Allowance for Loan Losses of Total Loans, Percentage

No definition available.

Name:	fnlc_AllowanceforLoanLossesofTotalLoansPercentage
Namespace Prefix:	fnlc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Allowance for Loan and Lease Losses, Related Loans, Percentage

+ References

No definition available.

+ Details

Name:	fnlc_AllowanceforLoanandLeaseLossesRelatedLoansPercentage
Namespace Prefix:	fnlc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	duration

- Definition

Allowance for Loan and Lease Losses, Related Loans, Period Increase (Decrease)

+ References

No definition available.

+ Details

Name:	fnlc_AllowanceforLoanandLeaseLossesRelatedLoansPeriodIncreaseDecrease
Namespace Prefix:	fnlc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	duration

- Definition

Collateralized Consumer Loans To Individuals Loan To Value

+ References

No definition available.

+ Details

Name:	fnlc_CollateralizedConsumerLoansToIndividualsLoanToValue
Namespace Prefix:	fnlc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The regulatory maximum allowed ratio of loan portfolio to Company capital for construction and non-owner-occupied commercial real estate.

+ References

No definition available.

+ Details

Name:	fnlc_ConstructionAndNonOwnerOccupiedCommercialRealEstateLoansMaximumLoanPortfolioToCompanyCapital
Namespace Prefix:	fnlc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The actual ratio of loan amount to Company capital for construction and non-owner-occupied commercial real estate.

+ References

No definition available.

+ Details

Name:	fnlc_ConstructionAndNonOwnerOccupiedCommercialRealEstateLoansPortfolioToCompanyCapital
Namespace Prefix:	fnlc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The regulatory maximum allowed ratio of loan portfolio to Company capital for construction loans.

+ References

No definition available.

+ Details

Name:	fnlc_ConstructionLoanPortfolioMaximumToCompanyCapital
Namespace Prefix:	fnlc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

The ratio of loan portfolio to Company capital for construction loans .

+ References

No definition available.

+ Details

Name:	fnlc_ConstructionLoansActualLoanPortfolioToCompanyCapital
Namespace Prefix:	fnlc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Delinquent Period Before Consumer Loans Charged Off

+ References

No definition available.

+ Details

Name:	fnlc_DelinquentPeriodBeforeConsumerLoansChargedOff
Namespace Prefix:	fnlc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

The minimum amount of days past due at which residential loans are placed on non-accrual status..

+ References

No definition available.

+ Details

Name:	fnlc_DelinquentPeriodBeforeResidentialLoansPlacedOnNonAccrualStatus
Namespace Prefix:	fnlc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Delinquent Period for Loans Charged Off

+ References

No definition available.

+ Details

Name:	fnlc_DelinquentPeriodforLoansChargedOff
Namespace Prefix:	fnlc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Delinquent Period for Loans Charged Off, Period After Receipt of Notification from Bankruptcy Court

+ References

No definition available.

+ Details

Name:	fnlc_DelinquentPeriodforLoansChargedOffPeriodAfterReceiptofNotificationfromBankruptcyCourt
Namespace Prefix:	fnlc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Loans and Leases Receivable, Amortization Term

+ References

No definition available.

+ Details

Name:	fnlc_LoansandLeasesReceivableAmortizationTerm
Namespace Prefix:	fnlc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Loans and Leases Receivable, Commercial, Number of Loan Classes

+ References

No definition available.

+ Details

Name:	fnlc_LoansandLeasesReceivableCommercialNumberofLoanClasses
Namespace Prefix:	fnlc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Loans and Leases Receivable, Loan to Value Ratio

+ References

No definition available.

+ Details

Name:	fnlc_LoansandLeasesReceivableLoantoValueRatio
Namespace Prefix:	fnlc_
Data Type:	xbrli:pureItemType
Balance Type:	na
Period Type:	duration

- Definition

Loans and Leases Receivable, Number of Loan Classes

+ References

No definition available.

+ Details

Name:	fnlc_LoansandLeasesReceivableNumberofLoanClasses
Namespace Prefix:	fnlc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Loans and Leases Receivable, Residential, Number of Loan Classes

+ References

No definition available.

+ Details

Name:	fnlc_LoansandLeasesReceivableResidentialNumberofLoanClasses
Namespace Prefix:	fnlc_
Data Type:	xbrli:integerItemType
Balance Type:	na
Period Type:	instant

- Definition

Loans and Leases Receivable, Term

+ References

No definition available.

+ Details

Name:	fnlc_LoansandLeasesReceivableTerm
Namespace Prefix:	fnlc_
Data Type:	xbrli:durationItemType
Balance Type:	na
Period Type:	duration

- Definition

Percentage of loans and commitments subject to review by an independent consulting firm each year.

