Allowance for Loan Losses (Details Textual) (USD $) In Thousands, unless otherwise specified	3 Months Ended
Mar. 31, 2013	Mar. 31, 2012
Allowance for Loan Losses (Textual) [Abstract]
Trouble debt restructuring during the period	$ 0	$ 0

Financing receivable troubled debt restructuring value.

No definition available.

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