Note 19 - Condensed Financial Information of Cathay General Bancorp - Balance Sheets (Details) (Parentheticals) - $ / shares	Dec. 31, 2021	Dec. 31, 2020
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)	90,871,860	90,643,206
Common stock, shares outstanding (in shares)	75,750,862	79,508,265
Treasury stock shares (in shares)	15,120,998	11,134,941
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)	90,871,860	90,643,206
Common stock, shares outstanding (in shares)	75,750,862	79,508,265
Treasury stock shares (in shares)	15,120,998	1,134,941