+ References

No definition available.

+ Details

Name:	fnlc_OutstandingLoansAndCommitmentsSubjectByIndependentConsultingFirm
Namespace Prefix:	fnlc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Percentage of Total Reserve Allowance accounted for by Loan Loss Allowances

+ References

No definition available.

+ Details

Name:	fnlc_PercentageofTotalReserveAllowanceaccountedforbyLoanLossAllowances
Namespace Prefix:	fnlc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- Definition

Residential Loans Typical Loan To Value

+ References

No definition available.

+ Details

Name:	fnlc_ResidentialLoansTypicalLoanToValue
Namespace Prefix:	fnlc_
Data Type:	num:percentItemType
Balance Type:	na
Period Type:	instant

- 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

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

- Definition

Amount of allowance to cover probable credit losses on loans and leases. Includes carryover of or adjustments to the allowance for loan losses in connection with business combinations. Excludes allowance for loans and leases covered under loss sharing agreements.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 942
-SubTopic 210
-Section S99
-Paragraph 1
-Subparagraph (SX 210.9-03.7(d))
-URI http://asc.fasb.org/extlink&oid=6876686&loc=d3e534808-122878

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (g)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

Reference 3: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 30
-Section 50
-Paragraph 2
-Subparagraph (b)(1)(ii)
-URI http://asc.fasb.org/extlink&oid=118939070&loc=d3e15032-111544

Reference 4: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section 50
-Paragraph 11B
-Subparagraph (c)(1)
-URI http://asc.fasb.org/extlink&oid=118936363&loc=SL6953423-111524

Reference 5: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 310
-SubTopic 10
-Section S99
-Paragraph 4
-Subparagraph (SAB Topic 6.L.1)
-URI http://asc.fasb.org/extlink&oid=27010918&loc=d3e74567-122707

+ Details

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

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ConsumerPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=us-gaap_ResidentialPortfolioSegmentMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	us-gaap_FinancingReceivablePortfolioSegmentAxis=fnlc_HomeEquityLIneofCreditPortfolioMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	fnlc_FinancingReceivableInformationByTypeOfReserveAxis=fnlc_UnallocatedReservesMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

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

- Details

Name:	srt_RangeAxis=srt_MinimumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

- Details

Name:	srt_RangeAxis=srt_MaximumMember
Namespace Prefix:
Data Type:	na
Balance Type:
Period Type:

Allowance for Loan Losses - Narrative (Details) $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2019 USD ($) loan_class	Dec. 31, 2018 USD ($)	Jun. 30, 2019 USD ($)	Sep. 30, 2018 USD ($)	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of classes in the loan portfolio \| loan_class	8
Allowance for loan and lease losses (as a percentage)	0.48%	0.45%
Allowance for loan and lease losses, period increase (decrease)	$ 438
Allowance for loan losses	$ 11,765	$ 11,232	$ 11,471	$ 11,682	$ 11,472	$ 10,729
Allowance for loan losses as a percent of total loans	0.93%	0.91%		0.94%
Number of classes in the commercial loan portfolio \| loan_class	3
Residential loans typical loan to value range (as a percentage)	80.00%
Number of classes in the residential loan portfolio \| loan_class	2
Construction loans accrual to company capital	27.60%
Constructions loan portfolio maximum to company capital	100.00%
Construction and non owner occupied commercial real estate	123.70%
Maximum loan portfolio to company capital	300.00%
Outstanding loans and commitments subject by independent consulting firm	60.00%
Consumer
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 680	$ 630	649	$ 740	575	545
Delinquent period before consumer loans charged off	120 days
Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loan-to-value ratio	0.80
Amortization term of residential loans	30 years
Delinquent period before residential loans placed on non accrual status	90 days
Delinquent period for loans charged off	180 days
Delinquency period for loans charged off after receipt of notification from bankruptcy court	60 days
Home equity line of credit
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 824	730	633	719	678	692
Loan-to-value ratio	0.80
Loan maturities	300 months
Unallocated Reserves
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 1,707	$ 1,216		1,678
Total reserve allowance accounted for by loan loss allowances (percent)	14.50%	10.80%
Construction \| Residential
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 23	$ 34	$ 23	$ 36	$ 29	$ 36
Loan maturities	1 year
Minimum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential loans typical loan to value range (as a percentage)	75.00%
Collateralized consumer loans to individuals loan to value maximum range (as a percentage)	80.00%
Maximum
Accounts, Notes, Loans and Financing Receivable [Line Items]
Residential loans typical loan to value range (as a percentage)	80.00%
Collateralized consumer loans to individuals loan to value maximum range (as a percentage)	90.00%