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Note 5 - Loans (Details) (USD $)	12 Months Ended
Note 5 - Loans (Details) (USD $)	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Note 5 - Loans (Details) [Line Items]
Servicing Asset, Amount	$ 240,100,000caty_ServicingAssetAmount
Impaired Financing Receivable, Recorded Investment	174,519,000	200,780,000
Impaired Financing Receivable, Average Recorded Investment	190,226,000	221,152,000	277,776,000
Impaired Financing Receivable, Interest Income, Accrual Method	5,339,000	5,599,000	9,305,000
Percentage of Charge-off to Contractual Balances for Impaired Loans	17.10%	23.90%
Financing Receivable, Modifications, Number of Contracts	60	64
Troubled Debt Restructurings, New Restructurings	13,300,000
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0
Real Estate Loans [Member]
Note 5 - Loans (Details) [Line Items]
Federal Home Loan Bank, Advances, General Debt Obligations, Disclosures, Collateral Pledged	3,800,000,000	1,600,000,000
Commercial Loans [Member] \| Accruing Troubled Debt Restructuring [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	16,506,000	14,736,000
Commercial Loans [Member]
Note 5 - Loans (Details) [Line Items]
Loans Pledged With Federal Reserve Bank	127,200,000	119,100,000
Servicing Asset, Amount	52,500,000
Construction [Member]
Note 5 - Loans (Details) [Line Items]
Servicing Asset, Amount	125,800,000
Commercial Real Estate Loans [Member]
Note 5 - Loans (Details) [Line Items]
Servicing Asset, Amount	31,200,000
Residential Mortgage Loans [Member] \| Accruing Troubled Debt Restructuring [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	8,497,000	6,105,000
Residential Mortgage Loans [Member]
Note 5 - Loans (Details) [Line Items]
Servicing Asset, Amount	30,600,000
Repossessed Assets	2,300,000	4,000,000
Nonaccrual Loans [Member]
Note 5 - Loans (Details) [Line Items]
Impaired Financing Receivable, Recorded Investment	70,200,000	83,200,000
Impaired Financing Receivable, Interest Income, Accrual Method	6,663,000	5,851,000	6,621,000
Accruing Troubled Debt Restructuring [Member]
Note 5 - Loans (Details) [Line Items]
Impaired Financing Receivable, Recorded Investment	104,300,000
Financing Receivable, Modifications, Recorded Investment	104,356,000	117,597,000
Nonaccrual Loans Held for Sale [Member]
Note 5 - Loans (Details) [Line Items]
Impaired Financing Receivable, Recorded Investment		117,600,000
Accruing Troubled Debt Restructuring [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	104,300,000	117,600,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	6,500,000	6,900,000
Financing Receivable, Modifications, Number of Contracts	14	25	43
Non Accruing Troubled Debt Restructuring [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	41,600,000	38,800,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	4,900,000	2,200,000
Commercial Loans [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	16,500,000	5,300,000
Financing Receivable, Modifications, Number of Contracts	9	5
Hotel Loan [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	15,700,000	17,200,000
Financing Receivable, Modifications, Number of Contracts	3	4
Single Family Residential Loan [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	13,600,000	20,000,000
Financing Receivable, Modifications, Number of Contracts	31	25
Industrial and Manufactural Building Loans [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	12,200,000
Financing Receivable, Modifications, Number of Contracts	2
Residential Vacant Land Loans [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	10,200,000
Financing Receivable, Modifications, Number of Contracts	2
Condominium [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	10,100,000
Financing Receivable, Modifications, Number of Contracts	4
Retail Shopping and Commercial Use Building [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	9,000,000	44,200,000
Financing Receivable, Modifications, Number of Contracts	3	13
Multi Family Residences [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	6,100,000	748,000
Financing Receivable, Modifications, Number of Contracts	1	5
Shopping Center Construction Loans [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	5,800,000
Financing Receivable, Modifications, Number of Contracts	1
Office and Commercial Use Building [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	3,500,000	28,600,000
Financing Receivable, Modifications, Number of Contracts	3	10
Warehouse Loans [Member]
Note 5 - Loans (Details) [Line Items]
Financing Receivable, Modifications, Recorded Investment	$ 1,600,000	$ 1,600,000
Financing Receivable, Modifications, Number of Contracts	1	2
Maximum [Member]
Note 5 - Loans (Details) [Line Items]
Period Loan Is In Payment Default	90 years
Minimum [Member]
Note 5 - Loans (Details) [Line Items]
Period Loan Is In Payment Default	60 days