Revenue from Contracts with Customers (Details) - USD ($) $ in Thousands	3 Months Ended
Mar. 31, 2018	Mar. 31, 2017
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 13,383	$ 14,259
Other sources of noninterest income	61,061	101,569
Total noninterest income	74,444	115,828
Retail Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9,880	10,110
Other sources of noninterest income	34,568	3,454
Total noninterest income	44,448	13,564
Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,345	4,044
Other sources of noninterest income	24,093	21,690
Total noninterest income	27,438	25,734
Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	158	105
Other sources of noninterest income	2,400	76,425
Total noninterest income	2,558	76,530
Deposit service charges and related fee income
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	9,186	8,684
Deposit service charges and related fee income \| Retail Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	6,014	5,837
Deposit service charges and related fee income \| Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	3,014	2,742
Deposit service charges and related fee income \| Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	158	105
Card income
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,244	1,240
Card income \| Retail Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	1,070	1,027
Card income \| Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	174	213
Card income \| Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	0	0
Wealth management fees
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,953	4,335
Wealth management fees \| Retail Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	2,796	3,246
Wealth management fees \| Commercial Banking
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	157	1,089
Wealth management fees \| Other
Disaggregation of Revenue [Line Items]
Revenue from contracts with customers	$ 0	$ 0

Other sources of noninterest income not derived from contracts with customers.

No definition available.

Name:	ewbc_OtherSourcesOfNoninterestIncome
Namespace Prefix:	ewbc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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_DisaggregationOfRevenueLineItems
Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

The total amount of noninterest income which may be derived from: (1) fees and commissions; (2) premiums earned; (3) insurance policy charges; (4) the sale or disposal of assets; and (5) other sources not otherwise specified.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 225
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-04.13)
-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

- Definition

Amount, excluding tax collected from customer, of revenue from satisfaction of performance obligation by transferring promised good or service to customer. Tax collected from customer is tax assessed by governmental authority that is both imposed on and concurrent with specific revenue-producing transaction, including, but not limited to, sales, use, value added and excise.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 32
-Paragraph 2A
-URI http://asc.fasb.org/extlink&oid=82859839&loc=SL82860478-203043

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 4
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130543-203045

Reference 3: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 1
-Subparagraph (a)
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130539-203045

Reference 4: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 606
-SubTopic 10
-Section 50
-Paragraph 5
-URI http://asc.fasb.org/extlink&oid=82913847&loc=SL49130545-203045

+ Details

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

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ewbc_RetailBankingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=ewbc_CommercialBankingMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_StatementBusinessSegmentsAxis=us-gaap_AllOtherSegmentsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=ewbc_DepositServiceChargesAndRelatedFeeIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=ewbc_CardIncomeMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ProductOrServiceAxis=ewbc_WealthManagementFeesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: