Note 21 - Condensed Financial Information of Cathay General Bancorp - Statements of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2022	Dec. 31, 2021	Dec. 31, 2020
Cash Flows from Operating Activities
Net income	$ 360,642	$ 298,304	$ 228,860
Write-downs on venture capital and other investments	42,065	45,447	58,131
Net change in accrued interest receivable and other assets	(80,411)	(34,196)	(21,247)
Net change in other liabilities	107,467	2,403	(18,948)
Net cash provided by operating activities	467,390	334,317	319,955
Cash Flows from Investing Activities
Proceeds from sale of equity securities	553	0	3,112
Net cash used for investing activities	(1,849,433)	(859,924)	(242,204)
Cash Flows from Financing Activities
Repayment of long-term debt	0	0	(7,663)
Cash dividends paid	(100,955)	(99,322)	(98,688)
Taxes paid related to net share settlement of RSUs	(2,905)	(2,632)	(1,911)
Purchase of treasury stock	(141,316)	(167,104)	(23,593)
Net cash provided by financing activities	94,741	1,554,233	749,549
(Decrease)/Increase in cash, cash equivalents, and restricted cash	(1,287,302)	1,028,626	827,300
Cash, cash equivalents, and restricted cash, beginning of the year	2,449,704	1,421,078	593,778
Cash, cash equivalents, and restricted cash, end of the period	1,162,402	2,449,704	1,421,078
Parent Company [Member]
Cash Flows from Operating Activities
Net income	360,642	298,304	228,860
Equity in undistributed earnings of subsidiaries	(133,433)	(72,338)	(90,306)
Loss/(gain) on equity securities	(733)	(122)	641
Write-downs on venture capital and other investments	268	73	107
(Gain)/loss in fair value of warrants	(27)	0	18
Stock issued to directors as compensation	849	850	800
Net change in accrued interest receivable and other assets	(434)	1,918	(1,182)
Net change in other liabilities	8,532	4,934	(9,853)
Net cash provided by operating activities	235,664	233,619	129,085
Cash Flows from Investing Activities
Proceeds from liquidation of subsidiary	0	0	2,399
Proceeds from sale of equity securities	0	0	3,112
Venture capital and other investments	(5)	357	116
Net cash used for investing activities	(5)	357	5,627
Cash Flows from Financing Activities
Repayment of long-term debt	0	0	(7,644)
Cash dividends paid	(100,955)	(99,322)	(98,688)
Proceeds from shares issued under the Dividend Reinvestment Plan	3,719	3,563	9,777
Taxes paid related to net share settlement of RSUs	(2,905)	(2,632)	(1,911)
Purchase of treasury stock	(141,316)	(167,104)	(23,593)
Net cash provided by financing activities	(241,457)	(265,495)	(122,059)
(Decrease)/Increase in cash, cash equivalents, and restricted cash	(5,798)	(31,519)	12,653
Cash, cash equivalents, and restricted cash, beginning of the year	20,700	52,219	39,566
Cash, cash equivalents, and restricted cash, end of the period	$ 14,902	$ 20,700	$ 52,219