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Note 15 - Financial Derivatives (Detail) (USD $) | 12 Months Ended
--- | ---
Dec. 31, 2012 | Dec. 31, 2011
Number Of Swap Agreements |  | 5
Interest Rate Swaps Notional Amount |  | $ 300,000,000
Net Accrued On Interest Rate Swaps | 288,000 | 4,900,000
Positive Fair Value Member |  |
Notional Amount Of Option Contract | 209,000,000,000 | 4,300,000
Open Option Contracts Written, at Fair Value | 2,000 | 29,000
Sum of Spot and Forward Contract Notional Amount | 188,100,000 | 238,600,000
Increase Decrease in Fair Value | 2,900,000 | 2,200,000
Negative Fair Value Member |  |
Sum of Spot and Forward Contract Notional Amount | 133,700,000 | 128,200,000
Increase Decrease in Fair Value | $ 1,600,000 | $ 486,000,000,000

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- Definition Increase Decrease in Fair Value + References No definition available. + Details
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Namespace Prefix: | caty_
Data Type: | xbrli:monetaryItemType
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Period Type: | duration

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- Definition interest rate swaps notional amount + References No definition available. + Details
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Namespace Prefix: | caty_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Net accrued on interest rate swaps + References No definition available. + Details
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Namespace Prefix: | caty_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | duration

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- Definition Notional Amount Of Option Contract + References No definition available. + Details
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Namespace Prefix: | caty_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

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- Definition Number Of Swap Agreements + References No definition available. + Details
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Namespace Prefix: | caty_
Data Type: | xbrli:positiveIntegerItemType
Balance Type: | na
Period Type: | instant

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- Definition Sum of Spot and Forward Contract Notional Amount + References No definition available. + Details
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Namespace Prefix: | caty_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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- Definition The fair value of the open option contracts written for the investment. + References Reference 1: http://www.xbrl.org/2003/role/presentationRef -Publisher FASB -Name Accounting Standards Codification -Topic 946 -SubTopic 320 -Section S99 -Paragraph 3 -Subparagraph (SX 210.12-12B.4,Column E) -URI http://asc.fasb.org/extlink&oid=6955306&loc=d3e611197-123010 Reference 2: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12B -Paragraph 4 -Article 12 Reference 3: http://www.xbrl.org/2003/role/presentationRef -Publisher SEC -Name Regulation S-X (SX) -Number 210 -Section 12B -Paragraph Column E -Article 12 + Details
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