Note 20 - Condensed Financial Information of Cathay General Bancorp (Details) - Balance Sheets - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	May. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Assets
Cash	$ 180,130	$ 176,830		$ 153,747	$ 144,909
Short-term certificates of deposit	536,880	489,614
Securities available for sale	1,586,352	1,318,935
Other assets	147,284	143,106
Total assets	13,254,126	11,516,846
Liabilities
Junior subordinated debt	119,136		$ 119,100
Other liabilities	144,197	80,772
Total liabilities	11,506,348	9,913,958
Stockholders' equity
Common stock, $0.01 par value, 100,000,000 shares authorized, 87,002,931 issued and 80,806,116 outstanding at December 31, 2015, and 84,022,118 issued and 79,814,553 outstanding at December 31, 2014	870	840
Additional paid-in-capital	880,822	789,519
Accumulated other comprehensive loss, net	(8,426)	(5,569)		(29,729)
Retained earnings	1,059,660	943,834
Treasury stock, at cost (6,196,815 shares at December 31, 2015, and 4,207,565 shares at December 31, 2014)	(185,148)	(125,736)
Total stockholders' equity	1,747,778	1,602,888
Total liabilities and stockholders' equity	13,254,126	11,516,846
Parent Company [Member]
Assets
Cash	5,048	7,420		$ 1,835	$ 639
Cash pledged as margin for interest rate swaps	7,936	7,465
Short-term certificates of deposit	24,324	23,203
Securities available for sale	11,911	10,244
Other assets	9,551	9,541
Total assets	1,872,574	1,726,742
Liabilities
Junior subordinated debt	119,136	119,136
Other liabilities	5,660	4,718
Total liabilities	124,796	123,854
Stockholders' equity
Common stock, $0.01 par value, 100,000,000 shares authorized, 87,002,931 issued and 80,806,116 outstanding at December 31, 2015, and 84,022,118 issued and 79,814,553 outstanding at December 31, 2014	870	840
Additional paid-in-capital	880,822	789,519
Accumulated other comprehensive loss, net	(8,426)	(5,569)
Retained earnings	1,059,660	943,834
Treasury stock, at cost (6,196,815 shares at December 31, 2015, and 4,207,565 shares at December 31, 2014)	(185,148)	(125,736)
Total stockholders' equity	1,747,778	1,602,888
Total liabilities and stockholders' equity	1,872,574	1,726,742
Bank Subsidiaries [Member] | Parent Company [Member]
Assets
Investment in subsidiaries	1,807,825	1,666,238
Non-Bank Subsidiaries [Member] | Parent Company [Member]
Assets
Investment in subsidiaries	$ 5,979	$ 2,631