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, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Note 4 - Earnings per Share (Details) - Earnings per Share [Line Items]
Net income attributable to Cathay General Bancorp (in Dollars)	$ 35,909	$ 32,478	$ 102,252	$ 91,241
Dividends on preferred stock and noncash charge from repayment (in Dollars)		(2,434)		(9,685)
Net income available to common stockholders (in Dollars)	$ 35,909	$ 30,044	$ 102,252	$ 81,556
Basic weighted-average number of common shares outstanding	79,677,952	78,894,262	79,639,202	78,853,333
Dilutive effect of weighted-average outstanding common share equivalents
Diluted weighted-average number of common shares outstanding	80,176,100	79,114,122	80,087,819	78,944,152
Average stock options and warrants with anti-dilutive effect	1,990,358	3,668,285	1,993,384	4,958,218
Basic (in Dollars per share)	$ 0.45	$ 0.38	$ 1.28	$ 1.03
Diluted (in Dollars per share)	$ 0.45	$ 0.38	$ 1.28	$ 1.03
Warrant [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Dilutive effect of weighted-average number of common shares outstanding	346,101	171,426	306,306	57,771
Equity Option [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Dilutive effect of weighted-average number of common shares outstanding	109,803		103,022
Restricted Stock Units (RSUs) [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Dilutive effect of weighted-average number of common shares outstanding	42,244	48,434	39,289	33,048