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Note 13 - Commitments and Contingencies (Details Textual) - USD ($) | 12 Months Ended
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Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016
Commitments To Extend Notional Amount | $ 2,691,579,000 | $ 2,366,368,000 |
Commitments to Fund Fixed Rate Loans | 200,400,000 |  |
Commitments to Fund Adjustable Rate Loans | 2,500,000,000 |  |
Operating Leases, Rent Expense, Total | 12,100,000 | 12,000,000 | $ 10,200,000
Operating Leases, Income Statement, Sublease Revenue | $ 400,000 | $ 400,000 | $ 400,000
Minimum [Member] |  |  |
Lessor, Operating Lease, Term of Contract | 1 year |  |
Maximum [Member] |  |  |
Lessor, Operating Lease, Term of Contract | 10 years 182 days |  |

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- Definition Commitments To Extend Notional Amount + References No definition available. + Details
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Namespace Prefix: | caty_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant

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- Definition Commitments to fund adjustable rate loans. + References No definition available. + Details
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- Definition Commitments to fund fixed rate loans. + References No definition available. + Details
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- Definition Amount of rent expense incurred for leased assets, including but not limited to, furniture and equipment, that is not directly or indirectly associated with the manufacture, sale or creation of a product or product line. + References No definition available. + Details
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- Definition Term of lessor's operating lease, in 'PnYnMnDTnHnMnS' format, for example, 'P1Y5M13D' represents reported fact of one year, five months, and thirteen days. + References Reference 1: http://www.xbrl.org/2009/role/commonPracticeRef -Publisher FASB -Name Accounting Standards Codification -Topic 842 -SubTopic 30 -Section 50 -Paragraph 3 -Subparagraph (a)(3) -URI http://asc.fasb.org/extlink&oid=77888428&loc=SL77919359-209981 + Details
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- Definition The amount of revenue recognized for the period under subleasing arrangements. + References Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef -Publisher FASB -Name Accounting Standards Codification -Topic 840 -SubTopic 20 -Section 55 -Paragraph 3 -URI http://asc.fasb.org/extlink&oid=77891322&loc=d3e41620-112719 + Details
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- Details
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