Note 20 - Condensed Financial Information of Cathay General Bancorp (Details) - Statements of Operations (USD $) In Thousands, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Condensed Income Statements, Captions [Line Items]
Interest income	$ 106,043	$ 106,335	$ 105,062	$ 101,207	$ 101,621	$ 102,462	$ 100,862	$ 102,051
Interest expense	18,292	19,580	19,445	18,549	19,659	19,854	20,868	21,919	75,866	82,300	108,491
Non-interest income	7,973	8,974	9,021	14,559	8,345	16,720	20,361	14,881	40,527	60,307	46,507
Non-interest expense	41,125	42,607	42,513	48,068	40,319	50,670	53,716	49,128	174,313	193,833	192,589
Income tax benefit	21,021	22,313	20,741	17,890	17,946	19,029	16,573	16,887	81,965	70,435	66,128
Income before undistributed earnings of subsidiaries	56,599	58,222	55,825	49,149	49,988	51,658	46,639	45,885	219,795	194,170	184,171
Net income	35,578	35,909	35,084	31,259	32,042	32,629	30,066	28,998	137,830	123,143	117,438
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Cash dividends from Cathay Bank									30,000	138,030	154,700
Interest income									88	157	196
Interest expense									4,469	2,994	3,228
Non-interest income									10,144	434	3,718
Non-interest expense									2,248	2,443	2,064
Income before income tax benefit									33,515	133,184	153,322
Income tax benefit									1,478	(2,037)	(579)
Income before undistributed earnings of subsidiaries									32,037	135,221	153,901
Distributions more than earnings of subsidiaries										(12,078)	(36,463)
Undistributed earnings of subsidiary									105,793
Net income									$ 137,830	$ 123,143	$ 117,438