Note 5 - Loans - Nonaccrual Loans and Related Allowance for Credit Losses (Details) - USD ($) $ in Thousands	Jun. 30, 2026	Dec. 31, 2025
Loans with no related allowance, unpaid principal balance	$ 77,697	$ 116,221
Loans with no related allowance, recorded investment	68,224	86,127
Loans with related allowance, unpaid principal balance	51,913	31,325
Loans with related allowance, recorded investment	43,472	26,236
Allowance	18,969	12,341
Unpaid principal balance	129,610	147,546
Recorded investment	111,696	112,363
Commercial Portfolio Segment [Member]
Loans with no related allowance, unpaid principal balance	5,916	25,154
Loans with no related allowance, recorded investment	5,753	14,899
Loans with related allowance, unpaid principal balance	5,256	6,887
Loans with related allowance, recorded investment	2,695	6,599
Allowance	1,177	3,409
Commercial Real Estate Portfolio Segment [Member]
Loans with no related allowance, unpaid principal balance	51,251	58,213
Loans with no related allowance, recorded investment	42,713	39,874
Loans with related allowance, unpaid principal balance	32,238	24,438
Loans with related allowance, recorded investment	27,444	19,637
Allowance	17,745	8,932
Residential Mortgage and Equity Lines Portfolio Segment [Member]
Loans with no related allowance, unpaid principal balance	20,530	32,854
Loans with no related allowance, recorded investment	19,758	$ 31,354
Loans with related allowance, unpaid principal balance	14,419
Loans with related allowance, recorded investment	13,333
Allowance	$ 47

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 excluding accrued interest, of financing receivable on nonaccrual status. 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 (a)
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147479319/326-20-50-16

Reference 2: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S45
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147477657/942-210-S45-1

Reference 3: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S50
-Paragraph 1
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478478/942-210-S50-1

Reference 4: http://www.xbrl.org/2003/role/disclosureRef
-Topic 942
-SubTopic 210
-Name Accounting Standards Codification
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03(7)(e)(2))
-Publisher FASB
-URI https://asc.fasb.org/1943274/2147478546/942-210-S99-1

+ Details

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

- Definition

Amortized cost excluding accrued interest, 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_FinancingReceivableExcludingAccruedInterestNonaccrualNoAllowance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_CommercialPortfolioSegmentMember
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: