Other Operating Expenses - Summary of Other Operating Expenses (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Other Income and Expenses [Abstract]
Marketing	$ 1,793us-gaap_MarketingExpense	$ 1,749us-gaap_MarketingExpense	$ 1,853us-gaap_MarketingExpense
Software maintenance/amortization	1,524	1,417	1,256
Legal and audit	1,072cnbka_LegalAndAuditFees	1,281cnbka_LegalAndAuditFees	1,179cnbka_LegalAndAuditFees
Contributions	735cnbka_Contributions	673cnbka_Contributions	1,074cnbka_Contributions
Processing services	944us-gaap_LoanProcessingFee	812us-gaap_LoanProcessingFee	921us-gaap_LoanProcessingFee
Consulting	964cnbka_ConsultingExpense	874cnbka_ConsultingExpense	890cnbka_ConsultingExpense
Postage and delivery	964cnbka_PostageAndDelivery	939cnbka_PostageAndDelivery	877cnbka_PostageAndDelivery
Supplies	870us-gaap_SuppliesExpense	848us-gaap_SuppliesExpense	849us-gaap_SuppliesExpense
Telephone	753cnbka_TelephoneExpenses	719cnbka_TelephoneExpenses	750cnbka_TelephoneExpenses
Directors' fees	389us-gaap_NoninterestExpenseDirectorsFees	373us-gaap_NoninterestExpenseDirectorsFees	330us-gaap_NoninterestExpenseDirectorsFees
Insurance	304us-gaap_GeneralInsuranceExpense	295us-gaap_GeneralInsuranceExpense	279us-gaap_GeneralInsuranceExpense
Core deposit intangible amortization			120cnbka_CoreDepositIntangibleAmortization
Other	1,520cnbka_OtherOperatingExpenses	1,500cnbka_OtherOperatingExpenses	1,230cnbka_OtherOperatingExpenses
Total	$ 11,832us-gaap_OtherNoninterestExpense	$ 11,480us-gaap_OtherNoninterestExpense	$ 11,608us-gaap_OtherNoninterestExpense

Consulting expense.

No definition available.

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

- Definition

Contributions.

+ References

No definition available.

+ Details

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

- Definition

Core deposit intangible amortization.

+ References

No definition available.

+ Details

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

- Definition

Legal and audit fees.

+ References

No definition available.

+ Details

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

- Definition

Other operating expenses.

+ References

No definition available.

+ Details

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

- Definition

Postage and delivery.

+ References

No definition available.

+ Details

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

- Definition

Software maintenance and amortization expenses.

+ References

No definition available.

+ Details

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

- Definition

Telephone expenses.

+ References

No definition available.

+ Details

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

- Definition

The expense in the period incurred with respect to protection provided by insurance entities against risks other than risks associated with production (which are allocated to cost of sales).

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 225

-SubTopic 10

-Section S99

-Paragraph 2

-Subparagraph (SX 210.5-03.4)

-URI http://asc.fasb.org/extlink&oid=26872669&loc=d3e20235-122688

+ Details

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

- Definition

Expenses paid for obtaining loans which includes expenses such as application and origination fees.

+ References

No definition available.

+ Details

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

- Definition

Expenditures for planning and executing the conception, pricing, promotion, and distribution of ideas, goods, and services. Costs of public relations and corporate promotions are typically considered to be marketing costs.

+ References

+ Details

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

- Definition

Noninterest expense related to directors' fees which are fees paid by an Entity to its directors. Directors' fees may be paid in addition to salary and other benefits.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 942

-SubTopic 225

-Section S99

-Paragraph 1

-Subparagraph (SX 210.9-04.14)

-URI http://asc.fasb.org/extlink&oid=6879574&loc=d3e536633-122882

+ Details

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

- Details

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

- Definition

Other noninterest expenses that are not separately presented in any other noninterest expense category.

+ References

+ Details

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

- Definition

Amount of expense associated with supplies that were used during the current accounting period.

+ References

+ Details

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