Note 19 - Condensed Financial Information of Cathay General Bancorp - Balance Sheets (Details) - USD ($) $ in Thousands	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	May 31, 2014
Assets
Cash pledged as margin for interest rate swaps	$ 24,300	$ 34,700
Equity securities	22,319	23,744
Other assets	195,403	170,889
Total assets	20,886,723	19,043,134
Liabilities
Junior subordinated debt	119,136				$ 119,100
Other liabilities	180,543	175,502
Total liabilities	18,440,472	16,624,990
Commitments and contingencies
Stockholders' equity
Common stock, $0.01 par value, 100,000,000 shares authorized, 90,871,860 issued and 75,750,862 outstanding at December 31, 2021, and 90,643,206 issued and 79,508,265 outstanding at December 31, 2020	909	906
Additional paid-in-capital	972,474	964,734
Accumulated other comprehensive income, net	(3,065)	5,310
Retained earnings	1,985,168	1,789,325
Treasury stock, at cost (15,120,998 shares at December 31, 2021, and 11,134,941 shares at December 31, 2020)	(509,235)	(342,131)
Total equity	2,446,251	2,418,144	$ 2,294,283	$ 2,121,866
Total liabilities and equity	20,886,723	19,043,134
Parent Company [Member]
Assets
Cash	19,629	50,060
Cash pledged as margin for interest rate swaps	1,071	2,159
Short-term certificates of deposit	333	332
Equity securities	15,627	15,505
Other assets	4,691	6,447
Total assets	2,573,008	2,542,991
Liabilities
Junior subordinated debt	119,136	119,136
Other liabilities	7,621	5,711
Total liabilities	126,757	124,847
Commitments and contingencies
Stockholders' equity
Common stock, $0.01 par value, 100,000,000 shares authorized, 90,871,860 issued and 75,750,862 outstanding at December 31, 2021, and 90,643,206 issued and 79,508,265 outstanding at December 31, 2020	909	906
Additional paid-in-capital	972,474	964,734
Accumulated other comprehensive income, net	(3,065)	5,310
Retained earnings	1,985,168	1,789,325
Treasury stock, at cost (15,120,998 shares at December 31, 2021, and 11,134,941 shares at December 31, 2020)	(509,235)	(342,131)
Total equity	2,446,251	2,418,144
Total liabilities and equity	2,573,008	2,542,991
Parent Company [Member] | Bank Subsidiaries [Member]
Assets
Investment in subsidiaries	2,530,850	2,467,643
Non Bank Subsidiaries [Member] | Bank Subsidiaries [Member]
Assets
Investment in subsidiaries	$ 807	$ 845