Note 12 - Fair Value of Financial Instruments (Details) - Fair Value Hierarchy of Financial Instruments (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Financial Assets
Cash and due from banks	$ 182,159	$ 176,830
Short-term investments	618,726us-gaap_ShortTermInvestments	489,614us-gaap_ShortTermInvestments
Securities available-for-sale	1,203,682us-gaap_AvailableForSaleSecurities	1,318,935us-gaap_AvailableForSaleSecurities
Loans held-for-sale		1,225
Loans, net	9,001,232	8,688,072
Investment in Federal Home Loan Bank stock	25,000	30,785
Warrants	21caty_WarrantsFairValueDisclosure	27caty_WarrantsFairValueDisclosure
Financial Liabilities
Deposits	9,114,489us-gaap_DepositsFairValueDisclosure	8,785,342us-gaap_DepositsFairValueDisclosure
Securities sold under agreement to repurchase	422,161	473,816
Advances from Federal Home Loan Bank	484,983	424,974
Other borrowings	19,396caty_OtherBorrowingsFairValueDisclosure	17,978caty_OtherBorrowingsFairValueDisclosure
Long-term debt	60,020us-gaap_LongTermDebtFairValue	59,425us-gaap_LongTermDebtFairValue
Fair Value, Inputs, Level 1 [Member]
Financial Assets
Cash and due from banks	182,159	176,830
Short-term investments	618,726	489,614
Securities available-for-sale	356,104	669,870
Fair Value, Inputs, Level 2 [Member]
Financial Assets
Securities available-for-sale	847,578	649,065
Investment in Federal Home Loan Bank stock	25,000	30,785
Financial Liabilities
Securities sold under agreement to repurchase	422,161	473,816
Advances from Federal Home Loan Bank	484,983	424,974
Long-term debt	60,020	59,425
Fair Value, Inputs, Level 3 [Member]
Financial Assets
Loans held-for-sale		1,225
Loans, net	9,001,232	8,688,072
Warrants	21	27
Financial Liabilities
Deposits	9,114,489	8,785,342
Other borrowings	$ 19,396	$ 17,978

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- Definition

Other borrowings fair value disclosure.

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- Definition

Warrants, fair value disclosure.

+ References

No definition available.

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- Definition

Amount of investment in debt and equity securities categorized neither as held-to-maturity nor trading.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 320

-SubTopic 10

-Section 25

-Paragraph 1

-Subparagraph (b)

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-Paragraph 5

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-Topic 320

-SubTopic 10

-Section 45

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- Definition

Fair value portion of currency on hand as well as demand deposits with banks or financial institutions. Includes other kinds of accounts that have the general characteristics of demand deposits. Also includes short-term, highly liquid investments that are both readily convertible to known amounts of cash and so near their maturity that they present insignificant risk of changes in value because of changes in interest rates.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash

-URI http://asc.fasb.org/extlink&oid=6506951

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-Publisher FASB

-Name Accounting Standards Codification

-Glossary Cash Equivalents

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- Definition

Fair value portion of deposit liabilities held by the entity, including, but not limited to, foreign and domestic, interest and noninterest bearing, demand deposits, saving deposits, negotiable orders of withdrawal (NOW) and time deposits.

+ References

No definition available.

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- Definition

Fair value portion of borrowing from Federal Home Loan Bank (FHLBank).

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 210

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-03.13(3)(a))

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- Definition

Fair value portion of investments in Federal Home Loan Bank (FHLBank) stock.

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 325

-SubTopic 20

-Section 25

-Paragraph 1

-URI http://asc.fasb.org/extlink&oid=29638263&loc=d3e39828-111592

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- Definition

Fair value portion of loans held-for-sale including, but not limited to, mortgage loans and finance receivables.

+ References

No definition available.

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- Definition

Fair value portion of loan receivable, including, but not limited to, mortgage loans held for investment, finance receivables held for investment, policy loans on insurance contracts.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Glossary Loan

-URI http://asc.fasb.org/extlink&oid=6517073

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- Definition

The fair value amount of long-term debt whether such amount is presented as a separate caption or as a parenthetical disclosure. Additionally, this element may be used in connection with the fair value disclosures required in the footnote disclosures to the financial statements. The element may be used in both the balance sheet and disclosure in the same submission.

+ References

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- Definition

Fair value portion of securities that an entity sells and agrees to repurchase at a specified date for a specified price.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 825

-SubTopic 10

-Section 50

-Paragraph 10

-URI http://asc.fasb.org/extlink&oid=35750535&loc=d3e13433-108611

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- Definition

Investments which are intended to be sold in the short term (usually less than one year or the normal operating cycle, whichever is longer) including trading securities, available-for-sale securities, held-to-maturity securities, and other short-term investments not otherwise listed in the existing taxonomy.

+ References

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-Publisher FASB

-Name Accounting Standards Codification

-Topic 210

-SubTopic 10

-Section S99

-Paragraph 1

-Subparagraph (SX 210.5-02.2)

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-Publisher SEC

-Name Regulation S-X (SX)

-Number 210

-Section 03

-Paragraph 1

-Subparagraph g

-Article 7

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