Note 4 - Earnings per Share (Detail) - Outstanding Stock Options - Antidilutive (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Net income attributable to Cathay General Bancorp (in Dollars)	$ 30,358	$ 26,084	$ 89,132	$ 72,449
Dividends on preferred stock (in Dollars)	(4,123)	(4,111)	(12,361)	(12,323)
Net income available to common stockholders (in Dollars)	$ 26,235	$ 21,973	$ 76,771	$ 60,126
Basic weighted-average number of common shares outstanding	78,729,272	78,640,308	78,706,150	78,628,477
Stock options	1,908	834	5,085	9,500
Diluted weighted-average number of common shares outstanding	78,731,180	78,641,142	78,711,235	78,637,977
Average stock options and warrants with anti-dilutive effect	6,080,292	6,294,961	6,133,089	6,265,913
Basic (in Dollars per share)	$ 0.33	$ 0.28	$ 0.98	$ 0.76
Diluted (in Dollars per share)	$ 0.33	$ 0.28	$ 0.98	$ 0.76