Condensed Financial Information Of Cathay General Bancorp (Condensed Statements Of Operations) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2011	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Dec. 31, 2010	Sep. 30, 2010	Jun. 30, 2010	Mar. 31, 2010	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Interest income	$ 111,076	$ 114,379	$ 114,339	$ 113,777	$ 118,332	$ 120,506	$ 124,287	$ 126,469	$ 453,571	$ 489,594	$ 528,731
Interest expense	31,759	33,426	36,024	38,672	43,095	47,165	49,680	51,748	139,881	191,688	246,039
Non-interest income/(loss)	8,986	16,827	12,453	12,626	16,169	3,886	7,412	4,784	50,892	32,251	78,654
Non-interest expense	43,990	48,383	45,410	47,783	56,348	34,881	40,319	44,163	185,566	175,711	183,037
(Loss)/income before income tax benefit	42,313	40,397	35,358	33,948	25,058	24,446	(3,300)	(48,658)	152,016	(2,454)	(128,691)
Income tax benefit	14,459	14,162	10,906	11,734	6,789	7,023	(5,373)	(23,068)	51,261	(14,629)	(61,912)
Net income/(loss)	27,701	26,084	24,302	22,063	18,111	17,272	1,923	(25,741)	100,150	11,565	(67,390)
Parent Company [Member]
Interest income									259	227	299
Interest expense									3,038	3,075	3,817
Non-interest income/(loss)									286	(782)	(1,929)
Non-interest expense									1,548	1,308	3,581
(Loss)/income before income tax benefit									(4,041)	(4,938)	(9,028)
Income tax benefit									(1,699)	(2,076)	(3,796)
(Loss)/income before undistributed earnings of subsidiaries									(2,342)	(2,862)	(5,232)
Undistributed earnings/(loss) of subsidiaries									102,492	14,427	(62,158)
Net income/(loss)									$ 100,150	$ 11,565	$ (67,390)