FAIR VALUE MEASUREMENT AND FAIR VALUE OF FINANCIAL INSTRUMENTS (Details 5) - Fair Value, Measurements, Nonrecurring - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2016	Dec. 31, 2015
OREO
Quantitative information
OREO	$ 3,490	$ 4,929
Loans Receivable \| Non-PCI loans
Quantitative information
Impaired loans	80,850	70,462
Significant Unobservable Inputs (Level 3) \| OREO
Quantitative information
OREO	3,490	4,929
Significant Unobservable Inputs (Level 3) \| OREO \| Appraisal
Quantitative information
OREO	$ 3,490	$ 4,929
Selling cost (as a percent)	8.00%	8.00%
Significant Unobservable Inputs (Level 3) \| OREO \| Appraisal \| Weighted Average
Quantitative information
Selling cost (as a percent)	8.00%	8.00%
Significant Unobservable Inputs (Level 3) \| Loans Receivable \| Non-PCI loans
Quantitative information
Impaired loans	$ 80,850	$ 70,462
Significant Unobservable Inputs (Level 3) \| Loans Receivable \| Non-PCI loans \| Discounted cash flow
Quantitative information
Impaired loans	$ 40,719	$ 27,522
Significant Unobservable Inputs (Level 3) \| Loans Receivable \| Non-PCI loans \| Discounted cash flow \| Minimum
Quantitative information
Discount rate (as a percent)	0.00%	0.00%
Significant Unobservable Inputs (Level 3) \| Loans Receivable \| Non-PCI loans \| Discounted cash flow \| Maximum
Quantitative information
Discount rate (as a percent)	84.00%	87.00%
Significant Unobservable Inputs (Level 3) \| Loans Receivable \| Non-PCI loans \| Discounted cash flow \| Weighted Average
Quantitative information
Discount rate (as a percent)	23.00%	30.00%
Significant Unobservable Inputs (Level 3) \| Loans Receivable \| Non-PCI loans \| Market comparables
Quantitative information
Impaired loans	$ 40,131	$ 42,940
Significant Unobservable Inputs (Level 3) \| Loans Receivable \| Non-PCI loans \| Market comparables \| Minimum
Quantitative information
Discount rate (as a percent)	0.00%	0.00%
Significant Unobservable Inputs (Level 3) \| Loans Receivable \| Non-PCI loans \| Market comparables \| Maximum
Quantitative information
Discount rate (as a percent)	43.00%	100.00%
Significant Unobservable Inputs (Level 3) \| Loans Receivable \| Non-PCI loans \| Market comparables \| Weighted Average
Quantitative information
Discount rate (as a percent)	12.00%	17.00%

Represents selling cost used as an input to measure fair value.

No definition available.

Name:	ewbc_FairValueInputsSellingCost
Namespace Prefix:	ewbc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
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.

+ References

No definition available.

+ Details

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

- Definition

Interest rate used to find the present value of an amount to be paid or received in the future as an input to measure fair value. For example, but not limited to, weighted average cost of capital (WACC), cost of capital, cost of equity and cost of debt.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (bbb)
-URI http://asc.fasb.org/extlink&oid=36462937&loc=d3e19207-110258

+ Details

Name:	us-gaap_FairValueInputsDiscountRate
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Glossary Loan
-URI http://asc.fasb.org/extlink&oid=6517073

+ Details

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

- Details

Name:	us-gaap_FairValueByMeasurementFrequencyAxis=us-gaap_FairValueMeasurementsNonrecurringMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=ewbc_OtherRealEstateOwnedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_LoansReceivableMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=ewbc_ReceivablesOriginatedOrAcquiredWithoutDeterioratedCreditQualityMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationTechniqueAxis=ewbc_AppraisalValuationTechniqueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_WeightedAverageMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationTechniqueAxis=ewbc_DiscountedCashFlowValuationTechniqueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_RangeAxis=us-gaap_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationTechniqueAxis=us-gaap_MarketApproachValuationTechniqueMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: