Income Taxes - Additional Information (Detail)	12 Months Ended
Dec. 31, 2016 USD ($)
Income Tax Disclosure [Abstract]
Valuation allowance on charitable contribution carryforward	$ 108,000
Charitable contribution carryforward period	4 years

Deferred tax assets charitable contribution carryforwards valuation allowance.

No definition available.

Name:	cnbka_DeferredTaxAssetsCharitableContributionCarryforwardsValuationAllowance
Namespace Prefix:	cnbka_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant