Securities (Schedule of Available-for-sale Debt Securities) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Schedule of Available-for-sale Debt Securities
Total available-for-sale debt investment securities, Amortized Cost	$ 2,585,505	$ 2,806,900
Gross Unrealized Gains	21,229	5,714
Gross Unrealized Losses	(13,821)	(70,767)
Available-for-sale debt securities, Fair Value	2,592,913	2,741,847
U.S. Treasury securities
Schedule of Available-for-sale Debt Securities
Total available-for-sale debt investment securities, Amortized Cost	329,209	577,561
Gross Unrealized Gains	0	153
Gross Unrealized Losses	(2,674)	(12,899)
Available-for-sale debt securities, Fair Value	326,535	564,815
U.S. government agency and U.S. government sponsored enterprise debt securities
Schedule of Available-for-sale Debt Securities
Total available-for-sale debt investment securities, Amortized Cost	239,732	219,485
Gross Unrealized Gains	2,252	382
Gross Unrealized Losses	(17)	(2,694)
Available-for-sale debt securities, Fair Value	241,967	217,173
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Commercial mortgage-backed securities
Schedule of Available-for-sale Debt Securities
Total available-for-sale debt investment securities, Amortized Cost	471,189	420,486
Gross Unrealized Gains	7,956	811
Gross Unrealized Losses	(4,313)	(12,694)
Available-for-sale debt securities, Fair Value	474,832	408,603
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities - Residential mortgage-backed securities
Schedule of Available-for-sale Debt Securities
Total available-for-sale debt investment securities, Amortized Cost	836,757	957,219
Gross Unrealized Gains	8,222	4,026
Gross Unrealized Losses	(1,405)	(14,552)
Available-for-sale debt securities, Fair Value	843,574	946,693
Municipal securities
Schedule of Available-for-sale Debt Securities
Total available-for-sale debt investment securities, Amortized Cost	86,776	82,965
Gross Unrealized Gains	791	87
Gross Unrealized Losses	(38)	(1,032)
Available-for-sale debt securities, Fair Value	87,529	82,020
Non-agency commercial mortgage-backed securities
Schedule of Available-for-sale Debt Securities
Total available-for-sale debt investment securities, Amortized Cost	68,675	25,826
Gross Unrealized Gains	1,878	226
Gross Unrealized Losses	(4)	0
Available-for-sale debt securities, Fair Value	70,549	26,052
Non-agency residential mortgage-backed securities
Schedule of Available-for-sale Debt Securities
Total available-for-sale debt investment securities, Amortized Cost	24,534	10,109
Gross Unrealized Gains	19	7
Gross Unrealized Losses	(14)	(185)
Available-for-sale debt securities, Fair Value	24,539	9,931
Corporate debt securities
Schedule of Available-for-sale Debt Securities
Total available-for-sale debt investment securities, Amortized Cost	11,250	11,250
Gross Unrealized Gains	0	0
Gross Unrealized Losses	(94)	(381)
Available-for-sale debt securities, Fair Value	11,156	10,869
Foreign bonds
Schedule of Available-for-sale Debt Securities
Total available-for-sale debt investment securities, Amortized Cost	489,392	489,378
Gross Unrealized Gains	111	0
Gross Unrealized Losses	(5,087)	(26,330)
Available-for-sale debt securities, Fair Value	484,416	463,048
Asset-backed securities
Schedule of Available-for-sale Debt Securities
Total available-for-sale debt investment securities, Amortized Cost	27,991	12,621
Gross Unrealized Gains	0	22
Gross Unrealized Losses	(175)	0
Available-for-sale debt securities, Fair Value	$ 27,816	$ 12,643

Amount, before tax, of unrealized gain in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

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

- Definition

Amount, before tax, of unrealized loss in accumulated other comprehensive income (AOCI) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

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

- Definition

Amortized cost of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

+ Details

Name:	us-gaap_AvailableForSaleDebtSecuritiesAmortizedCostBasis
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).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=118942338&loc=SL82898722-210454

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118954083&loc=d3e26610-111562

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecurities
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: