Derivatives (Derivatives Not Designated as Hedging Instruments - Foreign Exchange Contracts) (Details) - USD ($) $ in Thousands	Mar. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative assets - Fair value	$ 135,782	$ 107,816
Derivative liabilities - Fair value	109,587	118,305
Derivatives not designated as hedging instruments
Derivative [Line Items]
Notional amount	15,873,400	15,222,341
Derivative assets - Fair value	135,782	107,816
Derivative liabilities - Fair value	104,909	111,828
Derivatives not designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Notional amount	3,513,714	3,407,522
Derivative assets - Fair value	30,085	21,624
Derivative liabilities - Fair value	24,900	19,329
Foreign exchange contracts \| Customer Counterparty \| Derivatives not designated as hedging instruments \| Forwards and spot
Derivative [Line Items]
Notional amount	2,355,139	2,023,425
Derivative assets - Fair value	20,016	11,719
Derivative liabilities - Fair value	18,852	13,079
Foreign exchange contracts \| Customer Counterparty \| Derivatives not designated as hedging instruments \| Swaps
Derivative [Line Items]
Notional amount	31,174	21,108
Derivative assets - Fair value	97	348
Derivative liabilities - Fair value	223	243
Foreign exchange contracts \| Customer Counterparty \| Derivatives not designated as hedging instruments \| Written options
Derivative [Line Items]
Notional amount	549	537
Derivative assets - Fair value	7	16
Derivative liabilities - Fair value	0	0
Foreign exchange contracts \| Customer Counterparty \| Derivatives not designated as hedging instruments \| Collars
Derivative [Line Items]
Notional amount	90,743	83,864
Derivative assets - Fair value	17	0
Derivative liabilities - Fair value	741	370
Foreign exchange contracts \| Customer Counterparty \| Derivatives not designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Notional amount	2,477,605	2,128,934
Derivative assets - Fair value	20,137	12,083
Derivative liabilities - Fair value	19,816	13,692
Foreign exchange contracts \| Financial Counterparty \| Derivatives not designated as hedging instruments \| Forwards and spot
Derivative [Line Items]
Notional amount	239,101	506,342
Derivative assets - Fair value	2,685	3,407
Derivative liabilities - Fair value	1,414	2,285
Foreign exchange contracts \| Financial Counterparty \| Derivatives not designated as hedging instruments \| Swaps
Derivative [Line Items]
Notional amount	705,716	687,845
Derivative assets - Fair value	6,522	5,764
Derivative liabilities - Fair value	3,646	3,336
Foreign exchange contracts \| Financial Counterparty \| Derivatives not designated as hedging instruments \| Purchased options
Derivative [Line Items]
Notional amount	549	537
Derivative assets - Fair value	0	0
Derivative liabilities - Fair value	7	16
Foreign exchange contracts \| Financial Counterparty \| Derivatives not designated as hedging instruments \| Collars
Derivative [Line Items]
Notional amount	90,743	83,864
Derivative assets - Fair value	741	370
Derivative liabilities - Fair value	17	0
Foreign exchange contracts \| Financial Counterparty \| Derivatives not designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Notional amount	1,036,109	1,278,588
Derivative assets - Fair value	9,948	9,541
Derivative liabilities - Fair value	$ 5,084	$ 5,637

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

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://fasb.org/us-gaap/role/ref/legacyRef
-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

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

- Details

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

- Details

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

- Details

Name:	ewbc_DerivativeRiskCategoryAxis=us-gaap_ForeignExchangeContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_CounterpartyNameAxis=ewbc_CustomerCounterpartyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

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

- Details

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

- Details

Name:	srt_CounterpartyNameAxis=ewbc_FinancialCounterpartyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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