Note 20 - Condensed Financial Information of Cathay General Bancorp (Details) - Statements of Cash Flows (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Cash flows from Operating Activities
Net income	$ 137,830	$ 123,143	$ 117,438
Income associated with debt redemption	(555)
Write-downs on venture capital and other investments	436	409	309
Write-downs on impaired securities	820		181
Stock issued to officers as compensation	4,190	3,213	2,850
Excess tax short-fall from stock options	1,285	2,509	620
Net change in other assets	(2,776)	23,525	43,304
Net change in other liabilities	(11,256)	(4,973)	(2,256)
Net cash provided by operating activities	150,071	115,073	164,576
Cash flows from Investment Activities
Proceeds from sale of available-for-sale securities	160,451	575,358	60,951
Purchase of available-for-sale securities	(885,782)	(350,130)	(517,513)
Net cash provided by/(used in) investment activities	(459,361)	(311,806)	(46,536)
Cash flows from Financing Activities
Redemption of Series B preferred stock		(258,000)
Cash dividends	(23,104)	(12,606)	(16,049)
Proceeds from exercise of stock options	128	14,755	764
Taxes paid related to net share settlement of RSUs	(850)
Excess tax short-fall from share-based payment arrangements	(1,285)	(2,509)	(620)
Net cash used in financing activities	332,373	205,571	(91,019)
Increase/(decrease) in cash and cash equivalents	23,083	8,838	27,021
Cash and cash equivalents	176,830	153,747	144,909
Series B Preferred Stock [Member] | Parent Company [Member]
Cash flows from Financing Activities
Redemption of Series B preferred stock		(258,000)
Beginning of Period [Member] | Parent Company [Member]
Cash flows from Financing Activities
Cash and cash equivalents	1,835	639	809
End of Period [Member] | Parent Company [Member]
Cash flows from Financing Activities
Cash and cash equivalents	14,885	1,835	639
Parent Company [Member]
Cash flows from Operating Activities
Net income	137,830	123,143	117,438
Dividends in excess of earnings of subsidiaries		12,078	36,463
Equity in undistributed earnings of subsidiaries	(105,793)
Gains on sale of securities	(10,689)		(3,380)
Income associated with debt redemption	(555)
Write-downs on venture capital and other investments	432	357	262
Write-downs on impaired securities	264		181
Loss in fair value of warrants	3	56	114
Stock issued to officers as compensation	350
Excess tax short-fall from stock options	1,285	2,509	620
Net change in other assets	(3,445)	(1,684)	1,820
Net change in other liabilities	(1,294)	27	71
Net cash provided by operating activities	18,388	136,486	153,589
Cash flows from Investment Activities
Decrease/(increase) in short-term investment	14,797	123,300	(142,300)
Proceeds from sale of available-for-sale securities	12,083		4,849
Purchase of available-for-sale securities	(7,920)
Venture capital and other investments	(590)	(835)	(694)
Net cash provided by/(used in) investment activities	18,370	122,465	(138,145)
Cash flows from Financing Activities
Repayment of long-term debt	(1,445)
Cash dividends	(23,104)	(12,606)	(16,049)
Proceeds from shares issued under the Dividend Reinvestment Plan	2,848	605	291
Proceeds from exercise of stock options	128	14,755	764
Taxes paid related to net share settlement of RSUs	(850)
Excess tax short-fall from share-based payment arrangements	(1,285)	(2,509)	(620)
Net cash used in financing activities	(23,708)	(257,755)	(15,614)
Increase/(decrease) in cash and cash equivalents	13,050	1,196	(170)
Cash and cash equivalents	$ 7,420	$ 1,835