Cash And Cash Equivalents (Details) (USD $) In Millions, unless otherwise specified	12 Months Ended
Dec. 31, 2011	Dec. 31, 2010
Cash And Cash Equivalents [Abstract]
Average reserve balances required to be maintained with the federal bank	$ 12.2	$ 16.1

Average reserve balances required to be maintained with the federal bank.

No definition available.

Name:	caty_AverageReserveBalancesRequiredToBeMaintainedWithFederalBank
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration