Note 19 - Condensed Financial Information of Cathay General Bancorp - Balance Sheets (Details) (Parentheticals) - $ / shares	Dec. 31, 2016	Dec. 31, 2015
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)	87,820,920	87,002,931
Common stock, shares outstanding (in shares)	79,610,277	80,806,116
Treasury stock shares (in shares)	8,210,643	6,196,815
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)	87,820,920	87,002,931
Common stock, shares outstanding (in shares)	79,610,277	80,806,116
Treasury stock shares (in shares)	8,210,643	6,196,815