Condensed Financial Information Of Cathay General Bancorp (Condensed Statements Of Cash Flows) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Net income/(loss)	$ 100,150	$ 11,565	$ (67,390)
Write-downs on venture capital and other investments	379	515	1,982
Write-downs on impaired securities	200	492	817
Excess tax short-fall from stock options	(218)	(539)	(196)
Increase/(decrease) in other assets, net	(534)	34,594	(63,426)
Decrease in other liabilities	3,746	(13,368)	(30,461)
Net cash provided by operating activities	174,050	168,505	146,408
Decrease/(increase) in short-term investment	(88,634)	48,404	(229,726)
Increase in available-for-sale securities	(571,093)	(3,366,780)	(1,573,823)
Net cash provided by/(used in) investing activities	127,050	596,595	(279,583)
Cash dividends	(16,046)	(16,040)	(22,460)
Issuance of common stock		124,928	119,448
Proceeds from shares issued to Dividend Reinvestment Plan	287	310	1,160
Proceeds from exercise of stock options	1,306		13
Excess tax short-fall from share-based payment arrangements	(290)	(539)	(196)
Net cash (used in)/provided by financing actvities	(270,559)	(777,877)	148,481
Decrease in cash and cash equivalents	30,541	(12,777)	15,306
Cash and cash equivalents, beginning of the year	87,347	100,124	84,818
Cash and cash equivalents, end of the year	117,888	87,347	100,124
Parent Company [Member]
Net income/(loss)	100,150	11,565	(67,390)
Equity in undistributed (earnings)/loss of subsidiaries	(102,492)	(14,427)	62,158
Increase/(decrease) in accrued expense	24	3	(80)
Write-downs on venture capital and other investments	321	521	2,246
Write-downs on impaired securities	200	492
(Gains)/Loss in fair value of warrants	(215)	29	41
Excess tax short-fall from stock options	290	539	196
Increase/(decrease) in other assets, net	(121)	1,040	(332)
Decrease in other liabilities	(221)	(607)	(1,773)
Net cash provided by operating activities	(2,064)	(845)	(4,934)
Additional investment in subsidiary		(94,000)	(103,874)
Decrease/(increase) in short-term investment	17,500	(12,000)	14,800
Increase in available-for-sale securities		(418)	(2,846)
Venture capital investments	(671)	(1,056)	(897)
Net cash provided by/(used in) investing activities	16,829	(107,474)	(92,817)
Issuance of Series B preferred stock			(25)
Cash dividends	(16,046)	(16,041)	(22,460)
Issuance of common stock		124,928	119,447
Proceeds from shares issued to Dividend Reinvestment Plan	287	310	1,160
Proceeds from exercise of stock options	1,306		13
Excess tax short-fall from share-based payment arrangements	(290)	(539)	(196)
Net cash (used in)/provided by financing actvities	(14,743)	108,658	97,939
Decrease in cash and cash equivalents	22	339	188
Cash and cash equivalents, beginning of the year	787	448	260
Cash and cash equivalents, end of the year	$ 809	$ 787	$ 448