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		9 Months Ended
	Sep. 30, 2011	Sep. 30, 2010	Sep. 30, 2011	Sep. 30, 2010
Earnings/Loss Per Share [Abstract]
Net income/(loss) attributable to Cathay General Bancorp	$ 26,084	$ 17,272	$ 72,449	$ (6,546)
Dividends on preferred stock	(4,111)	(4,098)	(12,323)	(12,286)
Net income/(loss) available to common stockholders	$ 21,973	$ 13,174	$ 60,126	$ (18,832)
Basic weighted-average number of common shares outstanding	78,640,308	78,520,612	78,628,477	76,584,138
Dilutive effect of weighted-average outstanding common share equivalents stock options	834		9,500
Diluted weighted-average number of common shares outstanding	78,641,142	78,520,612	78,637,977	76,584,138
Average stock options and warrants with anti-dilutive effect	6,294,961	6,911,096	6,265,913	6,946,976
Basic	$ 0.28	$ 0.17	$ 0.76	$ (0.25)
Diluted	$ 0.28	$ 0.17	$ 0.76	$ (0.25)