Note 4 - Earnings per Share (Details) - Earnings per Share (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Note 4 - Earnings per Share (Details) - Earnings per Share [Line Items]
Net income attributable to Cathay General Bancorp (in Dollars)	$ 29,916	$ 29,861	$ 58,763	$ 58,774
Dividends on preferred stock and noncash charge from repayment (in Dollars)	(2,067)	(4,121)	(7,251)	(8,238)
Net income available to common stockholders (in Dollars)	$ 27,849	$ 25,740	$ 51,512	$ 50,536
Basic weighted-average number of common shares outstanding	78,869,089	78,710,279	78,832,530	78,694,462
Diluted weighted-average number of common shares outstanding	78,899,906	78,712,172	78,857,758	78,701,152
Average stock options and warrants with anti-dilutive effect	5,597,123	6,092,332	5,613,875	6,159,778
Basic (in Dollars per share)	$ 0.35	$ 0.33	$ 0.65	$ 0.64
Diluted (in Dollars per share)	$ 0.35	$ 0.33	$ 0.65	$ 0.64
Restricted Stock Units (RSUs) [Member]
Note 4 - Earnings per Share (Details) - Earnings per Share [Line Items]
Restricted stock units	30,817	1,893	25,228	6,690