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Note 4 - Investment Securities (Details) - Temporarily Impaired Securities (USD $) In Thousands, unless otherwise specified | 12 Months Ended
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Dec. 31, 2014 | Dec. 31, 2013
Securities Available-for-Sale |  |
Securities Available-for-Sale - Less than 12 Months - Fair Value | $ 376,601 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue | $ 877,208 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses | 3,998 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss | 64,562 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss
Securities Available-for-Sale - Less than 12 Months - No. of Issuances | 8 us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear | 30 us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear
Securities Available-for-Sale - 12 Months or longer - Fair Value | 494,754 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue | 106,378 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses | 7,801 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses | 5,246 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses
Securities Available-for-Sale - 12 Months or longer - No. of issuances | 22 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear | 19 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear
Securities Available-for-Sale - Fair Value | 871,355 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue | 983,586 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue
Securities Available-for-Sale - Unrealized Losses | 11,799 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses | 69,808 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses
Securities Available-for-Sale - No. of issuances | 30 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 | 49 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1
US Treasury Securities [Member] |  |
Securities Available-for-Sale |  |
Securities Available-for-Sale - Less than 12 Months - Fair Value | 374,153 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember | 75,064 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses | 265 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember | 1 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember
Securities Available-for-Sale - Less than 12 Months - No. of Issuances | 6 us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember | 1 us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember
Securities Available-for-Sale - Fair Value | 374,153 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember | 75,064 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember
Securities Available-for-Sale - Unrealized Losses | 265 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember | 1 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember
Securities Available-for-Sale - No. of issuances | 6 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember | 1 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = us-gaap_USTreasurySecuritiesMember
Collateralized Mortgage Backed Securities [Member] |  |
Securities Available-for-Sale |  |
Securities Available-for-Sale - Less than 12 Months - Fair Value |  | 792,012 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses |  | 64,526 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember
Securities Available-for-Sale - Less than 12 Months - No. of Issuances |  | 25 us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember
Securities Available-for-Sale - 12 Months or longer - Fair Value | 425,090 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember | 272 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses | 6,386 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember | 2 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember
Securities Available-for-Sale - 12 Months or longer - No. of issuances | 16 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember | 7 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember
Securities Available-for-Sale - Fair Value | 425,090 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember | 792,284 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember
Securities Available-for-Sale - Unrealized Losses | 6,386 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember | 64,528 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember
Securities Available-for-Sale - No. of issuances | 16 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember | 32 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = us-gaap_MortgageBackedSecuritiesMember
Collateralized Mortgage Obligations [Member] |  |
Securities Available-for-Sale |  |
Securities Available-for-Sale - Less than 12 Months - Fair Value |  | 68 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses |  | 4 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember
Securities Available-for-Sale - Less than 12 Months - No. of Issuances |  | 2 us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember
Securities Available-for-Sale - 12 Months or longer - Fair Value | 45 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember | 301 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses | 34 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember | 50 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember
Securities Available-for-Sale - 12 Months or longer - No. of issuances | 1 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember | 3 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember
Securities Available-for-Sale - Fair Value | 45 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember | 369 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember
Securities Available-for-Sale - Unrealized Losses | 34 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember | 54 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember
Securities Available-for-Sale - No. of issuances | 1 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember | 5 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = us-gaap_CollateralizedMortgageObligationsMember
Corporate Debt Securities [Member] |  |
Securities Available-for-Sale |  |
