Derivatives (Derivatives Not Designated as Hedging Instruments - Foreign Exchange Contracts) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Derivative [Line Items]
Derivative assets - Fair value	$ 834,204	$ 330,316
Derivative liabilities - Fair value	658,515	256,528
Derivatives not designated as hedging instruments
Derivative [Line Items]
Notional amount	21,826,497	20,540,031
Derivative assets - Fair value	834,131	330,316
Derivative liabilities - Fair value	657,340	251,744
Derivatives not designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Notional amount	4,958,834	4,839,661
Derivative assets - Fair value	64,310	54,637
Derivative liabilities - Fair value	55,627	47,024
Foreign exchange contracts \| Customer Counterparty \| Derivatives not designated as hedging instruments \| Forwards and spot
Derivative [Line Items]
Notional amount	3,658,965	3,581,036
Derivative assets - Fair value	50,674	45,911
Derivative liabilities - Fair value	38,564	40,591
Foreign exchange contracts \| Customer Counterparty \| Derivatives not designated as hedging instruments \| Swaps
Derivative [Line Items]
Notional amount	9,007	6,889
Derivative assets - Fair value	4	16
Derivative liabilities - Fair value	95	84
Foreign exchange contracts \| Customer Counterparty \| Derivatives not designated as hedging instruments \| Written options
Derivative [Line Items]
Notional amount	86,810	87,036
Derivative assets - Fair value	217	127
Derivative liabilities - Fair value	0	0
Foreign exchange contracts \| Customer Counterparty \| Derivatives not designated as hedging instruments \| Collars
Derivative [Line Items]
Notional amount	2,205	2,244
Derivative assets - Fair value	27	0
Derivative liabilities - Fair value	0	14
Foreign exchange contracts \| Customer Counterparty \| Derivatives not designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Notional amount	3,756,987	3,677,205
Derivative assets - Fair value	50,922	46,054
Derivative liabilities - Fair value	38,659	40,689
Foreign exchange contracts \| Financial Counterparty \| Derivatives not designated as hedging instruments \| Forwards and spot
Derivative [Line Items]
Notional amount	176,903	207,492
Derivative assets - Fair value	4,049	1,400
Derivative liabilities - Fair value	7,721	507
Foreign exchange contracts \| Financial Counterparty \| Derivatives not designated as hedging instruments \| Swaps
Derivative [Line Items]
Notional amount	773,059	702,391
Derivative assets - Fair value	7,569	6,156
Derivative liabilities - Fair value	7,256	4,712
Foreign exchange contracts \| Financial Counterparty \| Derivatives not designated as hedging instruments \| Purchased options
Derivative [Line Items]
Notional amount	86,810	87,036
Derivative assets - Fair value	0	0
Derivative liabilities - Fair value	217	127
Foreign exchange contracts \| Financial Counterparty \| Derivatives not designated as hedging instruments \| Collars
Derivative [Line Items]
Notional amount	165,075	165,537
Derivative assets - Fair value	1,770	1,027
Derivative liabilities - Fair value	1,774	989
Foreign exchange contracts \| Financial Counterparty \| Derivatives not designated as hedging instruments \| Foreign exchange contracts
Derivative [Line Items]
Notional amount	1,201,847	1,162,456
Derivative assets - Fair value	13,388	8,583
Derivative liabilities - Fair value	$ 16,968	$ 6,335

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: