Summary of Significant Accounting Policies (Nature of Operations and Principles of Consolidation) (Details)	Dec. 31, 2017 location trust
Accounting Policies [Abstract]
Number of banking locations \| location	130
Principles of Consolidation
Number of wholly owned subsidiaries that are statutory business trusts \| trust	6

Represents the number of wholly owned subsidiaries of the entity that are statutory business trusts, which are not consolidated.

No definition available.

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