Commitments and Contingencies (Details 2) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Guarantees
Allowance for unfunded credit reserves	$ 285,926	$ 260,520
Accrued Expenses and Other Liabilities
Other Commitments
Unfunded commitments in investments in qualified affordable housing partnerships, tax credit and other investments	166,600	174,300
Loans Sold or Securitized with Recourse \| Accrued Expenses and Other Liabilities
Guarantees
Allowance for unfunded credit reserves	256	373
Single Family and Multi-family Residential \| Loans Sold or Securitized with Recourse
Guarantees
Unpaid principal amount of loans sold or securitized with recourse	$ 121,200	$ 150,500

This is the principal amount outstanding for sold or securitized loans only (across all types of loans).

No definition available.

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

- Definition

A valuation allowance for financing receivables that are expected to be uncollectible.

+ References

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)(1)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953423-111524

+ Details

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

- Definition

Minimum amount of other commitment not otherwise specified in the taxonomy. Excludes commitments explicitly modeled in the taxonomy, including but not limited to, long-term and short-term purchase commitments, recorded and unrecorded purchase obligations, supply commitments, registration payment arrangements, leases, debt, product warranties, guarantees, environmental remediation obligations, and pensions.

+ References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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

- Details

Name:	us-gaap_BalanceSheetLocationAxis=ewbc_AccruedExpensesAndOtherLiabilitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_LossContingenciesByNatureOfContingencyAxis=us-gaap_GuaranteeObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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