Number of investments in debt securities 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.

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 6
-Subparagraph (b)(3)
-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 (b)(3)
-URI http://asc.fasb.org/extlink&oid=118955579&loc=SL82922888-210455

+ Details

Name:	us-gaap_DebtSecuritiesAvailableForSaleUnrealizedLossPositionNumberOfPositions
Namespace Prefix:	us-gaap_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

This item represents an increase to the cumulative amount of credit losses recognized in earnings for an other than temporary impairment (OTTI) of a debt security held for which no such other than temporary impairment (OTTI) was previously recognized.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 8B
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118939692&loc=SL6284393-111563

+ Details

Name:	us-gaap_OtherThanTemporaryImpairmentCreditLossesRecognizedInEarningsAdditionsNoPreviousImpairment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

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

- Details

Name:	us-gaap_InformationByCategoryOfDebtSecurityAxis=us-gaap_AvailableforsaleSecuritiesMember
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=ewbc_MortgageBackedSecuritiesIssuedByUSGovernmentAgenciesAndGovernmentSponsoredEnterpriseMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

Securities (Other-Than-Temporary Impairment) (Details)	3 Months Ended		6 Months Ended
Securities (Other-Than-Temporary Impairment) (Details)	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Jun. 30, 2019 USD ($) security	Jun. 30, 2018 USD ($)	Dec. 31, 2018 security
Other Than Temporary Impairment Credit Losses Recognized in Earnings
Number of available-for-sale debt securities in an unrealized loss position	76		76		184
Investment securities available-for-sale
Other Than Temporary Impairment Credit Losses Recognized in Earnings
OTTI credit losses \| $	$ 0	$ 0	$ 0	$ 0
Foreign bonds
Other Than Temporary Impairment Credit Losses Recognized in Earnings
Number of available-for-sale debt securities in an unrealized loss position	11		11		16
U.S. government agency and U.S. government sponsored enterprise mortgage-backed securities
Other Than Temporary Impairment Credit Losses Recognized in Earnings
Number of available-for-sale debt securities in an unrealized loss position	40		40		108
U.S. Treasury securities
Other Than Temporary Impairment Credit Losses Recognized in Earnings
Number of available-for-sale debt securities in an unrealized loss position	12		12		19