Note 21 - Condensed Financial Information of Cathay General Bancorp - Balance Sheets (Details) (Parentheticals) - $ / shares	Dec. 31, 2023	Dec. 31, 2022
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	91,392,480	91,090,614
Common stock, shares outstanding (in shares)	72,668,927	72,742,151
Treasury stock, shares (in shares)	18,723,553	18,348,463
Parent Company [Member]
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized (in shares)	100,000,000	100,000,000
Common stock, shares issued (in shares)	91,392,480	91,090,614
Common stock, shares outstanding (in shares)	72,668,927	72,742,151
Treasury stock, shares (in shares)	18,723,553	18,348,463