Note 8 - Loans - Nonaccrual Loans and Related Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Mar. 31, 2024	Dec. 31, 2023
Loans with no related allowance, unpaid principal balance	$ 112,088	$ 88,728
Loans with no related allowance, recorded investment	87,957	66,681
Loans with related allowance, unpaid principal balance	10,753
Loans with related allowance, recorded investment	10,150
Allowance	5,100	0
Unpaid principal balance	122,841	88,728
Recorded investment	98,107	66,681
Commercial Portfolio Segment [Member]
Loans with no related allowance, unpaid principal balance	16,329	26,310
Loans with no related allowance, recorded investment	4,492	14,404
Loans with related allowance, unpaid principal balance	10,753
Loans with related allowance, recorded investment	10,150
Allowance	5,100
Real Estate Construction Portfolio Segment [Member]
Loans with no related allowance, unpaid principal balance	22,998	7,736
Loans with no related allowance, recorded investment	22,998	7,736
Commercial Real Estate Portfolio Segment [Member]
Loans with no related allowance, unpaid principal balance	59,261	41,725
Loans with no related allowance, recorded investment	47,465	32,030
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans with no related allowance, unpaid principal balance	13,500	12,957
Loans with no related allowance, recorded investment	$ 13,002	$ 12,511

Allowance on financing receivable on nonaccrual status.

No definition available.

Name:	caty_FinancingReceivableNonaccrualAllowance
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Unpaid principal balance of financing receivable on nonaccrual status with no allowance. Excludes net investment in lease.

+ References

No definition available.

+ Details

Name:	caty_FinancingReceivableNonaccrualNoAllowanceUnpaidPrincipalBalance
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unpaid principal balance of financing receivable on nonaccrual status. Excludes net investment in lease.

+ References

No definition available.

+ Details

Name:	caty_FinancingReceivableNonaccrualUnpaidPrincipalBalance
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of financing receivable on nonaccrual status with allowance. Excludes net investment in lease.

+ References

No definition available.

+ Details

Name:	caty_FinancingReceivableNonaccrualWithAllowance
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unpaid principal balance of financing receivable on nonaccrual status with allowance. Excludes net investment in lease.

+ References

No definition available.

+ Details

Name:	caty_FinancingReceivableNonaccrualWithAllowanceUnpaidPrincipalBalance
Namespace Prefix:	caty_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amortized cost of financing receivable on nonaccrual status with no allowance for credit loss. Excludes net investment in lease.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (d)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

+ Details

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

- Definition

Amortized cost of financing receivable on nonaccrual status. Excludes net investment in lease.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/otherTransitionRef
-Topic 310
-SubTopic 10
-Name Accounting Standards Codification
-Section 50
-Paragraph 7
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147481962/310-10-50-7

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (3)
-Publisher SEC

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Name Regulation S-K (SK)
-Number 229
-Section 1405
-Paragraph a
-Subparagraph (2)
-Publisher SEC

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 326
-SubTopic 20
-Name Accounting Standards Codification
-Section 50
-Paragraph 16
-Subparagraph (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

+ Details

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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=caty_RealEstateConstructionPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialRealEstatePortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=caty_ResidentialMortgageAndEquityLinesPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: