Note 20 - Condensed Financial Information of Cathay General Bancorp - Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	May 31, 2014
Assets
Cash pledged as margin for interest rate swaps	$ 7,100
Equity securities	28,005	$ 25,098
Other assets	150,924	175,419
Total assets	18,094,144	16,784,737
Liabilities
Junior subordinated debt	119,136				$ 119,100
Long-term debt	119,136	189,448
Deferred payments from acquisition	7,644	18,458
Other liabilities	209,501	182,618
Total liabilities	15,799,861	14,662,871
Commitments and contingencies
Stockholders' equity
Common stock, $0.01 par value, 100,000,000 shares authorized, 90,064,382 issued and 79,729,419 outstanding at December 31, 2019, and 89,826,317 issued and 80,501,948 outstanding at December 31, 2018	900	898
Additional paid-in-capital	950,466	942,062
Accumulated other comprehensive income/(loss), net	2,302	(18,006)
Retained earnings	1,659,153	1,479,149
Treasury stock, at cost (10,334,963 shares at December 31, 2019, and 9,324,369 shares at December 31, 2018)	(318,538)	(282,237)
Total stockholders' equity	2,294,283	2,121,866	$ 1,973,304	$ 1,828,539
Total liabilities and stockholders' equity	18,094,144	16,784,737
Parent Company [Member]
Assets
Cash	32,468	19,861
Cash pledged as margin for interest rate swaps	7,098	1,766
Short-term certificates of deposit	330	328
Equity securities	19,258	17,564
Other assets	5,530	6,012
Total assets	2,434,348	2,340,256
Liabilities
Junior subordinated debt	119,136	119,136
Long-term debt	0	70,313
Deferred payments from acquisition	7,644	18,458
Other liabilities	13,285	10,483
Total liabilities	140,065	218,390
Commitments and contingencies
Stockholders' equity
Common stock, $0.01 par value, 100,000,000 shares authorized, 90,064,382 issued and 79,729,419 outstanding at December 31, 2019, and 89,826,317 issued and 80,501,948 outstanding at December 31, 2018	900	898
Additional paid-in-capital	950,466	942,062
Accumulated other comprehensive income/(loss), net	2,302	(18,006)
Retained earnings	1,659,153	1,479,149
Treasury stock, at cost (10,334,963 shares at December 31, 2019, and 9,324,369 shares at December 31, 2018)	(318,538)	(282,237)
Total stockholders' equity	2,294,283	2,121,866
Total liabilities and stockholders' equity	2,434,348	2,340,256
Parent Company [Member] | Bank Subsidiaries [Member]
Assets
Investment in Cathay Bank subsidiary	2,365,206	2,290,073
Investment in subsidiaries	2,365,206	2,290,073
Parent Company [Member] | Non Bank Subsidiaries [Member]
Assets
Investment in Cathay Bank subsidiary	4,458	4,652
Investment in subsidiaries	$ 4,458	$ 4,652