Earnings/Loss Per Share (Schedule Of Anti-Dilutive Securities Excluded From Computation Of Earnings Per Share) (Details) (USD $) In Thousands, except Share data	3 Months Ended	6 Months Ended
Jun. 30, 2011	Jun. 30, 2010	Jun. 30, 2011	Jun. 30, 2010
Earnings/Loss Per Share
Net income/(loss) attributable to Cathay General Bancorp	$ 24,302	$ 1,923	$ 46,365	$ (23,818)
Dividends on preferred stock	(4,107)	(4,096)	(8,212)	(8,188)
Net income/(loss) available to common stockholders	$ 20,195	$ (2,173)	$ 38,153	$ (32,006)
Basic weighted-average number of common shares outstanding	78,635,324	78,513,577	78,622,464	75,599,854
Stock Options	1,784,000		13,905,000
Diluted weighted-average number of common shares outstanding	78,637,108	78,513,577	78,636,369	75,599,854
Average shares of stock options and warrants with anti-dilutive effect	6,303,432	6,942,498	6,251,149	6,965,213
Basic	$ 0.26	$ (0.03)	$ 0.49	$ (0.42)
Diluted	$ 0.26	$ (0.03)	$ 0.49	$ (0.42)

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