Note 20 - Condensed Financial Information of Cathay General Bancorp (Details) - Statements of Operations - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Condensed Income Statements, Captions [Line Items]
Interest income	$ 119,519	$ 116,867	$ 112,386	$ 104,934	$ 106,043	$ 106,335	$ 105,062	$ 101,207
Interest expense	20,103	19,221	17,632	17,008	18,292	19,580	19,445	18,549	$ 73,964	$ 75,866	$ 82,300
Non-interest expense	53,533	57,471	47,585	44,131	41,125	42,607	42,513	48,068	202,720	174,313	193,833
Income tax (benefit)/expense	16,787	12,098	9,738	21,364	21,021	22,313	20,741	17,890	59,987	81,965	70,435
Income before undistributed earnings of subsidiaries	58,233	50,581	54,938	57,344	56,599	58,222	55,825	49,149	221,096	219,795	194,170
Net income	$ 41,446	$ 38,483	$ 45,200	$ 35,980	$ 35,578	$ 35,909	$ 35,084	$ 31,259	161,109	137,830	123,143
Parent Company [Member]
Condensed Income Statements, Captions [Line Items]
Cash dividends from Cathay Bank									163,301	30,000	138,030
Interest income									68	88	157
Interest expense									5,776	4,469	2,994
Non-interest (loss)/income									(1,858)	10,144	434
Non-interest expense									4,644	2,248	2,443
Income before income tax benefit									151,091	33,515	133,184
Income tax (benefit)/expense									(5,134)	1,478	(2,037)
Income before undistributed earnings of subsidiaries									156,225	32,037	135,221
Distributions more than earnings of subsidiaries											(12,078)
Undistributed earnings of subsidiary									4,884	105,793
Net income									$ 161,109	$ 137,830	$ 123,143