Note 7 - Loans (Details Textual)	6 Months Ended
Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Commercial Portfolio Segment [Member]
Financing Receivable, Modifications, Subsequent Default, Number of Contracts	0
Nonaccrual Loans [Member]
Impaired Financing Receivable, Recorded Investment	$ 53,100,000	$ 52,100,000
Accruing Troubled Debt Restructuring [Member]
Impaired Financing Receivable, Recorded Investment	74,700,000	81,700,000
Financing Receivable, Modifications, Recorded Investment	74,700,000	81,700,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	1,600,000	2,000,000
Non-accruing Troubled Debt Restructuring [Member]
Financing Receivable, Modifications, Recorded Investment	25,400,000	39,900,000
Allowance for Credit Losses, Change in Method of Calculating Impairment	$ 4,400,000	5,400,000
Rate Reduction [Member] \| Maximum [Member]
Troubled Debt Restructurings Length Of Modifications	90 days
Rate Reduction [Member] \| Minimum [Member]
Troubled Debt Restructurings Length Of Modifications	300 days
Maximum [Member]
Period Loan Is In Payment Default	90 days
Minimum [Member]
Period Loan Is In Payment Default	60 days
Impaired Financing Receivable, Recorded Investment	$ 127,846,000	$ 133,810,000
Loans and Leases Receivable, Impaired, Commitment to Lend	$ 0
Percentage Of Charge Off To Contractual Balances For Impaired Loans	17.20%	22.40%

Percentage of charge-off to contractual balances for impaired loans.

No definition available.

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Namespace Prefix:	caty_
Data Type:	num:percentItemType
Balance Type:	na
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- Definition

Period Loan Is In Payment Default

+ References

No definition available.

+ Details

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- Definition

Troubled debt restructurings length of modifications.

+ References

No definition available.

+ Details

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- Definition

Amount of allowance for credit losses related to receivables which had been measured under a general allowance for credit losses methodology that are now identified as troubled debt restructurings.

+ References

No definition available.

+ Details

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

- Definition

The amount of the outstanding recorded investment related to financing receivables that have been modified by troubled debt restructurings.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 4
-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

Reference 2: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Glossary Recorded Investment
-URI http://asc.fasb.org/extlink&oid=65880944

+ Details

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

- Definition

Number of financing receivables that have been modified by troubled debt restructurings within the previous 12 months and for which there was a payment default.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 34
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953682-111524

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Balance Type:	na
Period Type:	duration

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 14A
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=66008989&loc=SL6953550-111524

+ Details

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

- Definition

Reflects the unfunded portion of contractual agreements to lend funds to borrowers for loans whose terms have been modified by troubled debt restructuring.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 40
-Section 50
-Paragraph 1
-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18794-111554

+ Details

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- Details

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- Details

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Namespace Prefix:
Data Type:	na
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- Details

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Namespace Prefix:
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- Details

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- Details

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- Details

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