Loans - Composition of Nonaccrual Loans and Impaired Loans (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Debt Disclosure [Abstract]
Loans on nonaccrual	$ 4,146	$ 2,549	$ 4,471
Loans 90 days past due and still accruing	0	0	0
Impaired loans on nonaccrual included above	3,031cnbka_ImpairedLoansOnNonaccrual	1,819cnbka_ImpairedLoansOnNonaccrual	2,878cnbka_ImpairedLoansOnNonaccrual
Total recorded investment in impaired loans	6,327	7,788	5,925
Average recorded investment of impaired loans	7,434	6,776	7,043
Accruing troubled debt restructures	3,296	5,969	3,048
Interest income not recorded on nonaccrual loans according to their original terms	123	711	753
Interest income on nonaccrual loans actually recorded	0cnbka_InterestIncomeOnNonaccrualLoan	0cnbka_InterestIncomeOnNonaccrualLoan	0cnbka_InterestIncomeOnNonaccrualLoan
Interest income recognized on impaired loans	$ 144	$ 161	$ 180

Impaired financing receivable interest income.

No definition available.

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- Definition

Impaired loans on nonaccrual.

+ References

No definition available.

+ Details

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- Definition

Interest income on nonaccrual loan.

+ References

No definition available.

+ Details

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- Definition

Interest income on nonaccrual loan original terms.

+ References

No definition available.

+ Details

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- Definition

Recorded investment in financing receivables that are 90 days or more past due and still accruing.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5111-111524

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- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

+ Details

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- Definition

Reflects the amount of the write-down related to a troubled debt restructuring.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 40

-Section 50

-Paragraph 4

-URI http://asc.fasb.org/extlink&oid=25495931&loc=d3e18845-111554

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- Definition

Average amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (c)(1)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5212-111524

Reference 2: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 17

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5258-111524

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- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953550-111524

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