLoansWithInterestOnlyFeaturesToTotalSingleFamilyLoans
Namespace Prefix:	ewbc
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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.

+ Details

Name:	ewbc_ScheduleOfNonCoveredLoansReceivableLineItems
Namespace Prefix:	ewbc
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Total amount of single-family mortgage loans that offer the borrower interest-only features as of the balance sheet date.

+ Details

Name:	ewbc_SingleFamilyMortgageLoansWithInterestOnlyFeatures
Namespace Prefix:	ewbc
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- 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 Statement of Financial Accounting Standard (FAS)

-Number 140

-Paragraph 15

-Subparagraph a

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: 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=6965416&loc=d3e5086-111524

Reference 3: 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

- Definition

The aggregate carrying amount of loans receivable that will be sold to other entities. Includes mortgage and all other loans (collectively, loans) not classified as held for investment. Such loans are stated at the lower of cost or market, or elected fair value. Mortgage loans exclude mortgage-backed securities which are considered a debt security (other loan).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.7(a))

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

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

-Publisher AICPA

-Name Statement of Position (SOP)

-Number 01-6

-Paragraph 13

-Subparagraph d

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 65

-Paragraph 4, 5, 6, 7, 9, 12, 28, 29

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 35

-Paragraph 49

-URI http://asc.fasb.org/extlink&oid=6949992&loc=d3e3084-111518

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Article 9

-Section 03

-Paragraph 7

-Subparagraph a

Reference 6: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 948

-SubTopic 310

-Section 30

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6490209&loc=d3e48214-111002

Reference 7: http://www.xbrl.org/2003/role/presentationRef

-Publisher OTS

-Name Federal Regulation (FR)

-Number Title 12

-Chapter V

-Section 563c.102

-Subsection I

-Paragraph 8

-Subparagraph h

-LegacyDoc This is a non-GAAP reference that was included in the 2009 taxonomy. It will be removed from future versions of this taxonomy.

Reference 8: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 65

-Paragraph 4

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 9: 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=6375948&loc=d3e4428-111522

+ Details

Name:	us-gaap_LoansReceivableHeldForSaleNet
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_LoansReceivableHeldForSaleNetAbstract
Namespace Prefix:	us-gaap
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The cash inflow resulting from the sale of loans classified as held-for-sale, including proceeds from loans sold through mortgage securitization.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 21

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3461-108585

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 230

-SubTopic 10

-Section 45

-Paragraph 16

-URI http://asc.fasb.org/extlink&oid=6943989&loc=d3e3337-108585

Reference 3: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 102

-Paragraph 9

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 4: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 95

-Paragraph 3, 15, 16, 17, 22, 23, 147, 148, 149

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 5: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 230

-Section 55

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=6587932&loc=d3e60097-112785

+ Details

Name:	us-gaap_ProceedsFromSaleOfLoansHeldForSale
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Reflects the cumulative amount of fees paid by borrowers which have not yet been taken into income and unamortized costs incurred to originate loans and leases, unamortized loan commitments and loan syndication fees, and premiums over or discounts from face amounts of loans that are being amortized into income as an adjustment to yield.

+ References

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

-Publisher FASB

-Name Statement of Financial Accounting Standard (FAS)

-Number 91

-Paragraph 21

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 20

-Section 45

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6378536&loc=d3e10092-111533

+ Details

Name:	us-gaap_UnamortizedLoanCommitmentAndOriginationFeesAndUnamortizedDiscountsOrPremiums
Namespace Prefix:	us-gaap
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

NON-COVERED LOANS AND ALLOWANCE FOR LOAN LOSSES (Details) (USD $)	9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Dec. 31, 2010
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	$ 9,807,250,000		$ 8,717,388,000
Unearned fees, premiums, and discounts, net	(16,746,000)		(56,781,000)
Allowance for non-covered loans receivable	(211,738,000)		(230,408,000)
Non-covered loans receivable, excluding covered loans, net	9,578,766,000		8,430,199,000
Accrued interest on covered and non-covered loans receivable	66,000,000		65,600,000
Covered and non-covered loans receivable pledged to secure borrowings from the FHLB and Federal Reserve Bank	8,100,000,000		8,140,000,000
Number of units of which residential property securing fixed and adjustable rate first mortgage loans consist, minimum	1
Number of units of which residential property securing fixed and adjustable rate first mortgage loans consist, maximum	4
Amount of new first mortgage loans originated on single-family residential properties	585,000,000	299,300,000
Amount of new first mortgage loans originated on multifamily residential properties	34,100,000	19,100,000
Adjustable rate mortgage, term of initial fixed interest rates, minimum (in months)	6M
Adjustable rate mortgage, term of initial fixed interest rates, midrange (in years)	3Y
Adjustable rate mortgage, term of initial fixed interest rates, maximum (in years)	5Y
Amount of single-family loans with interest-only features	5,600,000		7,800,000
Ratio of single-family mortgage loans with interest-only features to total single-family loans (in hundredths)	1.00%		1.00%
Amount of acquired residential mortgage loans with variable payment option features	14,100,000		16,900,000
Ratio of residential mortgage loans with variable payment option features to total residential mortgage loans (in hundredths)	1.00%		1.00%
Credit Risk and Concentrations [Abstract]
Percentage of non-covered loans secured by real properties located in California (in hundredths)	93.00%
Purchased Loans [Abstract]
Loans acquired during the period	603,200,000
Carrying amount of student loans acquired during the period	513,700,000
Loans Held for Sale [Abstract]
Total loans held for sale	251,920,000		220,055,000
Percentage of loans held for sale that were student loans reclassified to loans held for sale during the period (in hundredths)	87.00%
Proceeds from sales of loans held for sale during the period	637,500,000	167,600,000
Net gain from sale of loans held for sale during the period	14,500,000	2,800,000
Residential [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	2,460,382,000		2,093,769,000
Residential [Member] \| Single-family [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	1,517,954,000		1,119,024,000
Residential [Member] \| Multifamily [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	942,428,000		974,745,000
Commercial Real Estate [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	3,831,141,000		3,906,738,000
Commercial Real Estate [Member] \| Income Producing [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	3,459,001,000		3,392,984,000
Commercial Real Estate [Member] \| Construction [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	192,988,000		278,047,000
Commercial Real Estate [Member] \| Land CRE [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	179,152,000		235,707,000
Commercial and Industrial [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	3,012,152,000		1,983,355,000
Commercial and Industrial [Member] \| Commercial Business [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	2,542,313,000		1,674,698,000
Commercial and Industrial [Member] \| Trade Finance [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	469,839,000		308,657,000
Consumer [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	503,575,000		733,526,000
Consumer [Member] \| Student Loans [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	260,283,000		490,314,000
Consumer [Member] \| Other Consumer [Member]
Schedule of Non-Covered Loans Receivable [Line Items]
Loans receivable, excluding covered loans, gross	$ 243,292,000		$ 243,212,000