Loans Receivable and Allowance for Credit Losses (Non-PCI Impaired Loans) (Details) - Non-PCI impaired loans - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Impaired loans disclosures
Unpaid Principal Balance	$ 266,772	$ 152,627
Recorded Investment With No Allowance	129,748	87,812
Recorded Investment With Allowance	68,369	31,106
Total Recorded Investment	198,117	118,918
Related Allowance	5,593	4,032
Average Recorded Investment	370,190	233,180	$ 185,132
Recognized Interest Income	4,318	2,330	2,989
Commercial Lending
Impaired loans disclosures
Unpaid Principal Balance	226,918	125,420
Recorded Investment With No Allowance	115,116	79,713
Recorded Investment With Allowance	44,699	13,287
Total Recorded Investment	159,815	93,000
Related Allowance	3,033	1,502
Average Recorded Investment	307,472	194,194	162,502
Recognized Interest Income	3,692	1,786	2,517
Commercial Lending \| C&I
Impaired loans disclosures
Unpaid Principal Balance	174,656	82,963
Recorded Investment With No Allowance	73,956	48,479
Recorded Investment With Allowance	40,086	8,609
Total Recorded Investment	114,042	57,088
Related Allowance	2,881	1,219
Average Recorded Investment	248,619	143,430	110,662
Recognized Interest Income	2,932	1,046	1,517
Commercial Lending \| CRE
Impaired loans disclosures
Unpaid Principal Balance	27,601	36,426
Recorded Investment With No Allowance	20,098	28,285
Recorded Investment With Allowance	1,520	2,067
Total Recorded Investment	21,618	30,352
Related Allowance	97	208
Average Recorded Investment	33,046	35,049	36,003
Recognized Interest Income	464	491	578
Commercial Lending \| Residential loan \| Multifamily
Impaired loans disclosures
Unpaid Principal Balance	4,965	6,031
Recorded Investment With No Allowance	1,371	2,949
Recorded Investment With Allowance	3,093	2,611
Total Recorded Investment	4,464	5,560
Related Allowance	55	75
Average Recorded Investment	6,116	11,742	11,455
Recognized Interest Income	228	249	422
Commercial Lending \| Construction and land
Impaired loans disclosures
Unpaid Principal Balance	19,696
Recorded Investment With No Allowance	19,691
Recorded Investment With Allowance	0
Total Recorded Investment	19,691
Related Allowance	0	0
Average Recorded Investment	19,691	3,973	4,382
Recognized Interest Income	68	0	0
Commercial Lending \| Total CRE
Impaired loans disclosures
Unpaid Principal Balance	52,262	42,457
Recorded Investment With No Allowance	41,160	31,234
Recorded Investment With Allowance	4,613	4,678
Total Recorded Investment	45,773	35,912
Related Allowance	152	283
Average Recorded Investment	58,853	50,764	51,840
Recognized Interest Income	760	740	1,000
Consumer Lending
Impaired loans disclosures
Unpaid Principal Balance	39,854	27,207
Recorded Investment With No Allowance	14,632	8,099
Recorded Investment With Allowance	23,670	17,819
Total Recorded Investment	38,302	25,918
Related Allowance	2,560	2,530
Average Recorded Investment	62,718	38,986	22,630
Recognized Interest Income	626	544	472
Consumer Lending \| Residential loan \| Single-family
Impaired loans disclosures
Unpaid Principal Balance	23,626	14,670
Recorded Investment With No Allowance	8,507	2,552
Recorded Investment With Allowance	13,704	10,908
Total Recorded Investment	22,211	13,460
Related Allowance	35	34
Average Recorded Investment	37,315	22,350	14,994
Recognized Interest Income	496	474	417
Consumer Lending \| HELOCs
Impaired loans disclosures
Unpaid Principal Balance	13,711	10,035
Recorded Investment With No Allowance	6,125	5,547
Recorded Investment With Allowance	7,449	4,409
Total Recorded Investment	13,574	9,956
Related Allowance	8	5
Average Recorded Investment	22,851	14,134	5,494
Recognized Interest Income	130	70	55
Consumer Lending \| Total residential mortgage
Impaired loans disclosures
Unpaid Principal Balance	37,337	24,705
Recorded Investment With No Allowance	14,632	8,099
Recorded Investment With Allowance	21,153	15,317
Total Recorded Investment	35,785	23,416
Related Allowance	43	39
Average Recorded Investment	60,166	36,484	20,488
Recognized Interest Income	626	544	472
Consumer Lending \| Other consumer
Impaired loans disclosures
Unpaid Principal Balance	2,517	2,502
Recorded Investment With No Allowance	0	0
Recorded Investment With Allowance	2,517	2,502
Total Recorded Investment	2,517	2,502
Related Allowance	2,517	2,491
Average Recorded Investment	2,552	2,502	2,142
Recognized Interest Income	$ 0	$ 0	$ 0

Amount of valuation allowance for financing receivables that are expected to be uncollectible that were individually evaluated for impairment.

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 (g)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

+ Details

Name:	us-gaap_FinancingReceivableAllowanceForCreditLossesIndividuallyEvaluatedForImpairment1
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_FinancingReceivableImpairedLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 15
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5212-111524

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 17
-URI http://asc.fasb.org/extlink&oid=118936363&loc=d3e5258-111524

+ Details

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

- Definition

Amount of interest income recognized that the financing receivables (with related allowance for credit losses and without a related allowance for credit losses) were impaired.

+ References

+ Details

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

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953550-111524

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

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

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

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

- Details

Name:	us-gaap_CreditLossStatusAxis=ewbc_ReceivablesOriginatedOrAcquiredWithoutDeterioratedCreditQualityMember
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:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_MultifamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ewbc_TotalCommercialRealEstateMember
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:	srt_MortgageLoansOnRealEstateDescriptionTypeOfPropertyAxis=srt_SingleFamilyMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=ewbc_TotalResidentialMortgageMember
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: