Note 7 - Deposits (Details Textual) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deposit Liabilities Reclassified as Loans Receivable	$ 62	$ 36
Deposit Liabilities Received on Terms Other than Normal Business	0	0
Investment Securities Pledged as Collateral for Municipal Deposits	235,000	286,400
Federal Home Loan Bank of Pittsburgh [Member]
Letters of Credit Outstanding, Amount	$ 60,000	$ 47,500

The amount of deposits that have been received on terms other than those available in the normal course of business.

No definition available.

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Namespace Prefix:	fncb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Represents the amount of investment securities, which were pledged to collateralize certain municipal deposits.

+ References

No definition available.

+ Details

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Namespace Prefix:	fncb_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of deposits held by the entity that have been reclassified as loan balances receivable, for example, but not limited to, overdrafts receivable.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 405
-Section 50
-Paragraph 1
-Subparagraph (c)
-URI http://asc.fasb.org/extlink&oid=116652737&loc=d3e64164-112818

+ Details

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Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The total amount of the contingent obligation under letters of credit outstanding as of the reporting date.

+ References

No definition available.

+ Details

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

- Details

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