Note 19 - Condensed Financial Information of Cathay General Bancorp - Statements of Operations (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Interest income	$ 130,668	$ 124,155	$ 121,902	$ 122,345	$ 119,519	$ 116,867	$ 112,386	$ 104,934
Interest expense	20,766	20,331	20,126	19,977	20,103	19,221	17,632	17,008	$ 81,200	$ 73,964	$ 75,866
Non-interest expense	53,503	50,737	68,879	51,571	53,533	57,471	47,585	44,131	224,690	202,720	174,313
Income tax (benefit)/expense	16,345	15,808	12,273	22,675	16,787	12,098	9,738	21,364	67,101	59,987	81,965
Income before undistributed earnings of subsidiaries	64,360	61,898	47,104	68,838	58,233	50,581	54,938	57,344	242,200	221,096	219,795
Net income	$ 48,015	$ 46,090	$ 34,831	$ 46,163	$ 41,446	$ 38,483	$ 45,200	$ 35,980	175,099	161,109	137,830
Parent Company [Member]
Interest income									48	68	88
Interest expense									5,791	5,776	4,469
Non-interest (loss)/income									(488)	(1,858)	10,144
Non-interest expense									3,756	4,644	2,248
Income before income tax benefit									104,411	151,091	33,515
Income tax (benefit)/expense									(4,199)	(5,134)	1,478
Income before undistributed earnings of subsidiaries									108,610	156,225	32,037
Undistributed earnings of subsidiary									66,489	4,884	105,793
Net income									175,099	161,109	137,830
Parent Company [Member] | Cathay Bank [Member]
Cash dividends									113,448	163,301	30,000
Parent Company [Member] | GBC Venture Capital [Member]
Cash dividends									$ 950