Note 20 - Condensed Financial Information of Cathay General Bancorp (Detail) - Balance Sheets (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009
Assets
Cash	$ 144,909	$ 117,888	$ 87,347	$ 100,124
Other assets	166,595	206,768
Total assets	10,694,089	10,644,864
Liabilities
Junior subordinated debt	121,136
Other liabilities	54,040	46,864
Total liabilities	9,064,585	9,129,231
Stockholders' equity
Preferred stock, 10,000,000 shares authorized, 258,000 issued and outstanding at December 31, 2012, and December 31, 2011	254,580	250,992
Common stock, $0.01 par value, 100,000,000 shares authorized, 82,985,853 issued and 78,778,288 outstanding at December 31, 2012, and 82,860,122 issued and 78,652,557 outstanding at December 31, 2011	830	829
Additional paid-in-capital	768,925	765,641
Accumulated other comprehensive loss, net	465	(8,732)
Retained earnings	721,993	624,192
Treasury stock, at cost (4,207,565 shares at December 31, 2012, and at December 31, 2011)	125,736	125,736
Total stockholders' equity	1,621,057	1,507,186
Total liabilities and stockholders' equity	10,694,089	10,644,864
Bank Subsidiaries [Member] | Parent Company [Member]
Assets
Investment in subsidiaries	1,569,902	1,593,831
Non-Bank Subsidiaries [Member] | Parent Company [Member]
Assets
Investment in subsidiaries	2,598	2,615
Parent Company [Member]
Assets
Cash	639	809
Short-term certificates of deposit	161,300	19,000
Other assets	9,936	14,189
Total assets	1,744,375	1,630,444
Liabilities
Junior subordinated debt	121,136	121,136
Other liabilities	2,182	2,122
Total liabilities	123,318	123,258
Stockholders' equity
Preferred stock, 10,000,000 shares authorized, 258,000 issued and outstanding at December 31, 2012, and December 31, 2011	254,580	250,992
Common stock, $0.01 par value, 100,000,000 shares authorized, 82,985,853 issued and 78,778,288 outstanding at December 31, 2012, and 82,860,122 issued and 78,652,557 outstanding at December 31, 2011	830	829
Additional paid-in-capital	768,925	765,641
Accumulated other comprehensive loss, net	465	(8,732)
Retained earnings	721,993	624,192
Treasury stock, at cost (4,207,565 shares at December 31, 2012, and at December 31, 2011)	(125,736)	(125,736)
Total stockholders' equity	1,621,057	1,507,186
Total liabilities and stockholders' equity	$ 1,744,375	$ 1,630,444