Note 4 - Earnings per Share (Detail) - Outstanding Stock Options - Antidilutive (USD $) In Thousands, except Share data, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2012	Jun. 30, 2011	Jun. 30, 2012	Jun. 30, 2011
Net income attributable to Cathay General Bancorp (in Dollars)	$ 29,861	$ 24,302	$ 58,774	$ 46,365
Dividends on preferred stock (in Dollars)	(4,121)	(4,107)	(8,238)	(8,212)
Net income available to common stockholders (in Dollars)	$ 25,740	$ 20,195	$ 50,536	$ 38,153
Basic weighted-average number of common shares outstanding	78,710,279	78,635,324	78,694,462	78,622,464
Stock options	1,893	1,784	6,690	13,905
Diluted weighted-average number of common shares outstanding	78,712,172	78,637,108	78,701,152	78,636,369
Average stock options and warrants with anti-dilutive effect	6,092,332	6,303,432	6,159,778	6,251,149
Basic (in Dollars per share)	$ 0.33	$ 0.26	$ 0.64	$ 0.49
Diluted (in Dollars per share)	$ 0.33	$ 0.26	$ 0.64	$ 0.49