Securities Purchased under Resale Agreements and Sold under Repurchase Agreements (Repurchase Agreements) (Details) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Amount of securities sold under repurchase agreements
Maturities Remainder of 2019	$ 0
Maturities 2020	0
Maturities 2021	0
Maturities 2022	150,000
Maturities 2023	300,000
Maturities thereafter	0
Gross repurchase agreements	$ 450,000	$ 450,000

Securities Sold Under Agreements To Repurchase Maturing Remainder of Fiscal Year

No definition available.

Name:	ewbc_SecuritiesSoldUnderAgreementsToRepurchaseMaturingRemainderofFiscalYear
Namespace Prefix:	ewbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Securities Sold Under Agreements To Repurchase Maturing in Year Five

+ References

No definition available.

+ Details

Name:	ewbc_SecuritiesSoldUnderAgreementsToRepurchaseMaturinginYearFive
Namespace Prefix:	ewbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Securities Sold Under Agreements To Repurchase Maturing in Year Four

+ References

No definition available.

+ Details

Name:	ewbc_SecuritiesSoldUnderAgreementsToRepurchaseMaturinginYearFour
Namespace Prefix:	ewbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Securities Sold Under Agreements To Repurchase Maturing in Year Three

+ References

No definition available.

+ Details

Name:	ewbc_SecuritiesSoldUnderAgreementsToRepurchaseMaturinginYearThree
Namespace Prefix:	ewbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Securities Sold Under Agreements To Repurchase Maturing in Year Two

+ References

No definition available.

+ Details

Name:	ewbc_SecuritiesSoldUnderAgreementsToRepurchaseMaturinginYearTwo
Namespace Prefix:	ewbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Securities Sold under Agreements to Repurchase Year Six And Thereafter

+ References

No definition available.

+ Details

Name:	ewbc_SecuritiesSoldUnderAgreementsToRepurchaseYearSixAndThereafter
Namespace Prefix:	ewbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- References

No definition available.

+ Details

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

- Definition

Amount, before effects of master netting arrangements, of funds outstanding borrowed in the form of a security repurchase agreement between the entity and another party for the sale and repurchase of identical or substantially the same securities at a date certain for a specified price. Includes liabilities elected not to be offset. Excludes liabilities not subject to a master netting arrangement.

+ 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

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 20
-Section 55
-Paragraph 7
-URI http://asc.fasb.org/extlink&oid=99393222&loc=SL20226000-175313

+ Details

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