Securities Available-for-Sale - Additional Information (Detail) (USD $)
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12 Months Ended | ||
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Dec. 31, 2014
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Dec. 31, 2013
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Dec. 31, 2012
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Schedule of Available-for-sale Securities [Line Items] | |||
Realized gross gain | $ 450,000us-gaap_AvailableForSaleSecuritiesGrossRealizedGains | $ 3,019,000us-gaap_AvailableForSaleSecuritiesGrossRealizedGains | $ 1,843,000us-gaap_AvailableForSaleSecuritiesGrossRealizedGains |
Proceeds from sales of securities available-for-sale | 40,285,000us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities | 224,045,000us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities | 294,881,000us-gaap_ProceedsFromSaleOfAvailableForSaleSecurities |
Weighted average remaining life of investment securities available-for-sale | 4 years 1 month 6 days | ||
Securities at floating rate or adjustable rate | 346,994,000cnbka_FloatingRateAdjustableRateAndRepricedAvailableForSaleSecurities | ||
Transfer of securities available-for-sale to held-to-maturity | 987,037,000cnbka_AvailableForSaleSecurityTransferredToHeldToMaturitySecurity | ||
Available-for-sale securities transferred to held-to-maturity securities unrealized loss | 25,333,000cnbka_AvailableForSaleSecuritiesTransferredToHeldToMaturitySecuritiesUnrealizedGainLoss | ||
Federal Home Loan Bank of Boston [Member] | |||
Schedule of Available-for-sale Securities [Line Items] | |||
Securities available-for-sale are securities pledged for borrowing | 24,810,000us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral / us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis = us-gaap_FederalHomeLoanBankOfBostonMember |
12,214,000us-gaap_AvailableForSaleSecuritiesPledgedAsCollateral / us-gaap_FederalHomeLoanBankAdvancesBranchOfFHLBBankAxis = us-gaap_FederalHomeLoanBankOfBostonMember |
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U.S. Government Agency and Sponsored Mortgage Backed Securities [Member] | |||
Schedule of Available-for-sale Securities [Line Items] | |||
Securities at fair value pledged to secure public deposits and repurchase agreements | $ 301,038,000cnbka_SecuritiesAtFairValuePledgedToSecurePublicDepositsAndRepurchaseAgreements / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
$ 368,137,000cnbka_SecuritiesAtFairValuePledgedToSecurePublicDepositsAndRepurchaseAgreements / us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis = us-gaap_MortgageBackedSecuritiesIssuedByUSGovernmentSponsoredEnterprisesMember |
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Securities AFS [Member] | |||
Schedule of Available-for-sale Securities [Line Items] | |||
Number of securities, temporarily impaired for less than 12 months | 3cnbka_NumberOfSecuritiesTemporarilyImpairedForLessThanTwelveMonths / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_AvailableforsaleSecuritiesMember |
47cnbka_NumberOfSecuritiesTemporarilyImpairedForLessThanTwelveMonths / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_AvailableforsaleSecuritiesMember |
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Number of securities, temporarily impaired for 12 months or longer | 14cnbka_NumberOfSecuritiesTemporarilyImpairedForTwelveMonthsOrLonger / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_AvailableforsaleSecuritiesMember |
7cnbka_NumberOfSecuritiesTemporarilyImpairedForTwelveMonthsOrLonger / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_AvailableforsaleSecuritiesMember |
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Number of securities, temporarily impaired, total | 262cnbka_NumberOfSecuritiesTemporarilyImpaired / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_AvailableforsaleSecuritiesMember |
234cnbka_NumberOfSecuritiesTemporarilyImpaired / us-gaap_InformationByCategoryOfDebtSecurityAxis = us-gaap_AvailableforsaleSecuritiesMember |
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Available For Sale Securities Transferred To Held To Maturity Securities Unrealized Gain Loss No definition available.
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Available for sale security transferred to held to maturity security. No definition available.
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Floating rate adjustable rate and repriced available for sale securities. No definition available.
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Number of securities temporarily impaired. No definition available.
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Number of securities temporarily impaired for less than 12 months. No definition available.
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Number of securities temporarily impaired for 12 months or longer. No definition available.
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Securities at fair value pledged to secure public deposits and repurchase agreements. No definition available.
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Weighted average remaining life of investment securities available for sale. No definition available.
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This item represents the gross profit realized on the sale of debt or equity securities categorized neither as held-to-maturity nor trading securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The fair value of available-for-sale securities that serve as collateral for borrowings. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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The cash inflow associated with the sale of debt and equity securities classified as available-for-sale securities. Reference 1: http://www.xbrl.org/2003/role/presentationRef
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