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Note 20 - Condensed Financial Information of Cathay General Bancorp (Details) - Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	May 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Assets
Cash	$ 176,830		$ 153,747	$ 144,909	$ 117,888
Short-term certificates of deposit	489,614us-gaap_ShortTermInvestments		516,938us-gaap_ShortTermInvestments
Securities available for sale	1,318,935us-gaap_AvailableForSaleSecurities		1,586,668us-gaap_AvailableForSaleSecurities
Other assets	143,106us-gaap_OtherAssets		190,634us-gaap_OtherAssets
Total assets	11,516,846us-gaap_Assets		10,989,286us-gaap_Assets
Liabilities
Junior subordinated debt	119,136us-gaap_JuniorSubordinatedNotes	119,100us-gaap_JuniorSubordinatedNotes
Other liabilities	80,772us-gaap_OtherLiabilities		55,418us-gaap_OtherLiabilities
Total liabilities	9,913,958us-gaap_Liabilities		9,530,315us-gaap_Liabilities
Stockholders' equity
Common stock, $0.01 par value, 100,000,000 shares authorized, 84,022,118 issued and 79,814,553 outstanding at December 31, 2014, and 83,797,434 issued and 79,589,869 outstanding at December 31, 2013	840us-gaap_CommonStockValue		838us-gaap_CommonStockValue
Additional paid-in-capital	789,519us-gaap_AdditionalPaidInCapital		784,489us-gaap_AdditionalPaidInCapital
Accumulated other comprehensive loss, net	(5,569)		(29,729)	465
Retained earnings	943,834		829,109
Treasury stock, at cost (4,207,565 shares at December 31, 2014, and at December 31, 2013)	(125,736)us-gaap_TreasuryStockValue		(125,736)us-gaap_TreasuryStockValue
Total liabilities and stockholders' equity	11,516,846		10,989,286
Bank Subsidiaries [Member] \| Parent Company [Member]
Assets
Investment in subsidiaries	1,666,238		1,525,459
Non-Bank Subsidiaries [Member] \| Parent Company [Member]
Assets
Investment in subsidiaries	2,631		2,536
Parent Company [Member]
Assets
Cash	7,420		1,835
Cash pledged as margin for interest rate swaps	7,465
Short-term certificates of deposit	23,203		38,000
Securities available for sale	10,244		11,404
Other assets	9,541		1,462
Total assets	1,726,742		1,580,696
Liabilities
Junior subordinated debt	119,136		121,136
Other liabilities	4,718		589
Total liabilities	123,854		121,725
Stockholders' equity
Common stock, $0.01 par value, 100,000,000 shares authorized, 84,022,118 issued and 79,814,553 outstanding at December 31, 2014, and 83,797,434 issued and 79,589,869 outstanding at December 31, 2013	840		838
Additional paid-in-capital	789,519		784,489
Accumulated other comprehensive loss, net	(5,569)		(29,729)
Retained earnings	943,834		829,109
Treasury stock, at cost (4,207,565 shares at December 31, 2014, and at December 31, 2013)	(125,736)		(125,736)
Total stockholders' equity	1,602,888		1,458,971
Total liabilities and stockholders' equity	$ 1,726,742		$ 1,580,696