Allowance for Unfunded Credit Commitments, Period Increase (Decrease)

No definition available.

Name:	ewbc_AllowanceForUnfundedCreditCommitmentsPeriodIncreaseDecrease
Namespace Prefix:	ewbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Financing Receivable And Off Balance Sheet Credit Loss Allowance

+ References

No definition available.

+ Details

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

- Definition

Financing Receivable And Off Balance Sheet Credit Loss Allowance, Period Increase (Decrease)

+ References

No definition available.

+ Details

Name:	ewbc_FinancingReceivableAndOffBalanceSheetCreditLossAllowancePeriodIncreaseDecrease
Namespace Prefix:	ewbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Financing Receivable, Collateral Dependent

+ References

No definition available.

+ Details

Name:	ewbc_FinancingReceivableCollateralDependent
Namespace Prefix:	ewbc_
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_FinancingReceivableAllowanceForCreditLossesLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of increase (decrease) in allowance for credit loss on financing receivable.

+ References

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesPeriodIncreaseDecrease
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	na
Period Type:	duration

- Definition

Amount of expense related loan transactions, lease transactions, credit loss from transactions other than loan and lease transactions, and other loss based on assessment of uncollectability from the counterparty to reduce the account to their net realizable value.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(2)
-URI http://asc.fasb.org/extlink&oid=121611835&loc=SL6953423-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 220
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.11)
-URI http://asc.fasb.org/extlink&oid=120399700&loc=SL114874048-224260

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=121586364&loc=d3e3602-108585

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=ewbc_CommercialandConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Loans Receivable and Allowance for Credit Losses (Allowance for Credit Losses Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Financing Receivable Allowance for Credit Losses
Financing receivable and off balance sheet credit loss allowance	$ 640,000		$ 653,600
Decrease in allowance for credit losses	(13,600)
Provision for (reversal of) credit losses	0	$ 73,870
Commercial lending
Financing Receivable Allowance for Credit Losses
Collateral dependent loan	99,900		97,200
Consumer lending
Financing Receivable Allowance for Credit Losses
Collateral dependent loan	16,600		$ 17,300
Commercial and consumer lending
Financing Receivable Allowance for Credit Losses
Decrease to allowance for loan losses	(12,500)
Decrease in allowance for unfunded credit commitments	$ (1,100)