Document And Entity Information (USD $)	12 Months Ended
	Dec. 31, 2012	Feb. 15, 2013	Jun. 30, 2012
Document and Entity Information [Abstract]
Entity Registrant Name	CATHAY GENERAL BANCORP
Document Type	10-K
Current Fiscal Year End Date	--12-31
Entity Common Stock, Shares Outstanding		78,785,472
Entity Public Float			$ 1,186,791,731
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	Dec. 31, 2012
Document Fiscal Year Focus	2012
Document Fiscal Period Focus	FY