Note 24 - Quarterly Results of Operations (Unaudited) (Details) - Selected Unaudited Quarterly Financial Data (USD $) In Thousands, except Per Share data, unless otherwise specified	3 Months Ended								12 Months Ended
	Dec. 31, 2013	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Selected Unaudited Quarterly Financial Data [Abstract]
Interest income	$ 101,621	$ 102,462	$ 100,862	$ 102,051	$ 105,281	$ 106,747	$ 107,581	$ 110,135
Interest expense	19,659	19,854	20,868	21,919	24,216	26,330	28,461	29,484	82,300	108,491	139,881
Net interest income	81,962	82,608	79,994	80,132	81,065	80,417	79,120	80,651	324,696	321,253	313,690
Reversal for credit losses		(3,000)					(5,000)	(4,000)	(3,000)	(9,000)	27,000
Net-interest income after provision for loan losses	81,962	85,608	79,994	80,132	81,065	80,417	84,120	84,651	327,696	330,253	286,690
Non-interest income	8,345	16,720	20,361	14,881	12,202	15,622	9,852	8,831	60,307	46,507	50,892
Non-interest expense	40,319	50,670	53,716	49,128	49,532	47,844	47,342	47,871	193,833	192,589	185,566
Income before income tax expense	49,988	51,658	46,639	45,885	43,735	48,195	46,630	45,611	194,170	184,171	152,016
Income tax expense	17,946	19,029	16,573	16,887	15,276	17,686	16,619	16,547	70,435	66,128	51,261
Net income	32,042	32,629	30,066	28,998	28,459	30,509	30,011	29,064	123,143	117,438	100,150
Less: net income attributable to noncontrolling interest	140	151	150	151	153	151	150	151	592	605	605
Net income attributable to Cathay General Bancorp	31,902	32,478	29,916	28,847	28,306	30,358	29,861	28,913	123,735	118,043	100,755
Dividends on preferred stock		(2,434)	(2,067)	(5,184)	(4,127)	(4,123)	(4,121)	(4,117)	9,685	16,488	16,437
Net income available to common stockholders	$ 31,902	$ 30,044	$ 27,849	$ 23,663	$ 24,179	$ 26,235	$ 25,740	$ 24,796	$ 113,458	$ 100,950	$ 83,713
Basic net income attributable to common stockholders per common share (in Dollars per share)	$ 0.40	$ 0.38	$ 0.35	$ 0.30	$ 0.31	$ 0.33	$ 0.33	$ 0.32	$ 1.44	$ 1.28	$ 1.06
Diluted net income attributable to common stockholders per common share (in Dollars per share)	$ 0.40	$ 0.38	$ 0.35	$ 0.30	$ 0.31	$ 0.33	$ 0.33	$ 0.32	$ 1.43	$ 1.28	$ 1.06