Document And Entity Information - shares	9 Months Ended
	Sep. 30, 2023	Oct. 31, 2023
Document Information [Line Items]
Entity, Registrant Name	CATHAY GENERAL BANCORP
Document, Type	10-Q/A
Document, Quarterly Report	true
Document, Period End Date	Sep. 30, 2023
Current Fiscal Year End Date	--12-31
Document, Fiscal Period Focus	Q3
Document, Fiscal Year Focus	2023
Document, Transition Report	false
Entity, File Number	001-31830
Entity, Incorporation, State or Country Code	DE
Entity, Tax Identification Number	95-4274680
Entity, Address, Address Line One	777 North Broadway
Entity, Address, City or Town	Los Angeles
Entity, Address, State or Province	CA
Entity, Address, Postal Zip Code	90012
City Area Code	213
Local Phone Number	625-4700
Title of 12(b) Security	Common Stock
Trading Symbol	CATY
Security Exchange Name	NASDAQ
Entity, Current Reporting Status	Yes
Entity, Interactive Data, Current	Yes
Entity, Filer Category	Large Accelerated Filer
Entity, Small Business	false
Entity, Emerging Growth Company	false
Entity, Shell Company	false
Entity, Common Stock Shares, Outstanding		72,648,863
Amendment Description	Cathay General Bancorp is filing this Amendment No. 1 on Form 10-Q/A (the “Amendment”) to its Quarterly Report on Form 10-Q for the quarter ended September 30, 2023, filed with the Securities and Exchange Commission on November 8, 2023 (the “Original Report”), solely to correct the signature page to the Original Report, which inadvertently omitted the date of signature.   Except for the adding of the date of signature, no other changes have been made to the Original Report. This Amendment does not reflect any subsequent events occurring after the original filing date of the Original Report or modify or update in any way disclosures made in the Original Report.
Amendment Flag	true
Entity, Central Index Key	0000861842