CUSTOMER DEPOSIT ACCOUNTS (Details2) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010
Scheduled maturities of time deposits
2012	$ 6,204,106
2013	511,317
2014	107,690
2015	88,927
2016	79,428
Thereafter	154,533
Total time deposits	7,146,001	6,765,453
Time deposits, less than $100,000.
Scheduled maturities of time deposits
2012	1,962,274
2013	165,990
2014	6,648
2015	45,776
2016	5,908
Thereafter	8
Total time deposits	2,186,604
Time deposits, $100,000 or greater
Scheduled maturities of time deposits
2012	4,241,832
2013	345,327
2014	101,042
2015	43,151
2016	73,520
Thereafter	154,525
Total time deposits	$ 4,959,397

Name:	ewbc_TimeDepositsByMaturityLineItems
Namespace Prefix:	ewbc_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

Amount of time deposits (including certificates of deposits, individual retirement accounts and open accounts) held by the entity with a remaining term of greater than five years.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher AICPA

-Name Audit and Accounting Guide (AAG)

-Number AAG-DEP

-Chapter 13

-Paragraph 45

-Subparagraph a

-IssueDate 2006-05-01

-LegacyDoc This reference is SUPERSEDED by the Accounting Standards Codification effective for interim and annual periods ending after September 15, 2009. This reference is included to help users transition from the previous accounting hierarchy and will be removed from future versions of this taxonomy.

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 470

-SubTopic 10

-Section 50

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=6802200&loc=d3e1835-112601

+ Details

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

- Definition

Amount of time deposits (including certificates of deposits, individual retirement accounts and open accounts) held by the entity with a remaining term of greater than four years but five years or less.

+ References

+ Details

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

- Definition

Amount of time deposits (including certificates of deposits, individual retirement accounts and open accounts) held by the entity with a remaining term of greater than three years but four years or less.

+ References

+ Details

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

- Definition

Amount of time deposits (including certificates of deposits, individual retirement accounts and open accounts) held by the entity with a remaining term of twelve months or less.

+ References

+ Details

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

- Definition

Amount of time deposits (including certificates of deposits, individual retirement accounts and open accounts) held by the entity with a remaining term of greater than two years but three years or less.

+ References

+ Details

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

- Definition

Amount of time deposits (including certificates of deposits, individual retirement accounts and open accounts) held by the entity with a remaining term of greater than twelve months, but two years or less.

+ References

+ Details

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

- Definition

The aggregate amount of time deposits, including certificates of deposits, individual retirement accounts and open accounts.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 12

-Article 9

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 210.9-03.12)

-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

+ Details

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