Note 4 - Earnings per Share (Detail) - Outstanding Stock Options - Antidilutive (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Net income attributable to Cathay General Bancorp (in Dollars)	$ 28,913	$ 22,063
Dividends on preferred stock (in Dollars)	(4,117)	(4,105)
Net income available to common stockholders (in Dollars)	$ 24,796	$ 17,958
Basic weighted-average number of common shares outstanding	78,678,645	78,609,460
Stock options	11,487	26,160
Diluted weighted-average number of common shares outstanding	78,690,132	78,635,620
Average stock options and warrants with anti-dilutive effect	6,227,224	6,198,286
Basic (in Dollars per share)	$ 0.32	$ 0.23
Diluted (in Dollars per share)	$ 0.32	$ 0.23