Note 4 - Earnings per Share (Details) - Earnings per Share (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Note 4 - Earnings per Share (Details) - Earnings per Share [Line Items]
Net income attributable to Cathay General Bancorp (in Dollars)	$ 31,259	$ 28,847
Dividends on preferred stock and noncash charge from repayment (in Dollars)		(5,184)
Net income available to common stockholders (in Dollars)	$ 31,259	$ 23,663
Basic weighted-average number of common shares outstanding	79,595,757	78,795,564
Dilutive effect of weighted-average outstanding common share equivalents
Diluted weighted-average number of common shares outstanding	80,039,382	78,815,141
Average stock options and warrants with anti-dilutive effect	1,985,848	5,630,813
Basic (in Dollars per share)	$ 0.39	$ 0.30
Diluted (in Dollars per share)	$ 0.39	$ 0.30
Warrant [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Dilutive effect of weighted-average number of common shares outstanding	298,535
Equity Option [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Dilutive effect of weighted-average number of common shares outstanding	101,698
Restricted Stock Units (RSUs) [Member]
Dilutive effect of weighted-average outstanding common share equivalents
Dilutive effect of weighted-average number of common shares outstanding	43,392	19,577