Note 13 - Fair Value Measurements and Fair Value of Financial Instruments - Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Mar. 31, 2022	Dec. 31, 2021
Securities available-for-sale	$ 1,219,541	$ 1,127,309
Equity securities	27,740	22,319
Assets, fair value disclosure	1,287,058	1,160,854
Liabilities, fair value disclosure	23,125	12,969
Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale	119,748	0
Equity securities	27,740	22,319
Assets, fair value disclosure	147,488	22,319
Liabilities, fair value disclosure	0	0
Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale	1,099,793	1,127,309
Equity securities	0	0
Assets, fair value disclosure	1,139,546	1,138,512
Liabilities, fair value disclosure	23,125	12,969
Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale	0	0
Equity securities	0	0
Assets, fair value disclosure	24	23
Liabilities, fair value disclosure	0	0
US Treasury Securities [Member]
Securities available-for-sale	119,748
US Treasury Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale	119,748
US Treasury Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale	0
US Treasury Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale	0
US Government Corporations and Agencies Securities [Member]
Securities available-for-sale	83,216	87,509
US Government Corporations and Agencies Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale	0	0
US Government Corporations and Agencies Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale	83,216	87,509
US Government Corporations and Agencies Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale	0	0
Commercial Mortgage-Backed Securities [Member]
Securities available-for-sale	873,505	888,665
Commercial Mortgage-Backed Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale	0	0
Commercial Mortgage-Backed Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale	873,505	888,665
Commercial Mortgage-Backed Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale	0	0
Collateralized Mortgage Obligations [Member]
Securities available-for-sale	8,388	9,117
Collateralized Mortgage Obligations [Member] \| Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale	0	0
Collateralized Mortgage Obligations [Member] \| Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale	8,388	9,117
Collateralized Mortgage Obligations [Member] \| Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale	0	0
Corporate Debt Securities [Member]
Securities available-for-sale	134,684	142,018
Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Securities available-for-sale	0	0
Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Securities available-for-sale	134,684	142,018
Corporate Debt Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Securities available-for-sale	0	0
Mutual Funds [Member]
Equity securities	1,857	6,230
Mutual Funds [Member] \| Fair Value, Inputs, Level 1 [Member]
Equity securities	1,857	6,230
Mutual Funds [Member] \| Fair Value, Inputs, Level 2 [Member]
Equity securities	0	0
Mutual Funds [Member] \| Fair Value, Inputs, Level 3 [Member]
Equity securities	0	0
Preferred Stock of Government Sponsored Entities [Member]
Equity securities	5,940	1,811
Preferred Stock of Government Sponsored Entities [Member] \| Fair Value, Inputs, Level 1 [Member]
Equity securities	5,940	1,811
Preferred Stock of Government Sponsored Entities [Member] \| Fair Value, Inputs, Level 2 [Member]
Equity securities	0	0
Preferred Stock of Government Sponsored Entities [Member] \| Fair Value, Inputs, Level 3 [Member]
Equity securities	0	0
Other Equity Securities [Member]
Equity securities	19,943	14,278
Other Equity Securities [Member] \| Fair Value, Inputs, Level 1 [Member]
Equity securities	19,943	14,278
Other Equity Securities [Member] \| Fair Value, Inputs, Level 2 [Member]
Equity securities	0	0
Other Equity Securities [Member] \| Fair Value, Inputs, Level 3 [Member]
Equity securities	0	0
Warrant [Member]
Assets, fair value disclosure	24	23
Warrant [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets, fair value disclosure	0	0
Warrant [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets, fair value disclosure	0	0
Warrant [Member] \| Fair Value, Inputs, Level 3 [Member]
Assets, fair value disclosure	24	23
Interest Rate Swap [Member]
Assets, fair value disclosure	38,377	10,090
Liabilities, fair value disclosure	22,983	12,642
Interest Rate Swap [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets, fair value disclosure	0	0
Liabilities, fair value disclosure	0	0
Interest Rate Swap [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets, fair value disclosure	38,377	10,090
Liabilities, fair value disclosure	22,983	12,642
Interest Rate Swap [Member] \| Fair Value, Inputs, Level 3 [Member]
Assets, fair value disclosure	0	0
Liabilities, fair value disclosure	0	0
Foreign Exchange Contract [Member]
Assets, fair value disclosure	1,376	1,113
Liabilities, fair value disclosure	142	327
Foreign Exchange Contract [Member] \| Fair Value, Inputs, Level 1 [Member]
Assets, fair value disclosure	0	0
Liabilities, fair value disclosure	0	0
Foreign Exchange Contract [Member] \| Fair Value, Inputs, Level 2 [Member]
Assets, fair value disclosure	1,376	1,113
Liabilities, fair value disclosure	142	327
Foreign Exchange Contract [Member] \| Fair Value, Inputs, Level 3 [Member]
Assets, fair value disclosure	0	0
Liabilities, fair value disclosure	$ 0	$ 0

Fair value portion of probable future economic benefits obtained or controlled by an entity as a result of past transactions or events.

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 820
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (a)
-URI https://asc.fasb.org/extlink&oid=126976982&loc=d3e19207-110258

+ Details

Name:	us-gaap_AssetsFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale).

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(6))
-URI https://asc.fasb.org/extlink&oid=126897435&loc=d3e534808-122878

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 326
-SubTopic 30
-Section 45
-Paragraph 1
-URI https://asc.fasb.org/extlink&oid=124258926&loc=SL82898722-210454

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (b)
-URI https://asc.fasb.org/extlink&oid=124260329&loc=d3e26610-111562

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 320
-SubTopic 10
-Section 50
-Paragraph 2
-Subparagraph (aa)
-URI https://asc.fasb.org/extlink&oid=126970911&loc=d3e27161-111563

+ Details

Name:	us-gaap_AvailableForSaleSecuritiesDebtSecurities
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in equity security measured at fair value with change in fair value recognized in net income (FV-NI), classified as current.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section S99
-Paragraph 1
-Subparagraph (SX 210.5-02(2))
-URI https://asc.fasb.org/extlink&oid=120391452&loc=d3e13212-122682

Reference 2: http://www.xbrl.org/2003/role/exampleRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 210
-SubTopic 10
-Section 45
-Paragraph 1
-Subparagraph (f)
-URI https://asc.fasb.org/extlink&oid=124098289&loc=d3e6676-107765

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 825
-SubTopic 10
-Section 45
-Paragraph 1A
-URI https://asc.fasb.org/extlink&oid=123594786&loc=SL75136599-209740

+ Details

Name:	us-gaap_EquitySecuritiesFvNi
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Fair value of financial and nonfinancial obligations.

+ References

+ Details

Name:	us-gaap_LiabilitiesFairValueDisclosure
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel1Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel2Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FairValueByFairValueHierarchyLevelAxis=us-gaap_FairValueInputsLevel3Member
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USTreasurySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_USGovernmentCorporationsAndAgenciesSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CommercialMortgageBackedSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CollateralizedMortgageObligationsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_CorporateDebtSecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=caty_MutualFundsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=caty_PreferredStockOfGovernmentSponsoredEntitiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=caty_OtherEquitySecuritiesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_WarrantMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_InterestRateSwapMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_InvestmentTypeAxis=us-gaap_ForeignExchangeContractMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: