Condensed Financial Information Of Cathay General Bancorp (Condensed Balance Sheets) (Details) (USD $) In Thousands, except Share data, unless otherwise specified	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2009	Dec. 31, 2008	Dec. 05, 2008
Cash	$ 117,888	$ 87,347	$ 100,124	$ 84,818
Other assets	206,768	209,868
Total assets	10,644,864	10,801,986
Junior subordinated debt	121,136
Other liabilities	46,864	50,309
Total liabilities	9,129,231	9,365,881
Commitments and contingencies
Preferred stock, 10,000,000 shares authorized, 258,000 issued and outstanding at December 31, 2011, and December 31, 2010	250,992	247,455			258,000
Common stock, $0.01 par value, 100,000,000 shares authorized, 82,860,122 issued and 78,652,557 outstanding at December 31, 2011, and 82,739,348 issued and 78,531,783 outstanding at December 31, 2010	829	827
Additional paid-in-capital	765,641	762,509
Accumulated other comprehensive loss, net	(8,732)	(1,022)
Retained earnings	624,192	543,625
Treasury stock, at cost (4,207,565 shares at December 31, 2011, and at December 31, 2010)	(125,736)	(125,736)
Total Cathay General Bancorp stockholders' equity	1,507,186	1,427,658
Total liabilities and equity	10,644,864	10,801,986
Preferred stock, shares authorized	10,000,000	10,000,000
Preferred stock, shares issued	258,000	258,000
Preferred stock, shares outstanding	258,000	258,000
Common stock, par value	$ 0.01	$ 0.01
Common stock, shares authorized	100,000,000	100,000,000
Common stock, shares issued	82,860,122	82,739,348
Common stock, shares outstanding	78,652,557	78,531,783
Treasury Stock, shares	4,207,565	4,207,565
Parent Company [Member]
Cash	809	787	448	260
Short-term certificates of deposit	19,000	36,500
Investment In bank subsidiaries	1,593,831	1,498,572
Investment in non-bank subsidiaries	2,615	2,611
Other assets	14,189	12,426
Total assets	1,630,444	1,550,896
Junior subordinated debt	121,136	121,136
Other liabilities	2,122	2,102
Total liabilities	123,258	123,238
Commitments and contingencies
Preferred stock, 10,000,000 shares authorized, 258,000 issued and outstanding at December 31, 2011, and December 31, 2010	250,992	247,455
Common stock, $0.01 par value, 100,000,000 shares authorized, 82,860,122 issued and 78,652,557 outstanding at December 31, 2011, and 82,739,348 issued and 78,531,783 outstanding at December 31, 2010	829	827
Additional paid-in-capital	765,641	762,509
Accumulated other comprehensive loss, net	(8,732)	(1,022)
Retained earnings	624,192	543,625
Treasury stock, at cost (4,207,565 shares at December 31, 2011, and at December 31, 2010)	(125,736)	(125,736)
Total Cathay General Bancorp stockholders' equity	1,507,186	1,427,658
Total liabilities and equity	$ 1,630,444	$ 1,550,896