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Note 14 - Financial Derivatives (Detail) (USD $) | 3 Months Ended | 12 Months Ended
--- | --- | ---
Mar. 31, 2013 | Dec. 31, 2012
Positive Fair Value Member |  |
Notional Amount Of Option Contract | $ 1,600,000 | $ 209,000
Open Option Contracts Written, at Fair Value | 5,700 | 2,000
Sum of Spot and Forward Contract Notional Amount | 211,700,000 | 188,100,000
Increase Decrease in Fair Value | 3,000,000 | 2,900,000
Negative Fair Value Member |  |
Sum of Spot and Forward Contract Notional Amount | 165,600,000 | 133,700,000
Increase Decrease in Fair Value | $ 1,900,000 | $ 1,600,000

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

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

X
- Definition Sum of Spot and Forward Contract Notional Amount + References No definition available. + Details
Name: | caty_SumOfSpotAndForwardContractNotionalAmount
Namespace Prefix: | caty_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
Period Type: | instant

X
- 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
Name: | us-gaap_OpenOptionContractsWrittenAtFairValue
Namespace Prefix: | us-gaap_
Data Type: | xbrli:monetaryItemType
Balance Type: | credit
Period Type: | instant