LOANS, Receivables Aging (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Financing Receivable, Recorded Investment, Aging [Abstract]
30 to 59 days past due	$ 2,087	$ 184
60 to 89 days past due	99	0
Past due 90 days or more and still accruing	0	0
Nonaccrual loans	1,704	3,596
Total past due & nonaccrual loans	3,890	3,780
Current	1,800,929	1,474,157
Total Loans	1,804,819	1,477,937	1,147,384
Commercial and Industrial [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
30 to 59 days past due	0	0
60 to 89 days past due	0	0
Past due 90 days or more and still accruing	0	0
Nonaccrual loans	0	0
Total past due & nonaccrual loans	0	0
Current	77,140	71,818
Total Loans	77,140	71,818
Commercial Portfolio Segment [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
Total Loans	77,140	71,818	54,339
Commercial Mortgages Multifamily [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
30 to 59 days past due	954	0
60 to 89 days past due	0	0
Past due 90 days or more and still accruing	0	0
Nonaccrual loans	303	347
Total past due & nonaccrual loans	1,257	347
Current	527,836	469,139
Total Loans	529,093	469,486	278,503
Commercial Mortgages Other [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
30 to 59 days past due	0	0
60 to 89 days past due	0	0
Past due 90 days or more and still accruing	0	0
Nonaccrual loans	0	1,311
Total past due & nonaccrual loans	0	1,311
Current	222,537	161,563
Total Loans	222,537	162,874	141,986
Commercial Mortgages Owner-Occupied [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
30 to 59 days past due	0	0
60 to 89 days past due	0	0
Past due 90 days or more and still accruing	0	0
Nonaccrual loans	630	657
Total past due & nonaccrual loans	630	657
Current	106,715	82,994
Total Loans	107,345	83,651	83,879
Residential Mortgages Closed End [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
30 to 59 days past due	1,059	67
60 to 89 days past due	0	0
Past due 90 days or more and still accruing	0	0
Nonaccrual loans	395	1,070
Total past due & nonaccrual loans	1,454	1,137
Current	778,540	604,206
Total Loans	779,994	605,343	502,367
Residential Mortgages Revolving Home Equity [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
30 to 59 days past due	74	112
60 to 89 days past due	99	0
Past due 90 days or more and still accruing	0	0
Nonaccrual loans	376	211
Total past due & nonaccrual loans	549	323
Current	82,560	77,258
Total Loans	83,109	77,581	81,975
Consumer [Member]
Financing Receivable, Recorded Investment, Aging [Abstract]
30 to 59 days past due	0	5
60 to 89 days past due	0	0
Past due 90 days or more and still accruing	0	0
Nonaccrual loans	0	0
Total past due & nonaccrual loans	0	5
Current	5,601	7,179
Total Loans	$ 5,601	$ 7,184	$ 4,335

Recorded Investment in financing receivables that are total of past due and nonaccruals at the balance sheet date.

No definition available.

Name:	flic_FinancingReceivableRecordedInvestmentPastDueAndNonaccrual
Namespace Prefix:	flic_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing receivables that are less than 60 days past due but more than 29 days past due.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7A

-URI http://asc.fasb.org/extlink&oid=35738203&loc=SL6953401-111524

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestment30To59DaysPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Financing receivables that are less than 90 days past due but more than 59 days past due.

+ References

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestment60To89DaysPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Details

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

- Definition

Financing receivables that are current.

+ References

+ Details

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

- Definition

Financing receivables that are equal to or greater than 90 days past due.

+ References

+ Details

Name:	us-gaap_FinancingReceivableRecordedInvestmentEqualToGreaterThan90DaysPastDue
Namespace Prefix:	us-gaap_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Recorded investment in financing receivables that are on nonaccrual status as of the balance sheet date.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 50

-Paragraph 7

-Subparagraph (d)

-URI http://asc.fasb.org/extlink&oid=35738203&loc=d3e5111-111524

+ Details

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

- Definition

Amount before allowance of loans and leases held in portfolio, including but not limited to, commercial and consumer loans. Includes deferred interest and fees, undisbursed portion of loan balance, unamortized costs and premiums and discounts from face amounts. Excludes loans and leases covered under loss sharing agreements.

+ References

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

-Publisher FASB

-Name Accounting Standards Codification

-Topic 310

-SubTopic 10

-Section 45

-Paragraph 2

-URI http://asc.fasb.org/extlink&oid=28367877&loc=d3e4428-111522

+ Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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

- Details

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