Note 4 - Earnings per Share (Details) - Earnings per Share (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2013	Sep. 30, 2012	Sep. 30, 2013	Sep. 30, 2012
Note 4 - Earnings per Share (Details) - Earnings per Share [Line Items]
Net income attributable to Cathay General Bancorp (in Dollars)	$ 32,478	$ 30,358	$ 91,241	$ 89,132
Dividends on preferred stock and noncash charge from repayment (in Dollars)	(2,434)	(4,123)	(9,685)	(12,361)
Net income available to common stockholders (in Dollars)	$ 30,044	$ 26,235	$ 81,556	$ 76,771
Basic weighted-average number of common shares outstanding	78,894,262	78,729,272	78,853,333	78,706,150
Dilutive effect of weighted-average outstanding common share equivalents
Diluted weighted-average number of common shares outstanding	79,114,122	78,731,180	78,944,152	78,711,235
Average stock options and warrants with anti-dilutive effect	3,668,285	6,080,292	4,958,218	6,133,089
Basic (in Dollars per share)	$ 0.38	$ 0.33	$ 1.03	$ 0.98
Diluted (in Dollars per share)	$ 0.38	$ 0.33	$ 1.03	$ 0.98
Warrant [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Dilutive effect of weighted-average number of common shares outstanding	171,426		57,771
Restricted Stock Units (RSUs) [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Dilutive effect of weighted-average number of common shares outstanding	48,434	1,908	33,048	5,085