Note 1 - Business (Details Textual)	Mar. 31, 2020
Number Of Limited Partnerships In Housing Investments	10
Percentage of Subsidiaries Common Securities Owned by Parent Company	100.00%
Southern California1 [Member]
Number Of Branch Locations	25
Northern California 1 [Member]
Number Of Branch Locations	13
NEW YORK
Number Of Branch Locations	10
WASHINGTON
Number Of Branch Locations	4
ILLINOIS
Number Of Branch Locations	3
TEXAS
Number Of Branch Locations	2
NEW JERSEY
Number Of Branch Locations	1
HONG KONG
Number Of Branch Locations	1

Percentage of subsidiaries common securities owned by parent company.

No definition available.

Name:	caty_PercentageOfSubsidiariesCommonSecuritiesOwnedByParentCompany
Namespace Prefix:	caty_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant