Loans Receivable and Allowance for Credit Losses (Loans Held-for-Sale Activity) (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Loans Held-for-Sale
Loans transferred from held-for-investment to held-for-sale	$ 155,767	$ 278,024
Sales	114,287	275,945
Purchases	80,046	147,242
Net gains from sales of loans held-for-sale during the period, excluding lower of cost or fair value adjustment	1,600	2,800
C & I and CRE \| Originated
Loans Held-for-Sale
Sales	89,700	29,300
Loans sold in secondary market \| Purchased
Loans Held-for-Sale
Sales	24,600	246,600
Commercial lending \| Commercial and industrial (“C&I”)
Loans Held-for-Sale
Sales	102,365	236,679
Purchases	64,747	147,116
Commercial lending \| Commercial real estate (“CRE”)
Loans Held-for-Sale
Sales	9,376	12,765
Purchases	0	0
Commercial lending \| Real estate loan \| Multifamily
Loans Held-for-Sale
Sales	0	0
Purchases	186	126
Consumer lending \| Real estate loan \| Single-family
Loans Held-for-Sale
Sales	2,546	4,310
Purchases	15,113	0
Consumer lending \| Other consumer
Loans Held-for-Sale
Sales	0	22,191
Purchases	0	0
Loans held-for-sale
Loans Held-for-Sale
Loans transferred from held-for-investment to held-for-sale	155,767	278,024
Write-down of loans transferred from loans held-for-investment to loans held-for-sale recorded to allowance for loan losses	85	92
Lower of cost or fair value adjustment		69
Loans held-for-sale \| Commercial lending \| Commercial and industrial (“C&I”)
Loans Held-for-Sale
Loans transferred from held-for-investment to held-for-sale	146,391	265,259
Loans held-for-sale \| Commercial lending \| Commercial real estate (“CRE”)
Loans Held-for-Sale
Loans transferred from held-for-investment to held-for-sale	9,376	12,765
Loans held-for-sale \| Commercial lending \| Real estate loan \| Multifamily
Loans Held-for-Sale
Loans transferred from held-for-investment to held-for-sale	0	0
Loans held-for-sale \| Consumer lending \| Real estate loan \| Single-family
Loans Held-for-Sale
Loans transferred from held-for-investment to held-for-sale	0	0
Loans held-for-sale \| Consumer lending \| Other consumer
Loans Held-for-Sale
Loans transferred from held-for-investment to held-for-sale	$ 0	$ 0

Amount of loans and leases that have been written off from both loan receivables and allowance reserve for credit loss.

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(3)
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953423-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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

- Definition

Amount of addition (reduction) to the amount at which an asset could be incurred (settled) in a current transaction between willing parties.

+ References

No definition available.

+ Details

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

- Definition

The amount of any significant purchases of financing receivables during the reporting period.

+ References

+ Details

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

- Definition

The amount of any significant sales of financing receivables during the reporting period.

+ References

+ Details

Name:	us-gaap_FinancingReceivableSignificantSales
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

The gains (losses) included in earnings that represent the difference between the sale price and the carrying value of loans and leases that were sold during the reporting period. This element refers to the gain (loss) and not to the cash proceeds of the sales. This element is a noncash adjustment to net income when calculating net cash generated by operating activities using the indirect method.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 24
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3521-108585

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=98514028&loc=d3e3602-108585

+ Details

Name:	us-gaap_GainLossOnSaleOfLoansAndLeases
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- References

No definition available.

+ Details

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

- Definition

Value of loans and leases held in the entity's portfolio transferred to loans and leases held-for-sale in noncash transactions.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 3
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4304-108586

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4332-108586

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=98513485&loc=d3e4313-108586

+ Details

Name:	us-gaap_TransferOfPortfolioLoansAndLeasesToHeldForSale1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ewbc_CommercialAndIndustrialAndCommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ewbc_LoansSoldInSecondaryMarketMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ewbc_CommercialAndIndustrialLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_RealEstateLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=us-gaap_MultifamilyMember
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_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=us-gaap_SingleFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ewbc_OtherConsumerMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByAssetClassAxis=ewbc_LoansHeldForSaleMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: