Basis of Presentation (Details)	Jun. 30, 2018 trust
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Number of wholly-owned subsidiaries that are statutory business trusts (the Trusts)	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