Document And Entity Information	3 Months Ended
	Mar. 31, 2013	Apr. 30, 2013
Document and Entity Information [Abstract]
Entity Registrant Name	CATHAY GENERAL BANCORP
Document Type	10-Q
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		78,864,841
Amendment Flag	false
Entity Central Index Key	0000861842
Entity Current Reporting Status	Yes
Entity Voluntary Filers	No
Entity Filer Category	Large Accelerated Filer
Entity Well-known Seasoned Issuer	No
Document Period End Date	Mar. 31, 2013
Document Fiscal Year Focus	2013
Document Fiscal Period Focus	Q1