Securities (Continuous Unrealized Losses) (Details) - USD ($) $ in Thousands	Mar. 31, 2020	Dec. 31, 2019
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value	$ 765,558	$ 1,388,661
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months	(45,457)	(18,990)
Available-for-sale debt securities, 12 Months or More, Fair Value	40,617	351,048
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More	(3,370)	(4,249)
Available-for-sale debt securities Fair Value, Total	806,175	1,739,709
Available-for-sale debt securities, Gross Unrealized Loss, Total	(48,827)	(23,239)
U.S. Treasury securities
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value		0
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months		0
Available-for-sale debt securities, 12 Months or More, Fair Value		176,422
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More		(793)
Available-for-sale debt securities Fair Value, Total		176,422
Available-for-sale debt securities, Gross Unrealized Loss, Total		(793)
U.S. government agency and U.S. government-sponsored enterprise debt securities
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value		310,349
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months		(4,407)
Available-for-sale debt securities, 12 Months or More, Fair Value		0
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More		0
Available-for-sale debt securities Fair Value, Total		310,349
Available-for-sale debt securities, Gross Unrealized Loss, Total		(4,407)
U.S. government agency and U.S. government-sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value	116,225	204,675
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months	(2,277)	(2,346)
Available-for-sale debt securities, 12 Months or More, Fair Value	19,252	108,314
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More	(1,891)	(2,548)
Available-for-sale debt securities Fair Value, Total	135,477	312,989
Available-for-sale debt securities, Gross Unrealized Loss, Total	(4,168)	(4,894)
U.S. government agency and U.S. government-sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value	192,572	325,354
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months	(2,408)	(1,234)
Available-for-sale debt securities, 12 Months or More, Fair Value	193	34,337
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More	(4)	(243)
Available-for-sale debt securities Fair Value, Total	192,765	359,691
Available-for-sale debt securities, Gross Unrealized Loss, Total	(2,412)	(1,477)
Municipal securities
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value	18,705	31,130
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months	(1,072)	(109)
Available-for-sale debt securities, 12 Months or More, Fair Value	0	0
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More	0	0
Available-for-sale debt securities Fair Value, Total	18,705	31,130
Available-for-sale debt securities, Gross Unrealized Loss, Total	(1,072)	(109)
Non-agency commercial mortgage-backed securities
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value	31,087	7,914
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months	(737)	(6)
Available-for-sale debt securities, 12 Months or More, Fair Value	0	0
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More	0	0
Available-for-sale debt securities Fair Value, Total	31,087	7,914
Available-for-sale debt securities, Gross Unrealized Loss, Total	(737)	(6)
Non-agency residential mortgage-backed securities
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value	47,044	42,894
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months	(2,134)	(285)
Available-for-sale debt securities, 12 Months or More, Fair Value	0	0
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More	0	0
Available-for-sale debt securities Fair Value, Total	47,044	42,894
Available-for-sale debt securities, Gross Unrealized Loss, Total	(2,134)	(285)
Corporate debt securities
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value	0	0
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months	0	0
Available-for-sale debt securities, 12 Months or More, Fair Value	9,713	9,888
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More	(288)	(113)
Available-for-sale debt securities Fair Value, Total	9,713	9,888
Available-for-sale debt securities, Gross Unrealized Loss, Total	(288)	(113)
Foreign bonds
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value	49,950	129,074
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months	(50)	(407)
Available-for-sale debt securities, 12 Months or More, Fair Value	0	9,900
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More	0	(100)
Available-for-sale debt securities Fair Value, Total	49,950	138,974
Available-for-sale debt securities, Gross Unrealized Loss, Total	(50)	(507)
Asset-backed securities
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value	50,097	52,565
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months	(2,657)	(902)
Available-for-sale debt securities, 12 Months or More, Fair Value	11,459	12,187
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More	(1,187)	(452)
Available-for-sale debt securities Fair Value, Total	61,556	64,752
Available-for-sale debt securities, Gross Unrealized Loss, Total	(3,844)	(1,354)
Collateralized loan obligations (“CLOs”)
Schedule of Available-for-sale Debt Securities
Available-for-sale debt securities, Less than 12 Months, Fair Value	259,878	284,706
Available-for-sale debt securities, Gross Unrealized Loss, Less than 12 Months	(34,122)	(9,294)
Available-for-sale debt securities, 12 Months or More, Fair Value	0	0
Available-for-sale debt securities, Gross Unrealized Loss, 12 Months or More	0	0
Available-for-sale debt securities Fair Value, Total	259,878	284,706
Available-for-sale debt securities, Gross Unrealized Loss, Total	$ (34,122)	$ (9,294)

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for more than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922890-210455

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118942371&loc=SL82922954-210456

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLonger
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for 12 months or longer, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPosition12MonthsOrLongerAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27337-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922890-210455

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118942371&loc=SL82922954-210456

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12Months
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in continuous unrealized loss position for less than 12 months, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position without allowance for credit loss.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27290-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 50
-Paragraph 4
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922888-210455

Reference 3: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 55
-Paragraph 8
-URI http://asc.fasb.org/extlink&oid=118942371&loc=SL82922954-210456

+ Details

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

- Definition

Amount of accumulated unrealized loss on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), in unrealized loss position, without allowance for credit loss. Includes beneficial interest in securitized financial asset.

+ References

+ Details

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

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USGovernmentSponsoredEnterprisesDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=ewbc_CommercialMortgageBackedSecuritiesIssuedByUSGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=ewbc_ResidentialMortgageBackedSecuritiesIssuedByUSGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ResidentialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=ewbc_ForeignGovernmentAndCorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_AssetBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_CollateralizedLoanObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: