Name:	fncb_DefinedContributionPlanEmployeeParticipantsVestingPercentage
Namespace Prefix:	fncb_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Represents the period of credited service, after which the employee participants will vest under the defined contribution plan.

No definition available.

Name:	fncb_DefinedContributionPlanPeriodOfCreditedServiceAfterWhichEmployeeParticipantsWillVest
Namespace Prefix:	fncb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

Represents the period of credited service, after which the employer discretionary contributions will start vesting annually under the defined contribution plan.

No definition available.

Name:	fncb_DefinedContributionPlanPeriodOfCreditedServiceAfterWhichEmployerDiscretionaryContributionsVestAnnually
Namespace Prefix:	fncb_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Details

Name:	fncb_ScheduleOfDefinedContributionPlanDisclosuresLineItem
Namespace Prefix:	fncb_
Data Type:	xbrli:stringItemType
Balance Type:	na
Period Type:	duration

- Details

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

Aggregate carrying value as of the balance sheet date of the liabilities for all deferred compensation arrangements. Represents currently earned compensation under compensation arrangements that is not actually paid until a later date.

No definition available.

Name:	us-gaap_DeferredCompensationLiabilityCurrentAndNoncurrent
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

Amount of discretionary contributions made by an employer to a defined contribution plan.

No definition available.

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

Percentage of employees' gross pay for which the employer contributes a matching contribution to a defined contribution plan.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployerMatchingContributionPercent
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Percentage of employer's matching contributions to a defined contribution plan that vests in a given year.

No definition available.

Name:	us-gaap_DefinedContributionPlanEmployersMatchingContributionAnnualVestingPercentage
Namespace Prefix:	us-gaap_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

Maximum percentage of employee gross pay, by the terms of the plan, that the employer may contribute to a defined contribution plan.

No definition available.