Note 19 - Condensed Financial Information of Cathay General Bancorp - Balance Sheets (Details) - USD ($)	Dec. 31, 2016	Dec. 31, 2015		Dec. 31, 2014	May 31, 2014	Dec. 31, 2013
Assets
Cash pledged as margin for interest rate swaps	$ 6,900,000
Short-term certificates of deposit	967,067,000	$ 536,880,000
Securities available-for-sale (amortized cost of $1,317,012 in 2016 and $1,595,723 in 2015)	1,314,345,000	1,586,352,000	[1]
Other assets	117,902,000	147,284,000
Total assets	14,520,769,000	13,254,126,000
Liabilities
Junior subordinated debt	119,136,000				$ 119,100,000
Other liabilities	168,524,000	144,197,000
Total liabilities	12,692,230,000	11,506,348,000
Commitments and contingencies
Stockholders' equity
Common stock, $0.01 par value, 100,000,000 shares authorized, 87,820,920 issued and 79,610,277 outstanding at December 31, 2016, and 87,002,931 issued and 80,806,116 outstanding at December 31, 2015	878,000	870,000
Additional paid-in-capital	895,480,000	880,822,000
Accumulated other comprehensive loss, net	(3,715,000)	(8,426,000)
Retained earnings	1,175,485,000	1,059,660,000
Treasury stock, at cost (8,210,643 shares at December 31, 2016, and 6,196,815 shares at December 31, 2015)	239,589,000	185,148,000
Total stockholders' equity	1,828,539,000	1,747,778,000		$ 1,602,888,000		$ 1,458,971,000
Total liabilities and stockholders' equity	14,520,769,000	13,254,126,000
Parent Company [Member]
Assets
Cash	34,596,000	5,048,000
Cash pledged as margin for interest rate swaps	6,895,000	7,936,000
Short-term certificates of deposit	325,000	24,324,000
Securities available-for-sale (amortized cost of $1,317,012 in 2016 and $1,595,723 in 2015)	18,129,000	11,911,000
Other assets	6,674,000	9,551,000
Total assets	1,951,935,000	1,872,574,000
Liabilities
Junior subordinated debt	119,136,000	119,136,000
Other liabilities	4,260,000	5,660,000
Total liabilities	123,396,000	124,796,000
Commitments and contingencies
Stockholders' equity
Common stock, $0.01 par value, 100,000,000 shares authorized, 87,820,920 issued and 79,610,277 outstanding at December 31, 2016, and 87,002,931 issued and 80,806,116 outstanding at December 31, 2015	878,000	870,000
Additional paid-in-capital	895,480,000	880,822,000
Accumulated other comprehensive loss, net	(3,715,000)	(8,426,000)
Retained earnings	1,175,485,000	1,059,660,000
Treasury stock, at cost (8,210,643 shares at December 31, 2016, and 6,196,815 shares at December 31, 2015)	(239,589,000)	(185,148,000)
Total stockholders' equity	1,828,539,000	1,747,778,000
Total liabilities and stockholders' equity	1,951,935,000	1,872,574,000
Parent Company [Member] | Bank Subsidiaries [Member]
Assets
Investment in subsidiaries	1,879,868,000	1,807,825,000
Parent Company [Member] | Non Bank Subsidiaries [Member]
Assets
Investment in subsidiaries	$ 5,448,000	$ 5,979,000

[1] Preferred stock of government sponsored entities and other equity securities as of December 31, 2015 were reclassified as level 1 rather than level 2 as originally classified due to the availability of quoted prices in active markets.