Derivatives (Derivatives Not Designated as Hedging Instruments - Foreign Exchange Contracts) (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Derivative [Line Items]
Derivative assets - Fair value	$ 330,316	$ 107,816
Derivative liabilities - Fair Value	256,528	118,305
Derivative instruments not designated as hedging instruments
Derivative [Line Items]
Notional amount	20,540,031	15,222,341
Derivative assets - Fair value	330,316	107,816
Derivative liabilities - Fair Value	251,744	111,828
Derivative instruments not designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Notional amount	4,839,661	3,407,522
Derivative assets - Fair value	54,637	21,624
Derivative liabilities - Fair Value	47,024	19,329
Foreign exchange contracts \| Customer Counterparty \| Derivative instruments not designated as hedging instruments \| Forwards and spot
Derivative [Line Items]
Notional amount	3,581,036	2,023,425
Derivative assets - Fair value	45,911	11,719
Derivative liabilities - Fair Value	40,591	13,079
Foreign exchange contracts \| Customer Counterparty \| Derivative instruments not designated as hedging instruments \| Swaps
Derivative [Line Items]
Notional amount	6,889	21,108
Derivative assets - Fair value	16	348
Derivative liabilities - Fair Value	84	243
Foreign exchange contracts \| Customer Counterparty \| Derivative instruments not designated as hedging instruments \| Written options
Derivative [Line Items]
Notional amount	87,036	537
Derivative assets - Fair value	127	16
Derivative liabilities - Fair Value	0	0
Foreign exchange contracts \| Customer Counterparty \| Derivative instruments not designated as hedging instruments \| Collars
Derivative [Line Items]
Notional amount	2,244	83,864
Derivative assets - Fair value	0	0
Derivative liabilities - Fair Value	14	370
Foreign exchange contracts \| Customer Counterparty \| Derivative instruments not designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Notional amount	3,677,205	2,128,934
Derivative assets - Fair value	46,054	12,083
Derivative liabilities - Fair Value	40,689	13,692
Foreign exchange contracts \| Financial Counterparty \| Derivative instruments not designated as hedging instruments \| Forwards and spot
Derivative [Line Items]
Notional amount	207,492	506,342
Derivative assets - Fair value	1,400	3,407
Derivative liabilities - Fair Value	507	2,285
Foreign exchange contracts \| Financial Counterparty \| Derivative instruments not designated as hedging instruments \| Swaps
Derivative [Line Items]
Notional amount	702,391	687,845
Derivative assets - Fair value	6,156	5,764
Derivative liabilities - Fair Value	4,712	3,336
Foreign exchange contracts \| Financial Counterparty \| Derivative instruments not designated as hedging instruments \| Purchased options
Derivative [Line Items]
Notional amount	87,036	537
Derivative assets - Fair value	0	0
Derivative liabilities - Fair Value	127	16
Foreign exchange contracts \| Financial Counterparty \| Derivative instruments not designated as hedging instruments \| Collars
Derivative [Line Items]
Notional amount	165,537	83,864
Derivative assets - Fair value	1,027	370
Derivative liabilities - Fair Value	989	0
Foreign exchange contracts \| Financial Counterparty \| Derivative instruments not designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Notional amount	1,162,456	1,278,588
Derivative assets - Fair value	8,583	9,541
Derivative liabilities - Fair Value	$ 6,335	$ 5,637

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.

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

- Definition

Nominal or face amount used to calculate payment on derivative.

+ References

Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1B
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5580258-113959

Reference 2: http://www.xbrl.org/2009/role/commonPracticeRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 815
-SubTopic 10
-Section 50
-Paragraph 1A
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=109980867&loc=SL5579245-113959

+ Details

Name:	us-gaap_DerivativeNotionalAmount
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	instant

- 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: