Note 20 - Condensed Financial Information of Cathay General Bancorp (Details) - Balance Sheets (Parentheticals) - $ / shares	Dec. 31, 2015	Dec. 31, 2014
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock, par value (in Dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	87,002,931	84,022,118
Common stock, shares outstanding	80,806,116	79,814,553
Treasury stock, shares	6,196,815	4,207,565
Parent Company [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock, par value (in Dollars per share)	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	87,002,931	84,022,118
Common stock, shares outstanding	80,806,116	79,814,553
Treasury stock, shares	6,196,815	4,207,565