Allowances for Loan Losses - Additional Information (Detail) - Commercial Portfolio Segment [Member]	6 Months Ended
Jun. 30, 2016 USD ($) Contracts
Financing Receivable, Allowance for Credit Losses [Line Items]
Number of troubled debt restructurings \| Contracts	1
Pre-modification outstanding recorded investment	$ 2,091,000
Post-modification outstanding recorded investment	2,091,000
Financing allowance reduction in principal payments	3,000
Financing allowance reduction in interest payments	$ 1,000

Financing allowance reduction in interest payments.

No definition available.

Name:	cnbka_FinancingAllowanceReductionInInterestPayments
Namespace Prefix:	cnbka_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Financing receivable modifications increase in principal.

+ References

No definition available.

+ Details

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Namespace Prefix:	cnbka_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Line items represent financial concepts included in a table. These concepts are used to disclose reportable information associated with domain members defined in one or many axes to the table.

+ References

No definition available.

+ Details

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Namespace Prefix:	us-gaap_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Definition

Number of 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 10
-Section 50
-Paragraph 33
-URI http://asc.fasb.org/extlink&oid=84173941&loc=SL6953676-111524

+ Details

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Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	duration

- Definition

Post-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

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

- Definition

Pre-modification amount of investment in financing receivables modified by troubled debt restructurings.

+ References

+ Details

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

- Details

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