Loans and the Allowance for Loan Losses (Details) - Loans by segment modified as troubled debt restructurings - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
Mar. 31, 2018	Dec. 31, 2017
Recorded Investment [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance	$ 20,518	$ 13,818
Additions	3,976	10,378
Payoffs/paydowns	(103)	(3,098)
Transfers		(580)
Note increases	302
Ending balance	24,693	20,518
ALLL [Member]
Financing Receivable, Allowance for Credit Losses [Line Items]
Beginning balance
Additions	147
Payoffs/paydowns
Transfers
Note increases
Ending balance	$ 147

Balance of troubled debt allowance for loan and lease losses.

No definition available.

Name:	cnob_FinancingReceivableTroubledDebtRestructuring
Namespace Prefix:	cnob_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Additions to the balance of troubled debt allowance for loan and lease losses.

+ References

No definition available.

+ Details

Name:	cnob_FinancingReceivableTroubledDebtRestructuringAdditions
Namespace Prefix:	cnob_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	duration

- Definition

Note increases in the balance of troubled debt allowance for loan and lease losses.

+ References

No definition available.

+ Details

Name:	cnob_FinancingReceivableTroubledDebtRestructuringNoteIncreases
Namespace Prefix:	cnob_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Payoffs or paydowns of troubled debt allowance for loan and lease losses.

+ References

No definition available.

+ Details

Name:	cnob_FinancingReceivableTroubledDebtRestructuringPayoffs
Namespace Prefix:	cnob_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Transfers into the balance of troubled debt allowance for loan and lease losses.

+ References

No definition available.

+ Details

Name:	cnob_FinancingReceivableTroubledDebtRestructuringTransfer
Namespace Prefix:	cnob_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
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

- Details

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Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_ValuationAllowancesAndReservesTypeAxis=us-gaap_AllowanceForLoanAndLeaseLossesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: