Derivatives (Notional and Fair Values) (Details) $ in Thousands, MMBTU in Millions, Boe in Millions	Jun. 30, 2018 USD ($) MMBTU Boe warrant	Dec. 31, 2017 USD ($) warrant
Fair Values of Derivative Instruments
Derivative assets	$ 81,456	$ 66,146
Derivative liabilities	114,542	74,935
Derivatives designated as hedging instruments
Fair Values of Derivative Instruments
Notional Amount	131,326	35,811
Derivative assets	2,316	0
Derivative liabilities	8,647	6,799
Derivatives designated as hedging instruments \| Interest rate swaps
Fair Values of Derivative Instruments
Notional Amount	35,811	35,811
Derivative assets	0	0
Derivative liabilities	8,647	6,799
Derivatives designated as hedging instruments \| Foreign exchange forwards
Fair Values of Derivative Instruments
Notional Amount	95,515	0
Derivative assets	2,316	0
Derivative liabilities	0	0
Derivatives not designated as hedging instruments
Fair Values of Derivative Instruments
Notional Amount	12,295,137	10,153,108
Derivative assets	79,140	66,146
Derivative liabilities	105,895	68,136
Derivatives not designated as hedging instruments \| Interest rate swaps and options
Fair Values of Derivative Instruments
Notional Amount	11,217,468	9,333,860
Derivative assets	64,225	58,633
Derivative liabilities	91,378	57,958
Derivatives not designated as hedging instruments \| Foreign exchange forwards, spot and swaps
Fair Values of Derivative Instruments
Notional Amount	959,645	770,215
Derivative assets	9,408	5,840
Derivative liabilities	11,281	10,170
Derivatives not designated as hedging instruments \| RPAs
Fair Values of Derivative Instruments
Notional Amount	118,024	49,033
Derivative assets	1	1
Derivative liabilities	77	8
Derivatives not designated as hedging instruments \| Equity warrants
Fair Values of Derivative Instruments
Notional Amount	0	0
Derivative assets	1,878	1,672
Derivative liabilities	$ 0	$ 0
Derivatives not designated as hedging instruments \| Warrant, Public Companies
Fair Values of Derivative Instruments
Number of warrants held \| warrant	4	4
Derivatives not designated as hedging instruments \| Warrant, Private Companies
Fair Values of Derivative Instruments
Number of warrants held \| warrant	14	11
Derivatives not designated as hedging instruments \| Commodity swaps and options
Fair Values of Derivative Instruments
Notional Amount	$ 0	$ 0
Derivative assets	3,628	0
Derivative liabilities	$ 3,159	$ 0
Oil
Fair Values of Derivative Instruments
Derivative, nonmonetary notional amount \| Boe	1.8
Natural gas
Fair Values of Derivative Instruments
Derivative, nonmonetary notional amount \| MMBTU	5.2

Aggregate notional amount of derivative expressed in nonmonetary units. For example, the number of barrels specified in a fuel oil forward purchase contract.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

Name:	invest_DerivativeNonmonetaryNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:decimalItemType
Balance Type:	na
Period Type:	instant

- Definition

Aggregate notional amount specified by the derivative(s). Expressed as an absolute value.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher SEC
-Name Regulation S-X (SX)
-Number 210
-Article 12
-Section 13
-Sentence Column B

+ Details

Name:	invest_DerivativeNotionalAmount
Namespace Prefix:	invest_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- Definition

Fair value, before effects of master netting arrangements, of a financial asset or other contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes assets not subject to a master netting arrangement and elected not to be offset.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 50
-Paragraph 3
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=51824906&loc=SL20225862-175312

+ Details

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

- Definition

Fair value, before effects of master netting arrangements, of a financial liability or contract with one or more underlyings, notional amount or payment provision or both, and the contract can be net settled by means outside the contract or delivery of an asset. Includes liabilities not subject to a master netting arrangement and elected not to be offset.

+ References

+ Details

Name:	us-gaap_DerivativeLiabilityFairValueGrossLiabilityIncludingNotSubjectToMasterNettingArrangement
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

The number of derivative instruments of a particular group held by the entity.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=84234895&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNumberOfInstrumentsHeld
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
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.

+ References

No definition available.

+ Details

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

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_DesignatedAsHedgingInstrumentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_ForeignExchangeForwardMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_HedgingDesignationAxis=us-gaap_NondesignatedMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_InterestRateContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ewbc_ForeignExchangeForwardsSpotandSwapsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CreditRiskContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_WarrantMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ewbc_WarrantPublicCompaniesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=ewbc_WarrantPrivateCompaniesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_DerivativeInstrumentRiskAxis=us-gaap_CommodityContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnergyAxis=us-gaap_OilReservesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_EnergyAxis=us-gaap_NaturalGasReservesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: