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BUSINESS SEGMENTS (Details) | Mar. 31, 2012 Segment
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BUSINESS SEGMENTS |
Number of operating segments | 3
Number of business divisions | 3
Number of segment whom broad administrative support are provided | 2

X
- Definition The total number of business divisions that meet the criteria of an operating segment. + References No definition available. + Details
Name: | ewbc_NumberOfBusinessDivisions
Namespace Prefix: | ewbc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition The total number of operating segments for the company. + References No definition available. + Details
Name: | ewbc_NumberOfOperatingSegments
Namespace Prefix: | ewbc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Definition Represents the number of segments that are provided broad administrative support. + References No definition available. + Details
Name: | ewbc_NumberOfSegmentWhomBroadAdministrativeSupportProvided
Namespace Prefix: | ewbc_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

X
- Details
Name: | us-gaap_SegmentReportingAbstract
Namespace Prefix: | us-gaap_
Data Type: | xbrli:stringItemType
Balance Type: | na
Period Type: | duration