Securities Available-for-Sale - Less than 12 Months - Fair Value |  | 9,970 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses |  | 30 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Securities Available-for-Sale - Less than 12 Months - No. of Issuances |  | 1 us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Securities Available-for-Sale - 12 Months or longer - Fair Value | 63,753 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember | 100,081 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses | 1,247 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember | 4,919 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Securities Available-for-Sale - 12 Months or longer - No. of issuances | 4 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember | 8 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Securities Available-for-Sale - Fair Value | 63,753 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember | 110,051 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Securities Available-for-Sale - Unrealized Losses | 1,247 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember | 4,949 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Securities Available-for-Sale - No. of issuances | 4 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember | 9 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = us-gaap_CorporateDebtSecuritiesMember
Mutual Funds [Member] |  |
Securities Available-for-Sale |  |
Securities Available-for-Sale - 12 Months or longer - Fair Value | 5,866 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember | 5,724 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionTwelveMonthsOrLongerFairValue / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember
Securities Available-for-Sale - 12 Months or longer - Unrealized Losses | 134 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember | 275 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPosition12MonthsOrLongerAggregateLosses / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember
Securities Available-for-Sale - 12 Months or longer - No. of issuances | 1 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember | 1 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsGreaterThanOrEqualToOneYear / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember
Securities Available-for-Sale - Fair Value | 5,866 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember | 5,724 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember
Securities Available-for-Sale - Unrealized Losses | 134 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember | 275 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember
Securities Available-for-Sale - No. of issuances | 1 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember | 1 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = caty_MutualFundsMember
Preferred Stock of Government Sponsored Entities [Member] |  |
Securities Available-for-Sale |  |
Securities Available-for-Sale - Less than 12 Months - Fair Value | 2,448 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_InvestmentTypeAxis = caty_PreferredStockOfGovernmentSponsoredEntitiesMember |
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses | 3,733 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_InvestmentTypeAxis = caty_PreferredStockOfGovernmentSponsoredEntitiesMember |
Securities Available-for-Sale - Less than 12 Months - No. of Issuances | 2 us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear / us-gaap_InvestmentTypeAxis = caty_PreferredStockOfGovernmentSponsoredEntitiesMember |
Securities Available-for-Sale - Fair Value | 2,448 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = caty_PreferredStockOfGovernmentSponsoredEntitiesMember |
Securities Available-for-Sale - Unrealized Losses | 3,733 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = caty_PreferredStockOfGovernmentSponsoredEntitiesMember |
Securities Available-for-Sale - No. of issuances | 2 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = caty_PreferredStockOfGovernmentSponsoredEntitiesMember |
Mortgage Backed Securities Non Agency [Member] |  |
Securities Available-for-Sale |  |
Securities Available-for-Sale - Less than 12 Months - Fair Value |  | 94 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThanTwelveMonthsFairValue / us-gaap_InvestmentTypeAxis = caty_MortgageBackedSecuritiesNonAgencyMember
Securities Available-for-Sale - Less than 12 Months - Unrealized Losses |  | 1 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionLessThan12MonthsAccumulatedLoss / us-gaap_InvestmentTypeAxis = caty_MortgageBackedSecuritiesNonAgencyMember
Securities Available-for-Sale - Less than 12 Months - No. of Issuances |  | 1 us-gaap_AvailableForSaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositionsLessThanOneYear / us-gaap_InvestmentTypeAxis = caty_MortgageBackedSecuritiesNonAgencyMember
Securities Available-for-Sale - Fair Value |  | 94 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionFairValue / us-gaap_InvestmentTypeAxis = caty_MortgageBackedSecuritiesNonAgencyMember
Securities Available-for-Sale - Unrealized Losses |  | $ 1 us-gaap_AvailableForSaleSecuritiesContinuousUnrealizedLossPositionAggregateLosses / us-gaap_InvestmentTypeAxis = caty_MortgageBackedSecuritiesNonAgencyMember
Securities Available-for-Sale - No. of issuances |  | 1 us-gaap_AvailableforsaleSecuritiesInUnrealizedLossPositionsQualitativeDisclosureNumberOfPositions1 / us-gaap_InvestmentTypeAxis = caty_MortgageBackedSecuritiesNonAgencyMember

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- Definition Number of investment positions in available-for-sale investments that have been in a continuous unrealized loss position for greater than or equal to a year for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. + References No definition available. + Details
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- Definition Number of investment positions in available-for-sale investments in a continuous unrealized loss position for less than one year or normal operating cycle, if longer, for which an other-than-temporary impairment (OTTI) has not been recognized in the income statement. + References No definition available. + Details
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Namespace Prefix: | us-gaap_
Data Type: | xbrli:integerItemType
Balance Type: | na
Period Type: | instant

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- Details
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Namespace Prefix: |
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Balance Type: |
Period Type: |

X
- Details
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Namespace Prefix: |
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X
- Details
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- Details
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X
- Details
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Balance Type: |
Period Type: |

X
- Details
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X
- Details
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