Mortgage Servicing Rights (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Transfers and Servicing [Abstract]
Outstanding principal balance of loans serviced for others	$ 261,654	$ 260,258
Net gain from sale of loans	490	(737)	$ (1,211)
Mortgage servicing rights capitalized	291	567
Amortization of mortgage servicing rights	204	362
Fair value of mortgage servicing rights	$ 2,586	2,321
Moving average of weekly prepayment data (in months)	3 months
Anticipated loan prepayment rate of servicing assets (in hundredths)	7.74%
Servicing assets and servicing liabilities at fair value, assumptions used to estimate fair value, discount rate adjustment factor (in hundredths)	9.50%
Summary of mortgage servicing rights [Abstract]
Mortgage servicing rights	$ 5,718	5,428
Accumulated amortization	(4,364)	(4,160)
Mortgage servicing rights, net	$ 1,354	$ 1,268

The cumulative amount of amortization for mortgage servicing rights that has been recognized in the income statement.

No definition available.

Name:	fnlc_AccumulatedAmortizationMortgageServicingRights
Namespace Prefix:	fnlc_
Data Type:	xbrli:monetaryItemType
Balance Type:	credit
Period Type:	instant

- Definition

Gross amount, as of the balance sheet date, of mortgage servicing rights.

+ References

No definition available.

+ Details

Name:	fnlc_MortgageServicingRightsGross
Namespace Prefix:	fnlc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

Net amount, as of the balance sheet date, of mortgage servicing rights.

+ References

No definition available.

+ Details

Name:	fnlc_MortgageServicingRightsNet
Namespace Prefix:	fnlc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The moving average period of weekly prepayment data used as assumption in evaluating the carrying value of mortgage servicing rights.

+ References

No definition available.

+ Details

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

- Definition

Net gain from the sale of loans held for sale.

+ References

No definition available.

+ Details

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

- Definition

Dollar amount of principal outstanding on loans being serviced for others at the balance sheet date.

+ References

No definition available.

+ Details

Name:	fnlc_ResidentialMortgageLoansServicedForOthersOutstandingPrincipal
Namespace Prefix:	fnlc_
Data Type:	xbrli:monetaryItemType
Balance Type:	debit
Period Type:	instant

- Definition

The amount of rate spread added to the ten-year US Treasury rate to derive the discount rate used in the fair value calculation for the loan servicing portfolio.

+ References

No definition available.

+ Details

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

- Definition

The periodic amortization (in proportion to and over the period of estimated net servicing income or loss) of capitalized servicing rights, which contractually entitle the servicer to receive fees and ancillary revenues for performing billing, collection, disbursement and recordkeeping services in connection with a mortgage portfolio. As a noncash expense, this element is added back to net income when calculating cash provided by or used in operations using the indirect method.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 230
-SubTopic 10
-Section 45
-Paragraph 28
-Subparagraph (b)
-URI http://asc.fasb.org/extlink&oid=109223946&loc=d3e3602-108585

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 4
-Subparagraph (a)(4)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122739-111746

+ Details

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

- Definition

The value of new servicing assets, subsequently measured at fair value, acquired or created during the current period through purchases or from transfers of financial assets.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(2)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

+ Details

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

- Definition

Fair value of an asset representing net future revenue from contractually specified servicing fees, late charges, and other ancillary revenues, in excess of future costs related to servicing arrangements.

+ References

Reference 1: http://www.xbrl.org/2003/role/disclosureRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 45
-Paragraph 2
-URI http://asc.fasb.org/extlink&oid=6469459&loc=d3e122501-111745

Reference 2: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 3
-Subparagraph (a)(1)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122625-111746

+ Details

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

- Definition

Estimated rate of prepayments of principal on servicing assets and servicing liabilities.

+ References

Reference 1: http://fasb.org/us-gaap/role/ref/legacyRef
-Publisher FASB
-Name Accounting Standards Codification
-Topic 860
-SubTopic 50
-Section 50
-Paragraph 2
-Subparagraph (d)
-URI http://asc.fasb.org/extlink&oid=68078379&loc=d3e122596-111746

+ Details

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

- References

No definition available.

+ Details

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

- References

No definition available.

+ Details

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