LOANS (Details 5) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Recorded Investment
With no allowance recorded	$ 5,750	$ 4,886
With a related allowance recorded	4,239	4,910
Total of impaired loans	9,989	9,796
Unpaid Principal Balance
With no allowance recorded	6,526	5,561
With a related allowance recorded	4,239	4,945
Total of impaired loans	10,765	10,506
Related Allowance
With no allowance recorded	0	0
With a related allowance recorded	417	384
Total of impaired loans	417	384
Consumer Loan [Member]
Recorded Investment
With no allowance recorded	0	0
With a related allowance recorded	358	361
Total of impaired loans	358	361
Unpaid Principal Balance
With no allowance recorded	0	0
With a related allowance recorded	358	361
Total of impaired loans	358	361
Related Allowance
With no allowance recorded	0	0
With a related allowance recorded	1	1
Total of impaired loans	1	1
Real estate [Member]
Recorded Investment
With no allowance recorded	5,719	4,854
With a related allowance recorded	3,881	4,549
Total of impaired loans	9,600	9,403
Unpaid Principal Balance
With no allowance recorded	6,468	5,502
With a related allowance recorded	3,881	4,584
Total of impaired loans	10,349	10,086
Related Allowance
With no allowance recorded	0	0
With a related allowance recorded	416	383
Total of impaired loans	416	383
Residential real estate [Member] \| Real estate [Member]
Recorded Investment
With no allowance recorded	1,177	385
With a related allowance recorded	1,558	2,102
Total of impaired loans	2,735	2,487
Unpaid Principal Balance
With no allowance recorded	1,234	410
With a related allowance recorded	1,558	2,137
Total of impaired loans	2,792	2,547
Related Allowance
With no allowance recorded	0	0
With a related allowance recorded	6	51
Total of impaired loans	6	51
Commercial real estate [Member] \| Real estate [Member]
Recorded Investment
With no allowance recorded	4,474	4,401
With a related allowance recorded	2,044	2,259
Total of impaired loans	6,518	6,660
Unpaid Principal Balance
With no allowance recorded	5,166	5,024
With a related allowance recorded	2,044	2,259
Total of impaired loans	7,210	7,283
Related Allowance
With no allowance recorded	0	0
With a related allowance recorded	315	331
Total of impaired loans	315	331
Construction, land acquisition and development [Member] \| Real estate [Member]
Recorded Investment
With no allowance recorded	68	68
With a related allowance recorded	279	188
Total of impaired loans	347	256
Unpaid Principal Balance
With no allowance recorded	68	68
With a related allowance recorded	279	188
Total of impaired loans	347	256
Related Allowance
With no allowance recorded	0	0
With a related allowance recorded	95	1
Total of impaired loans	95	1
Commercial and Industrial [Member]
Recorded Investment
With no allowance recorded	31	32
With a related allowance recorded	0	0
Total of impaired loans	31	32
Unpaid Principal Balance
With no allowance recorded	58	59
With a related allowance recorded	0	0
Total of impaired loans	58	59
Related Allowance
With no allowance recorded	0	0
With a related allowance recorded	0	0
Total of impaired loans	0	0
State and political subdivisions [Member]
Recorded Investment
With no allowance recorded	0	0
With a related allowance recorded	0	0
Total of impaired loans	0	0
Unpaid Principal Balance
With no allowance recorded	0	0
With a related allowance recorded	0	0
Total of impaired loans	0	0
Related Allowance
With no allowance recorded	0	0
With a related allowance recorded	0	0
Total of impaired loans	$ 0	$ 0

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

Amount of allowance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

No definition available.

+ Details

Name:	fncb_ImpairedFinancingReceivableWithNoRelatedAllowance
Namespace Prefix:	fncb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of allowance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

No definition available.

+ Details

Name:	fncb_ImpairedFinancingReceivableWithRelatedAllowance
Namespace Prefix:	fncb_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Amount of investment of impaired financing receivables with related allowance for credit losses and without a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 14A

-Subparagraph (b)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953550-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Definition

Amount of allowance for credit losses related to recorded investment.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)(3)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5212-111524

+ Details

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

- Definition

Amount of unpaid principal balance of impaired financing receivables with related allowance for credit losses and without related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)(4)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Definition

Amount of investment in impaired financing receivables for which there is no related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of unpaid principal balance of impaired financing receivables for which there is no related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)(4)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithNoRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Amount of investment in impaired financing receivables for which there is a related allowance for credit losses.

+ References

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceRecordedInvestment
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Unpaid principal balance of impaired financing receivables for which there is a related allowance for credit losses.

+ References

Reference 1: http://www.xbrl.org/2003/role/presentationRef

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 15

-Subparagraph (a)(4)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5212-111524

+ Details

Name:	us-gaap_ImpairedFinancingReceivableWithRelatedAllowanceUnpaidPrincipalBalance
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=fncb_CommercialAndIndustrialLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=fncb_ConstructionLandAcquisitionAndDevelopmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_CommercialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_ResidentialRealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_AccountsNotesLoansAndFinancingReceivableByReceivableTypeAxis=us-gaap_USStatesAndPoliticalSubdivisionsMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancialInstrumentAxis=us-gaap_ConsumerLoanMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentByClassOfFinancingReceivableAxis=us-gaap_RealEstateMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type: