Condensed Consolidated Statements of Operations and Comprehensive Income (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
INTEREST AND DIVIDEND INCOME
Loan receivable	$ 360,643	$ 364,580	$ 380,662
Investment securities- taxable	62,395	83,083	106,568
Investment securities- nontaxable	4,161	4,218	854
Federal Home Loan Bank stock	485	177	237
Federal funds sold and securities purchased under agreement to resell	18	83	14
Deposits with banks	2,042	1,430	1,259
Total interest and dividend income	429,744	453,571	489,594
INTEREST EXPENSE
Time deposits of $100,000 or more	33,441	42,204	54,219
Other deposits	13,932	20,010	29,943
Interest on securities sold under agreements to repurchase	55,699	60,733	66,141
Advances from the Federal Home Loan Bank	270	12,033	37,527
Long-term debt	5,149	4,890	3,852
Short-term borrowings		11	6
Total interest expense	108,491	139,881	191,688
Net interest income before provision for credit losses	321,253	313,690	297,906
(Reversal)/provision for credit losses	(9,000)	27,000	156,900
Net interest income/(loss) after provision for credit losses	330,253	286,690	141,006
NON-INTEREST INCOME
Securities gains, net	18,026	21,131	18,695
Letters of credit commissions	6,316	5,644	4,466
Depository service fees	5,453	5,420	5,220
Other operating income	16,712	18,697	3,870
Total non-interest income	46,507	50,892	32,251
NON-INTEREST EXPENSE
Salaries and employee benefits	78,377	71,849	58,835
Occupancy expense	14,608	14,225	12,188
Computer and equipment expense	9,591	8,508	8,230
Professional services expense	21,768	20,209	17,630
FDIC and State assessments	8,339	12,494	19,549
Marketing expense	4,607	3,175	3,160
Other real estate owned	15,116	10,583	16,011
Operations of investments in affordable housing	6,306	8,153	7,611
Amortization of core deposit premium	5,663	5,859	5,958
Cost associated with debt redemption	12,120	20,231	14,261
Other operating expense	16,094	10,280	12,278
Total non-interest expense	192,589	185,566	175,711
Income/(loss) before income tax (benefit)/expense	184,171	152,016	(2,454)
Income tax expense/(benefit)	66,128	51,261	(14,629)
Net income	118,043	100,755	12,175
Less: net income attributable to noncontrolling interest	605	605	610
Net income attributable to Cathay General Bancorp	117,438	100,150	11,565
Dividends on preferred stock	(16,488)	(16,437)	(16,388)
Net income/(loss) attributable to common stockholders	100,950	83,713	(4,823)
Other comprehensive loss, net of tax:
Unrealized holding gains arising during the year	19,645	4,538	7,714
Less: reclassification adjustment for gains included in net income	10,448	12,248	7,860
Total other comprehensive loss, net of tax	9,197	(7,710)	(146)
Total comprehensive income	$ 126,635	$ 92,440	$ 11,419
Net income/(loss) attributable to common stockholders per common share
Basic (in Dollars per share)	$ 1.28	$ 1.06	$ (0.06)
Diluted (in Dollars per share)	$ 1.28	$ 1.06	$ (0.06)
Basic average common shares outstanding (in Shares)	78,719,133	78,633,317	77,073,954
Diluted average common shares outstanding (in Shares)	78,723,297	78,640,652	77,073,954