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

Represents the number of segments that are provided broad administrative support.

No definition available.

Name:	ewbc_NumberOfSegmentWhomBroadAdministrativeSupportProvided
Namespace Prefix:	ewbc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant